Brandtocetus, a new genus of baleen whales (Cetacea, Cetotheriidae) from the late Miocene of Crimea, Ukraine

ABSTRACT A new cetotheriid baleen whale, Brandtocetus chongulek, gen. et sp. nov., is described from the late Miocene of Crimea, Ukraine. The type series is represented by three partial skulls with periotic bones and tympanic bullae, one of the three belonging to a juvenile. Brandtocetus chongulek has transversely expanded squamosals, ‘S’-shaped nuchal crests, an anterior margin of the occipital shield extending anterior to the center of the temporal fossa, and an elongated posterior process of the tympanoperiotic. The tympanoperiotic and postglenoid process of the squamosal are typical of cetotheriines (as opposed to herpetocetines). Comparison of the juvenile specimen with adults shows no differences in tympanoperiotic anatomy, moderate squamosal growth, and significant growth of the neurocranium after the age of at least 1 year. The phylogenetic analysis including 13 cetotheriids supports the monophyly of Cetotheriidae sensu stricto and suggests the monophyly of whales from the Eastern Paratethys (Brandtocetus, Cetotherium, Kurdalagonus, and possibly Eucetotherium). Brandtocetus and other cetotheriids from the Black Sea region possess cranial features hypothesized to be adaptations to a generalized filter feeding strategy combining different modes of suction feeding. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP


INTRODUCTION
Baleen whales of the extinct family Cetotheriidae (sensu Bouetel and Muizon, 2006;Steeman, 2007;Whitmore and Barnes, 2008;Kimura and Hasegawa, 2010;Steeman, 2010;Fordyce and Marx, 2012;Gol'din et al., in press) were widely distributed in the late Neogene. Their range included the eastern Paratethys, the area of present-day Black and Caspian Seas: Cetotherium Brandt 1843, the nominative genus with the type species Cetotherium rathkii Brandt, 1843, was described from this region. For decades, all late Miocene baleen whales found near the Black Sea have been referred to as Cetotherium. A number of species have been described from the late middle and early late Miocene (middle and late Sarmatian age sensu lato) of the northern Black Sea region ( Fig. 1): Cetotherium incertum Brandt, 1873;Cetotherium klinderi Brandt, 1871;Cetotherium maicopicum Spassky, 1951;Cetotherium mayeri Brandt, 1871;Cetotherium priscum Eichwald, 1840;Cetotherium pusillum Nordmann, 1860;Cetotherium riabinini Hofstein, 1948; and a few unnamed cetaceans (Riabinin, 1934;Spassky, 1951Spassky, , 1954Mchedlidze, 1964). Of them, only Cetotherium riabinini is identified as a member of the genus Cetotherium (Gol'din et al., in press). Tarasenko and Lopatin (2012a) described a new genus Kurdalagonus with two new species and included Cetotherium maicopicum into it. Kellogg (1931) identified Eucetotherium helmersenii (Brandt, 1871) as the type species for genus Eucetotherium. Tarasenko and Lopatin (2012b) described a new species named Vampalus sayasanicus and argued it to be congeneric with Eucetotherium helmersenii; in this case Vampalus would be a junior synonym for Eucetotherium. Two other genera of middle Miocene baleen whales from Caucasus were earlier described by Gurami Mchedlidze: Imerocetus Mchedlidze, 1964, from the Karaganian (= Badenian) and Otradnocetus Mchedlidze, 1984, from the middle Miocene. However, described taxa do not represent the total diversity of  Pilleri and Siber, 1989. A relationship of Plesiocetopsis hupschii Van Beneden, 1859, with cetotheriids cannot currently be demonstrated, because the holotype is unavailable for study (see Steeman, 2010). The status of the genus Vampalus, as well as taxonomy and phylogenetic relationships of Vampalus sayasanicus, requires further study. A possible relationship of neobalenids to cetotheriids (Fordyce and Marx, 2012) is under debate (Bisconti et al., 2013).
Diagnosis-A cetotheriid whale approximately 4-5 m long differing from all cetotheriids (in which the diagnostic traits have been preserved) by having a transversely expanded lateral portion of the squamosal; a rhomboid temporal fossa; an occipital shield extending anterior to the center of the temporal fossa; and an elongated posterior process of the tympanoperiotic with a proximodistally extended, and distally expanded, distal portion exposed as an oval surface on the posterolateral skull wall. Differs from all cetotheriids except Kurdalagonus mchedlidzei by having a strongly curved 'S'-shaped nuchal crest. Differs from Kurdalagonus mchedlidzei by having a high nuchal crest and external occipital crest; nuchal crest not overhanging the temporal fossa; a squamosal and parietal bone transversely bulging into the temporal fossa; high basioccipital crest; and a quadrangular anterior process of the periotic (not extremely transversely compressed and double-bladed, as in Kurdalagonus). Differs from 'Cetotherium' mayeri and Kurdalagonus adygeicus by having a postglenoid process distally squared in posterior view; a main ridge of the tympanic bulla that is not swollen; and a high anterior portion of the involucrum. Differs from Kurdalagonus ('Cetotherium') maicopicus by having a posteriorly extended paroc-cipital process, and a medial lobe of the tympanic bulla without a swelling. Differs from Cetotherium rathkii and Cetotherium riabinini by having a tympanic bulla gradually tapering anteriorly in medial view, a high nuchal crest, and an external occipital crest. Differs from Eucetotherium helmersenii by having ascending processes of the maxillae closely approximating each other; shorter nasals; a short and wide temporal fossa; and a proximodistally extended (not plug-like) 'cetotheriine' posterior process of the tympanoperiotic. Differs from all cetotheriids (except the abovementioned) by having a robust and dorsoventrally high zygomatic process of the squamosal bone.
