How to use Mammals in a sentence
The sea mammals include the common dolphin (Delphinus delphis).
Of smaller mammals, raccoons, squirrels and opossums are very common.
Only two land mammals are known to be indigenous.
If we get into mammals, the biggest killer of humans is dogs – and horses.
Bogdanov, Birds and Mammals of the Black-Earth Region of the Volga Basin (in Russian, Kazan, 1871); Karelin for the southern Urals; Kessler for fishes; Strauch, Die Schlangen des Russ.Advertisement
Bat droppings are similar to small mammals but on closer inspection are very crumbly due to the insect contents.
Marsupials may be defined as viviparous (that is non-egglaying) mammals, in which the young are born in an imperfect condition, and almost immediately attached to the teats of the mammary glands; the latter being generally enclosed in a pouch, and the front edge of the pelvis being always furnished with epipubic or "marsupial" bones.
From the number of its cheek-teeth, the banded ant-eater has been regarded as related to some of the primitive Jurassic mammals; but this view is disputed by Mr Bensley, who regards this multiplicity of teeth as a degenerate feature.
It may be added that a few traces of mammals have been obtained from the English Wealden, among which an incisor tooth foreshadows the rodent type.
The marsupials constitute two-thirds of all the Australian species of mammals.Advertisement
Sclater have been found to hold good for a large number of groups of animals as different in their mode of life as birds and mammals, and they may thus be accepted as based on nature.
E Here, as over so large a portion of the Australian region, we find birds constituting the supreme class - the scarcity of mammals being accounted for in some measure as a normal effect of insularity.
The Lebanon and the hills of north Galilee offer the greatest number of mammals.
According to Nordenskjold r it numbers only twenty-nine species of mammals, of which seven are marine and seventeen or eighteen may be safely considered as living beyond the forest limit.
Among the mammals are the opossum, raccoon, star-nosed mole (Condylura cristata), grey fox and fox squirrel.Advertisement
The second class contains enzymes from Myxococcus xanthus, methanogenic archaea, insects, fish and marsupial mammals.
The Life of Mammals describes and illustrates the remarkable diversity of mammals from the giant blue whale to the miniscule pigmy shrew.
The Act governs hunting wild mammals with dogs in England and Wales, and bans all hare coursing.
Our campaign has always focussed on ending wanton cruelty to Britain's wild mammals - perpetrated in the name of sport.
In some mammals the hairy covering is partial and limited to particular regions; in others, as the hippopotamus and the sea-cows, or Sirenia, though scattered over the whole surface, it is extremely short and scanty; xvir.Advertisement
These three are therefore reckoned as milk-molars, and their successors as premolars, while the last three correspond to the true molars of other mammals.
The mode of succession of the teeth in the mastodons exhibits so many stages of the process by which the dentition of elephants has been derived from that of more ordinary mammals.
According to one theory, these rudimentary teeth, together with the one pair of functional teeth in each jaw that has vertical successors, represent the milk-teeth of placental mammals.
On the other hand, it is noteworthy that this marsupial retains in its lower jaw the so-called mylo-hyoid groove, which is found in the aforesaid Jurassic mammals.
Among the plants the wild banana, pepper, orange and mangosteen, rhododendron, epiphytic orchids and the palm; among mammals the bats and rats; among birds the cassowary and rifle birds; and among reptiles the crocodile and tree snakes, characterize this element.Advertisement
There is a small pig (Sus andamanensis), important to the food of the people, and a wild cat (Paradoxurus tytleri); but the bats(sixteen species) and rats(thirteen species) constitute nearly three-fourths of the known mammals.
Then follows the rib-bearing portion and then the processus lateralis posterior; this also is the product of ribs, consequently the right and left processes together are equivalent to the xiphoid process or xiphisternum of the mammals.
The midbrain is represented chiefly by the optic lobes, the cortex of which alone is homologous with the corpora quadragemina of the mammals.
The Eye is essentially reptilian, but in sharpness of vision, power and quickness of accommodation it surpasses that of the mammals.
This so-called third, upper or posterior conch is not a true conch, nor is that of the vestibulum; only the middle one forms a scroll, and this corresponds to the only one of reptiles and the lower of the mammals.Advertisement
The birds of Liberia are not quite so peculiar as the mammals.
The majority of spiders, however, are soft-skinned and succulent, and are tasty morsels for insectivorous reptiles, birds and mammals.
A cursory inspection of the bird, which is not unfrequently brought alive to Europe, its size, and its enormous bill and talons, at once suggest the vast powers of destruction imputed to it, and are enough to account for the stories told of its ravages on mammals - sloths, fawns, peccaries and spidermonkeys.
Of the liver little need be said, except that in all living mammals it has been divided into a number of distinct lobes, which have received separate names.
It climbs well, prefers open forest in the neighbourhood of water, is often found in plantations where it retires into a hole in the ground, and lives chiefly on birds and small mammals.Advertisement
Besides the dog and the pig, which (with the domestic fowl) must have been introduced in early times, the only land mammals are certain species of rats and bats.
In all there are 90 different species of mammals, 248 species of birds, 377 of fishes and more than 13,000 of insects.
There appear to have been no indigenous mammals or reptiles.
The faunal aspect of the Tertiary periods differs strikingly from that of preceding Secondary or Mesozoic; in place of the great saurian reptiles we find the rapid development and finally the maximum expansion of mammals.
Among the mammals that fall under this head are the common genet (Genetta vulgaris), which extends, however, pretty far north, and is found also in the south of France, the fallowdeer, the porcupine (very rare), and a species of ichneumon (Herpestes Widdr-ingtonii), which is confined to the Peninsula, and is the only European species of this African genus.Advertisement
Of the mammals in which Spain shows more affinity to the fauna of central and northern Europe, some of the most characteristic are the Spanish lynx (Lynx pardinus), a species confined to the Peninsula, the Spanish hare (Lepus madritenss), and the species mentioned in the article PYRENEES.
Ibex live habitually at a greater height than chamois or any other Alpine mammals, their vertical limit being the line of perpetual snow.
The latter sends a horizontal or slightly ascending process backwards below the orbit to join the under surface of the zygomatic process of the squamosal, which is remarkably large, and instead of ending as usual behind the orbit, runs forwards to join the greatly developed post-orbital process of the frontal, and even forms part of the posterior and inferior boundary of the orbit, an arrangement not met with in other mammals.
The hoof of the horse corresponds to the nail or claw of other mammals, but is so constructed as to form a complete and solid case to the expanded termination of the toe, giving a firm basis of support formed of a non-sensitive substance, which is continually renewed by the addition of material from within, as its surface wears away by friction.
