Chalishevia cothurnata Ochev, 1980
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publication ID |
https://doi.org/ 10.4202/app.00648.2019 |
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persistent identifier |
https://treatment.plazi.org/id/03D08792-FFDD-4003-7B2A-F328AA54FA80 |
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treatment provided by |
Felipe |
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scientific name |
Chalishevia cothurnata Ochev, 1980 |
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Chalishevia cothurnata Ochev, 1980
Type material: Holotype: PIN 4366/1 (formerly SGU 104/3852, wrongly cited as PIN 4356/1 by Gower and Sennikov 2000), left maxilla and both nasals ( Ochev 1980: fig. 2a− c; Gower and Sennikov 2000: fig. 8.6). Paratypes: PIN 4366/2 (formerly SGU 104/3853), an incomplete right quadrate, and PIN 4366/3 (formerly SGU 104/3854), a tooth, both from the same locality and bed as the holotype.
Type locality: Bukobay VII locality ( Shishkin et al. 1995; Sennikov 1995, 2008; Gower and Sennikov 2000; wrongly cited as Bukobay VI by Ochev 1980), Sol-Iletsk distrinct, Orenburg Province, Russia ( Fig. 1 View Fig ). Tverdokhlebov et al. (2003) referred to this locality as Belyaevsky II (their locality 31).
Type horizon: Bukobay Gorizont, Ladinian, late Middle Triassic ( Shishkin et al. 1995, 2000).
Referred material.— PIN 4366/4, 4366/5, 4366/7, partial left pterygoid, originally preserved in three separately numbered pieces, and PIN 4366/8, a tooth. Both specimens come from the same locality and bed as the holotype ( Sennikov 1995, 2008). PIN 2867/18 (formerly SGU 104/3862), fragment of right nasal, from Koltaevo III, Kuyurgazinskiy district, Republic of Bashkortostan, Russia ( Ochev 1980). PIN 2867/7, partial right nasal from Koltaevo III ( Sennikov 1995, 2008). Tverdokhlebov et al. (2003) referred to this locality as Starokoltaevo I (their locality 8). All from the Bukobay Gorizont, Ladinian, late Middle Triassic ( Shishkin et al. 1995, 2000).
Emended diagnosis.— Chalishevia cothurnata is a large erythrosuchid that differs from other archosauromorphs in the following combination of features (autapomorphy indicated with an asterisk): large, subcircular accessory antorbital fenestra and fossa; maxillo-nasal tuberosity; maxilla with two rows of large foramina on the lateral surface; and maxilla with an edentulous anterior tip, mainly vertical ascending process, and oblique, anteroventrally-to-posterodorsally oriented ventral border of the antorbital fossa on the horizontal process* (modified from Ezcurra 2016).
Description.—The holotype consists of the left maxilla, partial left nasal and partial right nasal, all belonging to a single individual ( Ochev 1980). All bones articulate well with one another. The paratypic quadrate and tooth and referred pterygoid and tooth from the same locality (Bukobay VII) and bed were recovered close to the holotype remains and probably also represent the same individual based on similar size, preservation, and phylogenetic consistency of morphology.
Maxilla: The left maxilla of the holotype ( PIN 4366 View Materials /1) is nearly complete ( Figs. 2 View Fig , 3 View Fig ), but is damaged at the lateral extremity of the posterolateral end of the main body, below the posterior margin of the antorbital fenestra, at the posterodorsal tip of the ascending process, and anterodorsally, below the anterior part of the accessory antorbital fenestra. Medially, the palatal process is damaged at its base and is missing its distal tip ( Fig. 2A 2 View Fig , 3 View Fig ), and the medial surface of the maxilla is missing at the posterior end of the tooth row. The external bone surface is generally very well preserved. The maximum anteroposterior length of the maxilla as preserved is approximately 310 mm, and the maximum dorsoventral height as preserved is approximately 180 mm .
