Abstract
BackgroundThe earliest Miocene (Aquitanian) represents a crucial time interval in the evolution of European squamates (i.e., lizards and snakes), witnessing a high diversity of taxa, including an array of extinct forms but also representatives of extant genera. We here conduct a taxonomical survey along with a histological/microanatomical approach on new squamate remains from the earliest Miocene of Saint-Gérand-le-Puy, France, an area that has been well known for its fossil discoveries since the nineteenth century.ResultsWe document new occurrences of taxa, among which, the lacertid Janosikia and the anguid Ophisaurus holeci, were previously unknown from France. We provide a detailed description of the anatomical structures of the various cranial and postcranial remains of lizards and snakes from Saint-Gérand-le-Puy. By applying micro-CT scanning in the most complete cranial elements of our sample, we decipher previously unknown microanatomical features. We report in detail the subsurface distribution and 3D connectivity of vascular channels in the anguid parietal. The fine meshwork of channels and cavities or sinuses in the parietal of Ophisaurus could indicate some thermoregulatory function, as it has recently been demonstrated for other vertebrate groups, providing implications for the palaeophysiology of this earliest Miocene anguine lizard.ConclusionsA combination of anatomical and micro-anatomical/histological approach, aided by micro-CT scanning, enabled the documentation of these new earliest Miocene squamate remains. A distinct geographic expansion is provided for the extinct anguine Ophisaurus holeci and the lacertid Janosikia (the closest relative of the extant insular Gallotia from the Canary Islands).
Highlights
The earliest Miocene (Aquitanian) represents a crucial time interval in the evolution of European squamates, witnessing a high diversity of taxa, including an array of extinct forms and representatives of extant genera
A potential Aquitanian squamate fauna has been briefly described, without any figure, Georgalis and Scheyer BMC Ecol Evo (2021) 21:144 from Oschiri, Sardinia, the age of the locality is uncertain and could pertain even to the middle Miocene [18]. This limited number of available earliest Miocene localities hinders significantly our understanding on the evolution, diversity, and taxonomic composition of the oldest Neogene herpetofaunas, especially when considering that the Aquitanian of Europe hosted a diverse array of squamate lineages [11], which became extirpated or replaced by waves of new immigrant forms from other continents during the Burdigalian, that had a tremendous impact on lizard and snake faunas and reshaped drastically the European herpetofaunal assemblages [19,20,21]
Such diversity of squamates during the Aquitanian was apparently favored by the paratropical environments that were widespread in Europe and the rises in temperature compared to the preceding late Oligocene [8, 11, 22]
Summary
The earliest Miocene (Aquitanian) represents a crucial time interval in the evolution of European squamates (i.e., lizards and snakes), witnessing a high diversity of taxa, including an array of extinct forms and representatives of extant genera. Aquitanian squamates from Europe are Georgalis and Scheyer BMC Ecol Evo (2021) 21:144 from Oschiri, Sardinia, the age of the locality is uncertain and could pertain even to the middle Miocene [18] This limited number of available earliest Miocene localities hinders significantly our understanding on the evolution, diversity, and taxonomic composition of the oldest Neogene herpetofaunas, especially when considering that the Aquitanian of Europe hosted a diverse array of squamate lineages [11], which became extirpated or replaced by waves of new immigrant forms from other continents during the Burdigalian, that had a tremendous impact on lizard and snake faunas and reshaped drastically the European herpetofaunal assemblages [19,20,21]. Vertebrate fossil collections from that area are abundant and scattered across museums and institutions throughout Europe
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