Before the advent of the white man Nebraska was full of wild mammals, the buffalo, elk, black and white tailed deer, antelope, bears, timber wolves, panthers (pumas), lynx, otter and mink being common.Advertisement
Little is known of the habits of the clouded leopard, but it preys on small mammals and birds, and rarely comes to the ground.
That it was not much earlier is shown by the fact that some still living species of mammals, such as the thylacine, existed before"the separation.
The discovery of great Pampean mammals in the Pleistocene beds of that region shows that this upheaval of the latter is very recent, for in the heart of the Cordillera, as well as on the west coast of Bolivia and Peru, there have been discovered, in very recent deposits, the remains of some mammals which cannot have crossed the high range as it now exists.
This flora, however, is associated with a fauna of large mammals, the majority of which are extinct.
This lignite and the accompanying leaf-bearing clays underlie and are apparently older than the strata with Newer Pliocene mammals and mollusca.Advertisement
However extraordinary it may appear, especially to those who bring the living forms only into focus, that opposition should still be made to Huxley's primary division of the vertebrates other than mammals into Sauropsida (birds and reptiles) and Ichthyopsida (batrachians and fishes), it is certain that recent discoveries in palaeontology have reduced the gap between batrachians and reptiles to such a minimum as to cause the greatest embarrassment in the attempt to draw a satisfactory line of separation between the two; on the other hand the hiatus between fishes and batrachians remains as wide as it was at the time Huxley's article Amphibia (Encyclopaedia Britannica, 9th ed.) was written.
The outcome of our present knowledge points to the Stegocephalia, probably themselves derived from the Crossopterygian fishes (8), having yielded on the one hand the true batrachians (retrogressive series), with which they are to a certain extent connected through the Caudata and the Apoda, on the other hand the reptiles (progressive series), through the Rhynchocephalians and the Anomodonts, the latter being believed, on very suggestive evidence, to lead to the mammals (9).
The land fauna however is very poor; there are few mammals with the exception of dogs, rats and pigs; and amphibia and insects are also generally scarce.
Mammals are few in species, but remarkable, especially Macacus niger, an ape found nowhere else but in Bachian; Anoa depressicornis, a small ox-like quadruped which inhabits the mountainous districts; and the babirusa or pig-deer of the Malays.
Some of the animals are probably descendants of specimens introduced by man; others are allied in species, but not identical, with mammals of Java and Borneo; others again, including the three just mentioned, are wholly or practically confined to Celebes.
The same peculiarity of species holds in regard to the insects of the Celebes (so far as they are known) as to the mammals and birds.
If we get into mammals, the biggest killer of humans is dogs â€“ and horses.
There is a diversity of flora and fauna - 600 species of plants, 37 species of mammals and 190 different birds.
He was a pioneer in the use of the natural history diorama to exhibit large mammals against a representation of their habitat.
No large mammals ever reached the islands, so birds and reptiles remained dominant - as they had once dominated the Earth eons before.
Insects, spiders and crustaceans have them, while mammals, birds and fish have endoskeletons.
Mammals dominated the land fauna following the extinction of the dinosaurs at the end of the Cretaceous.
Typical mountain steppe mammals include Altai pika Ochotona alpina, arctic ground squirrel Citellus undulatus and Siberian chipmunk Tamias sibiricus.
Bright red haws ripen in October and provide food for birds and small mammals through much of the winter.
The abundant red haws or berries are probably the main winter food for wild birds and small mammals.
An old hawthorn hedge A mixture of species within a native hedgerow is an excellent habitat for small birds and mammals too.
Our analyzes have focused on insects, birds and mammals, but also other arthropods and a diverse range of simultaneous hermaphrodites.
Here organic material, channeled into gravels has yielded fossil mammals including hippopotamus.
Like all mammals, mouse embryos are relatively inaccessible within the mother.
Urea is the main form in which nitrogen is excreted in mammals UV radiation invisible rays that are part of the electromagnetic spectrum.
There are over 560 species of bird and huge mammals such as anteaters and the elusive jaguar.
In fact, Pusztai used a snowdrop lectin proven in peer-reviewed research to be harmless to mammals in its natural non-GM form.
It has over 150 different species of mammals, reptiles and birds in its collection including meerkats, ring tailed lemurs and wallabies.
Determining the evolutionary changes in MCPH genes through the primate lineages to lower mammals.
Some dinosaurs ate lizards, turtles, eggs, or early mammals.
Well, the bill is intended to'Make Provision about hunting wild mammals with dogs.
In domesticated mammals the retina is the reflective area at the back of the eye which responds to light.
The flu virus mutates frequently, changing its genetics, but it rarely goes through the changes that allow it to routinely infect mammals.
Aircraft can also be used to survey large areas for marine mammals.
These wild mammals of the ocean swim into the shallows to mingle with people.
They are one of Britain's most endangered mammals.
Compared with many terrestrial mammals, little is known of cetacean natural history.
The process and product claims extend to all similarly altered non-human mammals.
Sorry to be writing about sea mammals two weeks in a row!
The dolphins are the big attraction, but there is a wide range of fish and mammals on display, including the loveable manatees.
Marsupial lion bites strongest - 06/04/2005 Study reveals extinct marsupial lion bites strongest - 06/04/2005 Study reveals extinct marsupial lion may have had the strongest bite among mammals.
Marsupials and placental mammals marsupials and placental mammals Marsupials and placental mammals give birth to live young.
Terrestrial mammals such as sheep, stone marten and man have also been recorded as having been infected with EBLVs.
We also have a newly built reptile house and now have various mammals on display, including meerkats and asian short clawed otters.
The mammals include moose, wild boar, deer, beavers, wolves, badgers, otters and lynx.
Other smaller mammals include muskrat Ondatra zibethicus, cottontail rabbit Sylvilagus floridanus, and a number of mice, mole and shrew species.
They are able to compete for binding sites with circulating oestrogens of most mammals.
Maturation in vitro of immature oocytes has been achieved in small mammals, even from primordial follicles, using a number of methods.
Mammals include pipistrelle and Daubenton's bats, shrews and roe deer.
Other mammals include Indian porcupine Hystrix indica and Indian hare Lepus nigricollis.
From fish or marine mammals (including porpoises ).
In mammals, it is located in the anterior part of the visceral cavity, just posterior to the diaphragm.
We then move south to the more open, acacia savanna, with more grazing mammals and a greater chance of seeing predators.
A number of small mammals will also now be present, including shrews (left ), voles and mice.
There are nearly 5,000 species of mammals the smallest shrew weighing only 1.75 grams, the largest whale up to 140 tons.
It is home to more than 800 species of mammals, 2500 species of mammals, 2500 species of fish and 25,000 species of plants.
The current H5N1 strain of avian flu virus does not transmit easily from birds to mammals like cats.
The surface activity of pulmonary surfactant from diving mammals.
In addition Drosophila tests were not regarded as valid surrogates for in-vivo tests in mammals.
