Each skull has a story to tell. It can tell us what the animal ate, which senses it used to hunt or find food, and whether it was the predator or prey. Through scientific investigation, we can unravel the mysteries in a skull and learn more about the animal when it was alive. To read the story of the skull, you need to be able to identify and analyze the clues left behind. To understand the clues, you need to know the language of skulls.
Imagine you are walking through a National Forest and you find a skull. How can you tell what animal it was? First you need to know what animals live in that particular forest. This helps to narrow down the options.Can you name different animals that live in the Cherokee National Forest? What does each animal eat? Is it an herbivore, omnivore, or carnivore? Is the animal a predator or prey?
Skull identification can be determined by several
methods. If you are unsure of a skull's identification, you can compare
it with other known specimens. This, however, can be less than accurate
and most will not have access to a large collection of known species.
The most effective means of identifying a skull to species is with the
use of a dichotomous key. A dichotomous key allows a person, through a
series of questions, to identify an organism to species by process of
elimination.
Below are images of typical carnivore (bobcat),
omnivore (raccoon) and herbivore (beaver) skulls. Various parts of each
skull have been labeled to aid in comparative anatomy.
Bobcat Skull
Bobcat Skull
Raccoon Skull
A raccoon is classified as a carnivore; it is in the order Carnivora. But it is actually an omnivore. It eats both plants and animals.A raccoon’s cheek teeth are multicuspid and secodont. Secare-means “to cut.”Secodont dentition refers to the cutting edges on the tooth cusps.
Beaver Skull
A beaver is a large rodent, classified in the order Rodentia. A beaver has a large set of arc-shaped chisel-edged incisors. The beaver keeps its incisors sharp by using them. Its cheek teeth have wide flat surfaces with complex folds and ridges.
The Coyote, Wolf and Dog are classified as carnivores; it is in the order Carnivora. But it is actually an omnivore. It eats both plants and animals. It prefers to eat meat but will eat fruits, vegetables, and even garbage. It is an opportunistic eater; it will eat whatever it finds.
Black Bear
The black bear is classified as a carnivore; it is in the order Carnivora. But it is actually an omnivore. It eats both plants and animals
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| Black Bear |
White-Tailed DeerThe deer is an herbivore. Male deer (bucks) have antlers. They shed the antlers each year after the mating season. They grow the antlers again the next year.Why do male deer have antlers?
Deer and other herbivores have a large gap between their lower incisors and cheek teeth. Why? The cheek teeth of a deer are selenodont with crescent-shaped cusps.Deer have an antorbital pit located just in front of each eye socket. This is a slight depression in the skull where the antorbital gland or preorbital gland is located. The antorbital gland produces secretions containing pheromones,like a scent gland. The gland becomes enlarged during rut.
The Language of Skulls
Size of Eye Sockets
Are the eye sockets large or small relative to the skull size?Large eye sockets are indicative of sharper eyesight and nocturnal behavior.
Placement of Eye Sockets
How are the eye sockets placed in the skull? Do the eye sockets face forward or face to the side? This helps us figure out if the animal is a predator or prey.
Predators have eye sockets that face forward. An animal with forward-facing eyes has “binocular vision.” This provides excellent depth perception for hunting and killing prey.
Prey have eye sockets that face to the side. The side placement gives the animal a wider field of view to see predators coming from all directions.
Do humans have forward-facing or side-facing eye sockets? What about dogs? What about horses and cattle?
Size of Nasal Passages
How large are the nasal passages? Large nasal passages are indicative of a keen sense of smell.Inside the nasal passages, look for bony, web-like structures call nasal turbinates. These provide the framework for membranes that sense odor. Dogs have longer nasal passages and more complex nasal turbinates. This gives them a keen sense of smell.Cats have shorter nasal passages and less complex nasal turbinates. Cats rely on other senses for hunting.
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| Feline vs Canine |
Teeth
Humans have 20 “baby teeth” and 32 adult teeth. Our baby teeth emerge early and are smaller because our jaws aren’t big enough for adult teeth. We shed our baby teeth and replace them with permanent teeth when our jaws grow big enough to accommodate them.Most of our permanent teeth gradually emerge when we are between six and thirteen years old. Our last permanent teeth, referred to as our wisdom teeth, usually emerge when we are 17 to 25 years old. We have four kinds of adult teeth: incisors, canines, premolars, and molars.
