Revisiting the Early Cretaceous sauropod Agustinia ligabuei (Dinosauria: Diplodocoidea) from southern Neuquén Basin (Patagonia, Argentina), with implications on the early evolution of rebbachisaurids

ABSTRACT The Lohan Cura Formation (Albian) at the Cerro de los Leones locality (Neuquén Province, Patagonia, Argentina) yielded several fossil materials, especially sauropod specimens. Among these, Agustinia ligabuei includes postcranial elements of a single individual, with widely debated taxonomy and phylogeny. Here, we provide an extended osteological description and illustrations of the axial and appendicular elements of Agustinia, as well as a revised diagnosis. Moreover, the phylogenetic analysis including a new combination of morphological features recognises Agustinia as a basal Rebbachisauridae, closely related with other South American rebbachisaurids. Our results suggest a more diversified sauropod fauna in the Neuquén Basin, where different members of both neosauropod lineages (i.e. Macronaria and Diplodocoidea) survived in the same region during the Albian age. The reassessment of Agustinia as a basal rebbachisaurid improves our knowledge about the early stages of evolutionary history of Rebbachisauridae, adding new information on the morphological and taxonomic diversification of the clade during the Early Cretaceous of southwestern Gondwana.


Introduction
Palaeontological explorations carried out during 1996-1997 in southern Neuquén Province (Patagonia, Argentina) and focused on the Lohan Cura Formation (Albian) outcrops of the Cerro de los Leones locality, 12 km southwest to Picún Leufú town (Figure 1), allowed recovery of several vertebrate and invertebrate fossil specimens, including an incomplete, semi-articulated postcranial sauropod skeleton (Figure 2B-D).These bones came from the fossiliferous level n°3 (sensu Martinelli et al. 2007; Figure 2A) on the south-western flank of the hill (Figure 1C) and were described by Bonaparte (1999), formalising the midsized sauropod as Agustinia ligabuei.
The holotype and only known specimen (MCF-PVPH-110) comprises a nearly complete sequence of posterior dorsal, sacral, and anterior caudal neural spines, several cervical and dorsal incomplete ribs, articulated left tibia and fibula, and five right metatarsals (Figure 3A; Table S1).In this sense, the supposed dermal armour of Agustinia proposed by Bonaparte (1999), was recently reconsidered via paleohistological analysis (Bellardini and Cerda 2017) as cervical and dorsal ribs, and a fragment of the pelvic girdle.
Due to the fragmentary condition of the specimen and its poor preservation, the taxonomic validity and phylogenetic position of Agustinia have been the focus of debate.Indeed, Agustinia was first considered as the only known member of Agustiniidae, a distinct family composed of sauropods with well-defined dermal armour (Bonaparte 1999).Although preliminary, Bonaparte (1999) found a greater resemblance between Agustinia to rebbachisaurids than to titanosaurians, and thus, he interpreted Agustiniidae as a clade of uncertain affinities with sauropods.Upchurch et al. (2004) proposed Agustinia as a Titanosauria incertae sedis on the basis of a sacrum with six vertebrae and the presence of osteoderms.Shortly thereafter, Curry Rogers (2005) included Agustinia for the first time in a phylogenetic analysis focused on Titanosauria, recovering it as an armoured basal titanosaur.Although Agustinia was mentioned by several authors (Leanza et al. 2004;Martinelli et al. 2007;Salgado and Bonaparte 2007;D'Emic et al. 2009;Taylor 2010), the discussions were usually around the origin of the dermal ossifications, avoiding resolution of their phylogenetic relationships within Sauropoda.
Here, we provide a detailed osteological description of Agustinia and a new phylogenetic analysis using an updated sauropod data matrix.Therefore, we revised its original diagnosis, based upon a new unique combination of morphological features that support the taxonomic validity of this species.Our analysis recovers Agustinia as an early diverging member of Rebbachisauridae, increasing the diversity of this diplodocoid clade in the Neuquén Basin, at least during the Albian.
AMNH, American Museum of Natural History, New York, New York, USA; ANS, Academy of Natural Sciences, Philadelphia, PA, USA; BYU, Brigham Young University Museum of Palaeontology, Provo, Utah, USA; CM, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania, USA; DMNH, Denver Museum of Nature History, Denver, Colorado, USA; FMNH, Field Museum of Natural History, Chicago, Illinois, USA; HMNS,

Materials and methods
The complete list of the type-material of Agustinia is available in Table S1 (see SOM).All specimens here described were further prepared and housed at the Museo Municipal 'Carmen Funes' of Plaza Huincul (MCF; Coria 2022), under the acronym MCF-PVPH-110.For the osteological description, we followed Romer (1956), Wilson and Sereno (1998), Harris (2004), Upchurch et al. (2004) and Wilson (2006), whereas the terminology and abbreviations of vertebral laminae and fossae follow Wilson (1999Wilson ( , 2012) ) and Wilson et al. (2011), respectively.
In order to analyse the phylogenetic relationships of Agustinia within Sauropoda, we modified the data matrix proposed by Bellardini et al. (2022b), which, in turn, is an extended version from Gallina et al. (2021).We added two taxa (Agustinia and Itapeuasaurus), and four new characters (see SOM).The resulting data matrix is composed of 96 operational taxonomic units (OTUs) and 422 characters.It was edited using Mesquite V. 2.74 (Maddison and Maddison 2011) to score Agustinia for 34 characters (with 91% of missing data).The heuristic tree search was performed using the software TNT v. 1.5 (Goloboff et al. 2008;Goloboff and Catalano 2016) under equally weighted parsimony, starting from 3,000 replicates of Wagner trees with random addition sequence of taxa followed by TBR branch swapping and saving 10 trees per replicate.The resulting trees were subjected to an additional round of branch swapping (TBR) to count remaining MPTs.
Comments on the axial skeleton of Agustinia Bonaparte (1999) described a sequence of 18 axial elements of Agustinia, formed by three posterior dorsal, six sacral and nine anterior caudal neural spines.Recent lab-works and review of the type-material of Agustinia allowed us to recognise new axial elements, as well as to revise the original assignment of the neural spines.Bonaparte and his team recovered different blocks with axial elements from the type-quarry ('paquete 1.1, 1.2, 1.5, 1.6, 1.8, 1.9, 1.10, vert'., Figure 2B) but some of these were only partially prepared (1.1) or their content was heavily damaged during the field-works, as a missed caudal vertebrae (see vert, Figure 2B).Following Bonaparte (1999, p. 2), the axial elements come from two blocks, one ('paquete 1.2') containing a sequence of 11 neural spines, and the second ('paquete 1.5') with 9 neural spines; other blocks contained the cervical and dorsal partial ribs ('osteoderms' at that time).Thus, the block 1.1 from the type-quarry was found in the MCF during the revision of the type-material of Agustinia, and the apical portions of two additional neural spines were prepared (MCF-PVPH-110/12a-b). Considering the provenance of the block containing the dorsal, sacral and caudal elements, the new neural spines are closely related with the posterior dorsal vertebrae.
The re-evaluation of the axial elements is here proposed on the basis of the morphological variation of the neural spines, neural laminae, and neural fossae across the axial sequence of Agustinia, as well as comparisons with better preserved and more complete sauropod specimens, such as Brachiosaurus, Camarasaurus, Diplodocus, Euhelopus, Overosaurus, and Trigonosaurus (Marsh 1878(Marsh , p. 1889;;Riggs 1903;Campos et al. 2005;Taylor 2009; Wilson and Upchurch 2009;Coria et al. 2013).The top of the neural spines are rhomboidal to sub-rectangular, and wider than long in dorsal view.There is a reduction in the transversal expansion of the neural spines across Figure 2. Lithologic profile and quarry map.A) Schematic log of the lower section of the Cullin Grande Member (Bajada del Agrio Group, Lohan Cura Formation, Lower Cretaceous, Albian), showing the fossiliferous levels at the Cerro de los Leones locality (modified from .Martinelli et al. 2007).B) Original Bonaparte's picture of the quarry n° 1 (Agustinia quarry) during the fieldworks of 1996 (modified from Bonaparte's handbook).C-D) Pictures of the fieldworks 1997 showing the original condition and arrangement of the fossil bones of Agustinia on the fossiliferous level n°3 (C, photo by J. F. Bonaparte; D, photo by AGM).Abbreviations: CS, crevasse channel; FF, floodplain fines; FL, fossiliferous level; LV, levee; LA, lateral accretion; LS, laminated sand sheets; SB, sandy bedforms.Architectural element codes follow Miall (1996) the sequence, being the last elements (MCF-PVPH-110/29-32) slightly longer than wide.In ventral view, all neural spines show a tetraradiate arrangement of the neural laminae, with the lateral laminae (ll) orthogonal to the prespinal (prsl) and postspinal (posl) laminae.In the most proximal element (MCF-PVPH-110/12a-b, MCF-PVPH-110/21-26), the ll is anteriorly directed in lateral view, and the prsl is less prominent than posl in lateral view.Conversely, in most posterior elements (27)(28)(29)(30)(31)(32), the ll is posteriorly located and the prsl is more prominent than posl in lateral view.These trends suggest some kind of inflection point in the middle of the vertebral sequence, which we tentatively place in that sector where the neural spines are completely fused (MCF-PVPH -110/25-27).Taking into account that during the sauropod ontogeny the sacral centra and neural spines tend to fuse (e.g.Wilson and Sereno 1998;Canudo et al. 2008;Wilson 2011), with the thru sacral elements coalescing earlier than the adjacent sacrals (dorsosacral and cuadosacrals), we consider these three fused elements as the neural spines of the true sacral vertebrae (i.e.S1-S3, Wilson et al. 2011).Furthermore, considering that the anterior sacral vertebrae have greater resemblance to the dorsal than the caudal morphology (sacral dorsalization, sensu Wilson and Sereno 1998), the more proximal element MCF-PVPH-110/24 is here referred to the neural spine of the dorso-sacral vertebra (DS), which is partially fused with the sacral vertebra S1 across the posterior surface.On the other hand, we refer MCF-PVPH-110/28 to the neural spine of the caudo-sacral vertebra (CS), which is partially fused with sacral vertebra S3, across its anterior surface.In sum, due to the lack of a complete sacrum to test the sacral rib insertion in the medial wall of the ilium, we tentatively consider the sacrum of Agustinia with at least five sacral vertebrae, the condition of non-Somphospondyli Neosauropoda.Therefore, the type-material of Agustinia includes five dorsal, five sacral, and twelve caudal vertebral neural spines (Table S1).All axial elements of Agustinia are incomplete and poorly preserved, showing several signs of diagenetic and weathering alterations, such as slightly transversal deformations and different longitudinal, oblique, and transversal fractures.Additionally, they are exclusively represented for the dorsal portions of the neural spines, and no remains of centra of any vertebral element are preserved.
Etymology.The generic name was defined by Bonaparte (1999) in honour of A. G. Martinelli, who discovered the sauropod specimens at the Cerro de los Leones locality.