Brazilian tapirs are hoofed mammals, with three toes on each hind foot and four on each front foot.
It is a catholic feeder which will take mammals the size of a dik-dik but it eats termites.
In mammals we make use of RNAi techniques as well as in vitro transcription analysis.
This contrast to the situation in mammals, where the developing fetus receives a continuous external supply of nutrients from the mother's uterus.
In fact, most zoologists assert that cats have the best senses among mammals.
There are no indigenous land mammals.
Further, it is considered that too much weight has been assigned to the characters distinguishing monotremes from other mammals, foetal marsupials showing a monotreme type of coracoid, while it is probable that in the long run it will be found impossible to maintain the essential dissimilarity between the milk-glands of monotremes and other mammals.
Before proceeding further it may be mentioned that the remains of many of these mammals are very scarce, even in formations apparently in every -way suitable to the preservation of such fossils, and it hence seems probable that these creatures are stragglers from a country where primitive small mammals were abundant.
The epiphysis, or pineal body, is quite as degenerate as in mammals, although still forming a long stalk as in reptiles.
Its fine-grained, unstratified silt contains the remains of many terrestrial animals, including fifteen mammals.
The land mammals of Greenland are decidedly more American than European; the musk-ox, the banded lemming (Cuniculus torquatus), the white polar wolf, of which there seems to have been a new invasion recently round the northern part of the country to the east coast, the Eskimo and the dog - probably also the reindeer - have all come from America, while the other land mammals, the polar bear, the polar fox, the Arctic hare, the stoat (Mustela erminea), are perfectly circumpolar forms. The species of seals and whales are, if anything, more American than European, and so to some extent are the fishes.
Man himself, as well as other mammals, is the intermediate host of the dangerous parasite, Taenia echinococcus, in countries where cleanliness is neglected; the pig is the host of Taenia solium, and other cases may be seen from the table at the end of this article.
Its etymology has genus of carnivorous mammals (see Carnivora).
Among notable mammals the chimpanzee is found in Unyoro, Toro and north-west Ankole, and has only recently become extinct in Buganda; the okapi inhabits the Semliki forests on the Congo frontier; the giraffe (the male sometimes developing five horn cores) is common in the Northern, Eastern and Rudolf provinces; there are three types of buffalo - the Cape, the Congo and the Abyssinian; two species of zebra (one of them Grevy's), the African wild ass, the square-lipped (" white ") and pointed-lipped (" black ") rhinoceroses, the elephant, hippopotamus, water tragelaph (" Speke's antelope "), Cape ant-bear, aard-wolf (Proteles), hunting-dog, and nearly every genus and most of the species of African antelopes.
As Cuvier founded the palaeontology of mammals and reptiles, so Louis Agassiz's epoch-making works Recherches sur les poissons fossiles (1833-1845) laid the secure foundations of palaeichthyology, and were followed by Christian Heinrich Pander's (1794-1865) classic memoirs on the fossil fishes of Russia.
Illustrations of this law were set forth by Cope as early as 1861 (see " Origin of Genera," reprinted in the Origin of the Fittest, pp. 95 -106) in pointing out the extraordinary parallelisms between unrelated groups of amphibians, reptiles and mammals.
Among its characteristic mammals and birds are the sage cotton-tail, black-tailed jack-rabbit, Idaho rabbit, Oregon, Utah and Townsends ground squirrels, sage chipmunk, fivetoed kangaroo rats, pocket mice, grasshopper mice, burrowing owl, Brewers sparrow, Nevada sage sparrow, lazuli finch, sage thrasher, Nuttall s poor-will, Bullocks oriole and rough-winged swallow.
The fauna contains no indigenous mammals, a wild ass which roams the eastern plains, perhaps its oldest denizen, is probably of Nubian origin; while the domestic cattle, a peculiar, unhumped, small, shapely, Alderney-like breed, may be a race gradually developed from cattle imported at a distant period from Sind or Farther India.
Next in constancy are the " sublingual," closely associated with the last-named, at all events in the locality in which the secretion is poured out; and the " zygomatic," found only in some mammals in the cheek, just under cover of the anterior part of the zygomatic arch, the duct entering the mouth-cavity near that of the parotid.
In mammals both caecum and colon are often sacculated, a disposition caused by the arrangement of the longitudinal bands of muscular tissue in their walls; but the small intestine is always smooth and simple-walled externally, though its lining membrane often exhibits contrivances for increasing the absorbing surface without adding to the general bulk of the organ, such as the numerous small tags, or " villi," by which it is everywhere beset, and the more obvious transverse, longitudinal, or reticulating folds projecting into the interior, met with in many animals, of which the " valvulae conniventes " of man form well-known examples.
In mammals the quadrate bone is incorporated into the middle ear as the malleus.
In all there are 1000 olfactory genes scattered throughout the genome, evidence of the importance of smell to most mammals.
A number of small mammals will also now be present, including shrews (left), voles and mice.
Moreover, the gene introduced into the potatoes was a snowdrop flower lectin, a substance known to be toxic to mammals.
It is home to more than 800 species of mammals, 2500 species of fish and 25,000 species of plants.
The two marine mammals found on land are the subantarctic fur seals Arctocephalus tropicalis and southern elephant seals Mirounga leonina.
Can they unravel the ecological clues to safeguard Suffolk 's mammals.
This contrast to the situation in mammals, where the developing fetus receives a continuous external supply of nutrients from the mother 's uterus.
There are more native species of bat in the UK -- 16 breeding and several vagrant visitors -- than any other group of mammals.
The adult and immature stages are, however, by no means confined respectively to carnivorous and herbivorous species of mammals.
Finally, the laws of distribution of animals over Siberia cannot be made out until the changes undergone by its surface during the Glacial and Lacustrine periods are well established and the Post-Tertiary fauna is better known The remarkable finds of Quaternary mammals about Omsk and their importance for the history of the Equidae are merely a slight indication of what may be expected in this field.
Many Acari are parasitic on marine and freshwater molluscs, and others are found on the feathers of birds and the hair of mammals.
Endemic inferior animals and mammals are practically non-existent, except two bats and one scorpion, which are allied to Madagascar species or introduced.
In the Hunterian lectures delivered at the Royal College of Surgeons in 1863, Huxley divided the Vertebrata into Mammals, Sauroids and Ichthyoids, the latter division containing the Amphibia and Pisces.
Both the two former are iron-grey on the upper parts, and black below, a style of coloration rare among mammals, as the upper side of the body is in the great majority darker than the lower.
The indigenous fauna of Brazil is noteworthy not only for the variety and number of its genera and species, but also for its deficiency in the larger mammals.
It is the largest of the Brazilian mammals, and inhabits densely forested tracts near river courses.