The main body of the maxilla is anteroposteriorly elongated relative to its dorsoventral height, and tapers at its anterior and posterior ends in lateral view ( Fig. 2A View Fig 1 View Fig ). This condition differs from the mostly horizontal dorsal margin of the anterior process of the maxilla of Garjainia prima , whereas the condition in Erythrosuchus africanus and Shansisuchus shansisuchus seems to be intraspecifically variable ( Young 1964; Wang et al. 2013; Ezcurra et al. 2019). The alveolar margin is strongly convex centrally, becoming gently concave anteriorly (towards the contact with the premaxilla) and posteriorly, resembling the condition in a referred specimen of Shansisuchus shansisuchus ( Wang et al. 2013) . By contrast, the alveolar margin along the anterior process is straight in lateral view in Erythrosuchus africanus and Garjainia prima ( Gower 2003; Ezcurra et al. 2019). In dorsal or ventral view ( Fig. 3 View Fig ) the lateral surface of the maxilla is flat to gently convex anteriorly, but becomes gently concave posteriorly, towards the jugal contact.
The ascending process is strongly offset posterior to the anterior margin of the maxilla, with the base of the ascending process lying approximately one third of the distance along the anteroposterior length of the element, closely resembling the condition in Garjainia prima ( Ezcurra et al. 2019) and Shansisuchus shansisuchus ( IVPP V2501, V2505, V2508; Wang et al. 2013). The ascending process rises nearly vertically, and is excavated anteriorly (visible most clearly in anterior or dorsal views) by a fossa that bordered the accessory antorbital fenestra ( Figs. 2A View Fig 1 View Fig , 3A View Fig 2 View Fig : accessory antorbital fossa). This fossa is termed here the accessory antorbital fossa and is also present in Shansisuchus shansisuchus ( IVPP V2501, V2505, V2508). Posteriorly the ascending process is excavated by the maxillary antorbital fossa. Between these two excavations there is a very strongly raised bar or ridge of bone (the “maxillo-nasal tuberosity”; Ezcurra 2016) on the lateral surface of the ascending process ( Figs. 2A View Fig 1 View Fig , 3A View Fig 2 View Fig : maxillo-nasal tuberosity), which has been found as a synapomorphy of the clade that includes all erythrosuchids with the exception of Fugusuchus hejiapanensis and Guchengosuchus shiguaiensis ( Ezcurra 2016; Ezcurra et al. 2019; Butler et al. 2019). At its base, this ridge is anteroposteriorly expanded and smoothly merges with the lateral surface of the maxilla. Dorsally, this ridge curves first gently anteriorly and then gently posteriorly. Dorsal to the lower third of the contact of this ridge with the ventral process of the nasal (see below), the ridge becomes gradually reduced in transverse width, merging smoothly with the preserved dorsal tip of the ascending process. The lateral surface of this ridge is flattened and laterally facing along its ventral half, but it twists to face posterolaterally as it diminishes in transverse width towards its dorsal apex.
In lateral view the tapered anterior end of the maxilla has two distinct prong-like processes separated by a posterodorsally-tapering groove ( Fig. 2A View Fig 1 View Fig ), a condition that resembles that of Garjainia prima , though this species has shorter prong-like processes ( Ezcurra et al. 2019). The more ventral of these processes tapers to a bluntly rounded and slightly downturned tip ( Fig. 2A View Fig 1 View Fig : ventral anterolateral process). Based on comparison with the holotype of Garjainia prima ( PIN 2394/5; Ezcurra et al. 2019), this process did not articulate with the premaxilla, but instead projected into a subnarial notch along the tooth margin between the premaxilla and maxilla. The ventral surface of this process is edentulous ( Figs. 2A View Fig 1 View Fig , 3A View Fig 1 View Fig : edentulous margin), meaning that there was a short gap between maxillary and premaxillary tooth rows, as occurs in Garjainia prima ( Ezcurra et al. 2019) and Shansisuchus shansisuchus ( Young 1964) . The process projects slightly medially as preserved, but this likely reflects damage given that there is a substantial, dorsoventrally extending break at the base of the process.
The more dorsal of the two anterolateral processes is also slightly downturned towards its anterior end, and is bluntly squared off at its tip ( Fig. 2A View Fig 1 View Fig : dorsal anterolateral process). The tip is slightly bevelled, presumably forming a small, loose contact with the premaxilla. The groove between the two anterolateral processes is open at its anterior end and backed by bone more posteriorly; it tapers and connects to a foramen posteriorly.