Diagnosis.
As for the species.
Newly referred materials.Distal portions of two dorsal neural spines (MCF-PVPH-110/12a-b).They belong to the holotype specimen but were not included in Bonaparte (1999).
Etymology.The name of the type species was erected in honour of the Italian philanthropist G. Ligabue, who supported part of the fieldtrips of 1997 at the Cerro de los Leones locality and other fieldworks led by Dr. Bonaparte.

Locality and horizon.
Cerro de los Leones locality, 12 kilometres to the southwest of Picún Leufú city, Neuquén Province, Patagonia, Argentina (Figure 1).The fluvial deposits outcropping in this area were referred to the lower section of the Cullin Grande Member (Martinelli et al. 2007), which is the upper member of the Lohan Cura Formation (Bajada del Agrio Group, Early Cretaceous, Albian; Leanza and Hugo 1995;Leanza et al. 1997Leanza et al. , 2001;;Leanza 2003).The type-quarry was opened in the fossiliferous level n°3 (sensu Martinelli et al. 2007) in the southern flank of the Cerro de los Leones (Figure 1C).The sauropod remains were found in a thick variegated succession of mudstones with thin intercalations of fine grained sandstones, which are interpreted as distal flood basin deposits (Martinelli et al. 2007).These outcrops were considered as meandering fluvial deposits, and paleoenvironmentally arranged under semi-arid climatic conditions.
Comments on original diagnosis.Bonaparte (1999) formalised Agustinia identifying four diagnostic features: 1) top of the neural spines transversely expanded in the last dorsal, all the sacral, and the three anterior caudal vertebrae; 2) three types of osteoderms articulating on the tops of the neural spines: type a) unpaired leaf shaped, type b) laminar, transversely wide with lateral projections, and type c) elongate, flat or cylindrical dorsolaterally projected; 3) fibula with a pronounced posterior projection on its proximal section, and a bend internally directed, bounding the cnemial crest of the tibia; 4) metatarsals of the type present in titanosaurs.Considering the diagnostic feature 1), this is a wide spread condition within Sauropoda, recording it in several eusauropod and neosauropod taxa (e.g.Bellusaurus, Diplodocus, Overosaurus, Phuwiangosaurus, Rebbachisaurus;Marsh 1878;Dong 1990;Martin et al. 1994;Suteethorn et al. 2009;2010;Coria et al. 2013;Mo 2013).With respect to the second diagnostic feature, the paleohistological analysis of the osteological elements originally proposed as atypical osteoderms, allowed to reconsider them as cervical and dorsal ribs, as well as a dorsal fragment of the iliac blade (Bellardini and Cerda 2017).Furthermore, with the osteological revision of the Agustinia type-material, the appendicular element described by Bonaparte (1999) as a fibula (MCF-PVPH-110/ 01) is here reconsidered as a tibia.Thus, the autapomorphic anterior crest of the fibula is actually the cnemial crest of the tibia.Finally, although the titanosaur-like morphology of the metatarsus of Agustinia is considered as diagnostic by Bonaparte (1999), the original contribution lacks a specific description of the unique and derived condition.In this context, we consider that 1-4) are not autapomorphies and are excluded from the diagnosis of Agustinia.

Revised diagnosis.
With the new osteological analysis here presented, we propose that the taxonomic validity of Agustinia ligabuei is supported by the following autapomorphies and a unique combination of morphological traits: 1) posterior dorsal, sacral, and anterior caudal neural spines with deep, dorsoventrally expanded and elliptical sprf and spof, which are apically enclosed by transversely and anteroposteriorly expanded dorsolateral margins (Figure 4A-C) most posterior anterior caudal vertebrae with V-like and dorsally divergent lateral laminae in lateral view (Fig. 4H) metatarsal I with prominent and proximodistally elongated laminae on the proximal half of the anterior and posterior surfaces of the bone (Figure 4S).See below (Description and Discussion sections) for the comments on the revised diagnosis and the new diagnostic features of Agustinia.
Middle-to-posterior dorsal vertebra Dv-06?, MCF-PVPH-110/ 12a.This element preserves the apical portion of the neural spine, with part of the spinodiapophyseal (spdl), prespinal (prsl), and postspinal (posl) laminae.It was found associated with the apical portion of the following element (MCF-PVPH-110/12b), forming a unique block where both elements are partially deformed and overlapped (Figure 5).Like all other bones of Agustinia, MCF-PVPH-110/12a is poorly preserved, especially the right lateral surface.The dorsal surface of the neural spine is wider than long, as in the posterior dorsal elements MCF-PVPH-21-23, and not larger than wide as in the caudal elements (MCF-PVPH-110/29-32, MCF-PVPH-110/13-20).Moreover, the neural laminae and fossae are prominent and deep respectively, being more similar to the dorsal than the caudal condition (where they are less developed).Considering the bone arrangement on the field and these morphological features, we consider MCF-PVPH-110/12a as a middle-toposterior dorsal neural spine (Dv-06?), thus more proximal than the last presacral vertebrae MCF-PVPH-110/21-23.
Middle-to-posterior dorsal vertebra Dv-07?, MCF-PVPH-110/ 12b.This specimen represents the partial neural spine that follows MCF-PVPH-110/12a in the mid-dorsal vertebral sequence of Agustinia (Figure 5).Thus, we tentatively consider it as the 7th dorsal vertebra.As the element described above, the bone is poorly preserved and partially deformed, conserving part of the spdl, posl, prsl, and a laminar structure that tentatively refers to the distal portion of spinoprezygapophyseal lamina (sprl?; Figure 5B).
In dorsal view, the neural spine is rhomboidal in shape, wider than long with rounded edges, as in MCF-PVPH-110/12a.In lateral view (5A), the prsl is slightly prominent and bears small and smooth depression near to the anterodorsal portion of the neural spine.Conversely, the spdl is prominent and frames oval and dorsoventral elongated sprf and spof.Despite the fragmentary conditions, the neural laminae prsl, posl, and spdl have a tetraradiate arrangement in ventral view (Figure 5B).
Posterior dorsal vertebra Dv-08?, MCF-PVPH-110/21.The bone preserves the left portion of the distal neural spine of a posterior dorsal vertebra, including part of the prsl, posl, and spdl (Figure 6).The dorsal surface is slightly wider than long, being almost straight and slightly anteroventrally inclined in lateral view (Figure 6A).The prsl is prominent and convex, as in Comahuesaurus and Rebbachisaurus (Carballido et al. 2012;Wilson and Allain 2015) but less prominent than posl, as in Katepensaurus (Ibiricu et al. 2013(Ibiricu et al. , 2015)).Furthermore, a thin accessory lamina on the lateral surface of the prsl runs anteroventrally dividing an anteroventral sector from a smaller posterodorsal portion.In lateral view, the spdl is almost straight ventrally, whereas it is slightly anteriorly inclined at the dorsal half.Moreover, it is on the anterior half of the neural spine, as in the posterior dorsal vertebra of Rebbachisaurus MNHN-MRS-2000 (Wilson and Allain 2015) and the mid-to-posterior one of Katepensaurus UNPSJB-PV-1007/5 (Ibiricu et al. 2015).Thus, the prsl results less prominent than the posl.In ventral view, the lateral margin of the spdl is particularly robust, distinguished from the thin aspect of the rest of the lamina, as seen in the spdl of Rebbachisaurus.In anterior view, the most proximal portion of the spdl is laterally expanded, showing a 'festooned' aspect that is considered a synapomorphy of Rebbachisauridae.Between the spdl and posl opens a deep spof, which is divided by a thin subhorizontal accessory lamina in a ventral and a deeper dorsal subfossa.This, in turn, bears an anteroventrally directed accessory lamina to divide an anterior and a posterior subfossa.Further accessory laminae and fossae are evident close to the apex of the neural spine, as in MCF-PVPH-110/12a-b.
Posterior dorsal vertebra Dv-09?, MCF-PVPH-110/22.This partial neural spine represents the apical portion of the penultimate presacral element of Agustinia.In dorsal view (Figure 6B), the bone is sub-rectangular, wider than long due to the lateral expansion of the distal portions of spdl, as seen in posterior dorsal vertebra of Rebbachisaurus MNHN-MRS-2000 (Wilson and Allain 2015).In anterior view, the dorsal surface is medially concave, whereas the lateral edges are convex and slightly prominent, which is a condition also present in the posterior dorsal vertebrae of the indeterminate rebbachisaurid MMCh-PV-49 and several flagellicaudatans, such as Apatosaurus, Barosaurus, Diplodocus, and Supersaurus (Marsh 1877;1878, p. 1890;Lull 1919;Janensch 1914;Jensen 1985;Lovelace et al. 2007;Haluza et al. 2012).The prsl is slender ventrally and transversely expanded at the distal half, especially close to the apical portion of the neural spine.On the other hand, the prsl is straight and only slightly prominent in lateral view, not exceeding the anterior margin of the distal spine.There are several shallow and small depressions on the lateral surfaces of the prsl, together with two thin accessory laminae that divide dorsally the prsf on two oval, deep, and small sub-fossae.
In lateral view (Figure 6A), the spdl is on the anterior half of the spine, as in Katepensaurus (Ibiricu et al. 2015), being straight proximally and slightly anteriorly inclined on the distal half of the spine.On the other hand, the spdl is more robust proximally in ventral view, where it is triangular in shape and anteroposteriorly expanded.This morphology would suggest the presence of a laminar complex on the lateral surface of the neural spine of the posterior dorsal vertebrae of Agustinia, as seen in some rebbachisaurids (e.g.Comahuesaurus and Rebbachisaurus).Between the spdl and posl there is a wide spof, which is divided by a thin, subhorizontal accessory lamina in a deeper dorsal subfossa and a wider ventral one.In posterior view, the posl is proximally slender and transversely expanded close to the apex of the neural spine, although less than the prsl.Conversely, the posl is well prominent and proximally convex in lateral view (Figure 6A), as in Katepensaurus (Ibiricu et al. 2013(Ibiricu et al. , 2015)), exceeding the posterior margin of the apex of the neural spine.
Posterior dorsal vertebra Dv-10?, MCF-PVPH-110/23.The last presacral vertebra of Agustinia preserves the distal third of the prsl and spdl, and most of the posl (Figure 6).In dorsal view, the apex of the neural spine is rhomboidal (Figure 6B), wider than long, and slightly more transversely expanded on its right portion than left one, although this condition is probably linked with diagenetic processes.The dorsal surface is medially concave in anterior view, with lateral margins convex and dorsally prominent, as in the other dorsal elements of Agustinia.Near the anterodorsal margin of the spine, the prsl and spdl frame a sprf, which is divided by a subhorizontal accessory lamina in a small and shallow ventral and an oval and posteriorly deeper dorsal subfossae.The spdl is almost straight proximally and slightly anteriorly inclined at its distal portion, whereas it is more robust and triangular in ventral view, where it merges with other lamina forming a laminar complex, as in MCF-PVPH-110/22.The posl is convex in lateral view (Figure 6A), and is more prominent than the prsl due to the anterior position of the spdl on the lateral surface of the neural spine.Between the spdl and the posl opens a subcircular spof, which is slightly deeper anterodorsally.In the posterodorsal portion, the spof is divided by a thin sub-horizontal accessory lamina in two subfossae: the dorsal one is elliptical and anteroposteriorly extended, whereas the ventral one is almost oval and slightly wider.
Cervical rib MCF-PVPH-110/10.This specimen preserves part of the proximal portion and shaft (Fig. S3A-D).The proximal portion is laminar and dorsoventrally expanded, with a concave medial surface and a slightly convex lateral edge (Fig. S3A-B).In anterior view, the capitulum is ventromedially directed, whereas the tuberculum is dorsolaterally inclined (Fig. S3A).The capitulum is robust and more proximally expanded, bearing a subcircular and concave articular surface.Posteriorly to the capitulum, there is a triangular and wide depression (Fig. S3C), which is framed by a robust ventral crest and a thinner posterodorsal lamina.No foramina, pneumatopores, or other internal (camerae, camellae) or external (fossae) pneumatic features are regarded in the proximal portion of MCF-PVPH-110/10, unlike in most Titanosauriformes where pneumatic ribs are recorded.On the other hand, the capitulum is 46° angled in lateral view (Fig. S3C), as in other neosauropodans where the angle between capitulum and tuberculum is less than 90° (Wilson and Sereno 1998).On the posterodorsal margin of the tuberculum there is a slightly robust crest that extends posteriorly to the proximal half of the preserved shaft of the cervical rib.Moreover, a short and anteroventrally inclined lamina divides a wide ventral depression from a smaller and shallower dorsal depressed surface.The shaft of the rib is oval in cross-section (Fig. S3D) and slightly medially inclined in dorsal view (Fig. S3B), turning slender on the distal half.
Anterior dorsal rib, MCF-PVPH-110/05.This bone preserves part of the proximal portion and shaft (Fig. S3E).Following the almost complete rib sequence of the macronarian Camarasaurus (Waskow and Sander 2014) and the diplodocoids Apatosaurus and Dicraeosaurus (Janensch 1929;Gilmore 1936), the medial inflexion of the rib and the relative low angle between capitulum and tuberculum would suggest this element is a left anterior dorsal rib.The proximal portion is laminar and transversely compressed, with the medial surface concave and the lateral one convex in dorsal view.From the ventrolateral portion of the tubercular region, a prominent crest runs posteriorly to the proximal half of the preserved shaft.The tuberculum and capitulum are distally incomplete; however, the proximal portion of the capitulum is 49° angled in relation to the tuberculum (Fig. S3E).The shaft is transversely compressed and dorsoventrally expanded, as in other 'plake-like' anterior dorsal ribs of Titanosauriformes (Wilson and Sereno 1998;Wilson 2002), with a slightly medial inclination in dorsal view.In MCF-PVPH-110/05 no pneumatic-related features (e.g.fossae, foramina, pneumatopores) are observed.
Anterior-to-middle dorsal rib, MCF-PVPH-110/06.This specimen comprises part of the proximal portion and shaft (Fig. S3F).The proximal portion is laminar, transversely compressed and dorsoventrally expanded, with a concave medial surface and a slightly convex lateral margin.The capitulum is slenderer and longer than the tuberculum in lateral view, diverging from each other at a 70° angle, suggesting a more posterior position with respect to MCF-PVPH-110/05.The shaft is robust, medially inclined in dorsal view, and elliptical in cross-section.
Middle-to-posterior dorsal rib, MCF-PVPH-110/03.This bone is composed of the proximal portion and shaft (Fig. S3G-I).The proximal portion of the rib is triangular in lateral view (Fig. S3H), with the capitulum diverging 79° from the tuberculum, whereas the medial surface is concave and the lateral one is slightly convex in dorsal view.Posteriorly to the tuberculum region there are two parallel and prominent crests that run posteriorly to the proximal half of the shaft.In MCF-PVPH-110/03, the shaft is D-shaped in cross-section, being the medial surface convex and the lateral one almost straight (Fig. S3I).
Middle-to-posterior dorsal rib, MCF-PVPH-110/11.This element preserved part of the proximal portion, the shaft and an articulated axial fragment that we tentatively refer to the distal portion of the parapophysis of the corresponding dorsal vertebra (Fig. S3J).The proximal portion of the rib shows a laminar aspect, with a medial concave surface and an almost straight lateral surface.The capitulum is longer than the tuberculum, diverging from it at a 45° angle.The articular surface of the capitulum is slightly concave and dorsomedially inclined in lateral view.Furthermore, the capitulum is divided from the medial concavity by a short and robust crest, which results dorsally convex in lateral view.On the other hand, a longitudinal crest runs from the posterior region of the tuberculum to the medial surface of the shaft.In MCF-PVPH-110/11 the shaft is straight in lateral view, whereas shows a gentle medial bevelling in dorsal view.Its cross-section is oval, slightly compressed transversely, with a medial convex surface and a straight lateral margin.
Middle-to-posterior dorsal rib, MCF-PVPH-110/09.This bone is incomplete, preserving parts of the proximal portion and the shaft (Fig. S3K).The capitular and tubercular regions are poorly preserved and are represented by transversely compressed laminar structures medioventrally and mediodorsally directed, respectively.The proximal end of the capitulum articulates with a rounded fragment, which we tentatively refer to as a portion of parapophysis of the corresponding dorsal vertebra.The shaft of the rib is slightly medially inclined in anterior view, with a convex lateral surface and an almost straight medial surface.Proximally, the shaft shows a triangular cross-section due to the presence of a short and robust crest that runs from the base of the tubercular region to the lateral surface of the shaft, whereas the distal portion is semicircular in cross-section.
Posterior dorsal rib, MCF-PVPH-110/07.This specimen preserves only part of the proximal portion and the shaft (Fig. S3L).The proximal portion is laminar, transversely compressed, and slightly medially inclined in anterior view.The medial surface is convex, whereas the lateral one bears a wide and triangular depression between the poorly preserved tubercular and capitular regions.However, on the ventral margin of the proximal portion there is a longitudinal and robust crest that runs posteriorly to the half of the preserved shaft.The shaft has a D-shaped cross-section, with a convex medial surface and an almost straight lateral surface.

