LABORATORY MANUAL FOR MAMMALOGY - Rowan

Tribosphenic molars are basically triangles of three cusps (plus an extra pair on the lower
molars), but the upper and lower triangles are reversed in their orientation.
Examine the morphology of an upper tribosphenic molar in an opossum. Make sure you
can identify the following cusps: protocone, paracone, and metacone. Note the orientation of
the triangle that they form. Next, examine the lower molar of an opossum. Identify the
following cusps: protoconid, paraconid, metaconid, entoconid, and hypoconid. Note the
orientation of the triangle formed by the protoconid, paraconid, and metaconid. This triangle is
called the trigonid. The entoconid and hypoconid form a "heel" to the tooth that is called the
talonid. Note that the talonid forms a deep depression, called the talonid basin. The protocone
fits into the talonid basin during chewing. Observe this when you move the jaws of the opossum
skull together.
Many mammals have added cusps to the tribosphenic pattern in order to increase the
chewing surface. The hypocone is present in many mammals posterior to the protocone. This
fourth cusp allows the occlusal surface to form a rectangle. A similar result is obtained in the
lower teeth by reducing or losing a cusp, the paraconid. Examine a number of herbivorous or
omnivorous mammals and identify the hypocone.
Examine the teeth of a human skull. Identify the cusps of the molars. Note that the cusps
are low and rounded, compared to those of an opossum. Compare this condition with that of a
pig. Molars with low, rounded cusps are referred to as bunodont.
Examine the teeth of a dog skull. Note the large blade-like upper premolar and first
lower molar. These teeth are specialized for shearing or slicing and function in a scissors-like
manner. They are a specialization for eating meat. Such teeth are called sectorial. Note that
dog upper molars are bunodont and retain the tribosphenic pattern. Dogs are as much omnivores
as carnivores. (Check out the ingredients of dry dog food if you're skeptical.)
Lophs are present on many mammalian teeth. The outer (labial/buccal) edge of the molar
is called the ectoloph. Many herbivorous mammals possess multiple lophs crossing the tooth so
that they act like a file or millstone to grind and shred vegetation. Such teeth are referred to as
lophodont. Lophodonty (the condition of being lophodont) has evolved multiple times in
multiple ways. Sometimes a loph is formed by building up a ridge between two or more cusps.
In other cases, a cusp may be stretched into a loph. In many cases, it is still possible to identify
the homologues of the cusps of a tribosphenic molar on a lophodont tooth. Some mammals have
teeth with numerous lophs that defy any identification of cusps. Examine some of the lophodont
teeth on display and identify cusps when possible.
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