Abstract
The extant beaver, Castor, has played an important role shaping landscapes and ecosystems in Eurasia and North America, yet the origins and early evolution of this lineage remain poorly understood. Here we use a geometric morphometric approach to help re-evaluate the phylogenetic affinities of a fossil skull from the Late Miocene of China. This specimen was originally considered Sinocastor, and later transferred to Castor. The aim of this study was to determine whether this form is an early member of Castor, or if it represents a lineage outside of Castor. The specimen was compared to 38 specimens of modern Castor (both C. canadensis and C. fiber) as well as fossil specimens of C. fiber (Pleistocene), C. californicus (Pliocene) and the early castorids Steneofiber eseri (early Miocene). The results show that the specimen falls outside the Castor morphospace and that compared to Castor, Sinocastor possesses a: 1) narrower post-orbital constriction, 2) anteroposteriorly shortened basioccipital depression, 3) shortened incisive foramen, 4) more posteriorly located palatine foramen, 5) longer rostrum, and 6) longer braincase. Also the specimen shows a much shallower basiocciptal depression than what is seen in living Castor, as well as prominently rooted molars. We conclude that Sinocastor is a valid genus. Given the prevalence of apparently primitive traits, Sinocastor might be a near relative of the lineage that gave rise to Castor, implying a possible Asiatic origin for Castor.
Highlights
The fossil record of beavers (Castoridae) comprises roughly 30 genera, with the earliest representatives appearing in the latest Eocene of North America
Castor is reported to have appeared in Europe, North America, and Asia in the Late Miocene [13,14,15,16], the results of this study suggest that these Asian ‘‘Castor’’ specimens are likely attributable to Sinocastor
Relative Warp Analysis Separate relative warp analysis (RWA) were run for each view of the skull
Summary
The fossil record of beavers (Castoridae) comprises roughly 30 genera, with the earliest representatives appearing in the latest Eocene of North America. The third lineage exhibits skeletal proportions that indicate swimming specialization, hind-limb paddling locomotion [3,6,7]. This group of semi-aquatic beavers is represented by species spanning a wide range of body sizes, and includes the Pleistocene giant beaver, Castoroides, which is over 2 m in length [6]. The semi-aquatic group diversified greatly in the Miocene In this epoch there were at least ten genera in North America: Castor, Dipoides, Anchitheriomys, Dipoides, Monosaulax, Eucastor [6,7] Nothodipoides[9], Prodipoides[10], Priusaulax [11] and Temporocastor [12]. Castor is reported to have appeared in Europe, North America, and Asia in the Late Miocene [13,14,15,16], the results of this study suggest that these Asian ‘‘Castor’’ specimens are likely attributable to Sinocastor
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