Locality and Age-Late Sarmatian s.l. of the eastern Paratethys (= Tortonian), early late Miocene; Chersonian Formation. All the specimens were collected on the south coast of Tobechik Lake, Kerch Peninsula, Crimea. TNU Skull A (the holotype) was found by Sergey Kuchmarov in 2005 west of Kostyrino village (45 • 10 N, 36 • 21 E). TNU Skull 2 and TNU Skull 4 (the paratypes) were found together west of the Chorelek Valley, at the north margin of the Orteli anticlinal unit (geographic coordinates 45 • 11 N, 36 • 19 E), Chersonian Formation, by Elena Gladilina, Karina Vishnyakova, and the authors in 2010; both specimens were found in a block of calcareous siltstone with numerous Mactra (Chersonimactra) caspia bivalves, an endemic species for the late Sarmatian age, near the slope 25 m high. The slopes at the south coast of Tobechik Lake west of Kostyrino at the height of 0-60 m are dated as late Sarmatian s.l. (Naumenko, 1981). This age of the Eastern Paratethys in the Kerch and Taman regions corresponds to the Tortonian (Nevesskaya et al., 2003;Radionova et al., 2012).
Etymology-The genus is named after Johann Friedrich von Brandt (1802Brandt ( -1879 who made an outstanding contribution in describing fossil whales from the Black Sea region. The species name derives from the old name of Tobechik Lake and the village of Kostyrino.

DESCRIPTION
General-TNU Skull A (the holotype) is the neurocranium with preserved posterior portions of the rostral bones. TNU Skull 2 is a basicranium with associated tympanic bullae. Both skulls belong to adult individuals: many sutures between the bones are completely fused. However, many sutures are also obscured because both skulls are covered with hard sediment. TNU Skull 4 belongs to a juvenile animal; its squamosal sutures are unfused. It is represented by fragments: a right squamosal with a broken zygomatic process, a left glenoid portion of the squamosal, a right periotic, both incomplete pterygoids, a basioccipital with a basispenoid and both alisphenoids, an incomplete presphenoid, incomplete frontals, both tympanic bullae, and unidentified fragments. Premaxilla-Posterior portions of the premaxillae were badly eroded, thus their shape is unknown. The premaxilla terminates at the same level as the posterior margin of nasal.
Maxilla-In dorsal view, the ascending process tapers towards its apex. Its lateral margin is concave posterolaterally. Its medial margin cannot be traced, so it is unclear whether the ascending process overlapped the posterior portion of the premaxilla. The apices of the processes approximated each other posterior to the nasals or even possibly converged over a short distance. The angle between the lateral margins of the ascending processes is at least 120 • (Fig. 2).
Nasal-The nasal is a long and high triangular bone gradually narrowing posteriorly, and is not overlapped by the ascending process of the maxilla. Its posterior margin is at the same level as the anterior edge of the temporal fossa. The nasals are not sagittally keeled and not medially pointed: their anterior margins form a straight line. Frontal-The frontal is narrowly exposed on the skull vertex posterior to the ascending process of the maxilla (Fig. 2). In dorsal and ventral views, the anterior margin of the supraorbital process (as preserved) is directed anterolaterally (Figs. 2, 3). In anterior or posterior view, the supraorbital process is dorsally concave; it gradually slopes down at the angle of 15 • . There are two transverse crests at the dorsal surface of the supraorbital process: the anterior one, an anterolaterally directed low crest, is possibly an orbitotemporal crest sensu Mead and Fordyce (2009). Posterior to it, there is another well-developed crest, located near the posterior border of the supraorbital process. The posterior surface of the process is nearly vertical; it forms an approximately right angle with its dorsal surface in lateral view (Fig. 4A). A vertical frontal-parietal suture is partly seen in the temporal fossa in dorsal view; it runs anteroventrally from the vertex.
