A morphological analysis of carnivoran ossicles from Rancho La Brea.

The morphology of the mammalian middle ear-including the size, shape, and stiffness of individual ossicles-controls their vibrational response to sound and, is closely related to an animal's auditory capabilities. While the relationship between middle ear morphology and hearing frequency has been explored in living carnivorans, the size and shape of ossicles in fossil carnivorans have been sparsely documented. In this study, we present the first morphological data on four iconic carnivoran taxa from the Rancho La Brea Tar Pits: Smilodon fatalis, Panthera atrox, Canis dirus, and Arctodus simus. These data are contextualized with samples of extant felids, canids, and ursids to determine the extent to which the ossicles of these iconic fossil taxa resemble their living relatives. Six, five, and seven linear measurements were taken from the malleus, incus, and stapes, respectively. Comparisons of geometric means reveal that the ossicles of fossil canids and felids are similar in size to living analogs, but those of A. simus are significantly larger than those of any living ursid. Further, principal components analyses demonstrate close morphological affinities between fossil and extant taxa within canids and felids, and again, a greater disparity between fossil and extant ursids. Canids and ursids occupy distinct regions of the morphospace, yet both overlap the morphological range spanned by felids. While some elements-for example, the stapes-require further specimens to facilitate more nuanced interpretations of variation, our findings underscore the need for concerted efforts towards identifying and preserving these bones within fossil assemblages.

The howl of Rancho La Brea: Comparative anatomy of modern and fossil canid hyoid bones.

The Rancho La Brea (RLB) fossil collection housed at the La Brea Tar Pits and Museum in Los Angeles, California, is one of the richest collections of carnivoran fossils in the world. The collection is also particularly well known for the preservation of rare and understudied bones in the tar, including the small bony apparatus that is of particular interest to this study, the hyoid. The La Brea collection houses hyoids from several extinct carnivoran species, some of the most common being those of Canis dirus (the dire wolf) and Canis latrans (the coyote). In this study, we compare fossilized hyoid elements from these two canids to samples from modern large congeners, namely: Canis lupus (the gray wolf), Canis rufus (the red wolf), and modern C. latrans. Seven or nine measurements were taken on each bone of the hyoid apparatus, and principal component analyses were performed in order to determine statistical significance between species. For most of the bones, the majority of the variation was driven by size. Dire wolves could be clearly differentiated from all other canids for all elements; the hyoid apparatus of C. dirus is larger and more robust than that of C. lupus. Most of the bony elements could not be distinguished between red wolves or modern coyotes. However, there are enough, complete fossil coyote basihyoids to compare with those of their modern relatives, and in several metrics (both PC shapes and overall size), RLB and modern C. latrans are significantly different. As larger hyoids have been associated with a lower vocal frequency, this distinction would have resulted in the vocalizations of C. dirus occurring at a lower frequency than those produced by C. lupus and perhaps lower vocalizations in ice age coyotes than their modern relatives. RESEARCH HIGHLIGHTS: We quantify morphological differences in the hyoid of dire wolves (Canis dirus) relative to extant grey wolves (Canis lupus), and hypothesize that, as larger hyoids have been associated with a lower vocal frequency, the vocalizations of C. dirus might have occurred at a lower frequency than those by C. lupus. Likewise, modern and fossil coyotes (Canis latrans) show a significant difference in basihyoid size and shape, potentially indicating that modern and ancient coyotes might have sounded differently.