Incisors
Close your eyes and imagine I just handed you a big red apple. Now imagine biting into it. What teeth did you use? Your front teeth, which are your incisors. We have four incisors in our upper jaw and four incisors in our lower jaw. Our incisors are located in the front of our mouth and are used for grabbing or cutting.
Rodents have very large incisors. A rodent’s incisors are shaped like chisels and grow continuously throughout their lifetime. Why do you think a rodent has large incisors?
A deer doesn’t have any upper incisors but does have lower incisors. A deer’s front teeth and the shape of its mouth are like a scotch-tape dispenser! The deer uses its long tongue to grab onto a leaf and pull it into its mouth, then it uses its lower incisors to cut the leaf, just like rolling out and cutting a piece of scotch tape.
A rabbit has four upper incisors and two lower incisors. In a rabbit’s upper jaw, two of the incisors are large and shaped like chisels, and the other two incisors are much smaller, shaped like pegs, and located directly behind the larger incisors. Like the rodents, incisors of rabbits continue to grow throughout their lifetime. Why do you think rabbits and rodents grow their incisors throughout their lifetime? Carnivores have smaller incisors compared to rodents.
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| Objects used for size comparison |
Canines
Close your eyes and imagine that I hand you a piece of beef jerky. Now imagine biting into it. Which teeth did you use? Your canines.
Our canines are located behind our incisors. We have four canines, two in our upper jaw and two in our lower jaw.
Canines are also referred to as fangs and are long, pointed teeth.
Carnivores have the largest and most prominent canine teeth. Vampire bats and tigers, for example, have large and prominent canines. Carnivores use their canine teeth to puncture or hold their prey.
Rodents, rabbits, and deer don’t have any canines. Instead, herbivores have a large space or gap between their incisors and back teeth. This large space between their teeth gives the animal plenty of room to manipulate and grind up vegetation in their mouth.
Primates
Gorilla
Gorillas are the largest primates in the world, and they have parts of
their body that are very similar to those of humans. In addition to
their size, they are endowed with many striking and exciting features.
The most evident characteristic is their large and powerful body,
unlikely to be ignored. The height and weight vary depending on the
species, but in every case males are larger than females, and
“silverback” males have the larger size among all the individuals in
their group.
Usually, adult males are 5'6"-5'9" high, but Silverbacks
typically exceed 5'9". Members of the subspecies Western lowland
gorilla (Gorilla gorilla gorilla) reach 5'6" high while
females are only 4'9". Males weigh about 374lbs and
females 157lbs approximately. Eastern lowland gorillas (Gorilla beringei grauieri) weigh a little more than the Western subspecies, and males can reach more than 441 lbs.
Adult females weigh around 150-250 lbs. and males, 300-400 lbs, an
average of all subspecies. Moreover, the length between the tip of one
arm and the other is between 2.3 and 2.6 meters. This size is much
larger than its height!
Their body shape is robust. The belly area is bigger than the chest,
and an elongated head up is due to a prominent sagittal crest. Above
their eyes, there is a noticeable brow ridge, and they have small ears
on both sides of their head. Around the nose, there are a few wrinkles
unique to each gorilla, a fact used by scientists to quickly identify
them in the wild.
Their arms are longer than the legs. When walking, they do it on
their knuckles, resting their weight on the arms. Thumbs and toes are
opposable therefore they can easily manipulate objects. Like humans,
they have unique fingerprints and nails instead of claws.
Both skin and fur have dark color, sometimes black, brown or dark
gray. The pelage of lowland gorillas is shorter than the other species,
but all subspecies lack hair around the nose, lips, chest, ears, feet
fingers and palms of hands. As mountain gorillas inhabit the coldest
areas, they have thicker and longer fur than the other subspecies.
Internal Anatomy of Gorillas.
Their skeleton is adapted to hold the weight of their body. Their
spine is straighter compared with that of humans, and the muscles of
their arms, shoulders, neck and back allow them to have a strength up to
6 times higher.
