Erythrosuchidae
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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-FFD0-4000-7B5C-F042AC89FA6A |
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treatment provided by |
Felipe |
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scientific name |
Erythrosuchidae |
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Erythrosuchidae indet.
Figs. 10 View Fig , 11 View Fig .
Material.—PIN 525/30, partial left surangular, from Koltaevo III, Kuyurgazinskiy district, Republic of Bashkortostan ( Sennikov 1995, 2008). PIN 4165/18 (formerly SGU 104/3859), two cervical vertebrae, from Bukobay I, Sol-Iletsk district, Orenburg Province, Russia ( Ochev 1980). PIN 4188/97 (formerly SGU 104/3861), cervical centrum, from Bukobay V, Sol-Iletsk district, Orenburg Province, Russia ( Ochev 1980). PIN 4188/98 (formerly SGU 104/3861), dorsal vertebra, from Bukobay V ( Ochev 1980). The Bukobay I and V and Koltaevo III localities are in the Bukobay Gorizont (Ladinian, late Middle Triassic: Shishkin et al. 1995, 2000). Tverdokhlebov et al. (2003) referred to the Bukobay V locality as Belyaevsky I (their locality 30).
Description.— Surangular: A fragmentary posterior half of left surangular (PIN 525/30; Fig. 10 View Fig ) includes part of the dorsal margin of the element and the ventromedial expansion (preglenoid process) that would have articulated with the anterior surface of the articular and formed the anterior margin of the glenoid fossa. The surangular is broken anteriorly, ventrally, and posteriorly. The preserved portion of the surangular is 148 mm long, with the dorsal margin reaching a maximum width of 27 mm and the element being approximately 42 mm wide at the level of the preglenoid process. The dorsal margin is broadly expanded dorsally. The dorsal surface is slightly thickened into low ridges at its medial and lateral margins ( Fig. 10A View Fig 1 View Fig : ridge), between which the dorsal surface is gently concave transversely, with this concavity interrupted by a low anteroposteriorly extending ridge that shifts slightly laterally and becomes more prominent towards its anterior end. An almost identical transverse expansion of the dorsal margin that is gently concave with lateral, medial and median ridges is also present in surangulars of Garjainia prima (e.g., PIN 951/46), and the surangular is generally very similar to those of other erythrosuchids (e.g., Erythrosuchus africanus ; Gower 2003). The transverse expansion of the dorsal margin overhangs the (mostly missing) ventral, transversely compressed, and sheet like flange of the surangular ( Fig. 10A View Fig 2 View Fig : broken base of ventral flange), with the overhang being greater medially than laterally. The lateral expansion diminishes and the medial expansion increases in width anteriorly. The dorsal transverse expansion is dorsoventrally thickest medially and tapers laterally. There is a groove on its medial surface at the anterior preserved end ( Fig. 10A View Fig 4 View Fig : groove). An anteroventrally opening fossa is present on the ventral surface of the dorsal expansion adjacent to the broken anterior surface ( Fig. 10A View Fig 2 View Fig : fossa). At the posterior end of the dorsal expansion a slightly raised transverse ridge delimits the anterior margin of the glenoid region ( Fig. 10A View Fig 1 View Fig : ridge defining anterior border of glenoid region). Medial to this, the surangular is expanded ventromedially into the flange-like preglenoid process ( Fig. 10A View Fig 1 View Fig : preglenoid process), the anterior surface of which is twisted to face anterodorsally and is transversely concave. Posteriorly and posteroventrally there are two articular surfaces for the articular.
Vertebrae: From the Bukobay I locality there are two articulated vertebrae that probably represent posterior cervicals (PIN 4165/18; Fig. 11A View Fig ). These vertebrae are very erythrosuchid-like in appearance, with the very short and deep centra and large size consistent with being referable to the clade (e.g., Ezcurra 2016). The two vertebrae are poorly preserved, and the more posterior of the two is missing most of its centrum. Neurocentral sutures are closed but visible, indicating that these vertebrae do not belong to an ontogenetically mature individual. It is unclear whether or not intercentra would have been present. The centrum of the first (more anterior) vertebra is anteroposteriorly short, dorsoventrally deep and transversely broad (maximum length 33.9 mm; maximum depth of anterior margin 51.5 mm; maximum width of anterior margin 54 mm). The articular faces are gently concave, with sub-circular outlines, although the ventral margin of the anterior articular face of the first vertebra is slightly damaged, and the posterior articular face is incomplete ventrally. In ventral view, the lateral surfaces are arched strongly inwards giving the centrum a spool-like appearance. The parapophysis is placed very close to the anteroventral corner of the centrum, and has an oval outline, with the long axis of the oval aligned dorsoventrally. Posterodorsal to the parapophysis there is a deep blind fossa on the lateral surface of the centrum immediately below the neurocentral suture—a small nutrient foramen is present within this fossa on the left side. The centrum has a low median ridge on its ventral surface, resembling the condition in Garjainia madiba ( Gower et al. 2014) and Erythrosuchus africanus ( Gower 2003) . By contrast, Sarmatosuchus otschevi lacks a ventral keel on its posterior cervical and cervico-dorsal centra (PIN 2865/68).