The lateral surface of the more dorsal of the two anterolateral processes is flattened, and merges posteriorly with the accessory antorbital fossa ( Figs. 2A View Fig 1 View Fig , 3A View Fig 2 View Fig : accessory antorbital fossa). This fossa is delimited ventrally and posteriorly by a sharp ridge that forms the anterior margin of the ascending process in lateral view. The fossa excavates the anterior surface of the ascending process, and is deepest immediately anterior to the base of the process, as occurs in Shansisuchus shansisuchus (IVPP V2508) . The dorsal part of the maxilla anterior to the ascending process and the medial part of the anterior margin of the ascending process form the smoothly curved ventral and posterior margins of the accessory antorbital fenestra. Within the accessory antorbital fossa, medial to the ridge of the ascending process (at the point at which it begins to curve posteriorly and diminish in thickness), there is an articular surface for the ventral process of the nasal that is gently concave mediolaterally ( Fig. 3B View Fig : articular surface for the nasal).
The ventral and anterior rims of the antorbital fenestra ( Fig. 2A View Fig 1 View Fig : maxillary antorbital fenestra) are preserved, and are smoothly curved. The ventral margin of the antorbital fenestra is almost exactly level with the ventral margin of the accessory antorbital fenestra. The antorbital fenestra is surrounded ventrally, anteriorly and anterodorsally by an antorbital fossa ( Figs. 2A View Fig 1 View Fig , 3A View Fig 2 View Fig : antorbital fossa) that extends onto the dorsolateral surface of the main body of the maxilla and excavates the posterolateral part of its ascending process, as is the case in Erythrosuchus africanus ( Gower 2003) and Shansisuchus shansisuchus ( Young 1964) . By contrast, Fugusuchus hejiapanensis , Garjainia prima ( Ezcurra et al. 2019) and Guchengosuchus shiguaiensis ( Butler et al. 2019) lack an antorbital fossa on the horizontal process of the maxilla. The antorbital fossa of Chalishevia cothurnata is bounded by a sharp ridge on the ascending process, and a well-defined but low ridge on the main body. This latter ridge extends from anteroventral to posterodorsal, and its orientation is very similar to that of the boundary of the antorbital fenestra in Garjainia prima ( PIN 2394/5; Ezcurra et al. 2019). The orientation of the ventral margin of the antorbital fossa contrasts with the horizontal margin present in Erythrosuchus africanus ( Gower 2003) . The maxillary antorbital fossa of Shansisuchus shansisuchus becomes shallower posteriorly on the horizontal process and lacks a clearly defined posteroventral margin ( IVPP V2505, V2508). Within the fossa of the holotype of Chalishevia cothurnata , two small inflated areas that form volcano-like features are present. These are unusual, and may represent some kind of pathology, although this cannot be determined without histological or computed tomographic analysis.
There are numerous large nutrient foramina on the lateral surface of the maxilla ( Fig. 2A View Fig 1 View Fig ), and these are connected with broad and deeply incised grooves. Nine of these foramina are placed in a ventral convex row that extends parallel to the alveolar margin, with each foramen being positioned approximately above one of the alveoli. The anteriormost of this row of foramina is continuous with the anterior groove between the anterolateral processes described above. These foramina open towards the alveolar margin; broad, well-defined, and deeply impressed grooves extend from the foramina to the alveolar margin, as occurs in some other erythrosuchids and loricatans ( Ezcurra 2016). The foramina have oval to subcircular outlines. The posteriormost of the foramina is larger than those positioned more anteriorly.