Parietal-In dorsal view, the borders of the parietal bone are barely visible on the vertex owing to excessive development of the nuchal crest, which occupies much of the vertex. The intertemporal region is anteroposteriorly short. In dorsal view, the temporal fossa is rhomboid and transversely extended; it is more than one and a half times as wide transversely as it is long anteroposteriorly. The parietal and the squamosal bulge into the temporal fossa laterally, forming a domelike structure. The parietalsquamosal suture, generally oblique in lateral view, is keeled.
Palatine-Posterior portions of the palatines have been preserved in TNU Skull A and TNU Skull 2 (Fig. 3). The palatine extends posteriorly to the level of the foramen pseudovale. The palatine is posterolaterally notched: this portion surrounds and overlaps the anterior portion of the pterygoid.
Pterygoid-The pterygoid is widely exposed on the ventral side of the skull between the squamosal and the palatine (Fig. 3). Anteriorly, the pterygoid sinus fossa reaches the level of the foramen pseudovale. The medial lamina borders the vomer medially; its posterior margin borders the basioccipital crest. The thick dorsal lamina forms the roof of the pterygoid sinus fossa. The lateral lamina is anterolaterally elongated; in ventral view, it forms a round bulb anterior to the pterygoid hamulus. Its posterolateral margin borders the squamosal and forms the anterior margin of the foramen pseudovale. The ventral lamina forms the bottom of the pterygoid sinus fossa and borders the palatine anteriorly. The pterygoid hamulus (as preserved) is short and robust; however, it is unclear if it is entirely preserved.
Vomer-The posterior margin of the vomer extends to the anterior portions of the basioccipital crests and wedges between them. The posterior portion of the vomerine crest is high in TNU Skull A and low in TNU Skull 2. In the holotype, it extends further posteriorly, to the transverse line joining the anterior processes of the periotic bones.
Basisphenoid-The rectangular basisphenoid is seen in the disarticulated TNU Skull 4 (Fig. 5). The suture with the basioccipital is completely fused without a trace. There is a low crest dividing the basisphenoid and the basioccipital on the dorsal (inner) surface, a plesiomorphic trait.
Alisphenoid-The alisphenoid is well observed in the TNU Skull 4 (Fig. 5). In dorsal view, the alisphenoid is roughly quadrangular, dorsoventrally flat, articulated with the basisphenoid through a narrow short neck. It is elongated in an anteromedial to posterolateral direction. In ventral view, it is mostly overlapped by the squamosal and pterygoid. Surfaces for articulation with the parietal and squamosal are seen in dorsal and ventral views. The anterolateral margin is exposed in the ventral part of the medial wall of the temporal fossa. It is partly seen in TNU Skull A (Fig. 4A); the sutures at its borders are almost completely fused with adjoining bones. An oval foramen rotundum is seen at the lateral surface in TNU Skull A and TNU Skull 2 anterior to the alisphenoid margin.
Presphenoid-In ventrolateral view, a metoptic process is seen as the area dividing the foramen rotundum and the optic canal in the temporal fossa.
Orbitosphenoid-In ventral view, a relatively small triangular orbitosphenoid is seen anterior to the optic canal, ventral to the supraorbital process (Fig. 3).
Ethmoid-A large cribriform plate with an ethmoid labyrinth is located dorsal to the vomer and palatines (Fig. 3). In ventral or anterior view, tubular ethmoturbinals with large round olfactory foramina are located medial to the frontals at the level of the posterior portions of the nasals.
Squamosal-The squamosal (especially its lateral portion) is transversely wide. The portion bearing zygomatic and postglenoid processes (a glenoid process sensu Mead and Fordyce, 2009) is posterolaterally directed, oblique to the longitudinal axis of the skull, so the postglenoid and zygomatic processes are laterally expanded (Figs. 2, 3). There is a bulge at the posterolateral surface of the squamosal, above the base of the postglenoid process (Fig. 4A, B). The shallow glenoid fossa faces anteroventrally. The zygomatic process (partly preserved in TNU Skull 2 and fully preserved in TNU Skull 4) is robust and dorsoventrally high. In the juvenile TNU Skull 4, it is anteroposteriorly short, with a rounded apex. The zygomatic process is directed anterolaterally. Dorsally, there is a high and thick supramastoid crest of irregular shape, which joins the nuchal crest anterior to the paroccipital process at an acute angle (Fig. 2). In lateral view, there is a sternomastoid fossa (Bouetel and Muizon, 2006) between the supramastoid crest dorsally and the posterior process of the periotic ventrally (Fig. 4A). The postglenoid process is directed ventrally to posteroventrally. It is widened transversely and not twisted. In lateral view, its posterodorsal surface is concave and the anteroventral surface is convex; the distal portion is dorsoventrally constricted. The distal margin is transversely wide and squared in posterodorsal view (Fig. 4B). The falciform process is robust, roughly rectangular, anteroposteriorly elongated, with a rectangular anteromedial margin and a notched posterolateral margin (Fig. 3). Lateral and dorsal to it, separated by the foramen pseudovale, there is an anterolateral part of the bone extending anterior and covering the alisphenoid.
