Crocodylian forelimb musculature and its relevance to Archosauria

1. Crocodylian forelimb musculature and its relevance to Archosauria Mason B. Meers * Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, Baltimore, Maryland

2. Introduction • In the study they used comparative descriptions of the forelimb • They looked specifically at the attachment sites, innervation, and anatomical functions • The muscular anatomy of the crocodylian forelimb is highly conservative among the different species • However there are interspecific differences

3. Hypothesis • There where several hypothesis examined in this study • That anatomical variation correlates with locomotion behavior • Anatomical variation may reflect the phylogeny of Crocodilian • Phylogenetically constrained soft-tissue characters of the forelimb distinguish members of Crocodilian

4. Extrinsic muscles M. trapezius M. pectoralis M.costocoracoideus pars superficialis Pectoral Girdle musclature M. teres major M. deltoideus clavicularis Branchial musculature M. tricepts longus caudalis M. bicepts branchii Antebrachial musculature M.extensor carpi ulnares longus Manus M.flexor digitorum brevis superficialis digiti III M. flexor digitorum profundus digiti IV Muscles

5. Most of the specimens that were used in this study came from private captive breeding facilities All of the specimens died of natural causes Standard dissection techniques where used to determine muscle origin, insertion, relationships, and innervations. Methods and Material

7. Examples of specimens used A.mississippiens G.gangeticus C.Siamensis C.Actus

9. Extrinsic musculature - M. trapezus inserts fleshy in C. acutus and may extend to the suprascapular cartilage - M. pectoralis in C. acutus the origin extends caudally to the first three gastrula - m. costocoracoideus – musculature conserved in specimens Results

10. Pectoral girdle musculature - M.tres major in A. mississippiens this muscle intermingles with M. latissimus dorsi prior to formation of its tendon - M. deltoideus a distil slip of this muscle is found only in A, mississippiens Interspecific differences

11. Branchial musculature - M. tricepts longus in G. gangeticus the belly is prononced - M. bicepts branchii In G. gangeticus the origin is in a different place in a shaft of the coracoid Interspecific differences

12. Antebrachial M. extensor carpi ulnairs – in C. actus the tendon fans out to attach to the extensor fascia overlying digit one Continued

13. Manus M.flexor digitform in A. Mississippians the muscle gave off a lateral tendinous slip that attached to both sides of metacarpal III M. Flexor digitorum profundus seems to be irregularly split in two specimens A. Mississippians and C. actus Continued

14. Discussion • The hypothesis that anatomical variation correlates with locomotors behavior is supported because of the anatomical and inferred functional differences between aquatic and amphibious • The hypothesis that anatomical variation may reflect the phylogeny is also supported

15. Discussion continued this was demonstrated by the interspecific difference in the musculature of the different species • The hypothesis that phylogenetically constrained soft tissue of the forelimb distinguish members of crocodile was on partially supported interspecific variations seem to relate more toward function than to phylogeny