Dorsal to this first row of foramina there are six foramina in a second row, an unusual condition among early archosauromorphs. This second row of foramina could be autapomorphic for Chalishevia cothurnata , but a similar feature may be present in at least one specimen of Shansisuchus shansisuchus ( Young 1964: fig. 10a), and the condition in this latter taxon requires further investigation. The anteriormost of these foramina is small, and positioned ventral to the accessory antorbital fenestra, and is not connected to a well-defined groove. The second foramen in this row is positioned below the anterior margin of the ascending process, opens ventrally, and communicates with three grooves. The deepest of these grooves extends dorsally onto the ascending process, terminating adjacent to the anterior margin of the process immediately ventral to the articulation with the nasal. A second, weakly expressed groove extends ventrally towards the tooth row but fades out before reaching the more ventral row of foramina. A third, narrow groove extends anterodorsally, reaching the boundary of the accessory antorbital fossa. The third foramen is small, ventrally opening, and positioned below the ascending process. A shallow groove extends ventrally from this opening. The fourth is positioned below the posterior margin of the ascending process. It also opens ventrally and is partially obscured by a small thickening of the surface of the maxilla posterodorsal to it. There is no clearly developed groove extending ventrally from this opening, but a groove does extend dorsally along the posterior margin of the ascending process, fading out level with the dorsal margin of the volcano-like projections. This groove appears to subdivide close to its base, with a short groove extending to reach the anteroventral corner of the antorbital fossa. The fifth and sixth of this second row of foramina open posteroventrally. Well-developed grooves extend posterodorsally from these foramina, curving along their lengths. A clear groove also extends ventrally from the sixth foramen, connecting to the eighth foramen of the lower row.
There is a well-developed facet for the reception of the jugal laterally at the posterior end of the maxilla ( Figs. 2A View Fig 1 View Fig , 3A View Fig 2 View Fig : articular surface for the jugal). A slot for articulation with the jugal also appears to be present on the posterodorsal margin of the maxilla ( Fig. 3A View Fig 2 View Fig ). Anterodorsally, at the tip of the ascending process, a second facet for articulation with the nasal is present ( Fig. 3A View Fig 2 View Fig : articular surface for the nasal). Due to damage to the posterodorsal margin of the ascending process it cannot be determined if a contact surface was present for the lacrimal, a contact that occurs in Shansisuchus shansisuchus ( Wang et al. 2013) .
Medially the palatal process is broken at its tip, and has three longitudinal grooves separated by two ridges on its medial surface ( Fig. 2A 2 View Fig : palatal process). It has been broken at its base and displaced slightly laterally. There is a ventrally opening large foramen posteroventral to the base of the palatal process ( Fig. 3A View Fig 1 View Fig : foramen). Another very deep and large foramen is positioned below the antorbital fenestra ( Figs. 2A 2 View Fig , 3A View Fig 2 View Fig : foramen), posterior to the ascending process, opening into a groove that extends along the dorsal surface of the main body of the maxilla. The medial surface of the main body is convex dorsoventrally. A sharp ridge separates the main body from the alveolar region. Interdental plates are present and contact one another at their bases ( Fig. 2A 2 View Fig : interdental plates). The interdental plates extend ventrally to the same level as the ventrolateral margin of the bone, indicating a thecodont tooth implantation (sensu Bertin et al. 2018). Small foramina are present between them, and small parts of replacement crowns are visible in these foramina dorsal to the third and fifth alveoli ( Fig. 2A 2 View Fig : replacement crown). Almost no details of these crowns are visible, although the one above the third alveolus has several denticles preserved along the distal margin of the tip (the mesial margin is not preserved).
At least twelve (possibly 13) alveoli appear to be present ( Fig. 3A View Fig 1 View Fig ), rather than 10 as identified by Ochev (1980). Two alveoli appear to be present in the space identified by Ochev (1980) as for the first alveolus. It seems likely that, although preservation is poor, two alveoli (6 and 7) were present in the gap identified as for alveolus 5 by Ochev (1980). At the very posterior end of the tooth row it is unclear whether or not a thirteenth alveolus was present. The condition in Chalishevia cothurnata resembles the relatively low maxillary tooth counts of Guchengosuchus shiguaiensis ( IVPP V8808: maxillary tooth count 14 or 15), Garjainia prima ( PIN 2394/5: maxillary tooth count 13 or 14), Erythrosuchus africanus ( BP /1/5207: maxillary tooth count 11), Shansisuchus shansisuchus ( Young [1964] described 9 or possibly 10 tooth positions and Wang et al. [2013] probably 13 maxillary teeth), and Euparkeria capensis (Ewer, 1965; maxillary tooth count 13). By contrast, higher maxillary tooth counts are present in the less crownward archosauromorphs Tasmaniosaurus triassicus ( UTGD 54655;>21), Proterosuchus fergusi ( BP /1/3993, BSPG 1934 VIII 514, GHG 231, RC 59, 96, SAM-PK-11208, K140, K10603; maxillary tooth count 20–31, depending on ontogenetic stage; Ezcurra and Butler 2015), “ Chasmatosaurus ” yuani (> 23 in IVPP V90002 and ≥ 29 in IVPP V2719) and Prolacerta broomi ( BP /1/471, Modesto and Sues 2004; tooth count 24–25). There is no evidence of ankylosis between the base of the crowns and the alveolar margin of the bone.
