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Pectoral region of Cosesaurus. Note the stem-like coracoid, strap-like scapula and sternal complex (interclavicle + clavicle + sternum), as in fenestrasaurs including pterosaurs, not basal tanystropheids.

Here the coracoids are identified in blue, the scapulae in green, the interclavicle in red,
the clavicles in magenta and the sternum in yellow.
Cosesaurus pectoral area
Here all the elements in the pectoral area are identified.
Cosesaurus sister taxa
Basal fenestrasaurs:
Cosesaurus, Sharovipteryx, Longsisquama and basal pterosaurs. Click to enlarge.

The origin of the pterosaur wing began with the narrowing of the hand, the loss of the intermedium and the poor ossification of the carpus in Huehuecuetzpalli, a likely biped.

In Cosesaurus the two centralia were gone. A pteroid and preaxial carpal were present. Trailing fibers were wing membrane and aktinofibril precursors.

In Sharovipteryx and Longisquama the fingers were longer. Digit 4 was longer still in pterosaurs.

In Longisquama metatarsal 4 had rotated on its axis in order to fold the finger in the plane of the wing. The PILs were no longer continuous through digit 4 because it did not flex and extend in concert with the other three digits.

wing evolution


This GIF animation shows Sphenodon, Huehuecuetzpalli, Cosesaurus and Longisquama in sequence demonstrating the evolution of the pterosaur wing, including the migration of the centralia to the preaxial (medial) side of the wrist, the loss of the intermedium, the reduction of the space between the radius and ulna and other changes.

The origin and evolution of the prepubis in pterosaurs

The Origin and Evolution of the Prepubis
This sequence of sister taxa portrays the pelvis and prepubis of several tritosaurs, including Cosesaurus, Sharovipteryx, Longisquama and two basal pterosaurs. Note the gradual elongation of the ilium, the infilling of the thyroid fenestra (between the pubis and ischium), followed by the sudden appearance of the prepubis in Cosesaurus. Later fenestrasaurs and pterosaurs simply modified the various shapes of the elements.

Pterosaur pectoral girdle evolution

The evolution aof the pterosaur pectoral girdle as demonstrated in more primitive sister taxa, including Huehuecuetzpalli, Cosesaurus and Longisquama.

Cosesaurus is featured in The Pterosaur Heresies
Cosesaurus flapping
 
Pterosaur origins video

YouTube video on the origin of pterosaurs.
Click here or on the image at left to view.
Click here for pterosaur family tree.

 
Elessaurus hind limb

Elessaurus gondwanoccidens (De-Oliveira et al. 2020; UFSM 11471, Early Triassic, 245 mya) nests between Langobardisaurus and Cosesaurus and is similar in size to the former, which also has only two sacrals. The anterior process of the ilium indicates a tentative bipedal ability. Narrow-gauge and quadrupedal Rotodactylus tracks from the Early Triassic are a match for the pes preserved here.

 
 
Tritosauria
 
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Jesairosaurus
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BES SC 111
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Longisquama
 
Pterosauria
Bergamodactylus
other pterosaurs
 
pterosaur wings
pterosaur embryos
pterosaur family tree
origin of pterosaurs
 

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