Physical characteristics

Dasyuromorphians are quadrupedal (move on four legs), with four toes on the front feet, four or five toes (including

The Tasmanian devil (Sarcophilus laniarius) has teeth capable of crushing bone. (Photo by © Erwin & Peggy Bauer. Bruce Coleman, Inc. Reproduced by permission.)

a clawless toe called a hallux) on the hind feet, long tails and long, pointed snouts, and are considerably uniform in body shape despite the large size variation, from 0.14 oz (4 g) to more than 65 lb (30 kg). Extreme exceptions in body form include the kultarr, which has elongated hind legs and bounds rather than runs, and the robust form and massive skull, teeth and jaw musculature of the specialist scavenger, the Tasmanian devil. Unlike placental carnivores, the fleshy foot pad of thylacines and dasyures extends to the heel and wrist joint, which may contact the ground when stationary or moving slowly, although most species are digitigrade (run on the toes) when moving fast. Arboreal (tree-dwelling) species tend to have broader feet and a better-developed, more dexterous hallux. Some dasyurid species store fat in the tail. None are prehensile and in some such as the thylacine, the tail is semi-rigid. Tail length is generally shorter than body length, except in the numbat and in the long-tailed dunnart.

The dentition is polyprotodont, meaning many incisors (four upper, three lower), which distinguishes this group of marsupials from the Diprotodontia or herbivorous marsupials. Premolars number three in thylacines and numbats, two in dasyures. All molar teeth (four in thylacines and dasyures; five in numbats) are similar in form, in contrast with the differentiation of slicing and grinding functions into separate teeth in the placental carnivores. Thylacine and dasyure molars each retain meat-slicing (carnassial) cusps and function, and grinding surfaces. This marsupial feature may be a consequence of reproductive mode. Permanent teat-attachment during tooth development appears to suppress the eruption of the deciduous teeth, which remain vestigial, leading to early eruption of the permanent dentition. Each of these permanent molars must, in turn, function as slicing and grinding/crushing teeth when they first erupt, and then either specialized slicing or crushing teeth when they achieve their final position in the mature jaw. Tooth structure ranges from simple, cuspless molars in the termite-eating numbat, to the more complex slicing/crushing molars of the other two families. The degree of carnassiality (or meat-slicing function) grades with diet. Highly carnivorous taxa, such as thylacines and devils, have well-developed carnassial cusps, reduced crushing surfaces, and molar orientation is more antero-posterior. This is particularly the case in the two rear molars, which are biomechanically positioned in adults for maximal slicing function, in a position halfway along the jaw bone comparable to the carnassial tooth in placental carnivores. As the diet becomes more insectivorous, the crushing surfaces (the rear part of each molar tooth) become larger

A mulgara (Dasycercus cristicauda) searches grass tops for food near Alice Springs, Northern Territory, Australia. (Photo by Photo Researchers, Inc. Reproduced by permission.)

A spotted-tailed quoll (Dasyurus maculatus) gets a drink in eastern Australia. (Photo by E. & P. Bauer. Bruce Coleman, Inc. Reproduced by permission.)

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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