Skulls, Jaws And Internal Mouth Parts

Here we look at some of the internal jaw and mouth structure that might assist in identifying a species. Among the skeletal remains of animals the bones of the head, or skull, are always the most interesting and normally of most assistance in identifying a species.

Mammal skulls normally consist of two main sections - the cranium combined with the top jaw, and the lower jaw. Birds have these two parts while some mammals and most reptiles have the top section divided into several parts and the lower jaw divided. These divided skulls are held together in life by cartilage and ligaments.

Skulls

The first thing one will normally notice about a skull is the size, which is an important indicator. One should then look at the shape of the skull. Does it have any 'horn' support bones ? The position of the eye sockets, the length of the jaw. The next noticeable feature will be the beak, teeth or tusks. Beak shapes, which we have dealt with in the past, will help identify the species. Teeth, which I will deal with in detail, will normally indicate whether the animal is a herbivore, carnivore or specialised feeder. Among the carnivores, the width of skull at the back of the jaw, the length of the jaw and the area for muscle attachment, will usually help to indicate the species.

Muscle Attachment

Jaw muscle is normally attached to the side of the skull. From the attachment to the lower jaw, the muscles lie under the 'cheek bones' and attach to an area of the skull. The size of this muscle-attachment area will normally indicate the strength of the jaw. The occurrence of a 'sagittal crest', or bony ridge on the top, rear of the skull, which provides extra muscle attachment area, will also, normally, indicate jaw strength.

Because of the physics involved, jaws usually have greater 'biting power' at the back than in the front. As an indication of some jaw strengths, tests have shown that sharks bite at around 18 tons per square inch and hyaenas at around 23 tons per square inch. As in stiletto-heeled shoes, the area of tooth contact will have an effect on pressure and larger animals would be presumed to exert more powerful bites. The muscles for opening a mouth are invariably much weaker than the muscles for closing or biting.

Tongues

While on the subject of mouths, let us consider the role of tongues, especially where they are linked to jaw and 'palate' (roof of the mouth) design. The long tongue of the giraffe, for reaching out and gathering food, has been mentioned previously. Several other herbivores, many out of our range, have similar tongues. Of the highly specialised tongues, some are worthy of mention. The 'aardvark' (or ant-bear) and all species of pangolin (or scaly ant-eater) have very long, thin and sticky tongues that are able to penetrate deep into holes to extract the termites and ants on which they feed.

These species have no teeth on the front of the rather weak jaw and only round, flat molars at the back with which to squash the food. Another termite eater, the aardwolf - Proteles cristatus - (sometimes called 'maned jackal'), belongs to the Family Hyaenidae and is the only species in the Subfamily Protelinae. It feeds on carrion and small creatures but mainly on termites. It has much less powerful teeth and weak jaws in which the back teeth are reduced to simple, rounded points. It does not crush bones as do the true hyaenas.Due to the relatively ineffective molars and the main diet, the aardwolf has developed a particularly broad and hard tongue with which it squashes the termites against a matching broad palate (on the roof of the mouth). The large cats (e.g. lion and leopard), have tiny backward facing 'hooks' on the upper surface of their tongues, with which they can 'scrape off' particles of meat and also groom themselves.In the grooming process the 'combing' action sometimes gathers 'fur-balls' which are ingested and presumed to act as 'swabs' to help clean mucous out of the stomach. Whether this is intended or incidental is not clear (- rather the same as stones in a crocodile stomach although crocodiles and ostrich have been observed picking up stones which they swallow.) Some of the herbivores (like buffalo) also have rough (spiked or hooked) tongues which assist them in pulling vegetation into the mouth and with which they 'groom' themselves.

Jaws And Dentition

The relative density of the skull and jaw will give some indication of its strength. Robust jaw bones and size and type of teeth will be an indicator of function. The number of teeth normally correlate with the jaw length. The Felidae (cats) have rounded skulls with relatively short jaws containing only 30 teeth. The Canidae (dogs) - disregarding breeds with deformed jaws - have long jaws containing, normally, 42 teeth.

