Alligator, Alligator mississippiensis
1 of 20
Alligator, Alligator mississippiensis
2 of 20
Platypus, Oncorhinchus anatinus
3 of 20
African lion, Panthera leo
4 of 20
Black bear, Ursus americanus
5 of 20
Polar bear, Ursus maritimus
6 of 20
Sea otter, Enhydra lutris
7 of 20
Sea otter, Enhydra lutris
8 of 20
Harbor seal Phoca vitulina
9 of 20
Sea lion, Zalophus californianus
10 of 20
Sea lion, Zalophus californianus
11 of 20
Bighorn sheep, Ovis canadensis
12 of 20
Bighorn sheep, Ovis canadensis
13 of 20
Bighorn sheep, Ovis canadensis
14 of 20
Gnu, Connochaetus sp.
15 of 20
Cow, Bos taurus
16 of 20
Pronghorn, Antilocapra americana
17 of 20
Pronghorn, Antilocapra americana
18 of 20
Blacktail deer, Odocoileus hemionus
19 of 20
Blacktail deer, Odocoileus hemionus
20 of 20

View the entire gallery or click on the above images to enlarge.

In this gallery, we highlight a few of the vertebrate skulls in the museum's comparative biological collections. The vertebrate skull has changed significantly over time, but alligators like the one pictured here are “living fossils” that have remained relatively unchanged from their first forms. The other skulls in this gallery are from mammals. Mammals derive from a branch that split from the ancestors of reptiles and birds in the Permian, over 250 million years ago. All groups of mammals have two tiny inner-ear bones, the malleus and incus (hammer and anvil). These two bones evolved from bones found in the jaws of reptiles and birds, but are now used for hearing in mammals. The platypus is a monotreme, a mammal that still lays eggs, just as our Permian ancestors did. The remainder of the mammals in the gallery are placentals, growing their babies inside the mother.

The animals with horns and antlers in this gallery are ruminant artiodactyls, the group of cloven-hoofed animals that chew cud to aid their digestion. Ruminants include four well-known groups with headgear: bovids (cows, goats, antelope), cervids (deer, moose, elk), antilocaprids (pronghorn antelope), and giraffids (giraffe and okapi). Edward Davis is currently studying the origin of ruminant headgear. Each of the four groups has its own distinct kind of headgear: Bovids have true horns, made of bone horncores covered by skin and 'horn' made of keratin, the same protein as hair, hooves, and fingernails. Pronghorns have a horn that has evolved independently from bovid horns, with an inner bone horncore and an outer layer which they shed and regrow each year. Deer have antlers, which are dead bone that is shed and regrown each year. Deer have stem cells in the knobs (pedicles) at the base of their antlers and from them grow the new antlers each year. Photography by Kelsey Stilson, text by Kelsey Stilson and Edward Davis, and web development by Keith Hamm. Images © Museum of Natural and Cultural History.