Abstract
Myological reconstruction provides valuable information about functional anatomy, ecology, evolution and artistic restoration of extinct taxa. We propose regression-based methods built from a large osteo-myological dataset of extant herbivorous mammals to quantitatively reconstruct absolute masses and relative sizes of masticatory muscles. We used linear and geometric morphometrics variables to calculate equations and predictive errors. The mean predictive errors were acceptable in total sampled equations and remarkably low for specific morphotypes equations. We tested the methods on six disparate and challenging extinct taxa. The reconstructed myological features can be used to improve or complement other approaches, such as digital modeling. In most cases, the selected fossils obtained myological proportions similar to those previously proposed, while total masses were smaller in several cases. Inferences for fossils yielded similarities to a phylogenetically diverse sample of living species, but also identified unique traits. Archaeotherium, Diprotodon, and Megaladapis can be interpreted as possessing generalized, not markedly derived myological configurations. Telicomys was reconstructed as possessing muscles larger than all extant rodents but similar proportions to extant caviid caviomorphs. Paedotherium and Argyrolagus were reconstructed as possessing total masticatory masses similar to extant rodents. They also present myological proportions that partially resemble potoroids, sciuromorphs, and myomorphs, but also reveal unique traits for each of them, so they would represent exclusively extinct morphotypes. The here proposed quantitative, statistically-based tools will be useful for future researchers to infer muscle proportions and sizes in extinct taxa, and can be applied to diverse lineages and ecomorphs including those with no extant analogue.