(The Ursidae (bear family), which we don't have in this part of the world, have the same dentition.) Hyaenas, with their broad and slightly shorter jaws have 34 teeth, while the Viverridae (mongooses, civets and genets) all have 40 teeth in a relatively long jaw. Dentition varies between the different mammal families. The carnivores and omnivores generally have the 'fullest' mouths while herbivores and rodents lack certain types of teeth. On examination of a full mouth - say jackal or civet jaw - you would normally find the following :- The cutting or gripping teeth in the front are incisors.Behind these are the, quite often long (stabbing) canines, followed by (holding) premolars, and right at the back the (crushing) molars. 'Cats' normally lack, or have diminished, premolars, creating a gap with which to hold and drag prey, - hence only 30 teeth. 'Dogs', on the other hand, normally have large premolars that assist in carrying and ripping. The back molars vary with function. In hyaenas the premolars are relatively diminished while the molars are exaggerated for crushing bone.The rear molars are designed for cutting, the same as in the large cats, and are termed carnassials, where extreme force can be exerted. In omnivores the molars tend to be flatter for crushing and in herbivores the molars are sharply ridged for grinding. Generally, in omnivores, carnivores and insectivores the molars have rounded or pointed cusps and are termed 'bunodont'.Herbivores have cusps fused into ridges (as in rhino) which are termed 'lophodont', and in ruminants the crests wear away, exposing the underlying dentine which is surrounded by crescent-shaped bands of enamel to form molars which are termed 'selenodont'. Bear in mind, when examining teeth, that the first (or milk) teeth are normally shed and replaced, in a certain order, by the permanent teeth.The state of replacement, growth and wear on teeth is used as a method of ageing animals. The ruminants (which do not include the pig family), lack upper incisors and canines, so any skull without upper front teeth belongs to an antelope, buffalo, giraffe or 'cow'. You should be able to make an identification by size and possible horns. All the horse family (including zebra) have front, upper teeth and the males have 'canines' in the form of 'tushes' in the gap behind these. Occasionally there is a very small 'tush' in some females.Taking one whole quarter (or one half of the bottom or top jaw) there should be 3 incisors (I) - maybe one tush (canine) (C) - 3 premolars (Pm) and 3 molars (M) - making 6 teeth together (Pm+M) in the back of the jaw. Less than this will indicate a young or immature animal. The (I) replace first, then the Pm and then the M. The Pm are numbered 1,2,3 from the front as are the M and they are replaced in that order, so one will normally find the most wear in the longest serving teeth, which help in ageing the animal. The dental classification of teeth is well documented and can be of assistance to those interested. Some examples are :-

Cats: I 3 - C 1 - Pm 3 (upper) 2(lower) - M 1.

Dogs/bears: I 3 - C 1 - Pm 4 - M 2(upper) 3(lower).

Civets - 3 -1 - 4 - 2.

Hyaena - 3 - 1 - 4/3 - 1.

Cattle/giraffe/buffalo/most antelope:- 0/3 - 0/1 - 3 - 3.

Warthog:- 1/3 - 1 - 2/1 - 3.

Wild pig:- 3 - 1 - 4 - 3.

Hippo:- 2 - 1 - 4 - 3 .

Rhino (Asiatic):- 2 - 0 - 4 - 3. and (African):- 0 - 0 - 4 - 3.

Moles:- 3 - 1 - 4 - 3.

Shrews:- 3/1 - 1 - 3/1 - 3.

Rats:- 1 - 0 - 0 - 3.

Squirrel:- 1 - 0 - 2/1 - 3.

With bats the teeth vary with the species from 20 to 38, and it all begins to become a very interesting method of identification, combined with other skull features. By the way - human beings are:- I 2 - C 1 - Pm 2 - M 3, if you want to check the origin of your mate !

ENJOY YOUR INVESTIGATIONS BUT -- A GOOD MOUTHWASH !

PLEASE NOTE THAT - If you happen to come across a skull in the lowveld area don't immediately handle it. Remember that anthrax is endemic in the area and
there are annual outbreaks that kill many animals. If you are not sure how the animal died prevent contamination by using a stick to examine the skull. The same applies to any small, sickly mammal, that might have contracted bubonic plague.

You are not permitted to take animal parts out of the 'Red Line' veterinary cordon area to the highveld, or other 'clean' areas, without a veterinary clearance permit and before any necessary de-contamination. Remember that your tongue is the most powerful part of your body - for Good or Evil. What goes out of your mouth can never be fully retracted. To prevent untold suffering and harm - think before you speak !

By Dave Rushworth