Exoccipital-The exoccipital is completely fused with the supraoccipital (Fig. 4B). The dorsal condyloid fossa is well pronounced, and a transverse furrow extends laterally from it. The paroccipital process is large and robust, and directed posteromedially. It extends far posterior to the occipital condyle (Figs. 2, 3). The foramen magnum is oval and dorsoventrally high. In TNU Skull A, occipital condyles are large and widen ventrally; the condyles come close to each other ventral to the foramen magnum.
Supraoccipital-The anterior-most point of the occipital shield is slightly anterior to the center of the temporal fossa (Fig. 2). In dorsal view, the occipital shield is narrow and transversely constricted, particularly in comparison with transversely expanded squamosals. It is subtriangular, with a sharp apex, strongly Scurved nuchal crests, and a concave posterior margin. The nuchal crests are high, forming a shallow supraoccipital basin-like depression. The external occipital crest is high, especially in the anterior portion, but it is lower than the nuchal crests. The occiput is slightly asymmetrical: the left side with the nuchal crest and the occipital condyle extends posteriorly further than the right side, and the external occipital crest is rotated 5 • clockwise to the longitudinal axis of the cranium. No signs of distortion are seen, so this seems to be a natural condition.
Basioccipital-The basioccipital is fused with the basipshenoid and exoccipitals (Figs. 3,5,6). Basioccipital crests are wide and extremely high in adult specimens. They grow substantially  through ontogeny: in TNU Skull 4, the crests are low and occupy a small area. The ventral surface of the basioccipital is smooth, without any crests or fossae.
Periotic-Periotic bones have been preserved in all of the specimens; in TNU Skull 4, the right periotic is isolated but lacking the posterior process (Fig. 7). The periotic body is large in comparison with the pars cochlearis, roughly as long as it is high. In ventral view, the anterior process is short, blunt, and moderately transversely compressed; in medial view, it is quadrangular (Fig. 7B). A shallow groove divides it into two portions, of which the ventral one is slightly shifted laterally; there is no gulf or notch between them. The dorsal portion is subtriangular, with the long side converging with the pars cochlearis; it is covered with thin longitudinal grooves. The ventral portion is dorsoventrally compressed and relatively smooth. The shape of the ventral portion varies individually: it is short, anteromedially directed, medially curved, and laterally rounded in TNU Skull A; enlarged, anterolaterally extended, and elongated, with a shallow depression, in TNU Skull 2; broken, in TNU Skull 4. The hiatus Fallopii is small; the groove for tensor tympani is narrow. The lateral projection of the anterior process is short and triangular; it is perpendicular to the longitudinal axis of the pars cochlearis. The mallear fossa is shallow; its rim is poorly defined. The pars cochlearis is low and smooth. The tympanic opening of the facial canal is slit-like; its anterior margin is anterior to the adjacent anteroposteriorly short fenestra ovalis.
In dorsomedial view, the spiral cribriform tract (opening for the CN VIII) is subcircular; it is ventrally notched in TNU Skull 4. The endocranial opening of the facial canal (CN VII) is anteroposteriorly elongated. The crista transversa is deeply recessed, so CN VIII and CN VII form an internal acoustic meatus of oval to subtriangular shape (Fig. 7A). The aperture for the cochlear aqueduct (perilymphatic foramen) is positioned in line with the internal acoustic meatus and the fenestra rotunda, so the aperture for the cochlear aqueduct, the internal opening of the facial canal, and the spiral cribriform tract are aligned anteroposteriorly (see also Steeman, 2007). The aperture for the cochlear aqueduct is connected to the fenestra rotunda (but not confluent with it) through a short straight channel. The aperture for the vestibular aqueduct (endolymphatic foramen) is small and slit-shaped; it is located anterodorsally from the aperture for the cochlear aqueduct, so the foramina are closely dorsoventrally aligned and they form a common recess. A thin plate dividing them is oblique to the anteroposterior axis of the periotic. The pyramidal process is small and narrow. In dorsal view, a broad suprameatal fossa is seen (Fig. 7A). In lateral view, the squamosal fossa is shallow and almost indistinct. The ventral and dorsal lateral ridges are broad and low. The recessus meatus (external auditory meatus s.l.) is shallow and curved.
In posterior view, the fenestra rotunda is large and circular. The posterior cochlear crest (caudal tympanic process) is short, robust, and rounded. It reaches the base of the posterior process as a narrow high crest with a broad flange extending dorsomedially. The stylomastoid fossa is broad and shallow.
The compound posterior process of periotic and tympanic bulla is long in comparison with other cetotheriids. It is distally widened with an oblique posterior surface. The ventral and posterior surfaces form a blunt angle of approximately 110 • . The fa-cial sulcus is deep but open, not tube-like. The distal surface of the process wedges between the exoccipital and the squamosal. It is exposed at the lateral skull wall as an oval-shaped area with a wide dorsal portion.
