Dino cartilage: it is important to consider

["Thomas R. Holtz, Jr." <tholtz@umd.edu>]

This just out:

Holliday CM, Ridgely RC, Sedlmayr JC, Witmer LM (2010) Cartilaginous Epiphyses 
in Extant Archosaurs and Their Implications for
Reconstructing Limb Function in Dinosaurs. PLoS ONE 5(9): e13120. 
doi:10.1371/journal.pone.0013120

Abstract 
Extinct archosaurs, including many non-avian dinosaurs, exhibit relatively 
simply shaped condylar regions in their appendicular
bones, suggesting potentially large amounts of unpreserved epiphyseal 
(articular) cartilage. This "lost anatomy" is often
underappreciated such that the ends of bones are typically considered to be the 
joint surfaces, potentially having a major impact on
functional interpretation. Extant alligators and birds were used to establish 
an objective basis for inferences about cartilaginous
articular structures in such extinct archosaur clades as non-avian dinosaurs. 
Limb elements of alligators, ostriches, and other
birds were dissected, disarticulated, and defleshed. Lengths and condylar 
shapes of elements with intact epiphyses were measured.
Limbs were subsequently completely skeletonized and the measurements repeated. 
Removal of cartilaginous condylar regions resulted in
statistically significant changes in element length and condylar breadth. 
Moreover, there was marked loss of those cartilaginous
structures responsible for joint architecture and congruence. Compared to 
alligators, birds showed less dramatic, but still
significant changes. Condylar morphologies of dinosaur limb bones suggest that 
most non-coelurosaurian clades possessed large
cartilaginous epiphyses that relied on the maintenance of vascular channels 
that are otherwise eliminated early in ontogeny in
smaller-bodied tetrapods. A sensitivity analysis using cartilage correction 
factors (CCFs) obtained from extant taxa indicates that
whereas the presence of cartilaginous epiphyses only moderately increases 
estimates of dinosaur height and speed, it has important
implications for our ability to infer joint morphology, posture, and the 
complicated functional movements in the limbs of many
extinct archosaurs. Evidence suggests that the sizes of sauropod epiphyseal 
cartilages surpassed those of alligators, which account
for at least 10% of hindlimb length. These data suggest that large 
cartilaginous epiphyses were widely distributed among non-avian
archosaurs and must be considered when making inferences about locomotor 
functional morphology in fossil taxa.

http://www.ploscollections.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0013120;jsessionid=B9B65949F1CE7ED4687B62BB0309AE90.ambra
02

It's PLoS: go read it yourself! :-)

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA