The fossil record of appendicular muscle evolution in Synapsida on the line to mammals: Part I-Forelimb.

Anat Rec (Hoboken)

Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, USA.

Published: May 2024

AI Article Synopsis

  • This paper is part one of a two-part series examining the evolution of forelimb muscles in mammals, using fossil evidence from extinct synapsids.
  • It aims to improve our understanding of how forelimb muscular anatomy has changed from synapsids to modern mammals, influencing the diversity of forelimb functions we see today.
  • The study includes a comprehensive analysis of muscle attachments across various extinct and extant species within a phylogenetic framework, revealing a complex, nonlinear evolutionary history characterized by convergence and significant anatomical transformations.

Article Abstract

This paper is the first in a two-part series that charts the evolution of appendicular musculature along the mammalian stem lineage, drawing upon the exceptional fossil record of extinct synapsids. Here, attention is focused on muscles of the forelimb. Understanding forelimb muscular anatomy in extinct synapsids, and how this changed on the line to mammals, can provide important perspective for interpreting skeletal and functional evolution in this lineage, and how the diversity of forelimb functions in extant mammals arose. This study surveyed the osteological evidence for muscular attachments in extinct mammalian and nonmammalian synapsids, two extinct amniote outgroups, and a large selection of extant mammals, saurians, and salamanders. Observations were integrated into an explicit phylogenetic framework, comprising 73 character-state complexes covering all muscles crossing the shoulder, elbow, and wrist joints. These were coded for 33 operational taxonomic units spanning >330 Ma of tetrapod evolution, and ancestral state reconstruction was used to evaluate the sequence of muscular evolution along the stem lineage from Amniota to Theria. In addition to producing a comprehensive documentation of osteological evidence for muscle attachments in extinct synapsids, this work has clarified homology hypotheses across disparate taxa and helped resolve competing hypotheses of muscular anatomy in extinct species. The evolutionary history of mammalian forelimb musculature was a complex and nonlinear narrative, punctuated by multiple instances of convergence and concentrated phases of anatomical transformation. More broadly, this study highlights the great insight that a fossil-based perspective can provide for understanding the assembly of novel body plans.

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Source
http://dx.doi.org/10.1002/ar.25312DOI Listing

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