Taxonomic revision of the snakes of the genera Palaeopython and Paleryx (Serpentes, Constrictores) from the Paleogene of Europe

Abstract

Large constrictor snakes, referred to the genera Palaeopython and Paleryx, are an ecologically prominent part of the fauna of Europe during the Paleogene. Most species were named over a century ago and their taxonomy is largely based on isolated vertebrae. Furthermore, the majority of named taxa originate from imprecisely known localities within the Phosphorites du Quercy, in southern France, and thus their exact age is not known. We critically review and re-diagnose these genera based on personal examination of all existing type material, an array of new specimens, and a detailed literature review. We consider Palaeopython and Paleryx to be valid and propose vertebral characters to distinguish them. We recognize three valid species of Palaeopython, i.e. Palaeopythoncadurcensis (type species) from the Phosphorites du Quercy, Palaeopythonceciliensis from Geiseltal, and Palaeopythonhelveticus from Dielsdorf (Switzerland), and one valid species of Paleryx, i.e. Paleryxrhombifer (type species) from Hordle Cliff (England). Four other species, which were previously treated as members of Palaeopython and Paleryx, i.e. “Palaeopython” filholii and “Palaeopython” neglectus from the Phosphorites du Quercy, “Palaeopython” fischeri from Messel, and “Paleryx” spinifer from Geiseltal, are also considered as valid but pertain to other genera. Among these four taxa, “Palaeopython” fischeri has been recently assigned to its own genus, Eoconstrictor. A new genus, Phosphoroboa gen. nov. is established to accommodate “Palaeopython” filholii. We designate a lectotype for Palaeopythoncadurcensis and establish that the paralectotype maxilla and dentary are reasonably referred to this species. New material attributed to Palaeopythoncadurcensis is described from the old collections of the Phosphorites du Quercy. Paleryxcayluxi, another species established from the old collections of the Phosphorites du Quercy, is synonymized here with Palaeopythoncadurcensis. We further clarify important errors in the original description and figures of Paleryxcayluxi, identify the exact specimens that comprise the type series, and designate a lectotype. Much new material is described for Palaeopythonceciliensis from its type area in Geiseltal and intracolumnar variation is considered. We describe additional vertebral and cranial material of Paleryxrhombifer from its type area in Hordle Cliff. Based on this cranial material, we suggest non-booid affinities for Paleryxrhombifer. We designate a lectotype for Paleryxdepressus and agree with its previous suggested synonymy with Paleryxrhombifer. We re-describe the lectotype and paralectotypes of “Palaeopython” neglectus and refer and describe new material of this species from the Phosphorites du Quercy, paying special attention to intracolumnar variation; we also defer a decision on its generic relations until more abundant and complete material can be studied. We describe new vertebral material of the booid Eoconstrictor cf. fischeri from Geiseltal; similar material was previously known only from Messel and Dielsdorf. We determine that Eoconstrictorfischeri contains two distinct and unrelated species and describe intracolumnar variation in the nominotype. We clarify certain issues regarding the type series of Paleryxspinifer, designate a lectotype, and report previously unrecognized cranial material associated with the latter specimen; we transfer this species to Eoconstrictor based on cranial features and recombine it as Eoconstrictorspinifer comb. nov. We finally describe much new vertebral and cranial material of Phosphoroboafilholii comb. nov. from the Phosphorites du Quercy (both from the old collections but also from the late Eocene localities of Escamps A and C), paying special attention to intracolumnar variation. Based on this cranial material from Escamps, we identify Phosphoroboa gen. nov. as a booid. An analytical approach is undertaken in many isolated remains in order to quantify vertebral structures and assess intracolumnar variation, as well as associating isolated cranial elements to vertebral-based taxa. 3D models of the type material of the Geiseltal and Messel taxa are presented. The importance of vertebrae in the taxonomy of fossil Constrictores is addressed, although it is acknowledged that it is cranial material that can afford the most reliable phylogenetic conclusions. The diversity, distribution, biogeographic origins, and final demise and extinction of large Constrictores in the Paleogene of Europe are discussed.

First occurrence ofPsammophis(Serpentes) from Europe witnesses another Messinian herpetofaunal dispersal from Africa – biogeographic implications and a discussion of the vertebral morphology of psammophiid snakes

“…Mid‐trunk vertebrae (Figure 3a–e) closely match the morphology of the holotype. Similar to the holotype, the vaulting ratio (sensu Georgalis et al, 2021) of mid‐trunk vertebrae ranges between around 0.55 and 0.61. Towards the transition between mid‐trunk and posterior trunk vertebrae, the haemal keel gets distinctly wider and the subcentral grooves deeper (Figure 3f–t), but otherwise these vertebrae also bear a similar morphology with the preceding ones.…”

“…Also in posterior trunk vertebrae, the neural spine is dorsoventrally low (at least its posterior edge), judging from MNCN 150.108, which possesses the most‐well‐preserved (but still damaged) neural spine. Also, as it is generally typical for this portion of the column, the vaulting ratio (sensu Georgalis et al, 2021) of posterior trunk vertebrae has a slightly lower value, compared to the preceding ones, ranging between approximately 0.51 and 0.54. There are certain features that appear consistent throughout the trunk column, most notably the shape of the zygosphene in dorsal and anterior views, the distinctive paracotylar foramina, the distinct foramina on the edges of the postzygapophyses in posterior view, the extent of the neural spine in dorsal view, the horizontality of the prezygapophyses, and the ventral inclination of the prezygapophyseal accessory processes.…”

“…In posterior view (Figure 2b), the neural arch is vaulted and almost semicircular in shape. The vaulting ratio of the neural arch (sensu Georgalis et al, 2021), that is, the ratio of the height of the roof of the zygantrum from the so‐termed PO‐PO line [the distance between the outer edges of the postzygapophyses], measured on the midline, to the half‐width of PO‐PO line, corresponds to 0.56. One large foramen is situated at each lateral edge of the postzygapophyses, while another, smaller, one is situated between this and the zygantrum.…”

“…Anatomical terminology and measurements of snake vertebrae follow Szyndlar (1984) and Georgalis et al (2021). Taxonomy follows Kelly et al (2009) and Zaher et al (2009Zaher et al ( , 2019.…”

A New Species of the Pythonomorph Carentonosaurus from the Cenomanian of Algora (Guadalajara, Central Spain)

“…Pythonomorpha is composed by Ophidia, Mosasauroidea (i.e., a clade including both Mosasauridae and Aigialosaurus ), and other taxa whose phylogenetic position within the clade is currently under discussion, some of them being generally referred to Dolichosauridae (sensu Paparella et al [ 13 ]) (see below). In ophidians, the zygosphene is strongly developed and not notched, displaying a particularly straight zygosphene roof in the anterior view; and the zygosphenal articular facets are usually massive and/or widely divergent towards the lateral areas [ 11 , 22 , 24 , 55 , 56 , 57 , 58 , 59 ]. As pointed out by Lee and Scanlon [ 32 ] and Palci [ 60 ], the presence of vertebral zygapophyses inclined less than 30° may be considered and exclusive character for this clade.…”