In strong contrast to the poverty of Brazil in the larger mammals is the astonishing profusion of insect life in every part of the country.
Zworo oUvra Ev aurois, viviparous Enaema (= Mammals, including the Whale).
Owen not only occupied himself with the dissection of rare animals, such as the Pearly Nautilus, Lingula, Limulus, Protopterus, Apteryx, &c., and with the description and reconstruction of extinct reptiles, birds and mammals - following the Cuvierian tradition - but gave precision and currency to the morphological doctrines which had taken their rise in the beginning of the century by the introduction of two terms, " homology " and " analogy," which were defined so as to express two different kinds of agreement in animal structures, which, owing to the want of such " counters of thought," had been hitherto continually confused.
In warm-blooded animals, such as birds and mammals, protective mechanisms for the regulation of temperature enable them to endure exposure to extreme heat or cold, but in such cases the actually living cells do not appreciably rise or fall in temperature.
Milk sugar, lactose, lactobiose, C12H22011, found in the milk of mammals, in the amniotic liquid of cows, and as a pathological secretion, is prepared by evaporating whey and purifying the sugar which separates by crystallization.
Mammals are very few; they include the rat and Pteropus and other bats.
In the oases of the Jerid are found several species of tropical African mammals and two or three of Senegalese birds, and the vegetation seems to have as much affinity with tropical Africa as with Europe.
The fauna of Tunisia at the present day is much impoverished as regards mammals, birds and reptiles.
It has been shown in the mammals that blood-relationship, in the strict and literal sense, holds good.
The anatomical differences by which the platypus, and its only allies the echidnas, are separated from all other mammals, so as to form a distinct sub-class, are described in the article Monotremata, where also will be found the main distinctive characters of the two existing representatives of the group. It is there stated that the early stages of the development of the young are not yet fully known.
The tail is short, broad and depressed, and covered with coarse hairs, which in old animals generally become worn off from the under (From Gould's Mammals of Australia.) Platypus.
The moccasin-snake ranges fromMassachusetts and Kansas to Florida and Texas and into Mexico, preferring swampy localities or meadows with high grass, where it hunts for small mammals and birds.
Indigenous mammals are poor in species as well as few in number; birds are more abundant, but of no greater variety.
Some are said occasionally to resort to berries and other fruit for food, but as a rule they are carnivorous, feeding chiefly on birds and their eggs, small mammals, as squirrels, hares, rabbits and moles, but chiefly mice of various kinds, and occasionally snakes, lizards and frogs.
On the other hand in the Diplarthra, the tcl group to which the vast majority of modern Ungulates A i n belong, the second or lower row has been shifted altogether towards the inner side of the limb, so that the magnum is brought considerably into relation with the scaphoid, and is entirely removed from the cuneiform, as in most existing mammals.
Each foot is provided with a single strong claw which, opposed to a process on the shin, serves to grasp a hair of the host, all the lice being parasites on different mammals.
One Oriental species (Sciurus caniceps) presents almost the only known instance among mammals of the assumption during the breeding season of a distinctly ornamental coat, corresponding to the breeding plumage of birds.
In the Kisumu province of East Africa even, there are several West African mammals such as the broad-horned tragelaph and the forest pig.
The birds are more West African than the mammals, and include the grey parrot, all the genera of the splendidly-coloured turacoes, the unique " whale-headed stork," and the ostrich.
Be this as it may, the North American mammals described as Moropus and Morotherium, in the belief that they were ground-sloths, are really referable to the ungulate group Ancylopoda.
The indigenous mammals are very few, and the only reptiles are a small lizard and the green turtle.
The deposits near Caylus and in Quercy occupy fissures and pockets in Jurassic limestone, and have yielded a remarkable assemblage of the relics of Tertiary mammals and other fossils.
In their natural state the islands were without land mammals, and the Polynesian immigrants brought but two in their canoes - a dog, now extinct, and a black rat, now rarely seen.
Fossil remains of mammals, fish and reptiles found in the Tertiary deposits of south-western Montana are preserved in the Carnegie Museum at Pittsburg, Pennsylvania, and in the museum of the university of Montana.
Similarly, in the Asiatic islands are found the great mammals of the continent - the elephant, tiger, rhinoceros, anthropoid ape, &c., which are wanting in the Australian region, with which the eastern part of the archipelago is associated.
With the single exception of the Indian sloth-bear, all the species have forty-two teeth, of which the incisors and canines closely resemble those of purely carnivorous mammals; while the molars, and especially the one known as the " sectorial " or " carnassial," have their surfaces tuberculated so as to adapt.
It was said to exceed all other American mammals in ferocity of disposition and muscular strength.
It possesses all the active, courageous and bloodthirsty disposition of the rest of the genus, but its diminutive size prevents it attacking and destroying any but the smaller mammals and birds.
In animals galls occur mostly on or under the skin of living mammals and birds, and are produced by Acaridea, and by dipterous insects of the genus Oestrus.
Bonaparte was chief, placed them at the top of the class, conceiving that they were the analogues of the Primates among mammals.
It is open free to the public and generally contains a good collection of mammals.
The species and varieties of mammals and birds that have a commercial value as farmyard stock or as pets, are for the most part easy to keep, are attractive to the public and may be a source of profit.
Birds and mammals take the first place; the leading collections devote a good deal of attention to reptiles and batrachians; fishes and aquatic invertebrata are most often to be found only when there are special aquaria, whilst non-aquatic invertebrates are seldom to be seen and at most consist of a few moths and butterflies, spiders, scorpions and centipedes, molluscs and crustaceans.
Occasionally special expeditions are arranged to procure numbers of particular birds or mammals, but these are extremely costly and the mortality is usually high.
But the vast majority of birds and mammals not only can endure a large range of temperature, but thrive best when they are subjected to it.
The indigenous fauna of the islands is exceedingly poor in mammals, which are represented mainly by rats and bats.
Cattle and horses, where introduced, are found to degenerate rather rapidly unless the supply of fresh stock is kept up. Birds are more numerous than mammals, among the most important kinds being the pigeons and doves, especially the fruit-eating pigeons.
Most lizards live on animal food, varying from tiny insects and worms to lizards, snakes, birds and mammals, while others prefer a mixed or an entirely vegetable diet.
Early trained as a comparative anatomist, the discovery of Upper Eocene mammals in the gypsum quarries of Montmartre found him fully prepared (1798), and in 1812 appeared his Recherches sur les ossemens fossiles, brilliantly written and constituting the foundation of the modern study of the extinct vertebrates.
New and unheard-of orders of amphibians, reptiles and mammals came to the surface of knowledge, revolutionizing thought, demonstrating the evolution theory, and solving some of the most important problems of descent.
These latter discoveries supply us with the ancestry of the elephants and many other forms. They round out our knowledge of Tertiary history, but leave the problems of the Cretaceous mammals and of their relations to Tertiary mammals still unsolved.