The sagittal crest is large enough to hold the strong jaw muscles
used by gorillas when chewing tough, fibrous vegetation. The skull is
large compared to the size of their body, and they have a big and highly
developed brain. The large belly is the result of a long digestive
tract, essential to digest their fibrous food they consume.
Male gorillas grow in their backs silvery hair patterns, which works
as an optical illusion because make them look longer than they are.
Additionally, all gorillas have no tails.
Like humans, they have 32 teeth in their jaws. A single bone forms
the lower jaw, which has specialized teeth for cutting, grinding,
milling, and so on. In the case of adult males, protruding sharp canines
of considerable length are developed.
Adult males have underarm glands that expel off a pungent odor when they feel stress or excitement.
Gorilla Skull vs Human
When comparing a gorilla skull to a humans it is easy to see
that the gorilla has larger brow ridges, a projecting face and an
overall more robust skull. As mentioned the gorilla has many sites for
large muscle attachments with a particularly distinct sagittal crest.
This is located on the top of the cranium and is where the muscles for
mastication (chewing) attach. These are much larger than a humans due to
the type of foot the gorilla consumes. Their diet is quite varied from
fruits and leaves to ants and termites. However, due to the large amount
of roughage that they eat large, flat teeth and a strong jaw is needed,
hence the sagittal crest.
The position of the foramen magnum is also different compared
to a humans. In a gorilla this is situated further back in the skull
and is related to their posture when moving. Gorillas are knuckle
walkers and therefore use all four limbs to move about which results in a
different posture and postion compared to humans who walk on two legs.
One of the easiest ways to spot a primate skull is to examine the dentition. All primates have a similar dentition pattern although this differs between families. The apes, which include humans and gorillas, have a dental formula of 2.1.2.3 which translates as two incisors, one canine, two pre-molars and three molars on each side of the mouth. This is repeated in both the upper and lower jaw. Although we have the same dental formula there are obvious differences. As mentioned gorillas eat much harder food substances and therefore have larger molars. They also have larger incisors (see image) which assist with stripping and tearing fruit but also are used for display and threat purposes. Gorillas are a sexually dimorphic species (a notable size difference between males and females) and therefore males will use their teeth to display to attract females and to appear aggressive to frighten off other males.
Ape skeletons
Skulls
In comparison to human cranial anatomy, apes generally display a more projecting face, a larger brow ridge, a longer face, larger teeth in the front than in the back, larger jaws, and a posteriorly placed foramen magnum (the site on the skull where the spinal cord connects). A posteriorly placed foramen magnum is associated with quadrupedalism, while an anteriorly placed foramen magnum, like that in humans, is associated with bipedalism (allowing the head to sit atop the spine).
The gorilla has a distinct sagittal crest atop the cranium. This bony ridge at the top of the skull is a site for attachment of massive muscles for mastication. The gorilla, a large folivore who eats tough plants, requires such anatomy for its diet.
Postcranial
In comparison to human postcranial anatomy (skeletal anatomy that is below the skull), the ape pelvis is longer and narrower. A short, broad, bowl-shaped pelvis, like that of humans, is better adapted for bipedalism, as it better tolerates the pressure and shock of this locomotion pattern.
Characteristics
Apes tend towards large, barrel-shaped chests, which help balance the center of gravity for quadrupedalism. Also, apes have a relatively straight backbone. The human spine is curved into an S-shape instead of C-shaped (compare illustrations on page 35), making it comfortable and practical to stand upright for extended periods. The ape spine lacks this significant S-shaped curve, however, and thus continued bipedalism again causes high stress and impact.The ape foot is dexterous, allowing for flexible mobility. Compared to the double-arch of the human foot, the ape foot is flat, though both humans and apes walk plantigrade (heel to toe). The hallux (big toe) on each ape foot is opposable. The opposability of the hallux and thumb for apes is essential to their grasping abilities and fine motor skills.
