Snakes are one of the most successful groups of terrestrial Vertebrates, with over 3800 described extant species. Of these, about 620 are Blindsnakes, Scolecophidia, small, worm-like Snakes with reduced eyes covered by scales, subterminal mouths, and blunt snouts and tails which can make it hard to determine which end is the front. These Snakes are interesting taxonomically, as they retain more Lizard-like features than other Snakes, as well as having a set of derived adaptations for a burrowing environment all their own, which has led to the conclusion that they are the earliest-branching group of extant Snakes, something which has been supported by genetic analysis. However, if this is the case, then Blindsnakes should have appeared in the Late Jurassic or Early Cretaceous, whereas the oldest known fossils assigned to the group come from the Late Palaeocene of Morocco and Early Eocene of Europe.
In a paper published in the journal iScience on 19 November 2023, Thiago Schineider Fachini of the Laboratório de Paleontologia at the Universidade de São Paulo, Silvio Onary, also of the Laboratório de Paleontologia at the Universidade de São Paulo, and of the College of Science and Engineering at Flinders University, and the South Australian Museum, Alessandro Palci and Michael Lee, also of the College of Science and Engineering at Flinders University, and the South Australian Museum, Mario Bronzati of the Laboratório de Evolução e Biologia Integrativa at the Universidade de São Paulo, and Annie Schmaltz Hsiou, again of the Laboratório de Paleontologia at the Universidade de São Paulo, describe a new species of Blindsnake from the Late Cretaceous Adamantina Formation of São Paulo State, Brazil.
The new species is named Boipeba tayasuensis, where 'Boipeba' means 'flat Snake' in the Tupi-Guarani language of Brazil, and 'tayasuensis' means 'from Taiaçu' in reference to the location where the specimen was found. The new species is described on the basis of an isolated vertebra articulated with the anterior region of a fragmentary following vertebra, from a fossiliferous outcrop of the Adamantina Formation beside a rural road between the municipalities of Monte Alto and Taiaçu, in the Northwest of the state of São Paulo, Brazil. The Adamantia Formation here has not been precisely dated, but a maximum age of 87.8 million years has been established based upon of uranium-lead dating (uranium-lead dating can give absolute dates for igneous rocks, but only maximum age dates for sedimentary deposits containing derived materials), and the overlying Marília Formation contains Dinosaur bones, indicating that it was laid down before the End Cretaceous Extinction Event.
The specimen shows a number of features that are known only in members of the crown group Scolecophidia (the crown group comprises everything descended from the last common ancestor of all living members of a group). These include (1) dorsoventrally flattened vertebra, (2) absence of median notch in the posterior border of the neural arch, (3) narrow and cylindrical centrum, (4) absence of hemal keel and/or median ventral prominence between the cotyle and condyle, (5) presence of asymmetrical subcentral foramina, (6) weakly developed precondylar constriction, (7) cotyle and condyle oval in anteroposterior view, (8) the presence of well-developed prezygapophyseal processes, and (9) undivided synapophyses with no distinction between the para- and diapophyseal articular facets. Furthermore, the specimen has synapophyses located dorsal to the ventral margin of the cotyle, a feature seen only in members of the Family Typhlopidae.
Although the material assigned to Boipeba tayasuensis is extremely limited, it is entirely consistent with derivation from a Snake, and in particular a Blindsnake, showing no real similarity to any member of any other group. A phylogenetic analysis recovered the specimen as being firmly placed within the Scolecophidia, forming a sister group to the living Typhlopidae.
The vertebra of Boipeba tayasuensis has a centrum length of 6.8 mm, exceptionally large compared to that of most modern Blindsnakes, leading to an estimated total length of 110 cm. This is three and a half times the size of most living Typhlopoids, which are themselves among the largest Blindsnakes, although it would be a fairly average size for most modern Snake groups, as well as most known Mesozoic Snakes, suggesting that small size is a derived feature in modern Scolecophidians.
Until the oldest known Blindsnakes come from the Palaeocene of Morocco and the Eocene of Europe, making Biopeba the oldest known, and the fisrt Mesozoic member of the group, as well as between 10 and 28 million years older than the next oldest known member of the group. A phylogenetic study recovered Biopeba as the sister taxon to the Family Typhlopoidea, which is consistent with molecular clock predictions that that group originated in the Cretaceous.
This in turn has biogeographical implications for the origin of the Typhlopoidea, suggesting that the group may have emerged in Western Gondwana (i.e. modern South America), instead of Eastern Gondwana (India or Madagascar) as previously theorised. The find also supports the younger of two possible origin dates for the Typhlopoidea, at about 122 million years ago in the Early Cretaceous, rather than about 150 million years ago, in the Late Jurassic.
Because Biopeba is recovered as more closely related to the Family Typhlopoidea than the Family Leptotyphlopidae, it also provides a minimum age for the divergence of these two groups.
Biopeba is a giant among Blindsnakes, but of fairly average size for most Snake groups, with the exception of the living Boas and Pythons, and some extinct stem group Snakes (i.e. Animals more closely related to living Snakes than to any other living group, but not decended from the last common ancestor of all living Snakes). This suggests that the small size of modern Blindsnakes is a derived character, and that the ancestors of the group were much larger Animals than had previously been theorized. In addition, small size appears likely to have apeared separately in the three major Blindsnake lineages.
Large size is extremely rare in modern Blindsnakes, but may have been normal in Cretaceous members of the group. The small size of modern Blindsnakes may be a result of the End Cretaceous extinction, which smaller cryptic Animals had a better chance of surviving. It has been suggested that the earliest Snakes were small burrowing Animals, at least in part because the burrowing Blindsnakes are thought to be the earliest branching Snake group. However, the large size of Biopeba suggests that this extrapolation is false, and that the earliest Blindsnakes were more similar in size to other Snake groups, rather than the other way round.
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Online courses in Palaeontology.
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