Apeomyoides
Apeomyoides savagei is a fossil rodent from the Miocene of the United States, the only species in the genus Apeomyoides. It is known from fragmentary jaws and isolated teeth from a site in the early Barstovian, around 15–16 million years ago, of Nevada. Together with other species from scattered localities in the United States, Japan, and Europe, Apeomyoides is classified in the subfamily Apeomyinae of the extinct rodent family Eomyidae. Apeomyines are a rare but widespread group that may have been adapted to a relatively dry habitat.
As is characteristic of apeomyines, Apeomyoides was a large eomyid with high-crowned cheekteeth and a large gap between the incisors and cheekteeth. Furthermore, the cheekteeth—premolars and molars—approach a bilophodont pattern, with two distinct lobes. Other features distinguish Apeomyoides from other apeomyines, including the rectangular shape of the cheekteeth. The fourth lower premolar (p4) is larger than the molars behind it and has two roots, while the lower molars have three.
Apeomyoides is a member of the Eomyidae, a diverse rodent family that is now extinct. Eomyids first appeared in the Middle Eocene (~47 million years ago, mya) in North America, where they existed until the end of the Miocene (~5 mya). In Europe, they survived a little longer, until the end of the Pliocene (~2–3 mya).[1] Apeomyoides is further part of a distinctive subgroup of eomyids known as the Apeomyinae. The first apeomyine to be discovered was Apeomys tuerkheimae, named in 1968 based on fossils from the Early Miocene of Germany, and later discoveries have expanded the range of Apeomys and similar taxa. In 1998, Oldřich Fejfar and colleagues reviewed Apeomys and identified a second, related genus Megapeomys, from the Early Miocene of Germany, the Czech Republic, and Japan. These scientists also named a new eomyid subfamily, Apeomyinae, to house Apeomys and Megapeomys.[2] The Japanese Megapeomys was named as a separate species, Megapeomys repenningi, in 2011.[3] Further apeomyines have been identified in North America: Megapeomys bobwilsoni from the Hemingfordian of Nevada, Apeomyoides savagei from the Barstovian of Nevada,[4] Zophoapeomys indicum from the Late Oligocene of South Dakota,[5] and a possible second species of Zophoapeomys from the Late Oligocene of Nebraska.[6] Another North American eomyid, Arikareeomys skinneri, from the Arikareean of Nebraska, has also been reidentified as an apeomyine.[7]
In general, apeomyines are a widespread but generally rare group of dentally distinctive eomyids with a tendency towards large size.[8][9] Fejfar and colleagues suggested that apeomyines were ecologically distinct from other eomyids and probably preferred a drier habitat.[10] Although other scientists recognized Apeomyinae as a subfamily, in a 2008 summary of North American eomyids, Lawrence Flynn placed the group as a tribe, Apeomyini, within the subfamily Eomyinae.[9] Flynn described Apeomyoides as the most derived apeomyine.[11]
Apeomyoides savagei was described as a new genus and species by Kent Smith, Richard Cifelli, and Nicholas Czaplewski in 2006. The generic name, Apeomyoides, adds the Greek suffix -ides, indicating similarity, to the name of the related genus Apeomys,[12] while the specific name, savagei, honors Donald E. Savage for his work on fossil mammals and for assistance to Smith.[13] In the same paper, these scientists argued in favor of apeomyine affinities for Arikareeomys.[12]