The minute gradations observed by Hyatt, Waagen and all invertebrate palaeontologists, in the hard parts (shells) of molluscs, &c., are analogous to the equally minute gradations observed by vertebrate palaeontologists in the hard parts of reptiles and mammals.
The mutations of Waagen may possibly, in fact, prove to be identical with the " definite variations " or " rectigradations " observed by Osborn in the teeth of mammals.
The ingenuity of nature, however, in adapting animals is not infinite, because the same devices are repeatedly employed by her to accomplish the same adaptive ends whether in fishes, reptiles, birds or mammals; thus she has repeated herself at least twenty-four times in the evolution of long-snouted rapacious swimming types of animals.
Thus Huxley, with true prophetic instinct, found that the sum of primitive characters of all the higher placental mammals points to a stem form of a generalized insectivore type, a prophecy which has been fully confirmed by the latest research.
On the other hand, Huxley's summation of the primitive characters of all the mammals led him to an amphibian stem type, a prophecy which has proved faulty because based on erroneous analysis and comparison.
Among extinct Tertiary mammals we can actually trace the giving off of these radii in all directions, for taking advantage of every possibility to secure food, to escape enemies and to reproduce kind; further, among such well-known quadrupeds as the horses, rhinoceroses and titanotheres, the modifications involved in these radiations can be clearly traced.
Successive discoveries have revealed certain grand centres, such as (1) the marsupial radiation of Australia, (2) the littleknown Cretaceous radiation of placental mammals in the northern hemisphere, which was probably connected in part with the peopling of South America, (3) the Tertiary placental radiation in the northern hemisphere, partly connected with Africa, (4) the main Tertiary radiation in South America.
Food competition among mammals, especially intensified on islands, and the introduction of Carnivora constitute another class of causes.
Great waves of extinction have followed the long periods of the slow evolution of relatively inadaptive types of tooth and foot structure, as first demonstrated by Waldemar Kowalevsky; thus mammals are repeatedly observed in a cul-de-sac of structure from which there is no escape in an adaptive direction.
Little proof is afforded among the mammals of extinction through arrested evolution or through the limiting of variation, although such laws undoubtedly exist.
There are no indigenous mammals; the reptiles belong to New Zealand species.
By far the greater number of hosts are furnished by fishes, birds and mammals.
In considering the occurrence of Trypanosomes in mammals, careful distinction must be drawn between natural or true hosts, which are tolerant of the parasites, and casual ones, which are unaccustomed and unadapted to them.
Very many of the common domestic mammals can be successfully infected (either thus accidentally or else on purpose) with different " pathogenic " Trypanosomes, to which they succumb more or less readily, but they cannot be regarded as the natural hosts of those Trypanosomes.
Similarly with regard to the many other pathogenic Trypanosomes now known, there is undoubtedly, in each case, some indigenous wild animal tolerant of that particular form, which serves as a " latent source of supply " to strange mammals.
Here you find articles in the encyclopedia about mammals.
Most of the fossils of the bess are shells of terrestrial gastropods, but bones of land mammals are also found in not a few places.
Among its characteristic mammals and birds are the lynx, marten, porcupine, northern red squirrel, Beldings and Kennicotts ground squirrels, varyin and snowshoe rabbits, northern jumping mouse, white-throate sparrow, Blackburnian warbler, Audubon.
A southern portion of this zone, comprising a narrow strip along the Gulf Coast from Texas to Florida and up the Atlantic coast to South Carolina, is semi-tropical, and is the northernmost habitation of several small mammals, the alligator (Alligator mississippiensis), the ground dove, white-tailed kite, Florida screech owl and Chapman s night-hawk.
Some of its characteristic mammals and birds are the long-eared desert fox, four-toed kangaroo rats, Sonoran pocket mice, big-eared and tiny white-haired bats, road runner, cactus wren, canyon wren, desert thrashers, hooded oriole, black-throated desert sparrow, Texas night-hawk and Gambels quail.
The area in Florida is too small for characteristic tropical mammals, but it has the true crocodile (Crocodilus americanus) and is the home of a few tropical birds.
Most of the larger American mammals are not restricted to any one faunal zone.
In mammals Sir William Flower pointed out that a generalized type of liver exists, from which that of any mammal may be derived by suppression or fusion of lobes.
The gall-bladder is usually present in mammals, but is wanting in the odd-toed ungulates (Perissodactyla) and Procavia (Hyrax).
Most mammals have certain portions of the skin specially modified and provided with glands secreting odorous and fatty substances characteristic of the particular species.
Rodents may be characterized as terrestrial, or in some cases arboreal or aquatic, placental mammals of small or medium size, with a milk and a permanent series of teeth, plantigrade or partially plantigrade, and generally five-toed, clawed (rarely nailed or semi hoofed) feet, clavicles or collar-bones (occasionally imperfect or rudimentary), no canine teeth, and a single pair of lower incisors, opposed by only one similar and functional pair in the upper jaw.
Rodents include by far the greater number of species, and have the widest distribution, of any of the orders of terrestrial mammals, being in fact cosmopolitan, although more abundant in some parts, as in South America, which may be considered their headquarters, than in others, as in Australasia and Madagascar, where they are represented only by members of the mouse-group, or Myoidea.
As to the ancestral stock of the order, it has been suggested that this is represented by certain Lower Eocene European and North American mammals, at one time regarded as primitive Primates.
Whatever may be the true affinity of these problematical mammals, undoubted rodents are known from the Lower Eocene of both Europe and North America.
Mammals are not numerous; they include the cuscus, several species of bat, and some rats of great size.
A day-flying bat, whales and dolphins are about the only indigenous mammals; hogs, dogs and rats had been introduced before Cook's discovery.
The articulation between the tibia and astragalus is more complex than in other mammals, the end of the malleolus entering into it.
That the group originated in Africa there can be no reasonable doubt; and it is remarkable that so early as the Upper Eocene the types in existence differed comparatively little in structure from the modern forms. In fact the hyraxes were then almost as distinct from other mammals as they are at the present day.
With birds and mammals, however, there is no doubt that complete albino individuals do occur; and among species which, like the jackdaw, certain deer and rabbits, are normally deeply pigmented.
Since then (1904) Miss Florence Durham has shown that if the skins of young or embryonic mammals (rats, rabbits and guinea-pigs) be ground up and extracted in water, and the expressed juice be then incubated with solid tyrosin for twentyfour hours, with the addition of a very small amount of ferrous sulphate to act as an activator, a pigmentary substance is thrown down.
The skins of albinoes gave no results Not only have such results been obtained with sponges, insects, cephalopods, birds and mammals, but Em.
A long and bushy tail, for instance, is a useful balancer and is a not uncommon feature in mammals which lead an active arboreal life.
