Exquisitely Preserved Fossil Snakes of Messel: Insight into the Evolution, Biogeography, Habitat Preferences and Sensory Ecology of Early Boas

Abstract

Our knowledge of early evolution of snakes is improving, but all that we can infer about the evolution of modern clades of snakes such as boas (Booidea) is still based on isolated bones. Here, we resolve the phylogenetic relationships of Eoconstrictor fischeri comb. nov. and other booids from the early-middle Eocene of Messel (Germany), the best-known fossil snake assemblage yet discovered. Our combined analyses demonstrate an affinity of Eoconstrictor with Neotropical boas, thus entailing a South America-to-Europe dispersal event. Other booid species from Messel are related to different New World clades, reinforcing the cosmopolitan nature of the Messel booid fauna. Our analyses indicate that Eoconstrictor was a terrestrial, medium- to large-bodied snake that bore labial pit organs in the upper jaw, the earliest evidence that the visual system in snakes incorporated the infrared spectrum. Evaluation of the known palaeobiology of Eoconstrictor provides no evidence that pit organs played a role in the predator–prey relations of this stem boid. At the same time, the morphological diversity of Messel booids reflects the occupation of several terrestrial macrohabitats, and even in the earliest booid community the relation between pit organs and body size is similar to that seen in booids today.

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

“…Eoconstrictor fischeri and E. spinifer comb. nov.) afford a more precise taxonomic placement, as this genus has recently been demonstrated to pertain to Booidea (sensu Pyron et al, 2014), having in particular close phylogenetic affinities with extant Neotropical boas (Scanferla & Smith, 2020b). We also suggest booid affinities for Phosphoroboa filholii comb.…”

“…That material, along with other specimens from Dielsdorf, was subsequently extensively described and figured by Georgalis and Scheyer (2019a), who established another new species, Palaeopython helveticus. Finally, Scanferla and Smith (2020b) established the genus Eoconstrictor to accommodate the Messel species Palaeopython fischeri and, on the basis of a phylogenetic analysis, they suggested booid affinities for this taxon.…”

“…Remarks: Scanferla and Smith (2020b) erected the new genus Eoconstrictor to encompass Palaeopython fischeri, which they determined that was not closely related to Palaeopython. Their phylogenetic analyses found E. fischeri to be on the stem of Neotropical boas, i.e.…”

Pythons in the Eocene of Europe reveal a much older divergence of the group in sympatry with boas

“…Pythonids more likely originated in Laurasian than Gondwanan landmasses [4,5,41] and subsequently dispersed to Africa, Southeast Asia and Oceania [41]. Furthermore, the total lineages of both Pythonidae and Boidae were present in Europe during the Eocene [44]. This discovery is wholly unexpected given the extant distributions of Booidea and Pythonidae and shows that neither dispersal limitation nor strong competitive interactions are good explanations for hyper-macrostomatan biogeographic patterns in the early Cenozoic.…”

“…Given a molecular topology (e.g. [15]), their structural similarities, including the presence of pit organs for the perception of radiant heat [43,44], posteriorly expanded supratemporals and mandibles, and extended parallel-fibred adductor muscles [12] must be ascribed to convergence on a hyper-macrostomatan ecomorph. Allopatry today, in turn, suggests that either (i) dispersal limitation maintains lack of contact, or (ii) competition prevents one group from acquiring a foothold in a region already inhabited by the other group.…”