The external features of animal 'mouths' are the most easily observed and
the best field indicators of eating habits. Focus will be on size and shape. The internal features of tongue, jaw structure, palate and dentition will be dealt with in later articles. In the 'INSECT WORLD' a variety of 'mouth parts' can be identified - some only with magnification. Examples are - The stiff, needle-like probes for penetrating and sucking up fluids are seen among biting flies, some wasps and mosquitoes.
The long, supple probes, on moths and butterflies, for reaching deep into flowers and other food sources. The 'side cutter' like, paired jaws of the cricket / grasshopper family are ideally suited to cutting vegetation. The long, sharp, paired 'pincers' found on some beetles, centipedes, spiders, antlions etc, for gripping, piercing and sometimes injecting or sucking on prey. The serrated jaws of beetles, ants, wasps etc, for chewing tough food. The short, stout, paired jaws of the longhorned (borer) beetles, Carpenter bees, many larvae and most termites for gnawing at wood. The variety is endless!
In Birds and among REPTILES (specifically the Chelonia - or Testudines) beaks or bills take the place of lips and teeth. The 'bills' of tortoises, terrapins and turtles are much the same in shape, differing only in size with the age and species, and all are sharp and have a very powerful 'bite'. The larger species are quite capable of severing a human digit. Some are carnivorous but most are vegetarian and capable of cutting tough plants.
Some fish species have beak-like mouths for nipping off food while others that suck up soft food have developed fleshy and protruding lips to vacuum up their food. No snake species have functioning lips. The 'beaks' of BIRDS are as varied as the 1000 or so species we have in southern Africa. Some of the more interesting examples among our lowveld species are - The delicate, long and curved beaks of sunbirds and hoopoes for reaching deep into flowers for nectar and for picking out insects from holes and under loose bark.
The bee-eaters have long beaks for holding at bay stinging insects, to be dealt with before being swallowed. Hornbills have long beaks for a similar purpose to deal with snakes and scorpions but also to assist in feeding through narrow nest holes. The ibis family use their long beaks for probing the soil for food. The stout, sharp beaks of woodpeckers and barbets are serrated for holding food and for drilling into wood. The strong, stubby beaks of finches and weavers for picking up seeds and for cracking and discarding the cellulose covering from the seed kernel.
The hook-tipped beaks of most insectivorous species, for gripping prey and tearing off pieces, as in the shrikes, flycatchers and drongos. Cormorants and pelicans also have hook-tipped beaks for holding prey but do not tear it as they swallow them whole down an expansive gullet. Nightjars have a hook on their small, weak beaks to hold insects which are guided into the massive gape with the assistance of stiff, moustache bristles and swallowed whole. Long, straight, sharp pointed beaks are found on most storks, herons, bitterns, darters and kingfishers to assist in stabbing and holding fish and other prey which is swallowed whole.
The hammerkop has small hook on the bill-tip for holding and often tearing prey. Birds of prey are well known for their hooked beaks used in tearing up meat and insects. Some marine species such as petrels and skuas have the same adaptation. Not all birds of prey habitually tear up prey. Some, like the bat hawk and long-crested eagle swallow prey whole down a large gullet. Swifts and swallows, with very small beaks, habitually swallow insect food down their large gapes in flight but use the curved bill-tips for gathering and securing nest material. The variety is endless but beak adaptations are quite easy to interpret with careful observation.
With the exception of a few species such as the 'duck-billed platypus', mammals have fleshy lips at the mouth entrance. In many cases these lips indicate the feeding methods and food preference. An elephant 'trunk' can be construed as an elevated and elongated top lip combination with the 'nose', the same as found in tapirs and some shrews, where the proboscis is used to guide food into the mouth.
This is 'stretching' it a bit - others are more conventional and adapted for a particular function. The lips of the square-lipped rhino (white rhino) are broad and firm for grazing short grass. Similar lips are found on hippo which use only the lips to graze. The bovine animals such as buffalo and cattle have a firm, fleshy, upper lip against which they clamp their (lower) incisors - like a knife blade against your thumb - to cut short grass on which they feed. Long grass they can take into their mouths utilising the pre-molars for cutting.
Most of the antelope have mobile lips that can 'grab' food which is pulled into the mouth with the help of a long tongue where it is often cut using the pre-molars. Grass is grazed in the same way as buffalo but much more daintily. Some of the larger antelope like kudu bulls and eland use their horns to break branches to lower the 'browse' while sable and roan use their horns to part long, unpalatable grass to reach the tender shoots lower down. Black rhino have a prehensile top lip which can pull leaves and small branches into the mouth.
The skin of the lip is very thick and impervious to thorns. Giraffe have a similar top lip but in their case the inside surface of the top lip especially and bottom lip, are covered in stiff bristles like a toothbrush. This arrangement of bristles allows them to rake their lips along thorny branches removing the leaves without getting pricked. Many of the acacia species on which they browse show markedly bare branch ends where the giraffe have been feeding.
The only way in which the acacias can protect themselves is to grow longer thorns on the branch ends - something that Acacia nilotica does particularly well, with long, backward facing thorns which penetrate the bristles on the Giraffe lips as a deterrent. The giraffe also utilises its very long tongue to reach and pull food into the mouth where it is cut by the pre-molars. Warthog and bushpig dig with their snouts and although they have short lips, use their front teeth for grazing, as do the equine animals like zebra, donkeys and horses.
Other species use their tongues and teeth to access food but that will be dealt with in a future article. Carnivores do not usually use their lips in feeding but use them extensively in warning and threat behaviour. Lips are certainly an indicator of function and expression. At certain times flared to pick up female hormones - occasionally 'quivering' in suspense - drawn back to display the teeth as a warning when necessary and sometimes even giving what could be construed as a 'smile'. Very similar to human beings acctually - but lacking the colourful lipstick - which is also an indicator of the 'species'!
By Dave Rushworth