Ape Dentition
All apes share the same dental formula. A dental formula reflects the number of the four teeth types (incisor, canine, premolar and molar) a species has. The dental formula is determined by dividing the entire mouth into equal quadrants, and recording the number of incisors, canines, premolars, and molars found in one of the quadrants of the upper jaw, and then in one of the quadrants of the lower jaw. Multiplying each of these formulas by 2 gives the total number of teeth in the mouth.For apes, including humans (with wisdom teeth), the dental formula is: 2.1.2.3 / 2.1.2.3 (=32 total teeth)The incisors in apes are generally large to support frugivorous diets, as incisors are needed for piercing and stripping fruit. The molars are essential to pulping fruit. In gorillas, the molars are particularly broad for grinding plant materials.Ape premolars have one cusp, making them useful for sharpening the canine tooth. Human premolars are bicuspid. The two cusps serve to make the human premolar more like a molar, because of the importance of the back teeth in humans (who, compared to apes, have larger back teeth than front teeth for mouth size).
Orangutan Canines vs. Human Canines
Cranial Capacity
Cranial capacity is a measure of the total volume of the interior of the cranium or brain case. Comparatively among species, a larger cranial capacity in relation to body size is generally associated with enhanced cognitive abilities and behavioral complexity.
Encephalization is the evolutionary trend toward increase in brain size beyond that which would be expected of body size. Apes are characteristically known for their large brains, enhanced cognition and behavioral complexity.
The use of cranial capacity as a measure of intelligence is fiercely debated among scientific circles. To contextualize the relevance of cranial capacity as a measure, brain weight is often divided by body mass, and the quotient is known as the brain:body mass ratio. A higher brain:body mass ratio is associated with higher cognitive abilities and behavioral complexity.
Classifying Teeth:
There are four primary teeth types, each with a different role. Within a species, these teeth types are uniquely shaped and sized to suit the species’ particular diet.
These teeth types include:
1. Incisors – the front teeth, used for seizing, stripping, biting and puncturing
2. Canines – located between incisors and premolars, bladelike with varying length and sharpness; used in gripping, stabbing, tearing; can also be used by males for aggressive display behaviors
3. Premolars – located between canines and molars; used for crushing and grinding, in some cases also used to sharpen canines
4. Molars – back teeth, broadest; used for crushing and grinding
Distinguishing Among Primate Dentition:
The different classifications of primates can differ in dentition formula, teeth shape and size, and jaw shape and size. Consider the following:
• The lower jaw of apes and humans has a rounded angle. The lower jaw of other primates generally has a sharper angle.
• Human premolars are called bicuspids because they have two cusps, or points. Ape premolars have only one cusp, which is useful for sharpening canines. Also, the front teeth of apes are generally larger than the back teeth, while in humans, the back teeth are generally larger than the front.
• Canines in apes are pronounced, while in humans they are blunt and reduced. These large canines are more associated with display behaviors (e.g. showing off the large canine teeth to intimidate others) than with diet.
• A dental comb is a special adaptation seen in many prosimians. The front teeth of the lower jaw point forward together to form the dental comb, which is used for grooming.
To calculate dental formula: Draw a vertical line down the front half of the teeth (in between the front incisors), then draw a horizontal line between the upper and lower jaw. This should divide the teeth into equal-sized quadrants. Note that each half of the jaw is symmetrical. The two halves of the upper jaw are identical to each other, and the two halves of the lower jaw are identical to each other. However, the upper and lower jaws may differ.
Teeth and Diet:
Primates are not specialized eaters, but do generally eat one type of food more often than another. Therefore, we can deduce information about a primate’s diet by examining the size and shape of the different teeth types. Consider these general observation....
Ok, sorry, I got a wee bit sidetracked on apes.
Now back to teeth in general....
Premolars and Molars
Close your eyes and imagine that I gave you an ice cube to chew on. Which teeth did you use to grind up the ice? Your premolars and molars, also referred to as your “cheek teeth.” Adults have 8 premolars and 12 molars. The premolars are located behind the incisors and canines. The molars are located behind the premolars. Children have 8 premolars and no molars.
You can usually tell the difference between a carnivore and an herbivore skull based on the shape of the cheek teeth.
Carnivores, such as dogs and cats,have cheek teeth that are sharp and pointed for cutting and tearing flesh. The pointed tips are like a pair of scissors or knives, helping the animal tear meat tissue apart.