Sacral vertebrae
Dorsosacral vertebra Sv-01?, MCF-PVPH-110/24.This specimen preserves the dorsal part of the neural spine (Figure 7), including the prsl, the spdl, and the posl.In dorsal view, the apical surface of the neural spine is rhomboidal (Figure 7B), wider than long, and the posl is to be slightly more prominent than prsl.In lateral view (Figure 7A), both laminae are convex and slightly anteriorly inclined, as in Diplodocus and Brachiosaurus (Marsh 1878;Riggs 1903).Ventrally, between the spdl and the prsl, a wide sprf opens, whereas there are several smaller and shallower accessory fossae and thin laminae more dorsally, as in Rebbachisaurus (Wilson and Allain 2015).The spdl is proximally incomplete, slightly anteriorly inclined, and more robust dorsally.Near the apical surface of the neural spine, the spdl forms an anteroposteriorly and laterally prominent rough process, as in Brachiosaurus, Diplodocus, Haplocanthosaurus and some Titanosauriformes, such as Phuwiangosaurus and Tastavinsaurus (Marsh 1878;Hatcher 1903;Canudo et al. 2008;Suteethorn et al. 2009;Taylor 2009;Foster and Wedel 2014).The spdl is located at the anterior half of the neural spine, as in Rebbachisaurus; thus, the posl is longer than the prsl, a condition that differs from Tataouinea where the spdl is on the posterior half of the spine (Fanti et al. 2013(Fanti et al. , 2015)).Dorsally, between the spdl and the posl, there is a small and shallow, oval spof, slightly posteronventrally inclined.
Sacral vertebra Sv-02?, MCF-PVPH-110/25.This sacral element is composed of the dorsal portion of the neural spine, with part of the prsl, the posl, and both spdl (Figure 7).The neural spine is fused with adjacent elements across the prsl and posl laminae.The dorsal surface of the spine is rhomboidal, wider than long (Figure 7B).In lateral view, there is a wide sprf in the ventral portion of the neural spine (Figure 7A), whereas, more dorsally, there is a set of small subfossae and subvertical, thin accessory laminae, which are particularly abundant close to the anterodorsal portion of the spine.The spdl is slightly anteriorly inclined and posteriorly convex in lateral view.Furthermore, it is particularly robust and anteroposteriorly more prominent on the most dorsal portion, where the lateral edge of the neural spine is rough and prominent.On the other hand, the posl is slightly more prominent than the prsl, and bears a wide spof.This fossa is anteroposteriorly divided in a small and shallow dorsal subfossa and a wider and oval ventral subfossa, which is framed by two sub-horizontal and thin accessory laminae.
Sacral vertebra Sv-03?, MCF-PVPH-110/26.This specimen preserves part of the neural spine, the prsl, the posl, and both spdl (Figure 7).This sacral element is completely fused with adjacent neural spines across the prsl and posl, which are slightly thinner and smaller than previous elements (MCF-PVPH-110/24-25) in dorsal view (Figure 7B).The apical surface of the spine is rhomboidal, wider than long, with the spdl transversely prominent and anteroposteriorly extended.In lateral view, the sprf is wide, turning slightly deeper dorsally (Figure 7A).On the ventral portion of the prsl there is a sub-horizontal, thin accessory lamina that merges with their counterpart on the posl of the precedent element (MCF-PVPH-110/25).The contact surface with the adjacent sacral neural spines is represented by a dorsoventrally extended and prominent crest (Figure 7A).On the other hand, the spdl shows a gently anterior bevelling and a posterior convex outline.The spof is wide and confined to the dorsal portion of the spine, being slightly deeper anterodorsally.Near to the ventral portion of the spdl, the posl bears a prominent, posteroventrally inclined crest.
Sacral vertebra Sv-04?, MCF-PVPH-110/27.This partial neural spine preserves most of the prsl, posl, and both spdl laminae (Figure 7).As in MCF-PVPH-110/25-26, this neural spine is completely fused with adjacent sacral elements across the prsl and posl.In dorsal view, the apical surface of the spine is sub-rhomboidal, with transversely expanded and robust spdl, and short and slender prsl and posl (Figure 7B).On the other hand, the dorsal surface is slightly convex in anterior view and almost posterodorsally inclined in lateral view.The ventral portion of the spdl is posteriorly inclined and convex, whereas the dorsal half is anteriorly directed and prominent; thus, the spdl appears sinusoidal in lateral view.Furthermore, the spdl is located almost in the middle portion of the spine, so the prsl and the posl seem to be equally anteroposteriorly extended.
Caudosacral vertebra Sv-05?, MCF-PVPH-110/28.The last sacral element of Agustinia is composed of part of the neural spine, including prsl, posl, and both spdl laminae (Figure 7).This element is only partially fused with the previous neural spine across the prsl.In dorsal view, the spine is sub-rhomboidal, transversely wider than long, being the prsl and posl shorter and slender with respect to the robust and expanded spdl (Figure 7B).In anterior view, the apical surface of the neural spine is almost convex, although a narrow and shallow medial depression is present.In lateral view, the spdl is robust and posteriorly convex on the ventral portion, whereas it is slender and anteriorly inclined more dorsally (Figure 7A).However, near to the apical surface of the spine, the spdl is rough, transversely prominent and anteroposteriorly extended, forming a laterodorsal process as in the other axial elements of Agustinia.Moreover, in MCF-PVPH-110/28 the spdl is on the posterior half of the neural spine, as in Haplocanthosaurus and Diplodocus (Marsh 1878;Hatcher 1903), thus the prsl is more prominent than posl.Between the prsl and the spdl, there is a wide and oval sprf, which is divided in a dorsal and a ventral subfossa by a prominent and anteroventrally directed accessory lamina.The dorsal subfossa is divided in two oval depressions by a short and thin accessory lamina.On the other hand, between the posl and the spdl there is a spof, which results slightly deeper at the dorsal half of the spine, where the well-prominent posterior edge of the spdl partially recovers it.The spof is medially divided by a thin and posteroventrally directed accessory lamina in a dorsal and a ventral subfossa.
Caudal vertebrae (Fig. 8-12).Three blocks with 12 partially articulated caudal vertebral elements are known for Agustinia However, lacking any centra remains, we tentatively consider these caudal elements as a sequence of 12 anterior caudal neural spines.Anterior caudal vertebra Ca-01?, MCF-PVPH-110/29.The first caudal element of Agustinia is represented by the dorsal part of the caudal neural spine, including the prsl, the posl, and both ll (Figure 8).In dorsal view, the apical surface of the neural spine is elliptical (Figure 8B), much more transversely extended than anteroposteriorly long due to the well-prominent dorsal process of ll, as seen in the lateral margin of caudal neural spines of Rebbachisaurus and Demandasaurus (Torcida et al. 2011;Wilson and Allain 2015).In MCF-PVPH-110/29 the dorsal portion of prsl and posl are both short, as in Rebbachisaurus, but unlike other rebbachisaurids where the morphology of the prsl and posl shows a high variability.In the anterior caudal MMCh-PV-45/41 the prsl is well prominent and the posl is reduced to a short crest, whereas in the rebbachisaurids Demandasaurus (MPS-RV-II-15; Torcida et al., 2011), MMCh-PV -45/06, and MMCh-PV-45/09 the posl are well developed and the prsl are short and reduced.On the other hand, in Amazonsaurus (UFRJ-DG-58-R/7; Carvalho et al. 2003), Katepensaurus (UNPSJB-PV-580, UNPSJB-PV-1007/8; Ibiricu et al. 2015), and Zapalasaurus (Salgado et al. 2006) the neural laminae posl, prsl, and ll are similar in size, conferring a rhomboidal aspect to the dorsal surface of the caudal neural spines.In lateral view, the ll is on the posterior half of the neural spine, resulting in a prsl more prominent than the posl (Figure 8A), and the ll is posteriorly convex and anteriorly inclined, especially dorsally, as in Rebbachisaurus (Wilson and Allain 2015).
Anterior caudal vertebra Ca-02?, MCF-PVPH-110/30.The neural spine of the second anterior caudal vertebra of Agustinia shows an elliptical surface in dorsal view, wider than long due to the wellprominent laterodorsal margins of the ll (Figure 8B).In lateral view (Figure 8A), the dorsal surface is slightly convex, as occurs in some rebbachisaurids, such as Amazonsaurus, Demandasaurus, Limaysaurus, and Zapalasaurus (Calvo and Salgado 1995;Carvalho et al. 2003;Salgado et al. 2006;Torcida et al. 2011).On the other hand, the prsl is convex ventrally and almost straight more dorsally, as in Demandasaurus, and is slightly more prominent than the posl in lateral view (Torcida et al. 2011).The ll is well prominent and shows robust dorsolateral margins, which are anteroposteriorly expanded near to the dorsal surface of the neural spine.Between the prsl and ll there is a wide sprf, which is dorsally and ventrally divided by thin and anteroventrally inclined accessory laminae in shallow subfossae.Furthermore, several small depressions on the anterodorsal margin of the prsl are observed.Conversely, the spof is narrow and dorsoventrally extended, being ventrally divided by a thin horizontal accessory lamina in two subfossae.
Anterior caudal vertebra Ca-03?, MCF-PVPH-110/31.This specimen preserves most of the dorsal portion of the neural spine, including the prsl, posl, and ll (Figure 8).In dorsal view, the apical surface of the spine is rhomboidal (Figure 8B), slightly longer than wide, whereas it is slightly convex and posterodorsally inclined in lateral view (Figure 8A), as in Amazonsaurus (Carvalho et al. 2003).The ll is on the posterior half of the neural spine, showing a sinusoidal shape in lateral view, with the ventral portion posteriorly directed and a gently anteriorly bevelling close to the dorsal surface of the spine, as seen in the caudal vertebra of Cathartesaura (Gallina and Apesteguia 2005).Dorsally, the ll is robust and transversely prominent, forming an anteroposteriorly expanded and rough process close to the dorsolateral margin of the neural spine.In anterior view, the ll is well prominent and convex dorsally, as in Demandasaurus, Katepensaurus, Rebbachisaurus (Torcida et al. 2011;Ibiricu et al. 2013Ibiricu et al. , 2015;;Wilson and Allain 2015).The posl is poorly preserved, slightly posteriorly inclined, and shorter than prsl in lateral view, especially dorsally, due to the posterior inclination of the ll.On the dorsal portion of the posl there are several small accessory fossae and thin, subhorizontal laminae, as in the rebbachisaurid MMCh-Pv-49.Anterior caudal vertebra Ca-04?, MCF-PVPH-110/32.This bone represents the most fragmented element of the axial sequence of Agustinia, preserving only part of the dorsal surface of the neural spine and the posl (Figure 8).The prsl seems to be much more reduced than posl and the ll results anteroposteriorly expanded and slightly posteriorly inclined on the dorsal portion close to the dorsolateral margin of the apical surface of the neural spine.However, due to the poorly preserved condition of the specimen, no further morphological features of this anterior caudal neural spine are available.
Anterior caudal vertebra Ca-05?, MCF-PVPH-110/13.This specimen preserves part of the neural spine (Figure 9A-F), with prsl, posl, and ll, and the right portion of the bone being better preserved than the deformed and weathered left one.The dorsal surface of the neural spine is rhomboidal (Figure 9C), slightly longer than wide, with a convex and rounded anterior margin and a quadrangular and more robust posterior surface (Figure 9B).In anterior view (Figure 9A), the prsl is wide and rough, framed by thin and divergent laminae that may be tentatively regarded as spinoprezygapophyseal laminae (sprl).Similarly, on the posterior surface of the neural spine (Figure 9B), the posl is rough and prominent, being limited by thin and sub-parallel smooth laminae that we tentatively considered as spinopostzygapophyseal laminae (spol).A similar laminar complex is seen in Comahuesaurus and rebbachisaurid MIWG 5384 (Mannion et al. 2011;Carballido et al. 2012), where the anterior and posterior medial laminae (prsr/posr and amedl/ pmedl) are rough and wider, and framed by smooth and thin more lateral laminae (e.i.sprl and spol).On the other hand, the ll is thin and slightly anteriorly bevelled in lateral view (Figure 9D), as in Demandasaurus, Limaysaurus, Rebbachisaurus, and indeterminate rebbachisaurids MMCh-PV -45/06 and CCC-017 (Calvo and Salgado 1995;Castro et al. 2007;Torcida et al. 2011;Wilson and Allain 2015).However, near to the laterodorsal margin of the neural spine, the ll is particularly robust and anteroposteriorly expanded, forming a dorsal process that partially covers the sprf and spof in lateral view.The sprf is triangular, anteroposteriorly narrow and dorsoventrally expanded, whereas the spof is wider and slightly deeper anteroventrally.
Anterior caudal vertebra Ca-06?, MCF-PVPH-110/14.This bone preserves part of the dorsal portion of the neural spine, including the prsl, posl, and ll (Figure 9G-L).The dorsal surface of the spine is rhomboidal, longer than wide, with straight and anteriorly divergent lateral surfaces and the posterior margin slightly more prominent than anterior one (Figure 9G).In lateral view, the apical surface of the spine is convex and posterodorsally inclined (Figure 9J).The neural laminae (prsl, posl, ll) show a tetraradiate arrangement in ventral view (Figure 9K, L), framing a sprf wider and deeper than the spof.The prsl is wide and rough in anterior view (Figure 9G), being framed by thin and smooth sprl; the prsl also slightly diverges laterally near to the dorsal surface of the neural spine.The right ll shows a gently posterior bevelling, whereas the better preserved left one is anteroposteriorly expanded on its lateral margin, suggesting an expansion of the robust and prominent laterodorsal process of the laminae (Figure 9J).Similarly, the wide and rough posl is laterally framed by thin laminae that are here tentatively interpreted as the spol, which slightly diverge closer to the dorsal surface of the neural spine (Figure 9H, K).On the right lateral surface of the spine, the prsf and posf are divided by thin and subhorizontal accessory laminae in dorsoventrally higher and dorsally deeper subfossae, and transversely wider and shallower ventral subfossae.In the lateral surfaces of both prsl and posl there are several small depressions, as seen in MMCh-PV-49 (Haluza et al. 2012).
Anterior caudal vertebra Ca-07?, MCF-PVPH-110/15.This anterior caudal element is composed for the dorsal portion of the neural spine (Figure 10A-F), preserving prsl, posl, and ll.In dorsal view, the spine is rhomboidal, longer than wide, with straight and anterolaterally directed lateral surfaces, and both quadrangular anterior and posterior margins, being the posterior slightly more prominent than anterior one (Figure 10C).In lateral view, the dorsal surface is convex and both prsl and posl are parallel and show a slightly posterior inclination (Figure 10D).The ll are thin and well transversely expanded on the ventral portion.In ventral view, the neural laminae are orthogonally arranged, with the prsl more prominent than posl (Figure 10E-F).Both sprf and posf are wide and deep, but only the sprf show several secondary, small and smooth depressions, and is divided by a thin and horizontal accessory lamina in dorsal and ventral subfossae.
Anterior caudal vertebra Ca-08?, MCF-PVPH-110/16.This bone is represented for the dorsal portion of the neural spine, with prsl, posl, and both ll (Figure 10G-L).The dorsal surface of the neural spine is triangular, longer than wide, with a convex anterior margin and a quadrangular and more prominent posterior surface (Figure 10I).In lateral view, the dorsal surface is straight and slightly posterodorsally inclined, whereas the anterior and posterior surfaces are parallel and posteriorly directed (Figure 10J).In ventral view, the prsl, posl, and ll are orthogonal, with the prsl more prominent than posl and both laminae being more robust than the ll (Figure 10K, L).The prsl is rough and divergent dorsally (Figure 10G), being framed by a pair of thin laminae, here tentatively considered as sprl, which are clearly discernible only in ventral view (Figure 10K, L).Conversely, the posl is almost straight, and slightly divergent dorsally (Figure 10H), and along with thin spol, forms a prominent structure slightly concave medially near to the dorsal surface of the neural spine.The ll are well prominent transversely, especially in the ventral portion.Moreover, this lamina is wide in lateral view, extending anteroposteriorly close to the laterodorsal margin of the neural spine, where it forms a V-shaped, prominent structure (Figure 10J).Indeed, the ll seems to represent a laminar complex of, at least, two neural laminae, such as the spinodiapophyseal lamina (spdl) and the spinopostzygapophyseal lamina (spol).However, lacking most of the neural arch, the laminar waypoints and tracks across the neural spine are not discernible.Between the neural laminae there are oval and narrow sprf and spof, which result more reduced than in the preceding axial element.
Anterior caudal vertebra Ca-09?, MCF-PVPH-110/17.This specimen is one of the better preserved axial elements of Agustinia, preserving the neural spine and part of the base of the neural arch (Figure 11A-F).In dorsal view, the neural spine is oval, longer than wide, with a convex anterior margin and a quadrangular posterior surface (Figure 11C).The dorsal surface is straight and posterodorsally directed in lateral view (Figure 11D), whereas it is convex in anterior view (Figure 11A).In lateral view, the neural spine is slightly posteriorly inclined, with almost parallel anterior and posterior surfaces (Figure 11D).The prsl is more prominent and robust than the posl, whereas the ll are anteroposteriorly extended, especially dorsally, but poorly prominent in anterior view (Figure 11A).The sprf is wide and triangular, showing a set of small and shallow accessory depressions, especially near the anterodorsal margin of the spine.The spof is elliptical and dorsoventrally extended, turning slightly deeper close to the posterior surface of ll.In posterior view, the postzygapophysis is lateroventrally directed (Figure 11B) and connects dorsally with the neural spine with two thin laminae that we tentatively refer to as the medial and lateral spinopostzygapophyseal laminae (med.and lat.spol).The med. spol shows a sinusoidal outline in posterior view (Figure 11B), converging ventrally and diverging more dorsally.Furthermore, it frames a posl that is narrow and transversely concave ventrally and wider and more prominent dorsally.On the other hand, the lat.spol runs throughout the posterolateral surface of the neural spine, merging with the spdl to form a prominent and V-shaped laminar complex in lateral view (Figure 11D), as in MCF-PVPH-110/15-16.
Anterior caudal vertebra Ca-10?, MCF-PVPH-110/18.This specimen is represented for a partial anterior caudal neural spine (Figure 11G-I).The dorsal surface of MCF-PVPH-110/18 is elliptical in dorsal view, longer than wide, and with both anterior and posterior surfaces quadrangular in shape (Figure 11H).Moreover, it is straight and slightly posterodorsally inclined in lateral view (Figure 11I) and convex in anterior view (Figure 11G).The prsl is wide and rough, especially near to the anterodorsal margin of the spine, where the sprl diverges laterally.In lateral view, the prsl and posl are posteriorly inclined, with the prsl slightly more prominent than posl (Figure 11I).The lateral laminar complex, tentatively formed by lat.spol and spdl, is V-shaped and divergent dorsally (Figure 11I), and is more anteroposteriorly extended, than in MCF-PVPH-110/16-17, but less transversely prominent than in those precedent elements.Furthermore, on the left surface of the neural spine (Figure 11I), there is a short and robust accessory lamina that divides two small depressions on the ventral portion of the ll.The prsf and posf are shallow and reduced (Figure 11G, I), and lack of secondary fossae and laminae.In MCF-PVPH-110/18 only the left postzygapophysis is preserved, which shows a smooth and anteroposteriorly concave articular surface.
Anterior caudal vertebra Ca-11?, MCF-PVPH-110/19.This caudal element is composed of a neural spine strongly deformed, especially on the right surface (Figure 12A-B).In dorsal view, the surface is oval, longer than wide, with quadrangular anterior and posterior margins, being the posterior more robust and prominent than the anterior one (Figure 12B).In lateral view, the neural spine is almost dorsally directed, with the dorsal surface concave and posterodorsally inclined (Figure 12A).The anterior surface of the spine is straight, whereas the posterior one is slightly dorsoventrally concave.Both prsl and posl are thick, with the posl wider and more prominent than prsl.
Anterior caudal vertebra Ca-12?MCF-PVPH-110/20.This anterior caudal element is composed by the neural spine and part of the neural arch (Figure 12C-F).The dorsal surface of MCF-PVPH-110/ 20 is oval, longer than wide, and with both straight anterior and posterior margins (Figure 12D), with the posterior surface being more robust and prominent than the anterior one, as in preceding elements.In lateral view, the neural spine is dorsally directed, showing an almost straight and slightly posterodorsally inclined dorsal surface (Figure 12C).Furthermore, the anterior surface is straight, whereas the posterior one is more concave than MCF-PVPH-110/19.The prsl is wide and rough (Figure 12F), being laterally framed by a thin sprl, which gently diverges close to the dorsal portion of the neural spine.In lateral view, the prsl is more prominent than the posl (Figure 12C), whereas the ll are smooth and less prominent than in the other axial elements of Agustinia (e.g.MCF-PVPH-110/16-18).In MCF-PVPH-110/20 the ll is composed by a triangular laminar complex on the anterolateral surface of the neural spine, with a dorsoventrally convex anterior margin and a concave posterior one (Figure 12C).On the posterior surface, the posl is wide and rough, especially dorsally, where the spol gently diverge laterally (Figure 12E).The neural fossae are reduced to shallow depressions close to the prsl and posl margins.Due to the poorly preserved conditions of the neural arch, two laminar prominences are here tentatively considered as the basal portion of the left prezygapophysis and part of the right postzygapophysis (Figure 12C).