The mammals in Poland, however, do not exceed fifty species.
It is thoroughly terrestrial, selecting for its retreat in the daytime holes made by small mammals, or interstices between stones.
Besides editing his friend Willughby's books, Ray wrote several zoological works of his own, including Synopsis methodica Animalium Quadrupedum et Serpentini Generis (1693), that is to say, both mammals and reptiles, and Synopsis methodica Avium et Pisciurn (1713); the latter was published posthumously, as was also the more important Historia Insectorum (1710), which embodied a great mass of Willughby's notes.
The bear and fox are the only land mammals; insects are rare; but the avifauna is of interest, and the Jackson expedition distinguished several new species.
This rodent is one of the commonest of British mammals, and frequents fields, woods and gardens in numbers, often doing considerable damage owing to its fondness for garden produce.
The water-rat is perhaps the most often seen of all English mammals, owing to its diurnal habits.
The hinder part of the body is much contracted, and the femur long and vertically placed, so that the knee-joint is lower in position, and the thigh altogether more detached from the abdomen than in most mammals.
Finally, the Tylopoda differ not only from other ungulates, but from all other mammals, in the fact that the red corpuscles of the blood, instead of being circular in outline, are oval as in the inferior vertebrate classes.
In North America, apart from certain still older and more primitive mammals, with teeth of the tubercular type, the earliest known form which can definitely be included in the camel-series is Protylopus, of the Uinta or Upper Eocene.
The indigenous mammals of the Canary Islands are very few in number.
It has been calculated that about 595 different species of vertebrate animals are recorded or still to be found in Palestine - about 113 being mammals (including a few now extinct), 348 birds (including 30 species peculiar to the country), 91 reptiles and 43 fishes.
It may also be noticed that in mammals and birds which hop on two legs, such as jerboas, kangaroos, thrushes and finches, the proportionate length of the thigh-bone or femur to the tibia and foot (metatarsus and toes) is constant, being 2 to 5; in animals, on the other hand, such as hares, horses and frogs, which use all four feet, the corresponding lengths are 4 to 7.
When first seen by Europeans it contained no mammals except a large fruit-eating bat (Pteropus vulgaris), which is plentiful in the woods; but several mammals have been introduced, and are now numerous in the uncultivated region.
Although the Philippines are commonly held to form an eastern extension of the Indo-Malayan sub-region, there is a large amount of specialization in the fauna of the islands eastward of the Palawan group. Mammals are scarce.
The islands are as rich in birds as they are poor in mammals, the total number of species recorded up to 1906 being 693, of which about one-half are peculiar to the Philippines.
Most of the mammals characteristic of the latter region are lacking.
In this paper he made public the results of his discoveries in the cave of Aurignac, where evidence existed of the contemporaneous existence of man and extinct mammals.
On land, however, whither they resort to breed, they seek food of their own taking, whether small mammals, little birds, insects or berries; but even here their uncommon courage is exhibited, and they will defend their homes and offspring with the utmost spirit against any intruder, repeatedly shooting down on man or dog that invades their haunts, while every bird almost, from an eagle downwards, is repelled by buffets or something worse.
There seems to be no doubt that fossilized remains of the dingo occur intermingled with those of the extinct Australian mammals, such as giant kangaroos, giant wombats and the still more gigantic Diprotodon.
Ogilvy in a Catalogue of Australian Mammals, published at Sydney in 1892; the writer going however one step further and expressing the belief that the dingo is the ancestor of all domesticated dogs.
Bison no longer roam the plains, and the elk has been driven out; but among the larger mammals still to be found in certain districts are the deer, prong-horn (in small numbers), puma, coyote, timber wolf, lynx (Lynx rufus and Lynx Canadensis) and the black and grizzly bear.
Similarly nearly all our domestic mammals except the sheep have become feral somewhere or other, whether by intentional liberation or by escape; but the smaller ones more than the larger, such as pigs, goats, dogs and cats.
Blanford (Fauna of British India, " Mammals") thinks that the presence of the Indian form, Viverricula malaccensis, in Socotra, the Comoro Islands and Madagascar is due to the assistance of man.
The introduction of mammals has been largely influenced by economic conditions, when, indeed, it was not absolutely accidental and unavoidable; but in the case of birds it has been more gratuitous, so to speak, in many cases, and hence is looked upon with especial dislike by naturalists.
There are no large mammals in all this extensive region except the Cetacea and a species of the Phocidae of southern waters.
The Baluch Siwaliks afford us strange glimpses into a recent geological past, when the same gigantic mammals roamed along the foot of these wild hills as once inhabited the tangled forests below the Himalaya.
The Siwalik fossils contain 84 species of mammals of 45 genera, the whole bearing a marked resemblance to the Miocene fauna of Europe, but containing a larger number of genera still existing, especially of ruminants, and now held to be of Pliocene age.
Its animal life is in the main distinguished in species only from that of the Upper Sonoran belt, including among birds, the desert sparrow, desert thrasher, mocking-bird, hooded oriole; and among mammals small nocturnal species of kangaroo rats, pocket mice, mice and bats.
The country is so arid that it supports only desert birds and mammals.
The mammals include black bear, deer, lynx, porcupine, fox, squirrels, hares, rabbits, musk rats, minks, weasels, skunks and woodchucks.
This consists for the most part of the smaller mammals and poultry; although the association in packs enables these marauders to hunt down antelopes and sheep. When unable to obtain living prey, they feed on carrion and refuse of all kinds, and are thus useful in removing putrescent matter from the streets.
The red, or Virginia, deer and the grey fox are still found in circumscribed localities; and of the smaller mammals, the squirrel, chipmunk, rabbit, raccoon and opossum are still numerous.
The lists of insects, birds and mammals are especially noteworthy.'
Their food consists of any mammals or birds which they can overpower.
While it is evident that high importance must be attached to the adaptation of the human body to the life of diversified intelligence and occupation he has to lead, this must not be treated as though it were the principal element of the superiority of man, whose comparison with all lower genera of mammals must be mainly directed to the intellectual organ, the brain.
The fishes of the Palaeozoic age are in no respect the ancestors of the reptiles of the Secondary age, nor does man descend from the mammals which preceded him in the Tertiary age.
It is true that to some extent these means of utterance are common to the lower animals, the power of expressing emotion by cries and tones extending far down in the scale of animal life, while rudimentary gesture-signs are made by various mammals and birds.
Though, according to breeders, evidence of telegony has been found in nearly all the different kinds of domestic mammals and birds, most stress has been laid on instances of "infection" in the horse and dog families.
It is deficient in mammals, of which the only varieties are the rat and bat.
Moldavia and the Baragan Steppe resemble the Russian prairies in their variety of molluscs and the lower kinds of mammals.
