Smithosaurus echzellensis gen. et, 2022

Vasilyan, Davit, Cernansky, Andrej, Szyndlar, Zbigniew & Moers, Thomas, 2022, Amphibian and reptilian fauna from the early Miocene of Echzell, Germany, Fossil Record 25 (1), pp. 99-145 : 99

Smithosaurus echzellensis gen. et sp. nov.

Ophisaurus spinari 2014 Ophisaurus spinari - Böhme and Vasilyan: p. 29, fig. 3f.

Etymology.

Based on the locality Echzell in Germany - one of two known localities, where this taxon occurred.

Holotype.

One parietal UMJGP 204.749.

Paratype.

One parietal HLMD-Ez 1965.

Range.

Germany (Echzell), early Miocene; Austria (Gratkorn), late middle Miocene.

Remarks.

Both parietals - HLMD-Ez 1965 from the early Miocene Echzell locality and UMJGP 204.749 from the late middle Miocene Gratkorn locality in Austria (see Böhme and Vasilyan 2014; fig. 3f), exhibit the same unique combination of features and can be placed to a single taxon without any doubts. Because the parietal UMJGP 204.749 (Fig. 13A, B ) is better preserved than HLMD-Ez 1965 (Fig. 13C, F ), it has been designated as the holotype for the new taxon.

Diagnosis.

Anguine lizard distinguishable from Anguis , Pseudopus and Ophisaurus by two autapomorphic features:

the parietal table gradually expands laterally in the anterior direction in an extreme way; thus, it appears to be distinctly constricted at the level of the parietal foramen or slightly posterior to it. The lateral margins of the table markedly diverge anterolaterally from this point, inclining at an angle of about 30° from the median plane. Posteriorly located lateral margins diverge gradually posterolaterally and continue to more-or-less straight supratemporal processes. Due to the lateral expansion of the parietal table, the anterolateral corner of the parietal table reaches further laterally than the supratemporal process. The ornamented surface on the dorsal side of the bone gradually widens anteriorly as well (in contrast to being rectangular);

the parietal cranial crests diverge in the anterior direction to form a V that separates the cranial vault from the muscular surface laterally (the anteriormost section of the crests bents laterally rather than medially).

Besides these two autapomorphic features, this taxon is characterized by the unique combination of the following characters: (1) the occipital shield is large, its anteroposterior length is longer than the length of the posteriorly located smooth area; (2) a narrow muscular surface is present; (3) a short postfoveal crest is present; (4) anterior end of the ventrolateral ridge of the supratemporal process joins the parietal cranial crest at the level anterior to the posteromedial margin of the floor of the parietal fossa. The parietal crest is sharp in the area of the junction; (5) the virtual line, continuing from the ventrolateral ridge of the supratemporal process to the anterior margin of the parietal table, reaches the level as the lateral margin of the parietal foramen here; (6) the supratemporal process has a smooth ventrolateral surface, which fluently continues anteriorly to the muscular surface of the parietal table; and (7) the supratemporal process is straight.

Description.

Parietal: The parietal UMJGP 204.749 (Fig. 13A, B ) from Gratkorn is fairly preserved, whereas HLMD-Ez 1965 (Fig. 13C, D ) from Echzell represents the posterior half of the parietal table, with the left supratemporal process being, however, only partly preserved. The description is therefore based mostly on the holotype UMJGP 204.749. The ornamented surface of several fused headshield osteoderms covers most of the parietal table. The ornamentation consists of well-developed foramina and pits of various sizes, being densely distributed. At the periphery of the ornamented surface, radiated grooves and ridges are developed. The interparietal shield is well recognized in both specimens. This region is pierced by the large anteroposteriorly elongated parietal foramen. Unfortunately, its anterior margin is not preserved. The occipital shield is very large. Its anteroposterior length is twice as long as the length of the posteriorly located smooth area. The parietal notch is well developed. The lateral (=parietal) shields are preserved (but note that the almost entire lateral margins of the parietal table in HLMD-Ez 1965 are damaged). The arcuate edge runs on the dorsal surface of the bases of the supratemporal processes and diminishes laterally. The right supratemporal process is almost completely preserved, being straight. The parietal table extremely widens anteriorly - so it appears to be distinctly constricted at the level of the parietal foramen or slightly posterior to it. Thus, the lateral margins of the table markedly diverge anterolaterally from this point, inclining at an angle of about 30° from the median plane. Due to the lateral expansion of the parietal table, the anterolateral corner of the parietal table reaches further laterally than the supratemporal process. The anterolateral corners protrude into anterolateral processes. The ornamented surface is not rectangular but gradually widens anteriorly as well. The anterior end of the interparietal sulcus lies medial to the anterolateral corner of the ornamented surface.