Tympanic Bulla-The description of the tympanic bulla is based on TNU Skull 2 and TNU Skull 4 (Fig. 8). In ventral view, the tympanic bulla is box-shaped, with the prominent narrow main ridge and oblique anterolateral corner. In ventrolateral view, the bulla is close to an oval, with a rounded posterior contour and angular anterior portion. The main ridge is straight and parallel to the longitudinal axis of the bulla. The sigmoid process is transversely straight, short, robust, equally thickened  ava, aperture for the vestibular aqueduct; CN VII,; CN VIII,; ct, crista transversa; dlr, dorsal lateral ridge; fo, fenestra ovalis; fpcc, flange of the posterior cochlear crest; fr, fenestra rotunda; fs, facial sulcus; gtt, groove for tensor tympani; hf, hiatus Fallopii, lpap, lateral projection of the anterior process; maf, mallear fossa; mpg, median promontorial groove; pcc, posterior cochlear crest; pm, promontorium; pp, compound posterior process of the tympanoperiotic; pyp, pyramid process; smf, suprameatal fossa; sta, stapedial fossa; stl, stylomastoid fossa; tofc, tympanic opening of the facial canal; vlr, ventral lateral ridge. Scale bar equals 1 cm.
anteroposteriorly, and directed perpendicular to the main ridge ( Fig 8A). Its base is located at the level of the center of the bulla. The base of the process is slightly inflated. The median furrow is shallow (Fig. 8E). The conical process is short and rounded (Fig. 8A, D). In lateral view, the bulla appears box-shaped, narrowing anteriorly. In dorsal view, the bulla is box-shaped, and the involucrum is long and wide, with an angular lateral surface and bulbous dorsal posterior prominence. It is covered by sparse thin grooves, more numerous in the anterior portion. The Eustachian outlet is relatively narrow, quadrangular, and oblique to the longitudinal axis of the bulla. In medial view, the bulla is subtriangular. It gradually tapers anteriorly. Both main and involucral ridges are well developed but narrow; they join together at the anteriormost point of the bulla where they meet the anterodorsal crest (Fig. 8C). Ventrally, the main ridge is slightly convex; it is higher and thicker than the involucral ridge. There is a prominence in the posterior part of the involucral ridge. The median furrow is shallow and elongated; it is laterally curved along its longitudinal axis. The lateral lobe of the bulla extends slightly more posteriorly than the medial one. The involucrum is dorsoventrally flattened. In posterior view, the bulla is roughly hexagonal; the ventral part is slightly transversely wider than the dorsal part (Fig. 8E).
Malleus-The left malleus from TNU Skull A remains unprepared in the matrix containing the natural mold of the sigmoid process and adjoining area of the bulla. The description of the right malleus is based on TNU Skull 2 (Fig. 9). The anterior process is short and relatively thin. The head is large, bearing the articular facet for the incus divided into two facets (dorsal and ventral), of which the dorsal one is larger. There are large tubercles at the dorsal and medial surfaces of the head, which articulate with the periotic. The manubrium is very small, and the muscular process is short and robust.

INDIVIDUAL VARIATION
The holotype, TNU Skull A, and the paratype, TNU Skull 2, are close in size and identical in bone outlines. This is clearly seen when comparing the shapes of squamosals, pterygoids, and basioccipital crests (Figs. 2, 3). The specimens differ in their occipital condyle size; however, the latter is difficult to estimate due to its damage in TNU Skull 2. All specimens slightly differ in the shape and structure of the anterior process of the periotic bone.
The estimated body size (following Lambert et al., 2010) of the juvenile specimen TNU Skull 4 is 312 cm: it could be even larger, given that the formula underestimates the body length of 300 cm long Cetotherium riabinini by 25 cm (Gol'din et al., in press). Thus, the juvenile Brandtocetus chongulek attained 80% of the length of the adult specimen found near it (TNU Skull 2). This suggests rapid postnatal growth, as documented in living mysticetes: 76% of adult length in northern right whales (Fortune et al., 2012), 70% in blue and fin whales (Lockyer, 1981), and 60-70% in minke whales (Christensen, 1981) by the age of 12 months. The basioccipital-basisphenoid suture fuses, as it is in TNU Skull 4, in living baleen whales by the same age (Walsh and Berta, 2011). Thus, we estimate the age of the juvenile specimen as at least 1 year.