McEnery, who found worked flints in intimate association with the bones of extinct mammals.
The common sheep-tick (Ixodes vicinus) of England, for example, infects cattle and dogs as well as sheep; and the pathogenetic Ixodidae above mentioned occur parasitically upon other mammals than those to which they convey the diseases specified.
Reptiles are infested as well as mammals, and it is no uncommon thing to find specimens of Ixodidae of various kinds adherent to tortoises, snakes and lizards.
The class-name (modified by the French into Mammiferes, and replaced in German by the practically equivalent term Sugethiere) has been anglicized into " Mammals " (mammal, in the singular).
Of recent years, and more especially in America, it has become a custom to designate the study of mammals by the term " mammalogy."
As regards existing forms of life, the limitations of the class are perfectly well defined and easy of recognition; for although certain groups (not, by the way, whales, which, although excluded in popular estimation from the class, are in all essential respects typical mammals) are exceedingly aberrant, and present structural features connecting them with the lower vertebrate classes, yet they are by common consent retained in the class to which they are obviously most nearly affiliated by their preponderating characteristics.
There is thus at the present day a great interval, unbridged by any connecting links, between mammals and the other classes of vertebrates.
Not so, however, when the extinct forms of vertebrate life are taken into consideration, for there is a group of reptiles from the early part of the Secondary, or Mesozoic period, some of whose members must have been so intimately related to mammals that, were the whole group fully known, it would clearly be impossible to draw a distinction between Mammalia on the one hand and Reptilia on the other.
Considered collectively, mammals, which did not make their appearance on the earth for some time after reptiles had existed, are certainly the highest group of the whole vertebrate sub-kingdom.
In mammals, as in other classes, there are low as well as high forms; but by any tests that can be applied, especially those based on the state of development of the central nervous system, it will be seen that the average exceeds that of any other class, that many species of this class far excel those of any other in perfection of structure, and that it contains one form which is unquestionably the culminating point amongst organized beings.
Mammals, then, are vertebrated animals, possessing the normal characteristics of the members of that primary division of the animal kingdom.
A four-chambered heart, with a complete double circulation, and warm blood (less markedly so in the lowest group than in the rest of the class), distinguish mammals from existing reptiles, although not from birds.
In the majority of mammals both pairs of limbs are well developed and adapted for walking or running.
In the great majority of mammals the hind extremity of the axis of the body is prolonged into a tail.
Very generally the tail has distinctly the appearance of an appendage, but in some of the lower mammals, such as the thylacine among marsupials, and the aard-vark or ant-bear among the edentates, it is much thickened at the root, and passes insensibly into the body, after the fashion common among reptiles.
Among jumping animals it may serve as a balance, as in the case of jerboas and kangaroos, while in the latter it is also used as a support when resting; among many hoofed mammals it is used as a fly-whisk; and in whales and dolphins, as well as in the African Potamogale and the North American musquash, it plays an important part in swimming.
As already indicated, the limbs of different mammals are specially modified for various modes of life; and in many cases analogous modifications occur, in greater or less degree, throughout the entire body.
As regards the feet, a reduction in the number of digits from the typical five is a frequent feature, more especially among the hoofed mammals, where the culmination in this respect is attained by the existing members of the horse tribe and certain representatives of the extinct South American Proterotheriidae, both of which are monodactyle.
Brief reference may also be made to the morphological importance of extraordinary length or shortness in the skulls of mammals - dolichocephalism and brachycephalism; both these features being apparently characteristic of specialized types, the former condition being (as in the horse) often, although not invariably, connected with length of limb and neck, and adaptation to speed, while brachycephalism may be correlated with short limbs and an abbreviated neck.
In point of bodily size mammals present a greater range of variation than is exhibited by any other living terrestrial animals, the extremes in this respect being displayed by the African elephant on the one hand and certain species of shrewmice (whose head and body scarcely exceed an inch and a half in length) on the other.
In regard to sense-organs, ophthalmoscopic observations on the eyes of living mammals (other than man) have revealed the existence of great variation in the arrangement of the bloodvessels, as well as in the colour of the retina; blue and violet seem to be unknown, while red, yellow and green form the predominating shades.
In the main, the various types of minute ocular structure correspond very closely to the different groups into which mammals are divided, this correspondence affording important testimony in the favour of the general correctness of the classification.
Man and monkeys alone possess parallel and convergent vision of the two eyes, while a divergent, and consequently a very widely extended, vision is a prerogative of the lower mammals; squirrels, for instance, and probably also hares and rabbits, being able to see an object approaching them directly from behind without turning their heads.
The presence of only seven vertebrae in the neck is a very constant feature among mammals; the exceptions being very few.
A large number of mammals possess a perforation, or foramen, on the inner side of the lower end of the humerus, and also a projection on the shaft of the femur known as the third trochanter.
It is remarkable that it should persist in the spectacled bear of the Andes, although it has disappeared in all other living members of the group. The third trochanter of the femur, on the other hand, can scarcely be regarded as primitive, seeing that it is absent in several of the lower groups of mammals.
In the greater number of mammals the skin is more or less densely clothed with a peculiarly modified form of epidermis known as hair.
These tufts or groups likewise display an orderly and definite grouping in different mammals, which suggests the origin of such groups from the existence in primitive mammals of a scaly coat comparable to that of reptiles, and indeed directly inherited therefrom.
Remarkable differences in the direction or slope of the hair are noticeable on different parts'of the body and limbs of many mammals, especially in certain apes, where the hair of the fore-limbs is inclined towards the elbow from above and from below.
Many mammals have a longer hairy coat in winter, which is shed as summer comes on; and some few, which inhabit countries covered in winter with snow, as the Arctic fox, variable hare and ermine, undergo a complete change of colour in the two seasons, being white in winter and grey or brown in summer.
Trouessart, it appears that much the same kind of action takes place in the hairs of mammals that turn white in winter.
The winter whitening of mammals is, therefore, precisely similar to the senile bleaching of human hair, no shift of the coat taking place.
The African golden-moles (Chrysochloris), the desmans or water-moles (Myogale), and the West African Potamogale velox, are remarkable as being the only mammals whose hair reflects those iridescent tints so common in the feathers of tropical birds.
With few exceptions, the terminal extremities of the digits of both limbs of mammals are more or less protected or armed by epidermic plates or sheaths, constituting the various forms of nails, claws or hoofs.
Scent-glands, Eec. - Besides the universally distributed sweatglands connected with the hair-system, most mammals have special glands in modified portions of the skin, often involuted to form a shallow recess or a deep sac with a narrow opening, situated in various parts of the surface of the body, and secreting odorous substances, by the aid of which individuals recognize one another.
In the great majority of mammals the teeth form a definite series, of which the hinder elements are of a more or less complex type, while those in front are simpler.
