A morphological analysis of carnivoran ossicles from Rancho La Brea

Abstract

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.

Ecomorphological correlates of inner and middle ear anatomy within phyllostomid bats

“…A recent analysis of ossicular size in fossil and extant carnivorans (Dickinson et al, 2022) also reported similar trends in both canids (geometric mean vs. body mass: malleus, slope = 0.29, r 2 = .63; incus, slope = 0.37, r 2 = .84; stapes, slope = 0.59, r 2 = .24) and felids (malleus, slope = 0.49, r 2 = .90; incus, slope = 0.53, r 2 = .96; stapes, slope = 0.40, r 2 = .91). Finally, a cross‐mammalian analysis of ossicle mass relative to skull mass in 63 species (Nummela, 1995) reported a negatively allometric relationship of similar magnitude (slope = 0.51, r 2 = .90).…”

“…In the same sample, combined incus + malleus mass (slope = 0.477; r 2 = .864) and stapes mass (slope = 0.510, r 2 = .876) exhibit similar slopes to our own observations of incus (slope = 0.343, r 2 = .437), malleus (slope = 0.295, r 2 = .415) and stapes (slope = 0.521, r 2 = .595) volume scaling in phyllostomids (Table 5), though it should be noted that these previously published data were not analyzed with phylogenetic adjustments and thus not directly comparable to our own results. A recent analysis of ossicular size in fossil and extant carnivorans (Dickinson et al, 2022) also reported similar trends in both canids (geometric mean vs. body mass: malleus, slope = 0.29, r 2 = .63; incus, slope = 0.37, r 2 = .84; stapes, slope = 0.59, r 2 = .24) and felids (malleus, slope = 0.49, r 2 = .90; incus, slope = 0.53, r 2 = .96; stapes, slope = 0.40, r 2 = .91). Finally, a cross-mammalian analysis of ossicle mass relative to skull mass in 63 species (Nummela, 1995) reported a negatively allometric relationship of similar magnitude (slope = 0.51, r 2 = .90).…”

“…The morphology of several auditory structures is also strongly related to body size, with total ossicular mass and/or volume scaling closely with body mass across mammals (Dickinson et al, 2022;Mason, 2001;Nummela, 1995;Salih et al, 2012). As smaller ossicles are easier to excite with high frequency vibrations, smaller-bodied animals are generally better at detecting higher frequencies of sound (Heffner, 1983;Heffner et al, 2001Heffner et al, , 2006Hemilä et al, 1995;Huang et al, 2000;Nummela, 1995).…”

“…Accordingly, the anatomical diversity of the auditory apparatus has been explored in numerous mammalian lineages, including rodents (Argyle & Mason, 2008; Farr & Mason, 2008; Mason, 2013; Wilkins et al, 1999), carnivorans (Gürbüz et al, 2019; Martonos et al, 2022; Wible & Spaulding, 2012) and xenarthrans (Sidorkewicj & Casanave, 2012). Ossicular morphology has also been explored in numerous extinct taxa with reference to their living relatives (e.g., Dickinson et al, 2022; Orliac & Billet, 2016; Stoessel et al, 2016).…”

The roar of Rancho La Brea? Comparative anatomy of modern and fossil felid hyoid bones

“…While early excavations at the site primarily recovered large fossil bones, particularly craniodental material and limb bones, more recent excavations have produced large collections of well‐preserved smaller fossils (Shaw, 1982). The quantity and quality of preservation provide a unique opportunity for the quantitative examination of the functional morphology of small fossils, including clavicles (Hartstone‐Rose et al, 2012), bacula (Hartstone‐Rose et al, 2015), canid hyoids (Flores et al, 2020), and auditory ossicles (Dickinson et al, 2022).…”