Crocodylian forelimb musculature and its relevance to Archosauria

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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

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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

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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

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Muscles

• 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

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Methods and Material

• 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.

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Taxa Number (adults/juveniles) Source of specimens

Alligator Mississippians 4 (2/2) D. Weishampel, L. Witmer, St. Augustine Alligator Farm (SAAF)
Crocodiles siamensis 1 (0/1) SAAF
Crocodylus acutus 2 (1/1) P. Moler, Florida Wildlife Research
Osteolaemus tetraspis 2 (0/2) SAAF
Gavialis gangeticus 1 (0/1) American Museum of Natural History, AMNH 81802
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Examples of specimens used
A.mississippiens
G.gangeticus
C.Siamensis
C.Actus
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origin insertion action
M.trapezius thoracodorsal fascia scapula protraction of foralimb
M. pectoralis episternum humerus adductor of humerus
M.costocoracoideus ribs coracoid retract coracoid

M.trese major scapular blade humerus elevates the humerus
M. deltoideus acromion process deltopectoral crest protrator of the humerus

M. tricepts scapula superfical tricept tendon
M. bicepts coracoid proximal radius extension of humerus

M.extensor carpri epicondyle of humerus base of metacarpal II adductor of manus

m. flexor digitform breves metacarpophalangeal base of p2 flex of hand
M. flexor digitform profundus metacarpal IV ventral base of P2 stabilization of manus
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Results

• 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

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Interspecific differences

• 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

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Interspecific differences

• 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

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Continued

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

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Continued

• 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

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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

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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