Appendicular skeleton
The type-material of Agustinia includes a dorsal portion of the iliac blade, articulated left tibia and fibula, and the five right metatarsals, some of which are incomplete or poorly preserved.Ilium MCF-PVPH-110/08.Originally referred to an atypical osteoderm by Bonaparte (1999), this element was reconsidered as a fragment of the pelvic girdle by Bellardini and Cerda (2017), and is here figured and described as the dorsal portion of the iliac blade of Agustinia (Figure 13).The bone is laminar, transversely compressed and slightly medially bevelled in dorsal view (Figure 13C).Moreover, it bears two robust processes on the medial surface, which are dorsally directed and medially convergent in lateral view (Figure 13A).The anterior process is quadrangular, with two short and orthogonal crests, whereas the posterior one is slender and triangular in cross-section.Ventrally to the processes, two rough and prominent crests run across the medial surface of the bone with a gentle medial bevelling (Figure 13D).The prominent processes and the ventral crests of MCF-PVPH-110/08 would represent the distal portions of the sacral transverse processes and the scars of the sacral ribs on the medial surface of the ilium, respectively, as seen in the iliac blade of the titanosauriform Tambatitanis (Saegusa and Ikeda 2014) and the indeterminate rebbachisaurid MMCh-PV-45.As in Tambatitanis, where the sacral ribs n°3 and n°4 are medially convergent, we consider MCF-PVPH -110/08 as the dorsal portion of the left iliac blade (Figure 13A, D).
Tibia MCF-PVPH-110/02.This bone was originally described by Bonaparte (1999) as a right fibula, however recent re-evaluation allowed us to reconsider some morphological features (e.g.cnemial crest, distal condyles) as more pertinent for a left tibia (Figure 14A-E).MCF-PVPH-110/01 and MCF-PVPH-110/02 were found articulated via the cnemial fossa of the tibia and the anterior crest of the fibula.Once disarticulated, an anterolaterally bevelled cnemial crest (originally considered as an anterior crest of the fibula by Bonaparte 1999) and distinct distal condyles previously included into the sedimentary matrix were recognised (Figure 14A).
The tibia is incomplete and partially deformed, lacking part of both epiphyses and most of the external surface.In posterior view, the tibia of Agustina is slender and straight, transversely compressed, and with the medial surface distally concave and the lateral one slightly convex (Figure 14D).Both epiphyses are anteroposteriorly expanded with respect to the diaphysis in lateral view, with the proximal end more than the distal one (Figure 14C).The proximal articular surface is rough and elliptical, anteroposteriorly extended and transversely compressed (Figure 14A), which is a plesiomorphic condition within Sauropoda, seen in Omeisaurus, Tazoudasaurus, and different diplodocoids (e.g.Galeamopus), especially Rebbachisauridae, such as Lavocatisaurus, Zapalasaurus, MMCh-PV-45/34, and MPEF-PV-1698 (Salgado et al. 2006;Allain and Aquesbi 2008;Tschopp et al. 2015;Canudo et al. 2018).In lateral view, the proximal surface of the tibia is convex and posteriorly inclined, as in Dongbeititan, Janenschia, and Lavocatisaurus (Bonaparte et al. 2000;Wang et al. 2007;Mannion et al. 2019).The anterodorsal margin of the proximal epiphysis forms an almost right angle with the lateral surface of the bone (Figure 14C, E), whereas the posterodorsal margin is more prominent, as seen in the rebbachisaurids Lavocatisaurus and Zapalasaurus, and the derived Titanosauriformes Huabeisaurus, Sauroposeidon, and Uberabatitan (Salgado et al. 2006;Rose 2007;Salgado and Carvalho 2008;D'Emic et al. 2013;Canudo et al. 2018).The cnemial fossa of the tibia is on the proximolateral surface of the bone, being concave and triangular in lateral view (Figure 14C).It articulates with the anterior crest of the fibula (Figure 14A) and it is anteriorly framed by a prominent and rough cnemial crest (Figure 14C, D).The cnemial crest is on the anterolateral margin of the proximal third of the bone, proximodistally extended and slightly laterally bevelled on the distal portion, as in Gobititan and Tangvayosaurus (Allain et al. 1999;You et al. 2003).It is proximally and distally slender, whereas it is more robust medially, where it slopes posteriorly in lateral view.In Agustinia, the cnemial crest shows a rounded outline, as in several diplodocoids, such as Dicraeosaurus, Limaysaurus, Lavocatisaurus, and Zapalasaurus (Janensch 1914;Calvo and Salgado 1995;Salgado et al. 2006;Canudo et al. 2018).
In MCF-PVPH-110/02 the diaphysis is triangular in crosssection, being the anterior surface convex and the posterior one slightly concave.On the anterior surface there are two crests: a proximal, short and anteriorly inclined crest, and an almost straight, and more distally robust crest on the distal portion of the diaphysis.In lateral view, the anterior surface of the diaphysis is straight, whereas the posterior one is concave (Figure 14C).
On the other hand, the distal epiphysis of the tibia is transversely compressed and anteroposteriorly expanded, with a rounded anterodistal margin and a pointed posterodistal edge.Despite being partially covered by the sedimentary matrix, the distal articular surface has an oval outline.The posterior condyle is more distally prominent than the lateral condyle, which is, in turn, more robust in posterior view.
Fíbula MCF-PVPH-110/01.This bone is here interpreted as the left fibula of Agustinia, contrary to Bonaparte's (1999) original description of it as a right tibia.It is incomplete and poorly preserved, lacking the distal epiphysis and most of the external surface, especially on the proximal half of the bone (Figure 14A, F-J).It is slender, slightly longer than the tibia, transversely compressed, and with the proximal epiphysis much more anteroposteriorly expanded than the rest of the bone.In proximal view, the articular surface is elliptical, four times anteroposteriorly longer than transversely wide (Figure 14F), as seen in the diplodocid Galeamopus, the rebbachisaurids Lavocatisaurus and Limaysaurus, and several Titanosauriformes (e.g.Huabeisaurus, Mendozasaurus, and Vouivria) (Calvo and Salgado 1995  2015; Mannion et al. 2017;Canudo et al. 2018;González Riga et al. 2018).The lateral surface is convex, whereas the medial one is concave anteriorly and straight posteriorly, as in Lavocatisaurus (Canudo et al. 2018).In lateral view, the proximal surface is slightly convex, forming a prominent and rounded process with the posterior surface of the bone (Figure 14G, I), as in Bellusaurus, Lavocatisaurus and some Titanosauriformes (e.g.Bonatitan, Fukuititan, Huabeisaurus, and Tastavinsaurus).Conversely, the anteroproximal margin of the bone is anteriorly prominent, proximodistally extended, and rounded in lateral view, as in Apatosaurus, Lavocatisaurus, and some Titanosauriformes, such as Ferganasaurus and Uberabatitan (Marsh 1877;Alifanov and Averianov 2003;Salgado and Carvalho 2008;Canudo et al. 2018), representing the anterior prominence of the fibula that articulates with the cnemial fossa of the tibia.On the medial surface of the proximal third of the fibula there is a wide and rough, concave surface (Figure 14I), which represents the articular surface with the tibia (Wilson and Sereno 1998;Upchurch et al. 2004).
The diaphysis is slender, transversely compressed and slightly laterally bevelled on the distal portion.It is D-shaped in crosssection, with a straight medial surface and a convex lateral surface.The minimum diameter is on the distal third of the bone (Figure 14G, I).In lateral view, the anterior surface of the fibula is convex, whereas the posterior one is concave (Figure 14G).From the posterolateral portion of the mid-shaft, a lateral trochanter runs posterodistally to the distal third of the bone (Figure 14H, J), representing a slender crest for the insertion of the flexor digitorum longus muscle (Borsuk-Bialynicka 1977).On the anterior surface of the bone, and proximally to the lateral trochanter, the anterior trochanter is represented for a rough, shallow, and triangular surface (Figure 14H), representing the attachment of the musculus iliofibularis (Borsuk-Bialynicka 1977).
Most of the distal third of MCF-PVPH-110/01 is lost.However, it seems slightly anteroposteriorly expanded with respect to the diaphysis, transversely compressed, and slightly medially bevelled in anterior view (Figure 14H).
Metatarsals MCF-PVPH-110/33-37.The metapodials described for Bonaparte (1999) as belonging to the left pes, are here reconsidered as right metatarsals I to V (Figure 15).All bones are incomplete, fractured and partially deformed; however, the metatarsals I to IV preserve both epiphyses and most of the diaphyses, whereas the metatarsal V is represented only by the proximal portion of the bone.Across the series, the metatarsal I is the shortest element whereas the metatarsal III is the longest.The ends are transversely expanded with respect to the diaphyses and slightly anteroposteriorly compressed, with proximal articular surfaces rougher than the distal ones.In Agustinia, the metatarsals articulate proximally each other and diverge distally, conferring a spreading posture to the feet, which is a synapomorphic condition of Eusauropoda (Wilson 2002).For descriptive purposes, the principal axis of the bones is oriented proximodistally.
Metatarsal I MCF-PVPH-110/33.This specimen represents the better preserved metatarsal of Agustinia.It is short and robust with expanded epiphyses and transversely compressed diaphysis (Figure 15A-D).The proximal surface is slightly convex and posteriorly inclined in lateral view (Figure 15A), in a 14° angle with respect to the axis of the bone, as in Cetiosaurus and Euhelopus (Upchurch and Martin 2003;Wilson and Upchurch 2009), but differing from most diplodocoids where greater angles are recorded (e.g.Apatosaurus, 38°; Barosaurus, 20°; Diplodocus, 35°; Bonnan 2005).In proximal view, the rough articular surface is D-shaped, with a convex medial surface and a straight lateral surface (Figure 15B).However, there is a prominent process on the posterolateral margin, as seen in Sauroposeidon and Tastavinsaurus (Rose 2007;Canudo et al. 2008).In lateral view, the anterior and posterior margins of the proximal third of the bone are prominent and slightly convex, extending distally to the half of the metatarsal I.These margins are laminar in anterior view, forming slender crests that are laterally framed by small depressions, a condition not seen in other sauropods and here considered as an autapomorphic feature of Agustinia (see Revised diagnosis).In Lavocatisaurus MOZ-Pv-1232/81 the anterior and posterior edges are concave in lateral view, and only the posterior edge is prominent and laminar, forming a slender crest that is laterally framed by a small depression.
In MCF-PVPH-110/33 the diaphysis is transversely compressed, with a convex medial surface and a wide and triangular lateral concavity that represents the articular surface for the metatarsal II.Ventrally, this concavity is framed by two short, slender, and medially convergent crests, where the anterior and posterior ligaments between metatarsal I and II were inserted (alc, plc; Figure 15A).In lateral view, the anterior and posterior margin of the distal portion of the diaphysis are concave, as seen in the rebbachisaurids Lavocatisaurus and Zapalasaurus, and some Titanosauriformes, such as Dongbeititan and Tastavinsaurus (Salgado et al. 2006;Wang et al. 2007;Canudo et al. 2008;2018).
The distal third of metatarsal I is incomplete, lacking part of the ventral and posterior surfaces.However, it is slightly expanded with respect to the diaphysis and twisted with respect to the proximal epiphysis (Figure 15A, D).In ventral view, the articular surface is rough, rectangular, and transversely expanded, with a convex lateral margin and an almost straight medial one (Figure 15C).The distal condyles are not preserved.However, in lateral view there is a transversely extended concavity on the lateral portion of the distal surface that divides an anterior portion from a more ventrally prominent posterior half (Figure 15A), as in most sauropods (Upchurch et al. 2004).The laterodistal margin is poorly preserved.However, it seems to have a laterodistal process, as in most diplodocids (Wilson and Sereno 1998;Upchurch et al. 2004;Tschopp et al. 2015), Lavocatisaurus (MOZ-PV-1232/81), and some basal Titanosauriformes (McIntosh 1990;Upchurch 1995;Canudo et al. 2008;D'Emic 2012).
Metatarsal II MCF-PVPH-110/34.It is a slender bone with both epiphyses expanded with respect to a transversely compressed diaphysis (Figure 15E-H).MCF-PVPH-110/34 is slightly longer than metatarsal I, but shorter than metatarsal III and IV.In dorsal view, the proximal articular surface is P-shaped, as in Sauroposeidon (Rose 2007), being transversely compressed and anteroposteriorly extended, with a straight lateral surface and a posteriorly convex medial one (Figure 15F) that articulates with the proximolateral concavity of metatarsal I.In lateral view, the proximal articular surface is slightly convex (Figure 15E), as in Limaysaurus and Sauroposeidon (Calvo and Salgado 1995;Rose 2007), unlike the condition present in several Titanosauriformes where this surface is strongly posteriorly inclined (e.g.Antarctosaurus, Epachthosaurus, Gobititan, Venenosaurus, and Notocolossus;von Huene 1929;Tidwell et al. 2001;You et al. 2003;Martínez et al. 2004;González Riga et al. 2016).
The diaphysis is transversely compressed, being both lateral and medial surfaces concave proximally and convex distally.The anterior and posterior margins are concave in lateral view (Figure 15E), but less than metatarsal I.
The distal end is incomplete, lacking the posteromedial portion of the bone.However, it is slightly transversely expanded with respect to the diaphysis and twisted with respect to the proximal end (Figure 15G, H).The distal articular surface is rough and quadrangular in distal view, wider than long (Figure 15G).There is a shallow and transversely extended concavity that divides the distal surface on slightly prominent anterior and posterior halves.
Metatarsal III MCF-PVPH-110/35.This specimen is the largest metatarsal of the series, as in most Sauropoda (Upchurch et al. 2004).The metatarsal III of Agustinia is a slender and transversely compressed bone with both ends anteroposteriorly expanded, especially the proximal one (Figure 15I-L).In dorsal view, the proximal articular surface is oval, slightly longer than wide, with a convex medial margin and an almost straight lateral one (Figure 15J), and concave and anteriorly inclined in lateral view, with both medial and lateral margins dorsally prominent (Figure 15I).
The diaphysis shows a triangular cross-section, with a convex medial margin and a concave lateral one.On the lateral surface, there is a longitudinal crest on the proximal third of the bone to the half of the diaphysis, dividing two dorsoventrally extended and slightly concave surfaces near the anterior and posterior margin of the bone (Figure 15I).The medial surface is anteriorly concave, representing the articular surface for metatarsal II (Figure 15L).In lateral view, the anterior margin is less concave than the posterior one, whereas the minimum diameter is on the distal third of the bone (Figure 15I).
The distal epiphysis is well preserved and as transversely as anteroposteriorly expanded with respect to the diaphysis, but narrower than the proximal one.The articular surface is trapezoidal in distal view, being slightly longer than wide (Figure 15K), whereas, in lateral view, it is more transversely concave than metatarsal I and II (Figure 15I).
Metatarsal IV MCF-PVPH-110/36.This element is slender and shorter than metatarsal III, but longer than metatarsal I and II.The bone is incomplete, lacking most of the diaphysis and the proximolateral portion (Figure 15M-P).Both ends are slightly expanded with respect to the diaphysis, which is transversely compressed (Figure 15M).The proximal articular surface is incomplete, lacking the lateral half due to weathering.The preserved portion is rough, with rounded margins in proximal view (Figure 15N).In lateral view, it is convex and anteriorly inclined (Figure 15M).
The diaphysis is triangular in cross-section, with a straight medial surface and a convex lateral one.In ventral view, the distal articular surface is oval, with the lateral margin more prominent than the medial one (Figure 15O).This surface is slightly concave in medial view (Figure 15P) and posterodorsally bevelled in lateral view (Figure 15M).No distal condyles are present.
Metatarsal V? MCF-PVPH-110/37.This specimen preserved only part of the proximal half and the posterior portion of the distal end (Figure 15Q-S).The proximal articular surface is markedly rough and anteriorly prominent (Figure 15R), whereas it is straight and posteriorly inclined in lateral view (Figure 15Q).The medial surface of the diaphysis is convex, whereas the lateral one is slightly concave.The distal end is represented only by a fragment of the posterior portion.

