The scaling of postcranial muscles in cats (Felidae) I: forelimb, cervical, and thoracic muscles

Abstract

The body masses of cats (Mammalia, Carnivora, Felidae) span a ~300-fold range from the smallest to largest species. Despite this range, felid musculoskeletal anatomy remains remarkably conservative, including the maintenance of a crouched limb posture at unusually large sizes. The forelimbs in felids are important for body support and other aspects of locomotion, as well as climbing and prey capture, with the assistance of the vertebral (and hindlimb) muscles. Here, we examine the scaling of the anterior postcranial musculature across felids to assess scaling patterns between different species spanning the range of felid body sizes. The muscle architecture (lengths and masses of the muscle-tendon unit components) for the forelimb, cervical and thoracic muscles was quantified to analyse how the muscles scale with body mass. Our results demonstrate that physiological cross-sectional areas of the forelimb muscles scale positively with increasing body mass (i.e. becoming relatively larger). Many significantly allometric variables pertain to shoulder support, whereas the rest of the limb muscles become relatively weaker in larger felid species. However, when phylogenetic relationships were corrected for, most of these significant relationships disappeared, leaving no significantly allometric muscle metrics. The majority of cervical and thoracic muscle metrics are not significantly allometric, despite there being many allometric skeletal elements in these regions. When forelimb muscle data were considered in isolation or in combination with those of the vertebral muscles in principal components analyses and MANOVAs, there was no significant discrimination among species by either size or locomotory mode. Our results support the inference that larger felid species have relatively weaker anterior postcranial musculature compared with smaller species, due to an absence of significant positive allometry of forelimb or vertebral muscle architecture. This difference in strength is consistent with behavioural changes in larger felids, such as a reduction of maximal speed and other aspects of locomotor abilities.

Reconstruction of the musculoskeletal system in an extinct lion

“…Thus most of the distal muscles lacked complete tendons in the resulting .stl files. For those distal muscles for which there were no easily segmented tendons, the tendons were recreated by extending a section of the muscle belly so that the length and mass of each tendon matched the mean lengths and masses expected from the scaling equations of Cuff et al (2016aCuff et al ( , 2016b. All of the scaled muscles and tendons were then placed on the left side of the P. atrox reconstructed skeleton in the appropriate positions using any evident muscle scarring patterns on the bones and the origins and insertions observed during dissections of extant species, before mirroring to the right side (as with the bones) in Meshlab.…”

“…We were not able to segment the individual muscles of the vertebral column, so a gross segmentation of the cervical, thoracic, and lumbar regions of muscles was conducted. Using the scaling equations (inserting the 207 kg body mass estimate) from Cuff et al (2016aCuff et al ( , 2016b, the muscle belly length (i.e., length of the main striated muscle portion of the muscle-tendon unit, along its line of action) for each of the muscles was estimated for Panthera atrox. The expected muscle masses were also calculated from the Cuff et al (2016aCuff et al ( , 2016b nonphylogenetic scaling equations (Appendices 2-13).…”

“…Using the scaling equations (inserting the 207 kg body mass estimate) from Cuff et al (2016aCuff et al ( , 2016b, the muscle belly length (i.e., length of the main striated muscle portion of the muscle-tendon unit, along its line of action) for each of the muscles was estimated for Panthera atrox. The expected muscle masses were also calculated from the Cuff et al (2016aCuff et al ( , 2016b nonphylogenetic scaling equations (Appendices 2-13). The dataset from Cuff et al (2016aCuff et al ( , 2016b has no large non-pantherine species and as such using the phylogenetic correction would likely reduce any real allometric signals; this could be particularly problematic due to P. atrox being a very large felid.…”

“…The expected muscle masses were also calculated from the Cuff et al (2016aCuff et al ( , 2016b nonphylogenetic scaling equations (Appendices 2-13). The dataset from Cuff et al (2016aCuff et al ( , 2016b has no large non-pantherine species and as such using the phylogenetic correction would likely reduce any real allometric signals; this could be particularly problematic due to P. atrox being a very large felid. Regardless, most muscle lengths and masses across the postcrania of felids scale (indistinguishable from) isometrically -whether or not phylogeny is accounted for -so the results are unlikely to differ greatly depending on which equation is chosen.…”

“…Using muscle scaling equations from Cuff et al (2016aCuff et al ( , 2016b for extant felids, we were able to estimate muscle and tendon masses and lengths for the individual. Digital representations of actual muscles from an Asian lion were then scaled so that the dimensions of the locomotor musculature of the limbs and vertebral column were reconstructed and could be placed in the appropriate positions as determined from dissections of living relatives via the EPB method.…”