TNU Skull 4 differs from adult specimens in the following traits: small basicranium size with a particularly narrow medial part (the distance between the foramina pseudovale is twice as narrow as in adults; Table 1); unfused cranial sutures (only the basioccipital-basisphenoid suture is fused); small pterygoids; low supramastoid crest; extremely low basioccipital crest occupying a small area; and a tympanic bulla with less pronounced ridges and grooves. The squamosals of TNU Skull 4 are somewhat smaller than in adult Brandtocetus chongulek but they are otherwise well developed: if compared with other species, the dimensions of the squamosal expansion and temporal fossa of TNU Skull 4 are roughly equal to those of an adult Kurdalagonus mchedlidzei and exceed those of Cetotherium rathkii and Cetotherium riabinini, whereas the basicranium is far smaller (Table 1; see also Gol'din et al., in press). Further, the glenoid fossa is more clearly defined in TNU Skull 4, although it is still shallow, as in adults. The comparable parts of the periotic in the specimens of Brandtocetus chongulek do not significantly differ in shape and size: the pars cochlearis, periotic body, and dorsal portion of the anterior process are roughly equal in size. No ontogenetic variation is seen in the size and shape of the anterior process or its lateral projection, unlike in living balaenids and balaenopterids (Bisconti, 2001;Ekdale et al., 2011;Pavel Gol'din, pers. data). The tympanic bulla is even slightly larger in TNU Skull 4 than in TNU Skull 2 (Fig. 10). So growth and ontogenetic changes in Brandtocetus chongulek after the age of 1 year are limited in the periotic (including its processes), moderate in the squamosal, and significant in the neurocranium. This growth pattern seems to be unusual for mysticetes (e.g., Nakamura et al., 2012). Kemper and Leppard (1999) reported significant elongation of the supraoccipital shield in Caperea marginata Gray, 1846, after body length reached its asymptote, and it could be also the case for Brandtocetus chongulek, which is distinguished from other cetotheriids by its long neurocranium (Table 1).

COMPARISONS
Brandtocetus chongulek is assigned to Cetotheriidae on the basis of the following combination of characters (Gol'din et al., in press): strongly telescoped facial bones with the posterior edges of the nasal, premaxilla, and maxilla wedge-shaped and extending almost to the tip of the occipital shield ('X'-shaped vertex); in dorsal view, the ascending processes of the maxillae have concave lateral margins and approximate each other at their posterior edges; a shallow glenoid fossa; in dorsal view, a paroccipital process extending posterior to the posterior edge of the occipital condyle; a transversely short sigmoid process of the tympanic bulla lacking an inflated base; a well-developed anterior process and lateral tuberosity of the periotic; and a relatively short posterior process of the tympanoperiotic with a flattened distal surface broadly exposed on the posterolateral wall of the skull (Gol'din et al., in press).
Brandtocetus chongulek has cranial morphology typical for subfamily Cetotheriinae, as opposed to Herpetocetinae sensu Whitmore and Barnes (2008): a transversely wide squamosal  with a transversely expanded postglenoid process, rostral bones not extending posterior to the level of the orbit, and an open facial sulcus. Furthermore, Brandtocetus chongulek (as well as Cetotherium and Kurdalagonus) has a proximodistally elongated compound posterior process of the tympanoperiotic, unlike in Herpetocetus, Nannocetus, Metopocetus, Piscobalaena, Cephalotropis, and Eucetotherium, in which it is 'plug-like,' extremely short with a flat distal surface (Steeman, 2007;Whitmore and Barnes, 2008;Fordyce and Marx, 2012). Brandtocetus chongulek is similar to other cetotheriids from the Eastern Paratethys (Cetotherium, Kurdalagonus and Eucetotherium) in a robust and dorsoventrally high zygomatic process of the squamosal and wide cranium. Brandtocetus chongulek is a member of a group including Cetotherium, Kurdalagonus, and related whales from the eastern Paratethys (Fig. 11). These whales lack derived herpetocetine rostral and squamosal characters and have primitive anatomy of the compound posterior process of the tympanoperiotic (except Eucetotherium). A synapomorphy of this group is a high zygomatic process.
Brandtocetus chongulek differs from all cetotheriids (including Cetotherium and Kurdalagonus) by having a transversely expanded lateral portion of the squamosal with anterolaterally directed zygomatic processes: zygomatic width is 4.3-4.9 times greater than condylar width, whereas this ratio is 3.8 in Cetotherium riabinini, 2.8 in Kurdalagonus mchedlidzei (Table 1), and 2.8-3.4 in Piscobalaena nana (Bouetel and Muizon, 2006). Also, it differs from all cetotheriids in its rhomboid temporal fossa; occipital shield extending anterior to the level of the center of the temporal fossa; and particularly elongated posterior process of the tympanoperiotic, with the distal portion exposed as a large oval surface on the skull wall (not triangular, as in Cetotherium, nor roughly rhomboid, as in Kurdalagonus mchedlidzei) (Fig. 12). Another unusual feature of Brandtocetus is its widely exposed pterygoid; however, this trait is unknown or poorly seen in many cetotheres.  Bouetel and Muizon (2006). Abbreviation: pp, compound posterior process of the tympanoperiotic bone. Scale bars equal 5 cm.