Phylogenetic analysis
Due to the poorly preserved condition of the holotype, the taxonomic validity and the phylogenetic affinities of Agustinia were debated (Salgado et al. 2004;D'Emic et al. 2009; Mannion and Calvo 2011), and dismissed from several phylogenetic discussions (e.g.Wilson 2002;D'Emic 2012;Carballido and Sander 2013;Mannion et al. 2013;Tschopp et al. 2015;Upchurch et al. 2015).Only Curry Rogers (2005) codified Agustinia for its contribution to titanosaurian evolution and diversification, although this was based on the original assumption that Agustinia could bear osteoderms and six sacral vertebrae.
The osteological reassessment and the new morphological data obtained from the present redescription of the type materials, not only allowed us to propose a better supported diagnosis for Agustinia, but also a new phylogenetic position for this enigmatic sauropod taxon.In this context, we scored Agustinia using a modified version of the data matrix recently published by Bellardini et al. (2022b), adding Itapeuasaurus, a new rebbachisaurid from the Cenomanian of Brazil recently described, and four new characters (see SOM).
Alternative hypotheses.The new osteological and phylogenetic analyses carried out on the type-material of Agustinia suggest close relationships with the basal members of Rebbachisauridae.However, some authors proposed titanosaur affinities for Agustinia on the basis of the presence of osteoderms and six sacral vertebrae (Upchurch et al. 2004;Curry Rogers 2005).Although the histological features of its bony structures allowed reconsideration, and rejecting, the hypothesis that Agustinia was an armoured sauropod (Bellardini and Cerda 2017), the presence of a sacrum with five elements can be only inferred via indirect morphological features due to the poor preserved conditions of the specimen.Therefore, with the aim of testing the alternative hypothesis of Agustinia as a Titanosauria member, we force its position by improving the force constraint methodology set in TNT.When Agustinia is forced into the titanosaurian node as sister-taxon of Andesaurus, 12 extra steps are needed to resolve the monophyly of Titanosauria.In order to evaluate the statistical confidence of this result, we improved the Templeton test script (Carballido et al. 2019), which recovered 14 characters that are differently optimised in the compared topologies.Thirteen of these characters in conflict (char. n°196, 198, 199, 212, 237, 244, 363, 384, 391, 392, 419, 420, and 421) are better optimised in the MPT (Agustinia as Rebbachisauridae), whereas only one character (char.n° 370) is better optimised when Agustinia is forced as a basal titanosaur.Therefore, the difference of 12 extra steps between the two topologies is recovered because each character in conflict is causing a single extra step (+13-1 = +12 extra steps).Finally, the Templeton test values indicate that the forced topology can be rejected with a statistically significant confidence of 98% (p_W = 0.002).See Supplementary Online Material for the complete list of characters in conflict and statistical values.

