Myological and osteological approaches to gape and bite force reconstruction in Smilodon fatalis.

Masticatory gape and bite force are important behavioral and ecological variables. While much has been written about the highly derived masticatory anatomy of Smilodon fatalis, there remains a great deal of debate about their masticatory behaviors. To that end, we establish osteological proxies for masticatory adductor fascicle length (FL) based on extant felids and apply these along with previously validated techniques to S. fatalis to provide estimates of fascicle lengths, maximum osteological gapes, and bite force. While the best correlated FL proxies in extant felids do not predict particularly long fascicles, these proxies may be of value for less morphologically distinct felids. A slightly less well correlated proxy predicts a temporalis FL 15% longer than that of Panthera tigris. While angular maximum bony gape is significantly larger in S. fatalis than it is in extant felids, linear gape at the canine tip and carnassial notch were not significantly different from those of extant felids. Finally, we produce anatomical bite force estimates of 1283.74 N at the canine and 4671.41 N at the carnassial, which are similar in magnitude to estimates not of the largest felids but of the much smaller P. onca, with S. fatalis producing slightly less force at the canines and more at the carnassials. These estimates align with previous predictions that S. fatalis may have killed large prey with canine shearing bites produced, in part, by force contributions of the postcranial muscles.

The Effects of Onychectomy (Declawing) on Antebrachial Myology across the Full Body Size Range of Exotic Species of Felidae.

While people are familiar with the practice of declawing domestic cats, "onychectomy", as it is also known, is also performed on non-domesticated species, including pantherines, to prolong their use for entertainment purposes. Although the surgery (the partial or complete removal of the distal phalanx) has clear osteological implications, its myological effects have never been studied. As the mass of an animal increases cubically as a product of its volume, while the areas of its paws only increase as a square, larger felids have higher foot pressures and, therefore, the surgery may have particularly substantial functional effects on larger cats. In this study, we evaluate the forearms of clawed and declawed non-domestic felid specimens that spanned the body size range of the whole family to evaluate the effects of onychectomy on muscle fiber architecture. We found that the deep digital flexors (the muscles most directly affected by onychectomy) of declawed felids are significantly lighter (~73%) and less powerful (46-66%) than those of non-declawed felids, while other muscles do not make up for these reductions. Thus, onychectomy has a substantial effect on the myological capabilities of cats, and because these deficiencies are not compensated for in biomechanically disadvantaged larger felids, it probably has even more functionally devastating consequences for these species.