Herbivores, such as deer and rodents,have wider and flatter cheek teeth. The surfaces of an herbivore’s cheek teeth are highly corrugated with distinct grooves and edges. The complex tooth surfaces help the animal grind and chew up plant material.An herbivore moves its lower jaw from side to side to chew its food.
Omnivores, such as raccoons,have cheek teeth with a combination of pointed tips and complex surfaces.Cheek teeth are a combination of sharp scissor-like teeth for slicing meat and teeth with flatter and wider surfaces for grinding and crushing plant material. An omnivore doesn’t have side to side lower jaw movement.
Dental Formulas
Each species of mammal has a unique dental formula.The animal’s jaw is divided into four parts: upper left, upper right, lower left, lower right. Then we count the number of teeth by type (incisors, canines, cheek teeth) in each of the four parts. We write the dental formula separately for the upper jaw and lower jaw. Each number in the dental formula indicates the number of teeth by type of tooth in each of the four parts of the animal’s jaw.
Humans have 32 teeth. We have 8 incisors, 4 canines, and 20 cheek teeth. In each of the four parts of our jaw we have 2 incisors, 1 canine, and 5 cheek teeth.
Therefore, Our dental formula is:
Upper jaw 2 1 5
Lower jaw 2 1 5
A deer has 32 teeth: 6 lower incisors, 2 lower canines, and 24 cheek teeth.
Upper jaw 0 0 6
Lower jaw 3 1 6
A raccoon has 40 teeth: 12 incisors, 4 canines, and 24 cheek teeth.
Upper jaw 3 1 6
Lower jaw 3 1 6
A beaver has 20 teeth: 4 incisors, 0 canines, and 16 cheek teeth.
Upper jaw 1 0 4
Lower jaw 1 0 4
A coyote has 42 teeth: 12 incisors, 4 canines, and 26 cheek teeth
Upper jaw 3 1 6
Lower jaw 3 1 7
A woodchuck has 22 teeth: 4 incisors, 0 canines, and 18 cheek teeth
Upper jaw 1 0 5
Lower jaw 1 0 4
A muskrat has 16 teeth: 4 incisors, 0 canines, and 12 cheek teeth
Upper jaw 1 0 3
Lower jaw 1 0 3
A rabbit has 26 to 28 teeth: 6 incisors, 0 canines, and 20 or 22 cheek teeth
Upper jaw 2 0 5-6
Lower jaw 1 0 5
A black bear has 40 to 42 teeth: 10 or 12 incisors, 4 canines, and 26 cheek teeth. Its premolars may be small or absent.
Upper jaw 2-3 1 6
Lower jaw 3 1 7
Dental Formula FOR Mammal Skulls
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| How to use this chart |
This chart is useful for identifying skulls when there are still teeth
present.
Count the number of teeth of each type in the upper (U)
and lower (L) jaw. Each row in the chart shows the
number of each type of teeth in the Upper (U) and Lower (L)
jaw, and on the right and left side. The numbers are of the form "5-5"
(for example). This means that there are 5 teeth on the left side, and 5 teeth on
the right side.'
For example, the Opossum has 5 incisors on the left upper jaw, 5 incisors
on the right upper jaw, 4 incisors on the left lower jaw, and 4 incisors on the right
lower jaw.
If you can't tell the different types of teeth apart, start by getting the
total number of teeth in both upper and lower jaws. Then use the "Total"
column as a starting point. From there you may be able to narrow it down by the
size of the skull (a raccoon skull will be smaller than a bear skull, for example), or by
other characteristics.
The chart is arranged in order by the total number of teeth, from the most
down to the least number.
Incisors are the teeth closest to the
front of the skull, Molars are the farthest to the rear.
Sometimes there are multiple species listed in the
Latin Names and Common Names
columns. This means that all of the species listed have that particular dental
formula.
Sometimes a species will have a varying number of teeth.
