 |
| Vielasia sigei Hand, Maugoust, Beck & Orliac, 2023 |
Highlights
• A new bat species is described from a 50-million-year-old cave deposit in France
• Its well-preserved fossils include the oldest uncrushed skull of a bat yet known
• This stem bat appears to have been capable of advanced (laryngeal) echolocation
• The fossils suggest that advanced echolocation predates the crown bat radiation
Summary
Bats are among the most recognizable, numerous, and widespread of all mammals. But much of their fossil record is missing, and bat origins remain poorly understood, as do the relationships of early to modern bats. Here, we describe a new early Eocene bat that helps bridge the gap between archaic stem bats and the hyperdiverse modern bat radiation of more than 1,460 living species. Recovered from ∼50 million-year-old cave sediments in the Quercy Phosphorites of southwestern France, Vielasia sigei’s remains include a near-complete, three-dimensionally preserved skull—the oldest uncrushed bat cranium yet found. Phylogenetic analyses of a 2,665 craniodental character matrix, with and without 36.8 kb of DNA sequence data, place Vielasia outside modern bats, with total evidence tip-dating placing it sister to the crown clade. Vielasia retains the archaic dentition and skeletal features typical of early Eocene bats, but its inner ear shows specializations found in modern echolocating bats. These features, which include a petrosal only loosely attached to the basicranium, an expanded cochlea representing ∼25% basicranial width, and a long basilar membrane, collectively suggest that the kind of laryngeal echolocation used by most modern bats predates the crown radiation. At least 23 individuals of V. sigei are preserved together in a limestone cave deposit, indicating that cave roosting behavior had evolved in bats by the end of the early Eocene; this period saw the beginning of significant global climate cooling that may have been an evolutionary driver for bats to first congregate in caves.
Keywords: bat, Eocene, France, fossil, skull, echolocation, cochlea, paleontology, phylogeny, cave dwelling
Systematic paleontology
Order Chiroptera Blumenbach, 1779
Family indeterminate
Vielasia gen. nov.
Generic etymology. From the type locality Vielase.
Geological setting. Vielase is among the oldest fossil deposits identified in the karstic terrane of the Quercy Phosphorites, southwestern France.50,56,57 The Vielase fossils were extracted from a russet-colored bone breccia and a light-colored limestone by acid processing.50,58 More than 400 bat specimens referable to Vielasia sigei were recovered, with the most complete specimens (including the holotype cranium UM-VIE-250) being extracted from the light-colored limestone (B. Marandat, personal communication). Taphonomically, these bat fossils are consistent with in situ accumulation in a cave;59,60 the remains are well preserved but dissociated and include 3D-preserved cranial and postcranial specimens representing multiple individuals, with teeth and bones unworn and without rounding or size filtering indicative of transport, nor evidence of digestion or accumulation by (e.g.) predatory birds. Much rarer rodent, primate, and carnivorous mammal fossils recovered from the site50 have been used to biocorrelate the deposit as reference level MP10 in the European Palaeogene mammal biostratigraphy.49,50,51,52
Vielasia sigei sp. nov.
Synonymy. Archaeonycteridae gen. et sp. indet. in Sigé58 and in Legendre et al. (see figure 7)50
Suzanne J. Hand, Jacob Maugoust, Robin M.D. Beck and Maeva J. Orliac. 2023. A 50-million-year-old, three-dimensionally preserved Bat Skull supports an early Origin for Modern Echolocation. Current Biology. In Press, DOI: 10.1016/j.cub.2023.09.043
phys.org/news/2023-10-fossilized-skull-vital-piece-evolution.html
