Comparative myology of jaw, hyoid, and pectoral appendicular regions of new and old world hystricomorph rodents

About this book

"The musculature of 13 genera of New World and Old World hystricomorphous rodents was studied by dissection. The genera investigated were Proechimys, Echimys, Isothrix, Mesomys, Myocastor, Octodon, Ctenomys, Erethizon, Cavia, Chinchilla, and Dasyprocta of the New World, and Thryonomys and Petromus of the Old World. The objective of the investigation was to explore the myological characteristics of these rodents as an aid in better understanding their evolutionary history. The hystricognathous mandible that is found in most hystricomorphous rodents is associated with pars reflexa of the superficial masseter muscle. The elongated angular process is associated with the internal pterygoid muscle and with the superficial masseter. The posterior deep part of the lateral masseter muscle lies horizontally, and is associated with the post-condyloid process of these rodents. The temporal muscle is composed mainly of the posterior division. All of these specializations are probably related to the anterior-posterior movement of the jaw. The stylohyoid muscle is missing in all genera investigated (and in bathyergids). The scalenus anterior is present in all genera except Erethizon. The scapuloclavicularis muscle is found in all genera, and is similar in Thryonomys and Dasyprocta. The cutaneus maximus is similar in all genera and unlike the muscle in any other group of rodents. The evidence indicates that New World and Old World hystricomorphs probably represent a common group. This group might have evolved from a hystricognathous paramyid subgroup in the mid-Eocene. Another view is that the group might be a consequence of an invasion of South America by African froms via rafting across the then narrower Atlantic Ocean"--P. 119.