Nasal: A substantial portion of the left nasal is preserved ( Fig. 4 View Fig ), and articulates with the ascending process of the maxilla via a ventral process. The left nasal is broken and damaged at its anterior end, and posteriorly is broken posterior to the ventral process. A major crack extends from posterodorsal to anteroventral through the contact between the main body of the nasal and the ventral process ( Fig. 4 View Fig : cr), and this means that the orientation of these two parts of the element to one another (and thus the orientation of the anterior part of the nasal to the maxilla when in articulation) is not accurately preserved.
Medially, the left nasal is dorsoventrally thickened with a convex dorsal surface at its midline contact with the right nasal. The medial surface of the element is grooved for articulation with a ridge of the right nasal ( Fig. 4A View Fig 2 View Fig : articular surface for the nasal); below this groove there is a ridge that fits into a corresponding groove on the right nasal. At its anterior end there is a concavity for articulation with the prenarial process of the premaxilla ( Fig. 4A View Fig 2 View Fig : articular surface for the premaxilla). The external surface of the nasal is arched, facing dorsally at the midline and dorsolaterally towards the contact with the maxilla and the border of the accessory antorbital fenestra. It is covered with rugose ornamentation towards the posterior end of the preserved element.
Anteriorly, parts of the dorsal border of the naris are preserved ( Fig. 4A View Fig 1 View Fig : border of the external naris). Behind the naris, there is an elongate, narrow, posterodorsally extending and tapering slot ( Fig. 4A View Fig 1 View Fig : articular surface for the premaxilla), that would have accommodated a narrow, tapering postnarial process of the premaxilla, similar to that present in Shansisuchus shansisuchus ( Young 1964) . Dorsal to and adjacent to this slot, the external surface of the nasal is anteroposteriorly grooved ( Fig. 4A View Fig 1 View Fig : groove).
Posteroventral to the slot for the postnarial process of the premaxilla, the nasal forms the dorsal and posterodorsal margins of the accessory antorbital fenestra ( Fig. 4A View Fig 1 View Fig : accessory antorbital fenestra), as occurs in Shansisuchus shansisuchus ( Young 1964; Wang 2013). Several small foramina are present on the external surface of the nasal adjacent to the fenestra ( Fig. 4A View Fig 1 View Fig : foramen), and are associated with short anteroventrally extending grooves.
The ventral process of the nasal tapers towards its tip. An extensive facet for the ascending process of the maxilla is present on its posteromedial surface ( Fig. 4A View Fig 3 View Fig : articular surface for the maxilla). In medial and anterior views, a very deeply recessed fossa (= “sulcus” of Ochev 1980) is present adjacent to the dorsal margin of the accessory antorbital fenestra ( Fig. 4A View Fig 2 View Fig , A 3 View Fig : accessory antorbital fossa).
The right nasal is less complete than the left, and is broken anteriorly, just anterior to the beginning of the dorsal margin of the external naris, ventrolaterally, and posteriorly ( Fig. 5 View Fig ). The dorsal margin of the accessory antorbital fenestra is almost entirely missing, and the ventral process of the bone has broken away. It does not add anatomical information not present in the left nasal.
