A frequent misconception about bats is that the oldest bats are known from the early Eocene (~52.5 million years ago) Green River Formation of western North America. In fact, there are earlier fragmentary bats known from Eocene deposits of both Australia and Portugal. Australonycteris clarkae and Archaeonycteris? praecursor both date to likely earliest Eocene sediments (1,2), while the complete skeletons of Icaronycteris index and Onychonycteris finneyi from the Green River Formation date to slightly younger late early Eocene deposits (3,4). In a new paper out today in Biology Letters, colleagues and I describe the first early Eocene bat from Asia, which is also—along with Australonycteris and Archaeonycteris? praecursor—among the oldest bats currently known (5). Bats actually occur nearly worldwide during the early Eocene (spanning 56-48 million years ago), being found in Africa, Australia, Europe, North America, South America, and the Indian subcontinent--which likely hadn’t completely collided with Asia at that point—by the end of the early Eocene (6). Until now, however, the oldest bats from mainland Asia dated to the middle Eocene ~43-44 million years ago. The new bat from the Junggar Basin of northwestern China, which we have named Altaynycteris aurora, likely dates to the first million years of the early Eocene based on biostratigraphic correlation with fossils from Inner Mongolia (5). This places Altaynycteris approximately contemporary with Australonycteris and Archaeonycteris? praecursor from Australia and Europe. Holotype upper first molar of Altaynycteris aurora. SEM photograph by Ni Xijun, IVPP. Finding early Eocene bats in central Asia is important, since we know several other groups of animals originated in Asia around this time period. The origin of both rodents and lagomorphs (rabbits, hares, and pikas) can confidently be traced to Asia, while many other groups of placental mammals have been hypothesized to originate there (7). Morphologically, Altaynycteris also appears primitive enough to represent a very early branch of the bat tree.
Only two teeth of Altaynycteris are currently known, but they possess enough similarity to other early Eocene bats (e.g., exaggerated W-shaped crests, lack of a mesostyle) that we are confident they belong to bats. These teeth, however, possess other similarities to non-bat insectivorous mammals from the Paleocene and early Eocene. They lack the common hook-shaped parastyle of most bats, and possess small cusps and crests (the metaconule and postparaconule crista) that are absent in most bats. The fact that Altaynycteris appears so primitive lends credence to the idea that bats may have a central Asian origin. 1) Hand, S., Novacek, M., Godthelp, H., & Archer, M. (1994). First Eocene bat from Australia. Journal of Vertebrate Paleontology, 14: 375-381. 2) Tabuce, R., Antunes, M.T., & Sigé, B. (2009). A new primitive bat from the earliest Eocene of Europe. Journal of Vertebrate Paleontology, 29: 627-630. 3) Jepsen, G.L. (1966). Early Eocene bat from Wyoming. Science, 154: 1333-1339. 4) Simmons, N.B., Seymour, K.L., Habersetzer, J., & Gunnell, G.F. (2008). Primitive early Eocene bat from Wyoming and the evolution of flight and echolocation. Nature, 451: 818-821. 5) Jones, M.F., Li, Q., Ni, X., & Beard, K.C. (2021). The earliest Asian bats (Mammalia: Chiroptera) address major gaps in bat evolution. Biology Letters, 17: 20210185. 6) Smith, T., Habersetzer, J., Simmons, N.B., & Gunnell, G.F. (2012). Systematics and paleobiogeography of early bats. In Evolutionary History of Bats: Fossils, Molecules, and Morphology (G.F. Gunnell & N.B. Simmons, eds.), 23-66. 7) Bowen, G.J., Clyde, W.C., Koch, P.L., Ting, S., Alroy, J., Tsubamoto, T., Wang, Y, & Wang, Y. (2002). Mammalian dispersal at the Paleocene/Eocene boundary. Science, 295: 2062-2065.
0 Comments
|
Matthew JonesMusings on evolution and paleontology-related research and news. Archives
June 2021
Categories
All
|