Muscles of Fossil Animals

Part of the repertoire of a good anatomist is a working knowledge of the muscle groups of the typical organism. This allows the anatomist (and the biomechanic anatomist) to be able to determine how an animal moved, and much it could move (say, energetics and the force the muscle can generate). Comparative anatomy becomes almost the most important task for a student of biology, as such a student must be able to correctly place and identify the locations of muscles on the skeleton. When dealing with fossil animals of a highly unique nature, such as dinosaurs, which are intermediate evolutionarily between the croc-morph archosaurs and the bird-morph archosaurs, this is harder, because the range of variation is very great, and the extremes (crocs and birds) suffer a few problematic issues. The first of these is that avian anatomists had developed a nomenclature and identification system for muscles that departed from the typical veterinarian system that has been used for crocs and most mammals, and is certainly different from the system used for humans. (While this is an issue worthy of much more consuming time, I won’t get into that here).

Secondly, functional anatomy differs between crocs and birds: the former are either terrestrial or aquatic with a particular carriage, while the latter are more often than not aerial and arboreal, life styles that seem to lead to very different skeletal systems, and thus muscle systems.

This is even more difficult when dealing with pterosaurs, which may or may not be related to archosaurs, and much disagreement has occurred on locating the correct muscle and tendon groups, as well as recognizing many novel and fundamentally different muscle and ligament systems involved, especially in the wing.

Holotype of Jeholopterus ningchengensis (Wang et al., 2002), IVPP V12705, one of the best known anurognathid pterosaurs.

I decided to take a three-view crack at pterosaur myology with Jeholopterus ningchengensis, a pterosaur from the Early Cretaceous (or Late Jurassic) Daohugou fauna of northeastern China (which underlies the more famous Yxian/Jiufotang faunas).

Jeholopterus ningchengensis, in three views. A, dorsal; B, ventral; C, left lateral.

Here, I undertook an independent study of avian, croc, and literature muscle investigations, and produced a piece of art (or rather, three: each of these pieces is a whole unto itself). Much of the work was informed from Bennett (2003) and discussions in various fora and with various other workers discussing the problem, such as John Conway and Alex Kellner. To ensure it’s understood as a work of art, I also covered half the body with a fat, skin, and pycnofibre (“ptero-fuzz”) outline: on one side, you see the animal as in life (or as I imagined it) and on the other as in a surface dissection, before the deep muscles are exposed. Some surface muscles have been omitted: As with many muscle studies, artists are often compelled to leave off several sheets of muscle that obscure the subsurface layers, simply because those underlying layers provide more definition, or are related to the main limb motivators. Most muscle studies should explore the layer-by-layer reconstruction, and this is not undertaken here (and I really lack the expertise to even attempt it).

Pterosaur anatomy is bizarre, and so I don’t think that I got it right. For example, I have extended the uropatagium to the mid-tail, but it could have been longer, and the tail shorter; the inboard cheiropatagium is extended to the trunk wall and the trailing edge is roughly positioned at the anterior ilium. Much debate on the position of the trailing edge, the form of any of the patagia, or even the relation of the pteroid in the wing (here shown with a ligament from the tip to the shoulder, shown MUCH thicker I think than it should be).

Bennett, S. C. 2003. Morphological evolution of the pectoral girdle of pterosaurs myology and function. pg.191-125 in Buffetaut & Mazin (eds.) Evolution and Palaeobiology of Pterosaurs. Geological Society of London (London).
Wang X., Zhou Z., Zhang F.-c. & Xu X. 2002. A nearly completely articulated rhamphorhynchoid pterosaur with exceptionally well-preserved wing membranes and ‘hairs’ from Inner Mongolia, northeast China. Chinese Science Bulletin 47(3):226-232.

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5 Responses to Muscles of Fossil Animals

  1. Very cool stuff Jaimie.

  2. Not _Jeholornis_ ningch… (caption) ;-)

  3. Pingback: Näin piirrät dinosauruksesi, osa 1 « Erään planeetan ihmeitä

  4. Pingback: Head Full of Air | The Bite Stuff

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