Quadrate: A right quadrate ( PIN 4366/2), broken into two pieces, was referred to Chalishevia cothurnata by Ochev (1980), and was identified as from the same individual as the holotype but was not described ( Fig. 6 View Fig ). The two pieces of the quadrate do not fit together, and a section of the midshaft of the bone is missing. The maximum dorsoventral height of the bone would have been at least 220 mm. The pterygoid wing of the quadrate is missing, as is much of the lateral margin of the bone. Ventrally, the condyles are preserved along with part of the lateral expansion for articulation with the quadratojugal ( Fig. 6 View Fig : articular surface for the quadratojugal). The maximum transverse expansion at the condyles is 66.5 mm. The condyles are strongly compressed anteroposteriorly and expanded transversely ( Fig. 6A View Fig 5 View Fig ), with the medial condyle being broader anteroposteriorly. The medial condyle is slightly anteriorly projected, resembling the condition in Erythrosuchus africanus ( NHMUK PV R3592) and Shansisuchus shansisuchus ( Young 1964) . By contrast, the medial condyle is distinctly more anteriorly projected in Garjainia madiba ( BP /1/6232f) and, particularly, Garjainia prima , in which the quadrate acquires an L-shaped profile in ventral view ( Ezcurra et al. 2019). Both condyles have strongly convex articular surfaces, although the medial condyle is more strongly convex, resembling the condition in Garjainia prima and other erythrosuchids ( Ezcurra et al. 2019). The ventral condyles of the quadrate of Chalishevia cothrunata are separated from each other by a shallow, anteroposteriorly oriented notch, closely resembling the condition in Erythrosuchus africanus ( NHMUK PV R3592; Gower 2003) and Shansisuchus shansisuchus ( Young 1964) . By contrast, the separation between the ventral condyles is much deeper in posterior or anterior view in Garjainia prima ( Ezcurra et al. 2019) and an intermediate condition occurs in Garjainia madiba ( Gower et al. 2014) . Above the condyles, the posterior surface of the quadrate is flattened, and tapers in transverse width toward the midshaft. The anterior surface of the shaft is transversely concave above the condyles. Ventrolaterally the quadrate is expanded into a depressed articular surface for the quadratojugal. This surface tapers dorsally, and the shaft reaches a minimum transverse width just above the dorsal termination of the quadratojugal flange. The borders of the quadrate foramen (if present) are not preserved. The blind, laterally open pit present on the quadrate of other erythrosuchids (e.g., Gower 2003) may have been present immediately dorsal to the articular surface for the quadratojugal, but this area is poorly preserved.
The pterygoid wing is broken, but clearly would have originated some distance above the quadrate condyles, because the broken base of the wing is separated from the condyles on the medial surface by at least 30 mm ( Fig. 6A View Fig 4 View Fig ). Dorsally, the head has a triangular cross section ( Fig. 6A View Fig 5 View Fig ), with a flattened anterior surface (lacking the anterior projection that is present in Garjainia prima : PIN 951/57), a short flat to gently convex lateral surface (broken at its anterior margin) and a broad, gently concave posteromedial surface. The head is convex in posterior and lateral views.
Pterygoid: A partial left pterygoid was originally preserved in three pieces: the posterolateral process ( PIN 4366/4), the central part of the element, with broken anterior process, quadrate flange and basipterygoid articulation ( PIN 4366/5), and part of the anterior process ( PIN 4366/7). The three pieces have been reassembled ( Fig. 7 View Fig ), and show a pterygoid that is extremely similar in morphology and slightly larger in size than the holotype specimen of the erythrosuchid Uralosaurus magnus ( PIN 2973/70). No palatal teeth are present on any preserved part of the pterygoid, resembling the condition in Erythrosuchus africanus ( Gower 2003) , Uralosaurus magnus ( PIN 2973/70), Shansisuchus shansisuchus ( Young 1964: fig. 15a) and the holotype of Garjainia prima ( Ezcurra et al. 2019) . The posterolateral process is elongate and projects strongly posteriorly and ventrally, and slightly laterally ( Fig. 7 View Fig : posterolateral process), resembling the condition in Erythrosuchus africanus NHMUK PV R 3592), Shansisuchus shansisuchus ( Young, 1964: fig. 15a), Uralosaurus magnus ( PIN 2973/70) and Sarmatosuchus otschevi ( PIN 2865/68). It tapers strongly distally to a point and is slightly curved anteriorly at its distal end. The process is broken along its anterior margin, except for the distal third, which is complete. The dorsal surface of the process is convex anteroposteriorly, with the apex of this convexity offset posteriorly. Ventrally, there is a deeply inset facet along the anterior margin for articulation with the ectopterygoid along the entire preserved length of the process ( Fig. 7A View Fig 3 View Fig : articular surface for the ectopterygoid). This facet is offset by a distinct step from the rest of the ventral surface, and is flattened medially and slightly convex with low ridges within it laterally. Due to poor preservation, it is unclear if the ectopterygoid also articulated with the dorsal surface of the posterolateral process. The ventral surface of the posterolateral process posterior to this facet is anteroposteriorly convex.
