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COMPARATIVE ANATOMY HOME	COMPARATIVE ANATOMY TABLE OF CONTENTS	OBL HOME	OBL REFERENCES
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The first vertebrates to evolve a humerus were the rhipidistian sarcopterygians which preceded the amphibians. They possessed a joint in the region of the elbow, although the rest of the fin was fairly stiff (Carroll, p. 161). In amphibians, the humerus was modified so that it could be held out from the body, allowing a greater range of movement including rotation (Carroll). In amniotes, the humerus became more narrow (Carroll) and developed a supinator process (Carroll). Sphenacodonts evolved more gracile limbs which were longer and more slender (Carroll, p. 366; Kemp, 1982, p. 33). The limbs of therapsids were longer still and allowed a dual gait capable of both sprawling and erect locomotion (Kemp, 1982, p. 108). In the most advanced cynodonts, the humerus had become more slender and was held upright (Kemp, 1982). The Jurassic mammal Fruitafossor represents a basal mammalian lineage which evolved shortly after the monotreme lineage diverged from that of the therian mammals. Its humerus possessed an intertubercular groove but lacked a round head and its radial and ulnar condyles were spherical in shape (Luo, 2005). After the earliest mammals, separate centers of ossification existed in the epiphyses of the humerus and the ectepicondylar foramen was lost (Carroll, p. 409). In Proconsul the elbow was similar to that of higher apes (Carroll).
Eusthenopteron

salamander

frog

turtle
alligator
platypus
anteater
cat

mink

monkey