This is
indicated, for example, as follows:
Rangifer (32/34) (which means that they will have either 32 or 34 teeth in total), or Dasypus (28-32) which means that they will have between 28 and 32 teeth in total. |
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TRY DENTAL FORMULAS YOURSELF
Try your hand at the dentition of this red fox skull. I'm
going to try to stump you here, because this was a relatively young
animal when it perished. Look at the lower jaw, you can
see that one side has erupted teeth, and one side does not, just behind
the canine. Assume that if it had lived, it would have had a complete
set of erupted teeth.
First, is it a carnivore, herbivore, or omnivore?
I __/___ C __/___ P __/___ M___/___= ______ x2= _____ total teeth
Here's the
answer if you're not sure: I 3/3, C1/1, PM 4/4, M 2/3 = 21 x 2 = 42.
INCOMPLETE SKULLS
Often times you'll find skulls that are missing their lower jaws,
teeth have fallen out, or various and sundry things have happened to the
skull, so the teeth are hard to count or may be missing. Here are a
few examples. See if you can guess the dentition.
Ok, this opossum skull is rough. It has both upper and lower jaw, but
many teeth are missing and the jaw image is from only one direction.
Try the dentition yourself first, then scroll to the bottom of the "jaw"
image to see if you're correct.
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| American opossum skull upper mandible (the North American mammal with the most teeth by the way!) |
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| American Opossum Dentition: I 5/4 C 1/1 P 3/3 M 4/4 = 25 x 2 = 50 |
Here's a really challenging skull. It's a rabbit, specifically a jackrabbit, not a rodent. Notice, some of the back molars are just erupting, and we only have the top mandible.
Because this is a rabbit, it has an additional set of teeth behind its
long front teeth (unique to hares and rabbits, not found in rodents), so
the count is: I 2 C 0 P 3 M 3= 8 total or 16 in the top jaw alone.
To further simplify your task, below is a color chart to help you identify the type of teeth you are examining.
Incisors (dark blue) are at the front of the mouth and are usually for scraping or biting, so they are scoop shaped and smaller. Canines (green) are usually for ripping or tearing meat, so they are long and pointed. Premolars
(pink), are behind the canines, and can be flat for grinding, like in
the mouth of beavers, or they can be sharp and serrated like in dogs and
canines, for tearing meat. Molars (turquoise)
also vary, depending on their use. Often they are for grinding food,
like in humans, but in meat eating creatures they too may be serrated and have sharp edges for ripping and tearing meat.
The number, shape, and size of teeth can help you determine what type
of animal skull you've found. Knowing where molars and premolars begin
and end can be tricky. There's no hard and fast rule for telling them
apart, and often they can look very similar. The other types of teeth
are much easier. You'll have to practice skull identification, and
looking at different types of teeth to get comfortable. For now, if it
helps, focus mostly on the incisors, canines and molars (farthest back
two pairs of teeth) if you're not sure.
The last tidbit you should know, is about bilateral symmetry.
All mammals, like you and me, have bodies with mirror halves. The right
side of our skeleton, and our external body, matches the left. This
means, that when you study the teeth of a mammal you only need to study
one side of the mouth, or count teeth on one side of the skull. The
other half of the jaw is exactly the same (for dental formulas you then
multiply by two). For example, in the image above, there are three
incisors, one canine, four premolars, and two molars on one side. You
would double that for a full tooth count.
Just remember that animal skulls will not always have the same number of teeth in their upper and lower jaws.
This is because each jaw may have a different function. In deer (and
sheep, horses, etc.), the upper jaw has no incisors, but the lower jaw
has a full set of incisors. This is because they use their lower jaw to
"scoop" grass and leaves, and then the vegetation is passed to the back
molars for grinding (this scooping action is what animal trackers look
at to know the difference between the shearing cuts of rabbit teeth and
the ragged scoop of deer teeth on vegetation).
See our other article on Teeth.
Southern SASquatch Expeditions
Author: Angela Ashton, Founder
#southernsasquatchexpeditions #bigfoot #sasquatch
https://www.facebook.com/southernsasquatchexpeditions/
Southern SASquatch Expeditions
Author: Angela Ashton, Founder
#southernsasquatchexpeditions #bigfoot #sasquatch
https://www.facebook.com/southernsasquatchexpeditions/
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