Eoconstrictor Scanferla & Smith, 2020

Palci, Alessandro, Onary, Silvio, Lee, Michael S. Y., Smith, Krister T., Wings, Oliver, Rabi, Márton & Georgalis, Georgios L., 2024, A new booid snake from the Eocene (Lutetian) Konservat-Lagerstätte of Geiseltal, Germany, and a new phylogenetic analysis of Booidea, Zoological Journal of the Linnean Society 202 (2), pp. 1-27 : 4

Genus Eoconstrictor Scanferla & Smith , 2 0 2 0a

Type species: Palaeopython fischeri Schaal, 2004 (original combination), currently Eoconstrictor fischeri ( Schaal, 2004) following the work of Scanferla and Smith (2020a).

Type species locality and age: Messel Pit, Germany ( Smith et al. 2018). All known specimens of E. fischeri come from the lacustrine ‘oil-shale’ of the Middle Messel Formation (near the Ypresian–Lutetian boundary, ~48 Mya) ( Lenz et al. 2015).

Emended diagnosis: Eoconstrictor can be distinguished from all other snakes in having the following combination of features: edentulous premaxilla with bifid vomerine processes (unique autapomorphy); prootic with dorsoventrally compressed opening for exit of maxillary branch of trigeminal nerve ( V 2), posterior margin of this foramen pointed (unique autapomorphy); between one and four labial foramina on the maxilla; 15–18 maxillary teeth; palatine with 5–6 teeth; pterygoid with 10–11 teeth; dentary with 17–19 teeth; mid-sagittal keel along the ventral side of the basioccipital contributing to V-shaped cross-section (adult feature, may be absent in juveniles); ectopterygoid process of pterygoid merging anteriorly with dentigerous process via gently concave (almost straight) margin (i.e. no deep emargination between dentigerous ramus and ectopterygoid process). This feature, in combination with a broad basipterygoid flange located immediately opposite on the medial side, gives the mid-portion of the pterygoid a broad, diamond-shaped to sub-elliptical appearance in dorsoventral view; total vertebral count up to 369 vertebrae, of which c. 246–303 are precloacal vertebrae, three are cloacal vertebrae (three vertebrae with lymphapophyses are visible in E. fischeri SMF-ME 1607 ), and up to c. 71 are caudal vertebrae. Eoconstrictor can be differentiated from Palaeopython Rochebrune, 1880, in having a thinner zygosphene bearing a prominent median lamellar tubercle, and in lacking a palatine foramen and a sigmoidal lateral margin of the maxilla (in dorsal view). Eoconstrictor can be differentiated from Paleryx Owen, 1850 , in lacking a palatine foramen, in having a comparatively taller neural spine (especially on posterior trunk vertebrae), and in lacking a depressed neural arch on posterior trunk vertebrae. Eoconstrictor further differs from Phosphoroboa Georgalis , Rabi & Smith, 2021, in having a lower pterygoid tooth count (10–11 vs. 14), in lacking an anteromedial projection of the pterygoid at the palatine articulation, and in having a generally U-shaped frontoparietal suture (rather than V-shaped).

Remarks: The number of precloacal vertebrae is best known in the type species of the genus, E. fischeri (cf. Schaal 2004 and Smith and Scanferla 2022). SMF-ME 1004 and SMF-ME 2504 have a very high number of vertebrae (around 300 precloacals in SMF-ME 2504), whereas SMF-ME 1607 has notably fewer (around 246 precloacals). Given the stratigraphic distribution of these specimens, the variation does not seem to indicate secular change through time. SMF-ME 1002 is from 1–3 m above marked bed Alpha, SMF-ME 2504 is from 6– 3 m below Alpha (at c. 7000 yr/m, 28,000 –63,000 years apart), and SMF-ME 1607 is from in between.

Based on data from Szyndlar and Georgalis (2023) on the minimum and maximum number of precloacal vertebrae in non-Caenophidian snakes (Supporting Information, File S3), precloacal variability [calculated as (Max—Min)/Min, where Max = maximum number of precloacals and Min = minimum number of precloacals] ranges between 0 and 0.5. Eoconstrictor fischeri , with a variability of (303 – 246)/246 = 0.23, would thus be close to the median value (Supporting Information, File S1: Fig. S3 ).

Figures

Figure 3. Eoconstrictor barnesi, GMH XXXVIII-20-1964, holotype, digital renderings of the segmented skull. A, skull in dorsal view and disarticulated left lower jaw in lateral view.B, skull in ventral view and disarticulated left lower jaw in medial view. Abbreviations: c, coronoid; co, compound; d, dentary; f, frontal; j, fragment of jugal?; ma, maxilla; p, parietal; pa, palatine; pt, pterygoid; sp, splenial; st, supratemporal.