Discussion
With the redescription of the type-material of Agustinia we recognised a combination of plesiomorphic and apomorphic features that allowed us to consider it as a sauropod dinosaur.Thus, Agustinia shows columnar limb-bones, four or more sacral vertebrae, and proximal areas of metatarsals I and V subequal to that of metatarsals II and IV, as in all others Sauropoda.Moreover, several morphological features of the postcranial elements of MCF-PVPH -110 are shared with different members of Rebbachisauridae, such as well prominent spinodiapophyseal and lateral laminae on dorsal, sacral, and caudal neural spines, tetraradiate arrangement of neural laminae of all preserved vertebrae, transversely compressed proximal condyle of the tibia, and metatarsal I with proximolateral crest and distolateral process.Furthermore, we have performed a new phylogenetic analysis on the basis of a broader codification with respect to previous contributions (Curry Rogers 2005), recovering Agustinia as a basal member of Rebbachisauridae.This attribution was only briefly mentioned by Bonaparte (1999, p. 11) in the conclusions of the original description of Agustinia (i.e.' . . .based on the morphology of the neural spine, with four laminae at right angles, Agustinia is more similar to members of the Rebbachisauridae (Rebbachisaurus garasbae and "Rebbachisaurus" tessonei) than to those of the Titanosauridae . . .').However, considering the presence of osteoderms, Bonaparte (1999) erected Agustiniidae, as a new clade of incertae sedis sauropods, which was posteriorly related to other armoured sauropods: Titanosauria (e.g.Leanza et al. 2004;Curry Rogers 2005).In this sense, the recent histological analysis (Bellardini and Cerda 2017) and the new phylogenetic results presented here, definitively reject the hypothesis of titanosaurian affinities for Agustinia, supporting, in turn, close rebbachisaurid relationships.

