COMPARATIVE ANATOMY HOME
COMPARATIVE ANATOMY TABLE OF CONTENTS
  OBL HOME OBL REFERENCES
ARM
    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

Eusthenopteron

salamander

salamander

salamander

salamander

frog

frog

turtle

turtle

turtle

alligator

alligator

platypus

platypus

platypus

anteater

anteater

cat

cat

mink

mink

mink

monkey

monkey

monkey
human human
human
human