Eoconstrictor Scanferla & Smith 2020
Creators: name: Palci, Alessandro
name: Onary, Silvio
name: Lee, Michael S. Y.
name: Smith, Krister T.
name: Wings, Oliver
name: Rabi, Márton
name: Georgalis, Georgios L.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Constrictores
Eoconstrictor

description: 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).
description: Published as part of 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, pp. 1-27 in Zoological Journal of the Linnean Society 202 (2) on page 4, DOI: 10.1093/zoolinnean/zlad179, http://zenodo.org/record/14542189