Comments on revised diagnosis of Agustinia
Despite the poorly preserved condition of the type material, the axial and appendicular elements of Agustinia preserved different diagnostic features that led us to define a new diagnosis for the Cerro de los Leones taxon.Thus, a unique combination of three morphological conditions (autapomorphies 1-3; Figure 4) was identified (see Revised diagnosis of Systematic palaeontology).With respect to the first autapomorphic feature it is apically narrow and laminar in shape (although in some diplodocoids (e.g.Apatosaurus, Diplodocus) and several rebbachisaurids (e.g.Demandasaurus, Nigersaurus, and Rebbachisaurus) there are prominent and proximodistally well-developed spinodiapophyseal (spdl) or lateral (ll) laminae in the dorsal, sacral and caudal elements (Marsh 1877;1878;Sereno et al. 2007;Torcida et al. 2011;Wilson and Allain 2015)).Conversely, in Agustinia the ll are robust, transversally prominent and anteroposteriorly expanded, forming apical process that involve and delimit the spinoprezygapophyseal (sprf) and spinopostzygapophyseal (spof) fossae in the last dorsal, sacral, and anterior caudal neural spines.The presence of this condition in the axial sequence of Agustinia is here considered as an autapomorphic feature within Sauropoda.Also, in Tataouinea the spdl and ll are transversally prominent in the sacral and caudal neural spines (Fanti et al. 2013(Fanti et al. , 2015)), but not well anteroposteriorly expanded as in Agustinia, and the dorsolateral processes of the caudal spines do not involve and delimit deep sprf and spof in Tataouinea.Similarly, in Tambatitanis the dorsolateral process is laterally prominent but not elongated in the caudal neural spines (Saegusa and Ikeda 2014), and does not delimit apically the sprf and spof.On the other hand, some Titanosauriformes (e.g. Brachiosaurus, Phuwiangosaurus, and Tastavinsaurus) show prominent and expanded spdl in the sacral neural spines, but lacking apically robust laminae in the dorsal and anterior caudal vertebrae (Martín et al. 1994;Canudo et al. 2008;Suteethorn et al. 2009;Taylor 2009Taylor , 2010;;Royo Torres et al. 2012).Considering the deep, dorsoventrally expanded and elliptical sprf and spof (second autapomorphy; Figure 4D-G), in some neosauropods (e.g.Apatosaurus, Brachiosaurus, and Supersaurus) and several rebbachisaurids (e.g.Cathartesaura, Limaysaurus, and Nigersaurus) the spdl, ll, prsl and posl delimit deep sprf or spof in some dorsal, sacral, or caudal neural spines (e.g.Marsh 1877;Riggs 1903;Jensen 1985;Calvo and Salgado 1995;Sereno et al. 1999;Gallina and Apesteguía 2005;Taylor 2009).However, both sprf and spof of Agustinia are well developed through all the preserved neural spines (Figure 4A-C).In Rebbachisaurus and Tataouinea the sprf and spof are deep in the caudal neural spines but not in the sacrals (Figure 4D-E), whereas the spof are elongated but the sprf are reduced and shallow in the caudal neural spines of Demandasaurus and Diplodocus (Figure 4F) (Marsh 1878;Torcida et al. 2011;Fanti et al. 2013;2015;Wilson and Allain 2015).Conversely, in Apatosaurus, Limaysaurus, and Supersaurus the sprf are elongated and the spof are reduced in the caudal neural spines (Marsh 1877;Jensen 1985;Calvo and Salgado 1995).Finally, in Bellusaurus, Brachiosaurus, Diplodocus, and Phuwiangosaurus there are deep sprf and spof in the sacral vertebrae but not in the dorsal and caudal neural spines (Figure 4G) (Marsh 1878;Dong 1990;Martín et al. 1994;Taylor 2009;Suteethorn et al. 2009;2010;Mo 2013).
In Agustinia, the most posterior anterior caudal vertebrae show V-like and dorsally divergent lateral laminae in lateral view, a morphological condition that we include as the second autapomorphy in the new diagnosis (Figure 4H).In some diplodocoids and several rebbachisaurids (e.g.Marsh 1877; Calvo and Salgado 1995;Carvalho et al. 2003;Gallina and Apesteguía 2005;Fanti et al. 2013;Ibiricu et al. 2013;Wilson and Allain 2015) the ll is a laminar complex resulting from the merging of different neural laminae (Figure 4I-R).In Amazonsaurus, Limaysaurus, and Tataouinea the ll is composed for the sprl+spol, whereas in Apatosaurus it is the lat.spol that merges with the spdl.Conversely, in Cathartesaura the ll is a laminar complex that includes sprl+lat.spol+spdl, whereas in Katepensaurus and Rebbachisaurus the sprl merges with the spdl.In these taxa the neural laminae locate proximally, usually on the lateral surface of the base of the neural spines, forming a structure ⅄-like, whereas in Agustinia the ll is Y-like, diverging distally in an anterior and posterior branch, a condition not recorded in any other sauropod taxa.
With regard to the third autapomorphic feature of Agustinia (Figure 4S), in most sauropods, the metatarsal I are short and robust bones with both concave anterior and posterior surfaces (Upchurch et al. 2004) (Figure 4T-AE).On the other hand, in Agustinia, the anterior and posterior surfaces of metatarsal I are straight and sub-parallel in lateral view, at least up to half of the bone, a unique condition within Sauropoda (Figure 4S).In Tazoudasaurus the anterior and posterior surfaces are straight in lateral view but only in the proximal third of the metatarsal I (Figure 4U), whereas in Venenosaurus only the anterior edge is straight in lateral view up to half of the bone (Fig. 4AC) (Tidwell et al. 2001;Allain et al. 2004;Allain and Aquesbi 2008;Peyer and Allain 2010).Conversely, the metatarsal I of the rebbachisaurid Lavocatisaurus MAU-PV-1232/81 (Figure 4A) shows a laminar and prominent posterior surface that strongly resembles the condition seen in Agustinia, although the anterior surface is shallow and concave in lateral view.