Brandtocetus chongulek further differs from Kurdalagonus mchedlidzei in a quadrangular, moderately transversely compressed anterior process of the periotic (not an extremely compressed double-bladed process, as in Kurdalagonus mchedlidzei) (plesiomorphic). Brandtocetus is distinguished by its narrow, transversely constricted occipital region (not particularly wide, as in Kurdalagonus mchedlidzei) (Table 1). It differs from Kurdalagonus mchedlidzei by having a paroccipital process that extends far posterior to the level of the occipital condyles, and forms a semicircular contour in dorsal view; a vertical nuchal crest that does not overhang the temporal fossa; and a foramen magnum that is higher than wide. A synapomorphy of Brandtocetus chongulek and Kurdalagonus mchedlidzei, unique to these taxa among cetotheriids but also present in Uranocetus gramensis Steeman, 2009, is a strongly curved 'S'-shaped nuchal crest. Brandtocetus chongulek differs from Cetotherium rathkii and Cetotherium riabinini by having a tympanic bulla that gradually tapers anteriorly in medial view (not as wide and high anteriorly as it is posteriorly, as in Cetotherium spp.). Brandtocetus chongulek differs from both Cetotherium spp. and Kurdalagonus mchedlidzei by having a thick and high nuchal crest and external occipital crest, a posteriorly projecting paroccipital process and a larger skull size. Brandtocetus chongulek differs from 'Cetotherium' mayeri and Kurdalagonus adygeicus (both taxa known from incomplete crania), in squared (not tapering distally) postglenoid processes, and the shape of its tympanic bulla: the posterior portion of the outer lip is not swollen, so the bulla in posterior view is roughly hexagonal (not roughly globular with a middle constriction); in dorsal view, the involucrum is as high anteriorly as posteriorly. Brandtocetus chongulek differs also from Kurdalagonus (Cetotherium) maicopicus in the medial lobe of the tympanic bulla, which is not swollen.

Methods
Phylogenetic analysis was performed with 59 ingroup taxa of mysticetes, 13 of which were hypothetical Cetotheriidae or Cetotheroidea sensu Steeman, 2007, and two odontocete taxa. Zygorhiza kochii (Reichenbach in Carus et al., 1847) was chosen as the outgroup taxon. The data matrix with 150 characters was adopted from Marx (2011), excluding Aulocetus latus Kellogg, 1940, andCephalotropis nectus Kellogg, 1940, with five new characters added to it; Supplementary Data 1, Appendix S1). This matrix was used as one of the most recent published studies and the largest matrices containing data for many cetotheriid operational taxonomic units. The character codings for Joumocetus shimizui Kimura and Hasegawa 2010, Cetotherium rathkii, and Cetotherium riabinini were adopted from Gol'din et al. (in press). Eucetotherium helmersenii and Kurdalagonus mchedlidzei, as well as Brandtocetus chongulek, were added to the analysis with new codings (Supplementary Data 1, Appendix S2). Heuristic parsimony analysis of the matrix was performed in TNT version 1.1 (Goloboff et al., 2003). The 'traditional search' option was used. The resulting most parsimonious trees were summarized using strict consensus trees with zero-length branches collapsed (Goloboff et al., 2003). The topologies generated by the parsimony analysis were evaluated by bootstrap resampling, compiled from 1000 replicates.

Results and Discussion
A strict consensus tree of 13 equally most parsimonious trees with the length of 433 steps (consistency index [CI] = 0.51, retention index [RI] = 0.83) is presented in Figure 13. Cetotheriidae are confirmed to be a monophyletic family, a sister clade to the clade including families Neobalaenidae, Eschrichtiidae, and Balaenopteridae. The basal-most member of Cetotheriidae is Mixocetus elysius; followed by Joumocetus shimizui. Derived cetotheriids are tentatively grouped in three clusters, all poorly supported by bootstrap resampling (Fig. 13). The cetotheriids from the eastern Paratethys form a clade: Brandtocetus chongulek, genus Cetotherium with two species (C. rathkii and C. riabinini), Kurdalagonus mchedlidzei and Eucetotherium helmersenii. This clade is supported by a single synapomorphy: a blunt dorsoventrally high zygomatic process. Another clade includes oceanic cetotheriids: 'Metopocetus' (Cetotherium) vandelli Van Beneden and Gervais, 1868, (the basal-most member), Metopocetus durinasus, Piscobalaena nana, Nannocetus eremus Kellogg, 1929, andHerpetocetus transatalanticus Whitmore andBarnes, 2008. This clade is characterized by strong development of rostral telescoping: ascending processes of the maxillae extend posterior to the level of the postorbital processes of the frontals. The derived members of this clade have ascending processes of the maxillae overlapping or constricting the posterior portions of the premaxillae and nasals. This trait is absent in 'Metopocetus' (Cetotherium) vandelli, which Whitmore and Barnes (2008) did not consider to be a species of Metopocetus. We share this view, but at the same time we do not consider it to be a species of Cetotherium (Gol'din et al., in press). A third clade is represented by 'Cetotherium' megalophysum.
