Bones

I always experience a little burst of excitement when I find a skeleton.  This may be a carryover from my Elementary School days when I had visions of becoming a paleontologist, or it could be from my Junior High period of reading everything I could about adventurous archaeologists/treasure hunters searching for amazing discoveries.  In the books, treasure usually wasn’t far behind the discovery of a skeleton.  I found this wonderful specimen in the midst of a cedar thicket.

Many times you can identify the species, or at least the genus, from the shape of the skull.  Opossum was the first animal that came to mind when I saw the shape of this skull.

The size however, indicated a much smaller animal.  This is only about half the size of a typical Opossum skull.

The skull holds the key to identification in the form of a dental record.  Using the pattern of dentition, the range of possible animals can be narrowed considerably.  Step one is to determine the total number of teeth.  Here we have a total of 20 teeth in the upper jaw.

A check of the lower jaw shows 10 teeth on one side, so doubling that gives us a total of 20 lower teeth.  That tells us to suspect mammals with 40 total teeth.

There is only one native Ohio mammal with a total tooth count of 40.  That is the Raccoon.  The trouble is that this doesn’t look like the skull of a Raccoon.  Total tooth count helps narrow your search, but to fine tune or verify a choice, you need to look at the dental formula.  That formula takes the total number of teeth and breaks it down into the number of incisors, canines, premolars and molars in the upper or lower jaws.  One side of this upper jaw appears to have five incisors in front of the long canines.

A closer examination confirms that fact.  The jaw clearly contains five incisors on each side.  Raccoons only have three incisors per side, so this is clearly not a Raccoon.  Browsing through the dental formulae reveals only one mammal with five incisors to a side and that is the Opossum.  So, why the small size and only 40 teeth?

This is apparently the skeleton of an immature Opossum.  A close examination of the lower jaw reveals undeveloped teeth that have not yet emerged.  Many mammals do not get their full complement of teeth until maturity.  Had this little fellow survived a few more months, it would have acquired all 50 teeth characteristic of the species.  Proper identification of most living things requires consideration of many details.  Don’t be eager to make an identification based on just a single point.