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 Stolen Nutcracker

Of all my work, the most popular seems to be that of the leptoceratopsid Udanoceratops tschizhovi (Kurzanov, 1992). This is not because this is some supreme piece of masterwork, my open or of any quality of the piece itself, but because it was, at the time I produced it, the only illustration of a complete skull of Udanoceratops (whom I’ve lovingly nicknamed “the Nutcracker” for the massive jaw) available. Originally posted to the now defunct Dinosauricon website, hosted by T. Michael Keesey for the purposes of collected a massive database of illustration on dinosaurs well over 8 years ago, the skull essentially went viral.

Beaky Crocs – WP#18

This one will be short, as I need to work on other things, and this has been the reason for the reduced activity of late.

"Sphenosuchian" crocodilians from the Morrison Formation; Hallopus victor is shown "sandwiched" between the holotype (large) and referred collection (small) of Macelognathus vagans. Scaled, and accurately sized.

There’s quite a lot to say about these taxa, and I intend to. For now, tiny, long-legged, apparently cursorial crocs with edentulous beaks on the mandible seen above will have to do based on what is known.

Osteological Neutral Pose – WP#16

“Osteological Neutral Pose,” or ONP, was first introduced into the literature by Stevens and Parrish [1] in utilizing a method to attempt a “neutral,” or unbiased, attempt at articulating skeletons from which to then manipulate for range of motion studies. Applied initially to sauropods, it projected that virtually all sauropods had a neutral neck posture that was nearly horizontal, even those with the longest necks, or deflected or curved below the horizontal [2,3]. This idea came under scrutiny from various workers, although formal publication of criticism would not arrive until much later [4,5].

Spinosaurus Spines – WP#3

The vertebral series of Spinosaurus aegyptiacus, IPHG 1912 VIII 19, modified from the original plates of von Stromer’s description of the material. I have grayed-out the regions of the vertebrae that are not preserved, under the scheme shown below, including virtually all of the sacrum, although I have not treated the “extraneous” caudal.

The Origin of Oviraptorosaurs (Diet in Oviraptorosaurs III)

The loss of teeth in the basal oviraptorosaurs is oftern overshadowed by their more famous (and larger) relatives, the Caenagnathidae and the Oviraptoridae. The former are largely grouped under a complex of bizarre long, broad, and fused mandibles (fusion in the mandible is particular only to them among oviraptorosaurs, or in fact among dinosaurs in general — excluding birds); the latter are noted for having very, very short and deep jaws, short and deep snouts, and distinctive features of the palate.

One of the characteristic synapomorphies for Oviraptorosauria in fact relates to the exposure of the three primary palatal bones below the oral margin (premaxilla, maxilla, jugal, and quadratojugal), as ordinarily only the pterygoid and at times a portion of the ectopterygoid are exposed. But more curious is the placement and evolution of the taxa that lie outside the Caenagnathidae and Oviraptoridae. These are the “Toothed Oviraptorosaurs,” even though some of them do not appear to possess teeth in all portions of their jaws. Teeth are preserved in the premaxilla and progressively lost posteriorly in the maxilla, while in the mandible the symphyseal region is devoid of teeth, but they are preserved more extensively posteriorly.

Basal Oviraptorosauria: Top left, Incisivosaurus gauthieri; top right, Caudipteryx sp., based on IVPP V12430; bottom left, Avimimus portentosus, based on PIN 3907/3; bottom right, Caudipteryx zoui, based on the paratype, NGMC 97-9. Hatching represents reconstructed material. Each square in the grid represents 1 centimeter.

Precision in Nomenclature #1 (Phalanges)

Yay! Another series, and more of a break. This time, it’s about terminology, one of my more favorite aspects of methodological science. Without knowing what to name stuff, we lapse into grunting and rude gestures, and nobody likes that. Well, I mean, I guess some of you do — perverts.

But terminology has two broad aspects, and in most cases, they are both highly useful, but you need to keep an eye on them.

Oviraptorid Snouts – WP#1

Also, still breaking from the next post on oviraptorosaur diet (which will concern the group commonly referred to as “caenagnathids,” but also some outlying taxa and oddities involved). This will begin a series that will allow me to show off technical illustrations I’ve produced over the years (some for papers, some not). We’ll see what people make of them.