By By JOHN EBY / Dowagiac Daily News
An animal's skull contains a cranium full of clues, armchair sleuths armed with clipboards learned Wednesday night at The Museum of Southwestern Michigan College's first installment in its monthly spring lecture series.
Wendy Jones is the naturalist at Fernwood Nature Center, 13988 Range Line Road, Niles.
Jones has been with Fernwood for 17 years.
She challenged her audience to identify 18 Michiana "critters" based on skull size, skull shape and teeth.
She taught them the dental formula that could decide it's a coyote with 42 teeth or a deer with 34.
Skull size reflects animal size. A deer skull is larger than a mouse skill.
But in some species, size can also indicate gender.
Male skulls are typically larger than female skulls – 10 percent larger in mink.
A mink's last upper molar is shaped like a dumbbell.
Jones also explained what the skull's overall shape indicates.
Deer heads have long, pointed front ends, while skunk skulls are compact and rounded.
Teeth reflect the animal's diet. Presence of sharp, pointed teeth – especially in the canines – indicates meat-eating carnivores.
Flattened, squared teeth are a sign of plant-grinding herbivores.
A combination of the two is a tip-off to an omnivore, such as a raccoon.
"Think of rabbits, chipmunks, mice. They have a couple sharp teeth in front like scissors to nip off plant material, then flatter teeth at the back. Omnivores have teeth that are a little bit of both," Jones said.
Looking for wear patterns can help you guess the relative age of an animal. Younger animals have cleaner, sharper teeth than older animals' dirty, rounded and smooth choppers.
Her grey fox at some point in its life bit into a porcupine. She showed how its jaw then grew around the quill.
In deer and horses, exact age can be determined by counting teeth and noting their arrangement.
The dental formula, or "I/C/P/M," uses a mathematical equation to count the four kinds of teeth – incisors, canines, premolars and molars.
First, the upper left minus the upper right over the lower left minus the lower right equals the total upper teeth over the total lower teeth, which, added together yield a grand total.
Coyotes have 42 teeth – three incisors top and bottom, one canine top and bottom, four premolars top and bottom, two top molars and three bottom molars for a total of 20 on top and 22 below, or 42.
Deer only possess 34 teeth – no upper incisors; less premolars than coyotes (three instead of four). Raccoons have 40 teeth because of fewer molars in back, but more premolars.
The toothiest Michiana mammal? Opossums, with 50.
Skulls contain more parts than one might imagine: rostrum (nose); zygomatic arches (cheekbones); orbits (eye sockets; if a barred owl was human its peepers would be the size of grapefruits); sagittal crest (ridge on top of the skull); auditory bulb (ear); foramen magnum (spinal cord opening); and the four kinds of teeth.
Her students identified wolf, cardinal, grey fox, white-tailed deer, otter, red fox, muskrat, bear, beaver, wood duck, red-tailed hawk, snapping turtle, barred owl, baby raccoon (head plates not yet fused), opossum, groundhog, fox squirrel and cow.
"A lot of people look at these skulls and go, 'That's a lot smaller than I would think the animal's head would be' " because they're not used to their noggins being bereft of muscle, skin and fur, Jones said.
Eye position can indicate whether an animal is a predator or prey.
If they point forward it's for hunting, while side vision watches out for attackers while herbivores graze.
Black bears' skulls grow until 6 years of age. Red-tailed hawks have sharp, curved beaks for tearing flash. Wood ducks have serrations along their bills to strain plants and animals from the water. Snapping turtles use their bony jaws instead of teeth to rip plants and animal tissue.