At its base, where the posterolateral process merges into the ventral margin of the quadrate flange, the posterior surface of the posterolateral process bears a dorsoventrally extending and posteromedially opening fossa that continues onto the base of the quadrate flange ( Fig. 7A View Fig 1 View Fig : fossa on the posterior surface of the posterolateral process), as occurs in Erythrosuchus africanus ( Gower 2003: fig. 14b), Shansisuchus shansisuchus ( Young 1964: fig. 15a) and Uralosaurus magnus ( PIN 2973/70). This fossa is delimited by ridges medially and laterally in these species, but it is absent in Sarmatosuchus otschevi ( PIN 2865/68-2). The anterior process of the pterygoid is very incomplete, but a deep ventromedially opening fossa is present on the ventral surface of the pterygoid at the point at which the anterior and posterolateral processes join ( Fig. 7A View Fig 1 View Fig , A 3 View Fig : fossa on the ventral surface of the anterior process), and expands anteriorly onto the ventral surface of the anterior process, a condition widespread among early archosauriforms (e.g., Erythrosuchus africanus : Gower 2003: fig. 14; Shansisuchus shansisuchus : Young 1964: fig. 15a; Uralosaurus magnus : PIN 2973/70; Sarmatosuchus otschevi : PIN 2865/68-2). The medial margin of the anterior process is drawn out dorsally into a transversely compressed flange, and the lateral surface of the anterior process is dorsoventrally concave. Posterodorsally, only the transversely expanded base of the quadrate wing is preserved, and a medial part of the dorsally expanding anterior wall of the fossa for the basipterygoid process is preserved, although this fossa itself is infilled with matrix and its lateral wall is completely broken away.
Dentition: PIN 4366/3 is an isolated tooth including the crown and root ( Fig. 8A View Fig ) that was collected from the type locality and referred to Chalishevia cothurnata by Ochev (1980). It is generally well preserved but damaged at the tip and broken basally, with some damage to labial and lingual surfaces. The entire tooth is 92 mm high and has a mesiodistal length of 25 mm at the base of the crown. The crown is gently recurved in labial and lingual views. One surface of the crown (interpreted as labial) is more strongly convex than the other (lingual). Chisel-like, fine serrations orthogonal to the carina are present along the mesial and distal margins, extending from the base of the crown to the preserved apex. They vary in size along the carinae, being small basally, reaching a maximum size at the dorsoventral midpoint of the crown, and then decreasing slightly apically. There are no blood grooves. Along the mesial margin of the lingual surface, faint crenulations (enamel wrinkles) are present, curving basally away from the carina ( Fig. 8A View Fig 5 View Fig ). No other enamel ornamentation or wear facets are present in the preserved portion of crown. There is no constriction or expansion at the base of the crown with respect to the root.
PIN 4366/8 is a second tooth including the complete crown and nearly the entire root ( Fig. 8B View Fig ). The tooth is 123 mm long as preserved, and the crown makes up approximately the apical 38 mm. The root is oval in cross section, being slightly longer mesiodistally than labiolingually. It tapers strongly towards its base. The crown is recurved, with the apex extending distal to the distal margin. The mesial and distal margins possess finely serrated carinae, with serrations extending from the very base of the crown right to the apex. Variation in denticle size is similar to the other crown. Labial and lingual crown surfaces are equally convex mesiodistally. Faint, basally curved wrinkles in the enamel surface are present ( Fig. 8J View Fig ), but only on one surface and more extensively developed adjacent to the distal carina.
Two fragments of right nasal from the Koltaevo III locality are referred to Chalishevia cothurnata ( Fig. 9 View Fig ). One fragment ( PIN 2867 View Materials /7) corresponds to the main body ( Fig. 9A View Fig 3 View Fig , B 1 View Fig ), 99 mm in length with a maximum width of 43 mm as preserved. It is broken posteriorly before the beginning of the ventral process and anteriorly before the margin of the external naris. The size of this specimen, particularly the transverse distance between the midline and the facet for the premaxilla (20 mm) compares well with the right nasal of the holotype (17.5 mm). By contrast, a second fragment ( PIN 2867 View Materials /18), also of a right nasal but consisting of the ventral process and base of anterior ramus of main body ( Fig. 9A View Fig 1 View Fig , A 2 View Fig ), is smaller than the holotype specimen, probably juvenile, and represents a second individual from this locality .