This double series of teeth thus forms a very characteristic feature of mammals generally.
In mammals with two sets of teeth the number of those of the permanent series preceded by milk-teeth varies greatly, being sometimes, as in marsupials and some rodents, as few as one on each side of each jaw, and in other cases including the larger portion of the series.
In mammals, such as dolphins and some armadillos, which have a large series of similar teeth, not always constant in number in different individuals, there may indeed be differences in the two sides; but, apart from these in describing the dentition of any mammal, it is generally sufficient to give the number and characters of the teeth of one side only.
In a very large number of mammals the teeth of different parts of the series are more or less differentiated in character; and, accordingly, have different functions to perform.
Many mammals have, between these two sets, a tooth at each corner of the mouth, longer and more pointed than the others, adapted for tearing or stabbing, or for fixing struggling prey.
This general arrangement is obvious in a considerable number of mammals; and examination shows that, under great modifications in detail, there is a remarkable uniformity of essential characters in the dentition of a large number of members of the class belonging to different orders and not otherwise closely allied, so much that it LS ' 'C FIG.
When, as is the case among nearly all existing mammals with the exception of the members of the genera Sus (pigs), Gymnura (ratshrew), Talpa (moles) and Myogale (desmans) the number of teeth is reduced below the typical forty-four, it appears to be an almost universal rule that if one of the incisors is missing it is the second, or middle one, while the premolars commence to disappear from the front end of the series and the molars from the hinder end.
With the exception of the Cetacea, most of the Edentata, and the Sirenia, in which the teeth, when present, have been specialized in a retrograde or aberrant manner, the placental mammals as a whole have a dentition conforming more or less closely to the foregoing type.
In very few mammals are teeth entirely absent.
Even in the whalebone whales their germs are formed in the same manner and at the same period of life as in other mammals, and even become partially calcified, although they never rise above the gums, and completely disappear before birth.
In different groups of mammals the dentition is variously specialized in accordance with the nature of the food on which the members of these groups subsist.
Opinions differ as to the mode in which the more complicated cheek-teeth of mammals have been evolved from a simpler type of tooth.
The type is, moreover, common among the mammals of the early Eocene, and still more so in those of the Jurassic epoch; this forming one of the strongest arguments in favour of the tritubercular theory.
The mouth of the great majority of mammals is peculiar for being guarded by thick fleshy lips, which are, however, absent in the Cetacea; their principal function being to seize the food, for which purpose they are endowed, as a rule, with more or less strongly marked prehensile power.
Its modifications of form in different mammals are numerous.
Salivary glands, of which the most constant are the parotid and the submaxillary, are always present in terrestrial mammals.
The alimentary,or intestinal, canal varies greatly in relative length and capacity in different mammals, and also offers manifold peculiarities of form, being sometimes a simple cylindrical tube of nearly uniform calibre throughout, but more often subject to alterations of form and capacity in different portions of its course - the most characteristic and constant being the division into an upper and narrower and a lower and wider portion, called respectively the small and the large intestine; the former being arbitrarily divided into duodenum, jejunum and ileum, and the latter into colon and rectum.
It is only in herbivorous mammals that the caecum is developed to this great extent, and among these there is a complementary relationship between the size and complexity of the organ and that of the stomach.
These caeca occur in birds (as in mammals) at the junction of the small with the large intestine; and while in ordinary perching-birds they are reduced to small nipplelike buds of no functional importance, in many other birds - owls for instance - they form quite long receptacles.
With the aid of these instances of paired caeca, coupled with the frequent existence of a rudiment of its missing fellow when only one is functional, the author has been enabled to demonstrate conclusively that these double organs in birds correspond in relations with their normally single representative in mammals.
It has, indeed, been suggested that in the earlier mammals the liver was a simple undivided organ.
Of the European Jurassic (or Oolitic) mammals our knowledge is unfortunately very imperfect; and from the scarcity of their remains it is quite probable that they are merely stragglers from the region (possibly Africa) where the class was first differentiated.
It is not till the early Eocene that mammals become a dominant type in the northern hemisphere.
It is now practically certain that mammals are descended from reptiles.
This does not mean that any of the living groups of reptiles can claim their honour of ancestry, but it means that the mammals have branched where the principal reptilian groups meet, and that is a long way back.
It may be explained that the Theromorpha, or Anomodontia, are those extinct reptiles so common in the early Secondary (Triassic) deposits of South Africa, some of which present a remarkable resemblance in their dentition and skeleton to mammals, while others come equally near amphibians.
A difficulty naturally arises with regard to the fact that in reptiles the occipital condyle by which the skull articulates with the vertebral column is single, although composed of three elements, whereas in amphibians and mammals the articulation is formed by a pair of condyles.
The fate of the reptilian quadrate bone (which is reduced to very small dimensions in the Anomodontia) has been referred to in an earlier section of the present article, where some mention has also been made of the disappearance in mammals of the hinder elements of the reptilian lower jaw, so as to leave the single bone (dentary) of each half of this part of the skeleton in mammals.
Most of the earliest known mammals appear to be related to the Marsupialia and Insectivora.
Others however (inclusive of Tritylodon and Microlestes, if they be really mammals), seem nearer to the Monotremata; and the question has yet to be decided whether placentals and marsupials on the one hand, and monotremes on the other are not independently derived from reptilian ancestors.
Matthew, an American palaeontologist, considers himself provisionally justified in so extending it as to include all mammals.
That is to say, he believes that, with the exception of the duckbill and the echidna, the mammalian class as a whole can lay claim to descent from small arboreal forms. This view is, of course, almost entirely based upon palaeontological considerations; and these, in the author's opinion, admit of the conclusion that all modern placental and marsupial mammals are descended from a common ancestral stock, of which the members were small in bodily size.
These ancestral mammals, in addition to their small size, were characterized by the presence of five toes to each foot, of which the first was more or less completely opposable to the other four.
Accordingly, it was at this epoch that the small ancestral insectivorous mammals first forsook their arboreal habitat to try a life on the open plains, where their descendants developed on the one hand into the carnivorous and other groups, in which the toes are armed with nails or claws, and on the other into the hoofed group, inclusive of such monsters as the elephant and the giraffe.
Existing mammals may be primarily divided into three main groups, or subclasses, of which the second and third are much more closely related to one another than is either of them to the first.
The Insectivora are certainly the lowest group of existing placental mammals, and exhibit many signs of affinity with marsupials; they may even be a more generalized group than the latter.
If, however, the so-called Proglires of the lower Eocene are really ancestral rodents, the order is brought into comparatively close connexion with the early generalized types of clawed, or unguiculate mammals.
There is the further possibility that creodonts may be directly descended from the carnivorous reptiles; a descent which if proved might introduce some difficulty with regard to the abovementioned theory as to the arboreal ancestry of mammals generally.