From fish to modern humans – comparative anatomy, homologies and evolution of the pectoral and forelimb musculature

Abstract

In a recent study Diogo & Abdala [(2007) J Morphol 268 , 504-517] reported the results of the first part of a research project on the comparative anatomy, homologies and evolution of the pectoral muscles of osteichthyans (bony fish and tetrapods). That report mainly focused on actinopterygian fish but also compared these fish with certain non-mammalian sarcopterygians. This study, which reports the second part of the research project, focuses mainly on sarcopterygians and particularly on how the pectoral and forelimb muscles have evolved during the transitions from sarcopterygian fish and non-mammalian tetrapods to monotreme and therian mammals and humans. The data obtained by our own dissections of all the pectoral and forelimb muscles of representative members of groups as diverse as sarcopterygian fish, amphibians, reptiles, monotremes and therian mammals such as rodents, treeshrews, colugos and primates, including humans, are compared with the information available in the literature. Our observations and comparisons clearly stress that, with regard to the number of pectoral and forelimb muscles, the most striking transition within sarcopterygian evolutionary history was that leading to the origin of tetrapods. Whereas extant sarcopterygian fish have an abductor and adductor of the fin and a largely undifferentiated hypaxial and epaxial musculature, extant salamanders such as Ambystoma have more than 40 pectoral and forelimb muscles. There is no clear increase in the number of pectoral and forelimb muscles within the evolutionary transition that led to the origin of mammals and surely not to that leading to the origin of primates and humans.

Hypertrophic reversed palmaris longus muscle: a cadaveric finding

“…It is fusiform in bats, and in an elephant dissected by Greenwood, according to Le Double [10] the PLM was long and fleshy until it reached the carpal region. In rats, the PLM is blended with the proximal portion of the flexor carpi ulnaris muscle [8].…”

Reconstructing pectoral appendicular muscle anatomy in fossil fish and tetrapods over the fins‐to‐limbs transition

“…3) (Romer, 1924). Diogo et al (2009) and Diogo & Abdala (2010) likewise concluded that sarcopterygians plesiomorphically had mainly undivided dorsal ('adductor') and ventral ('abductor') muscle masses from which all the intrinsic appendicular muscles of tetrapods were derived.…”

“…7I, J); these two muscles are separate in Sphenodon. Iguana does not have a separate anconaeus, but this muscle is present in some other lepidosaurs, including Sphenodon (Diogo et al, 2009).…”

Musculoskeletal integration at the wrist underlies modular development of limb tendons

“…In mammals, muscles are largely restricted to a single limb segment and do not cross the wrist or elbow (Diogo et al, 2009). In amphibians, however, extrinsic muscles of the hand extend across the wrist and connect to tendons that are all contained within the autopod (Ashley-Ross, 1992; Diogo et al, 2009;Walthall and Ashley-Ross, 2006).…”