Eoconstrictor Scanferla & Smith, 2020

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

Genus Eoconstrictor Scanferla & Smith , 2&2&a

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

Type species locality and age: Messel Pit, Germanv ( 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 boundarv, ~48 Mva) ( 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 autapomorphv); prootic with dorsoventrallv compressed opening for exit of maxillarv branch of trigeminal nerve ( V 2), posterior margin of this foramen pointed (unique autapomorphv); between one and four labial foramina on the maxilla; 15–18 maxillarv teeth; palatine with 5–6 teeth; ptervgoid with 10–11 teeth; dentarv with 17–19 teeth; mid-sagiưal keel along the ventral side of the basioccipital contributing to V-shaped cross-section (adult feature, mav be absent in juveniles); ectoptervgoid process of ptervgoid merging anteriorlv with dentigerous process via gentlv concave (almost straight) margin (i.e. no deep emargination between dentigerous ramus and ectoptervgoid process). Ŋis feature, in combination with a broad basiptervgoid flange located immediatelv opposite on the medial side, gives the mid-portion of the ptervgoid 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 lvmphapophvses are visible in E. fischeri SMF-ME 1607 ), and up to c. 71 are caudal vertebrae. Eoconstrictor can be differentiated from Palaeopython ºochebrune, 1880, in having a thinner zvgosphene 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 comparativelv taller neural spine (especiallv on posterior trunk vertebrae), and in lacking a depressed neural arch on posterior trunk vertebrae. Eoconstrictor further differs from Phosphoroboa Georgalis , ºabi & Smith, 2021, in having a lower ptervgoid tooth count (10–11 vs. 14), in lacking an anteromedial projection of the ptervgoid at the palatine articulation, and in having a generallv U-shaped frontoparietal suture (rather than V-shaped).

Remarks: Ŋe number of precloacal vertebrae is best known in the tvpe species of the genus, E. fischeri (cf. Schaal 2004 and Smith and Scanferla 2022). SMF-ME 1004 and SMF-ME 2504 have a verv high number of vertebrae (around 300 precloacals in SMF-ME 2504), whereas SMF-ME 1607 has notablv 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 vr/m, 28,000 –63,000 vears apart), and SMF-ME 1607 is from in between.

Based on data from Szvndlar and Georgalis (2023) on the minimum and maximum number of precloacal vertebrae in non-Caenophidian snakes (Supporting Information, File S3), precloacal variabilitv [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 variabilitv 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, holotvpe, digital renderings of the segmented skull. A, skull in dorsal view and disarticulated leħ lower jaw in lateral view.B, skull in ventral view and disarticulated leħ lower jaw in medial view. Abbreviations: c, coronoid; co, compound; d, dentarv; f, frontal; j, fragment of jugal?; ma, maxilla; p, parietal; pa, palatine; pt, ptervgoid; sp, splenial; st, supratemporal.