On the ventral surface, many diagnostic features can be recognized. The oval parietal fossa is small, located in the central posteriormost region of the parietal table. The short postfoveal crests are well developed. In ventral view, both cranial crests are preserved, especially the complete right one, including the anterior portions missing in the Echzell specimen. The cranial crests are sharp. They diverge anteriorly, forming a V-shaped outline that separates the cranial vault from the muscular surface laterally. The muscular surface is narrow, but present. The virtual line, continuing from the ventrolateral ridge of the supratemporal process to the anterior margin of the parietal table, reaches the level as the lateral margin of the parietal foramen here. The ventrolateral ridge of the supratemporal process is well developed and preserved on the right side in UMJGP 204.749 and left side in HLMD-Ez 1965. Its anterior end joins the parietal cranial crest at the level anterior to the posteromedial margin of the parietal fossa. The cranial crest is sharp in this region. The root portion of the supratemporal process is broad. The other distal portion distinctly narrows posteriorly. The ventrolateral ridge is well developed. The supratemporal articulation extends anteriorly, being well visible on the lateral surface of the supratemporal process. Anteriorly to it, between the most anterior portion of the ventrolateral ridge and the anterolateral margin of the supratemporal process, a short ventrolateral surface can be recognized. This surface lies posterior to the parietal cranial crest-supratemporal process junction (note that it is broadly damaged in the Echzell specimen).

Remarks.

See the discussion part.

Phylogenetic analysis of Smithosaurus echzellensis .

The phylogenetic trees presented here are based on limited fossil material - the parietal, and thus more complete fossil specimens of this taxon are needed to draw more robust conclusions. However, in both two analyses, Smithosaurus echzellensis is consistently recovered as the sister taxon to either [ Ophisauriscus quadrupes + Ophisaurus holeci ] + [ Anguis + Ophisaurus ] (in the first analysis) or [ Anguis + Ophisaurus ] (in the second analysis). In overall, the support for the clade is very low (no strict synapomorphy; the calculating Bremer supports collapsed the node into polytomy, see below) and thus, the interpretation of the Smithosaurus relationship among anguines needs to be met with caution.

A New Technology (NT) search in TNT produced a single tree (Fig. 14A ). The position of Smithosaurus echzellensis is recovered as being sister to the clade [[ Ophisauriscus quadrupes + Ophisaurus holeci ] + [ Anguis + Ophisaurus (all others except of O. holeci )]]. The calculating Bremer supports collapsed the node (Bremer value 1, relative Bremer 25; Fig. 14B ), with the relationship among Smithosaurus echzellensis and the clades [ Ophisauriscus quadrupes + Ophisaurus holeci ] (Bremer value 3, relative Bremer 50) and [ Anguis + Ophisaurus ] (Bremer 2, relative Bremer 50) being unresolved.

The heuristic search in TNT produced two equally parsimonious trees. In both, Smithosaurus echzellensis is recovered as sister to [ Anguis + Ophisaurus (all others except of O. holeci )], whereas Ophisauriscus quadrupes and Ophisaurus holeci are sister to the clade formed by Smithosaurus , Anguis and Ophisaurus (all others except of O. holeci). This is contrary to the results from the NT analysis (see above). In the strict consensus tree, however, the position of Smithosaurus is unresolved among [ Ophisauriscus quadrupes + Ophisaurus holeci ] and [ Anguis + Ophisaurus (all others except of O. holeci )], although all these taxa together form a clade. Thus, the topology of examined taxa in this strict consensus tree is identical to that figured in Fig. 14B .

Figures

Figure 13. Smithosaurus echzellensis gen. et sp. nov. Holotypic parietal UMJGP 204.749 from the Gratkorn locality in (A) dorsal, and (B) ventral views. Paratypic parietal HLMD-Ez 1965 from the Echzell locality in (C) dorsal and (D) ventral views.

Figure 14. Phylogenetic position of Smithosaurus echzellensis. A. Single parsimonious tree recovered by TNT using NT (New Technology) search (with ratchet) and 1000 iterations; B. Tree showing Bremer / relative Bremer values at nodes recovered by TNT.