The neural arch is poorly preserved in both vertebrae and the neural spines are broken away. The neural canal is dorsoventrally deep with an oval outline. The base of the transverse process is partially preserved only on the right side of the second vertebra and its base is placed lateral to the dorsolateral corner of the neural canal and at about mid length of the neural arch, resembling the condition in the cervico-dorsal vertebrae of Garjainia prima ( Ezcurra et al. 2019) and Sarmatosuchus otschevi ( Gower and Sennikov 1997) . The transverse process is strongly downturned but is eroded at its distal end such that the diapophyseal articulation is not preserved. Ventral to the transverse process, an anteroposteriorly narrow and dorsoventrally deep fossa is present (clearly visible on the right side of the second vertebra) and is bounded by a sharp and narrow anterior centrodiapophyseal lamina, and a thick posterior centrodiapophyseal lamina. A deep and broad fossa is also present anterior to the transverse process and is bounded by the anterior centrodiapophyseal lamina and a very broad ridge in an equivalent position to the prezygodiapophyseal lamina. Posterior to the transverse process is a poorly developed third fossa, delimited by the posterior centrodiapophyseal and postzygodiapophyseal laminae. The presence of the set of four laminae originating from the diapophysis also occurs in other erythrosuchids ( Ezcurra 2016). The pre- and postzygapophyses are large but project only short distances beyond the anterior and posterior articular surfaces. There are deep pre-and postspinal fossae. There is no development of a fossa on the neural arch lateral to the base of the neural spine. The base of the neural spine is subrectangular in cross-section, being approximately 1.2 times anteroposteriorly longer than transversely wide, and located approximately at mid-length on the neural arch.
Two isolated partial vertebrae from the Bukobay V locality have also been previously assigned to Chalishevia cothurnata . PIN 4188/97 is a relatively deep and short (superficially erythrosuchid-like) cervical centrum ( Fig. 11B View Fig ), missing the neural arch and damaged at its posterolateral corner. The ventral parts of the anterior and posterior articular faces are slightly bevelled, but it is unclear if these represent articular surfaces for intercentra. The anterior and posterior articular faces have shield shaped outlines and concave surfaces. The centrum is anteroposteriorly compressed and the lateral surfaces are gently concave in ventral view with shallow blind fossae immediately ventral to the neurocentral suture. A low median ridge is present on the ventral margin, as is the case in Sarmatosuchus otschevi (PIN 2865/68), Guchengosuchus shiguaiensis ( Butler et al. 2019) , Garjainia prima ( Ezcurra et al. 2019) and Erythrosuchus africanus ( Gower 2003) . The parapophysis is placed very low on the anterior margin of the centrum. The centrum has a maximum dorsoventral height of the anterior face of 52.7 mm; the maximum width of the anterior face is 45 mm; and the anteroposterior length of centrum is 32 mm.
PIN 4188/98 is a probable dorsal vertebra that includes the neural arch, but lacking the neural spine, pre- and postzygapophyses, and diapophyses ( Fig. 11C View Fig ). It generally resembles an early archosauriform, but little more can be said about its taxonomic identity. The neurocentral suture is visible and unfused. The vertebra is probably too small to belong to the same individual as PIN 4188/97 from the same locality. The centrum has a maximum dorsoventral height of the anterior face of 30 mm; the maximum width of the anterior face is 34 mm; and the anteroposterior length of centrum is 28 mm. The articular surfaces of the centrum are subcircular with flattened dorsal margins and the anterior face is gently concave whereas the posterior face is flattened. In lateral view, the parapophysis is not clearly recognizable, but may be an eroded, thickening at the dorsal margin of the anterior end of the centrum. There is no ventral keel or ridge on the centrum and the lateral surfaces are gently concave, as occurs in the cervico-dorsal and dorsal centra of other erythrosuchids ( Ezcurra et al. 2019). The transverse process would have been at least slightly downturned (although only the base is preserved), and the bases of anterior centrodiapophyseal (or possibly paradiapophyseal, if the parapophysis was indeed on the centrum), posterior centrodiapophyseal, and pre- and postzygodiapophyseal laminae are preserved, delimiting fossae. There is no fossa on the neural arch dorsal to the transverse process.
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