Comparisons with other rebbachisaurids from the lohan cura formation
The sauropod fossil record of Lohan Cura Formation includes two taxa in addition to Agustinia: Comahuesaurus windhauseni and Ligabuesaurus leanzai.The first taxon represents a basal rebbachisaurid from the upper section of the Puesto Quiroga Member of Cerro Aguada del León locality (Picún Leufú, Neuquén Province, Argentina).Originally referred to Limaysaurus sp. by Salgado et al. (2004), the fossil bones from Cerro Aguada del León were redescribed by Carballido et al. (2012) and included in the type-material of the new taxon Comahuesaurus, which includes different juvenile and subadult specimens.On the other hand, Ligabuesaurus was described as a basal titanosaur by Bonaparte et al. (2006) on the basis of several isolated teeth and semi-articulated postcranial elements belonging to a single individual from the lower section of the Cullín Grande Member of the Cerro de los Leones locality (Picún Leufú, Neuquén Province, Argentina).Recently, Bellardini et al. (2022b) redescribed the type-material of Ligabuesaurus, including new axial and appendicular bones of different individuals from the same fossiliferous level of holotype, and performed a new phylogenetic analysis that recovered it as a non-titanosaur somphospondylan.
In order to explore the morphological and taxonomic diversity of Rebbachisauridae from Lohan Cura Formation, we provide below a brief comparison between the overlapping elements of Comahuesaurus and Agustinia.
In Agustinia, the lateral laminae (ll) are prominent and proximodistally developed in the caudal neural spines, where, together with the prominent prespinal (prsl) and postspinal (posl) laminae, frame deep and dorsoventrally elongated spinoprezygapophyseal (sprf) and spinopostzygapophyseal (spof) fossae.These conditions differ from the caudal vertebrae of Comahuesaurus, where the ll are reduced and there are no V-shaped structures on the lateral surface of the spines, nor deep sprf and spof.In the tibia of Comahuesaurus (MOZ-6764), the proximal condyle is rounded and the posterodorsal margin is almost straight, whereas in Agustinia, it is transversely compressed and posterodorsally prominent and pointed.In lateral view, the posterior surface of the tibia is concave in Agustinia and straight in Comahuesaurus.In both elements, the proximal articular surface is slightly convex, although in Agustinia it is more posteroventrally inclined than in Comahuesaurus (MOZ-6764).
In Agustinia the proximal surface of the fibula shows a sinusoidal outline in dorsal view and is slightly convex in lateral view, whereas in Comahuesaurus (MOZ-6727) it is oval and posteriorly concave.Also, the posterior surface is more proximodistally concave in Agustinia than Comahuesaurus.Finally, Comahuesaurus lacks different diagnostic features recorded for Agustinia, such as the expanded dorsolateral margins, deep sprf and spof, V-shaped ll on the caudal neural spines, and sinusoidal proximal articular surface of the fibula.

Implications on the diversity and evolution of Rebbachisauridae
Following Sereno et al. (1999), Rebbachisauridae is a diplodocoid clade defined as the stem-based clade diverging from Flagellicaudata that includes all diplodocoids more closely related to Rebbachisaurus than to Diplodocus and Dicraeosaurus.The fossil record of this clade extends from the Hauterivian of Europe (Dalla Vecchia 1998, 2005) to the Cenomanian-Turonian of Patagonia (Calvo and Salgado 1995;Gallina and Apesteguía 2005;Ibiricu et al. 2013Ibiricu et al. , 2015Ibiricu et al. , 2020;;Salgado et al. 2022;Bellardini et al. 2022a).However, an older divergence from Flagellicaudata, as well as the presence of a 'ghost-lineage' including earliest rebbachisaurid members, are argued by different authors (Xu et al. 2018;Whitlock and Wilson Mantilla 2020;Salgado et al. 2022;Bellardini et al. 2022a).Despite the controversies on the origin of the clade, Rebbachisauridae is represented by several members from Gondwana and Laurasia, which suggest a wide geographical distribution and taxonomic diversification since the beginning of the Cretaceous.Up to present, and considering the rebbachisaurid fossil record (e.g.Carballido et al. 2012;Wilson and Allain 2015;Canudo et al. 2018;Whitlock and Wilson Mantilla 2020;Salgado et al. 2022;Bellardini et al. 2022a), two main dispersal events and a main diversification area are considered.In this sense, a first dispersal event was during the Early Cretaceous (Hauterivian-Barremian), with evidence from Europe, Africa, and South American (Dalla Vecchia 1998;Pereda Suberbiola 2003;Salgado et al. 2006;Apesteguía 2007;Mannion 2009;Mannion et al. 2011), whereas a last spread occurred during the Late Cretaceous (Cenomanian), where only Patagonian taxa are known (Bellardini et al. 2022a).On the other hand, most of the rebbachisaurid come from Gondwana, especially from Patagonia, with the Neuquén Basin playing a crucial role in the diversification of the clade.Indeed, three of most basal rebbachisaurids come from the Early Cretaceous of Neuquén Basin (Agustinia, Comahuesaurus, and Zapalasaurus), whereas Amazonsaurus, from the Aptian-Albian of Brazil, and Histriasaurus from the Hauterivian-Barremian of Apulian Plate (Canudo et al. 2009), are the only non-Patagonian basal members of Rebbachisauridae so far recorded.Moreover, amongst most derived rebbachisaurids, the youngest records correspond to specimens from the Cenomanian-Turonian transition of the San Jorge Basin (e.g.Katepensaurus and the indeterminate rebbachisaurids from the Bajo Barreal Formation UNPSJB- PV -580, 1004PV -580, , 1005PV -580, , 1098;;Ibiricu et al. 2012Ibiricu et al. , 2013Ibiricu et al. , 2015Ibiricu et al. , 2020)), the Neuquén Basin (e.g.Cathartesaura, Limaysaurus sp., and the indeterminate rebbachisaurids from Huincul Formation MAU-PV- EO -633, 634, 666;Calvo and Salgado 1995;Gallina and Apesteguía 2005;Salgado et al. 2022;Bellardini et al. 2022a).This evidence, together with Lavocatisaurus from the Albian of the central Neuquén Basin, suggests that in that region ruled paleoenvironmental conditions that allowed inhabitation of different populations of basal and derived rebbachisaurids, at least from the Hautherivian up to the Cenomanian-Turonian transition.Thus, considering the record of Agustinia from the Albian of the Neuquén Basin, together with that Amazonsaurus, Comahuesaurus, Lavocatisaurus, Nigersaurus, Tataouinea, and different indeterminate rebbachisaurids from the Albian of Tunisia and Brazil (Sereno et al. 1999;Carvalho et al. 2003;Carballido et al. 2012;Fanti et al. 2015;Canudo et al. 2018;Lindoso et al. 2019;Bellardini et al. 2022a), a new main dispersal event during the Aptian-Albian, at least in Gondwana, is proposed.

Conclusions
The osteological redescription of the holotype of Agustinia ligabuei allowed us to review the original diagnosis, as well as to gather a unique set of diagnostic features that support the taxonomic validity of this sauropod species.Moreover, the new phylogenetic analysis shows Agustinia well nested within Rebbachisauridae, reassessing it as a basal member of the clade.This evidence increases the diversity of Rebbachisauridae from the Lohan Cura Formation, during the Early-Late Cretaceous transition.Thus, this new taxonomic attribution not only improves our knowledge of the rebbachisaurid fauna from the central Patagonia during the Albian, but also adds new phylogenetic information on the early stages of the evolutionary history of Rebbachisauridae.

Figure 1 .
Figure 1.Location map.A) Satellite map of northern Patagonia (Argentina) showing the approximate limits of Neuquén Basin (white dotted line).B) The Cerro de los Leones locality is about 10 kilometres to the southwest of Picún Leufú city, on the south of the Neuquén Province (white crossed pickaxes).C) Satellite map of the Cerro de los Leones, where the fluvial sediments of the Lohan Cura Formation (Albian) outcrop.The holotype of Agustinia ligabuei was recovered in 1997 from the southwestern flank of the hill (yellow waypoint).Modified from Bellardini et al. 2022b.Satellite image modified from earth.google.comwebsite (date 11/05/2020).

Figure 16 .
Figure 16.Time-calibrated phylogenetic tree showing geographical distribution and chronostratigraphic range of Rebbachisauridae, based on the agreement subtree of the reduced strict consensus.Dicraeosauridae and Diplodocidae have been collapsed into the single lineage Flagellicaudata.Agustinia ligabuei (red narrows) from the Lohan Cura Formation (Albian), was recovered as a basal rebbachisaurid, more derived than Amazonsaurus.