Within the Eastern Paratethyan clade, the genus Cetotherium (the monophyly of which is relatively well supported by bootstrap resampling) is characterized by a narrow rostrum, twisted postglenoid processes, an anteriorly rounded tympanic bulla, and a triangular distal surface of the posterior process of the tympanoperiotic. Among Paratethyan genera, Brandtocetus chongulek has two autapomorphies: transverse expansion of the squamosals and an oval distal surface of the posterior process of the tympanoperiotic. Eucetotherium helmersenii has a single autapomorphy: the anteroposteriorly elongated temporal fossa, which is a rare trait among mysticetes (a similar specimen was also reported by Spassky [1954]).
Kurdalagonus mchedlidzei has a posterior process of the tympanoperiotic with a small rhomboid distal surface, similar to Joumocetus shimizui or Piscobalaena nana (Fig. 12): it is likely a plesiomorphic shape for derived cetotheriids, and both the triangular surface of Cetotherium and the large oval surface of Brandtocetus may be derived from it. In the same manner, the small triangular occipital shield of Cetotherium and the anteriorly extended occipital shield with 'S'-shaped nuchal crests of Brandtocetus may be derived from the small occipital shield with 'S'-shaped nuchal crests of Kurdalagonus mchedlidzei. Thus, Kurdalagonus mchedlidzei from the late middle Miocene may possess ancestral morphology for features seen in the early late Miocene genera Cetotherium and Brandtocetus. However, this hypothesis is not corroborated by the cladistic analysis.
The proposed phylogeny should be treated as provisional, given a number of poorly known and undescribed cetotheriid taxa. Nevertheless, our attempt to reconstruct the phylogeny of cetotheriids can serve as a basis for further studies. The difficulties in resolving the phylogeny of Cetotheriidae, as demonstrated by contradictions between recent published schemes (Bouetel and Muizon, 2006;Steeman, 2007;Bisconti, 2008;Marx, 2011;Bisconti et al., 2013;Fordyce and Marx, 2013), are perhaps explained by multiple parallelisms in anatomy across genera. For example, Brandtocetus chongulek and Herpetocetus spp. have a similar box-shaped tympanic bulla gradually narrowing anteriorly in medial view, with an anteriorly high involucrum (Whitmore and Barnes, 2008); Kurdalagonus mchedlidzei and Herpetocetus spp. have a transversely extremely compressed double-bladed anterior process of the periotic (Whitmore and Barnes, 2008); and Eucetotherium helmersenii has a 'herpetocetine' plug-like posterior process of the tympanoperiotic and a laterally compressed and twisted postglenoid process. However, the Paratethyan whales differ significantly from Herpetocetus spp. in cranial anatomy, and none of them shares the overall herpetocetine pattern of tympanoperiotic anatomy, so a close phylogenetic relationionship is questionable and not confirmed by the analysis presented here.
Anatomical differences within the cetotheriid family partly result from variation in feeding strategies. A suction feeding strategy is hypothesized for cetotheriids (Kimura, 2002(Kimura, , 2005El Adli and Boessenecker, 2011;Gol'din et al., in press), and possibly it involves a kind of continuous suction feeding, similar to that of filter-feeding ducks (Anatidae) (Kimura, 2008;Gol'din et al., in press). A cetotheriid cranial trait clearly hindering effective gulp feeding is the shallow glenoid fossa, which suggests limited rotation of the mandibles (Lambertsen, 1983). In Herpetocetinae sensu Whitmore and Barnes, 2008, the transverse compression, twisting and vertical orientation of postglenoid processes further limits mandible movements; however, in other cetotheriids it does not, so their generalized feeding strategy could combine the anatine-like herpetocetine feeding and other feeding modes like intermittent suction feeding in living gray whales (Ray and Schevill, 1974;Sanderson and Wassersug, 1993;Gol'din et al., in press). We suggest anatine-like feeding was effective at a small body size; a generalized feeding strategy was necessary with an increase in body size. Transversely expanded squamosals, enlarged pterygoids, and thick nuchal crests, indicating simultaneous strengthening of temporal, external pterygoid, and internal pterygoid muscles, suggest this generalized feeding strategy, and are observed in various forms in large and medium-sized cetotheriids: Brandtocetus chongulek, Eucetotherium helmersenii and possibly Metopocetus durinasus, and 'Cetotherium' megalophysum (as preserved in the fragmentary holotype skulls). Among them, Brandtocetus chongulek is characterized by extreme transverse widening of the cranium and anteriorly directed telescoping of the occipital shield, traits approaching the typical cranial morphology of balaenopterids.
After the analysis by Bouetel and Muizon (2006), the family Cetotheriidae, now defined as Cetotheriidae s.s., was restricted to six or seven described genera. However, a great diversity of cetotheriids with varying morphology and ecology discovered in recent studies, including this work, demonstrates the necessity for further research into the taxonomy and phylogeny of this family.