In PIN 2867/7 the posterior end of the narrow and posterodorsally tapering sutural surface for the postnarial process of the premaxilla is visible ( Fig. 9B View Fig 1 View Fig : articular surface for the premaxilla). Posterior and lateral to this the preserved lateral margin appears to have been broken and worn, such that it superficially resembles a finished edge. Thus, the dorsal border of the accessory antorbital fenestra does not appear to be preserved. Medial to the premaxillary facet, the external surface of the nasal is transversely convex, and the longitudinal depression extending from the posterior end of the external naris parallel to the premaxillary facet that is present in the holotype of Chalishevia cothurnata is absent. Medially, close to the midline, there is a deep and sharply delimited groove that extends anteroposteriorly ( Fig. 9B View Fig 1 View Fig : groove); this groove is truncated anteriorly by the breakage of the anterior end of the bone, and it is not clear whether a foramen was present at this point. The external surface of the posterior part of the bone is rugose and ornamented.
Ventrally, there is a well-developed, anteroposteriorly extending ridge that runs parallel to the medial margin of the bone ( Fig. 9B View Fig 2 View Fig : ridge), separated from it by approximately 12 mm anteriorly, but diverging from the midline slightly and fading out towards the posterior end of the bone. This ridge is not present in the holotype of Chalishevia cothurnata . At the lateral margin the bone appears to be broken, but the base of the deep fossa that surrounds the accessory antorbital fenestra in the holotype of Chalishevia cothurnata is preserved ( Fig. 9B View Fig 2 View Fig : accessory antorbital fossa).
The bone differs from the holotype specimen of Chalishevia cothurnata in the ventral ridge, the absence of an external groove adjacent to the facet for the postnarial process of the premaxilla, and the presence of a more medially placed groove on the external surface. It is strongly similar to Chalishevia cothurnata in possessing the fossa surrounding the accessory antorbital fenestra, and the very strongly tapered postnarial process of the premaxilla, although these features are also present in Shansisuchus shansisuchus ( Young 1964) .
The second nasal fragment ( PIN 2867/18) includes a more posterior part of the main body and the almost complete ventral process (the tip is missing) for articulation with the dorsal process of the maxilla ( Fig. 9A View Fig 1 View Fig , A 2 View Fig ). The external surface of the bone is convex and rugose, with several foramina present, and is very similar to the same region in the holotype. The ventral process is triangular in lateral view ( Fig. 9A View Fig 1 View Fig : ventral process). In anterior view, the anterodorsal surface of the ventral process and the ventral surface of the main body are deeply excavated to form an accessory antorbital fossa as in the holotype of Chalishevia cothurnata ( Fig. 9A View Fig 2 View Fig : accessory antorbital fossa). The anterior border of the ventral process and the preserved ventral margin of the main body would have formed the posterodorsal margins of an accessory antorbital fenestra, as in the holotype of Chalishevia cothurnata and Shansisuchus shansisuchus . Medially, the main body is transversely concave, and at its medial margin forms an articular surface for the opposite nasal with two grooves and a median ridge. The posteromedial surface of the ventral process is bevelled ventrally for the ascending process of the maxilla.
Based on the strong similarities of these nasal fragments to those in the holotype, and their occurrence within the same stratigraphic horizon, we retain their referral to Chalishevia cothurnata . Minor differences between PIN 2867/7 and the nasals of Chalishevia cothurnata are interpreted as individual intraspecific variation.
Stratigraphic and geographic range.— Bukobay Gorizont, Ladinian, late Middle Triassic; Sol-Iletsk district , Orenburg Province and Kuyurgazinskiy district , Republic of Bashkortostan, Russia .
| PIN |
Paleontological Institute, Russian Academy of Sciences |
| IVPP |
Institute of Vertebrate Paleontology and Paleoanthropology |
| UTGD |
Geology Department, The University of Tasmania |
| BSPG |
Bayerische Staatssammlung fuer Palaeontologie und Geologie |
| GHG |
Council for Geosciences |
| NHMUK |
Natural History Museum, London |
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