Carnivora And Pholidota

The final clade to be noted within Laurasiatheria consists of Carnivora plus Pholidota. This rather surprising pairing of carnivorous mammals with pangolins emerges from recent molecular studies (see Box 10.6), and it was not particularly expected from morphological studies. The pairing of Carnivora and Artiodactyla within Ferungulata was, on the other hand, long argued by mammalogists.

The living meat-eaters, cats, dogs, hyaenas, weasels and seals are members of the Order Carnivora. These animals are characterized by the possession of a pair of carnassial teeth on each side of the jaws: the upper premolar 4 and the lower molar 1 are enlarged as longitudinal blades that shear across each other like a powerful pair of scissor blades (Figure 10.38(a,b)). Certain forms that crush bones, such as the hyaenas, have broad premolars with thick enamel and powerful jaw adductors. Bone-crushing dogs have broad molars. The canine teeth are generally long and used in puncturing the skin of prey animals, whereas carnivores use their incisors for grasping and tearing flesh, as well as for grooming.

It has usually been assumed that the modern carnivores are related to certain creodonts (see p. 333), but the exact origins of modern cats, dogs, bears and seals

Hesperocyon Teeth

Fig. 10.38 Carnivore teeth and jaws: (a,b) teeth of the modern cat Felis in occlusal and lateral views, showing the camassials (upper premolar 4 (P4) and lower molar 1 (Mj)); (c) skull of the Eocene miacid Vulpavus; (d) the modern tiger Panthera; (e) piercing and tearing flesh by the Pleistocene sabre-tooth Smilodon; (f) the late Eocene dog Hesperocyon. [Figures (a,b,d) after Savage and Long, 1986; (c,f) after Matthew, 1909; (e) based on Akersten, 1985.]

Fig. 10.38 Carnivore teeth and jaws: (a,b) teeth of the modern cat Felis in occlusal and lateral views, showing the camassials (upper premolar 4 (P4) and lower molar 1 (Mj)); (c) skull of the Eocene miacid Vulpavus; (d) the modern tiger Panthera; (e) piercing and tearing flesh by the Pleistocene sabre-tooth Smilodon; (f) the late Eocene dog Hesperocyon. [Figures (a,b,d) after Savage and Long, 1986; (c,f) after Matthew, 1909; (e) based on Akersten, 1985.]

are still controversial (Wyss and Flynn, 1993; Flynn and Nedbal, 1998).

10.11.1 Terrestrial carnivores

The earliest true carnivores date from the late Palaeocene and early Eocene. The miacid Vulpavus has a long skull (Figure 10.38(c)) and probably hunted small tree-living mammals. Miacids were small cat-like tree-and ground-dwellers, with short powerful limbs and plantigrade feet. The auditory region of miacids was presumably covered by connective tissue, without an ossified auditory bulla, as in many primitive mammals of the Palaeocene and Eocene. In later carnivores the auditory bulla became ossified, but in two different ways, and these define two major lines of carnivore evolution. In the feliforms, a main component of the auditory bulla is the ectotympanic, the bony ring that primitively supported the ear drum (see p. 295). In the caniforms, the auditory bulla is formed mainly from entotympanics, new bony structures. In addition, feliforms have intrabullar septa, which caniforms lack.

The modern groups began to diverge in the late Eocene and early Oligocene. The feliforms include the cats, civets, mongooses, hyaenas and the extinct nim-ravids. The nimravids, from the Eocene to Miocene of Europe,Asia,Africa and North America (Peigne,2003), were extremely cat-like in form and generally have sabre teeth. The civets (Viverridae) date back to the late Eocene, and the mongooses (Herpestidae) to the late Oligocene. They are abundant today in tropical Africa and Asia and feed on a mixed diet of insects, small vertebrates and fruit. Early viverrids gave rise to the hyaenas (Hyaenidae) in the Miocene, and the cats (Felidae), which are known from the early Oligocene onwards.

During the evolution of the nimravids and cats, dagger- and sabre-teeth arose independently several times (Turner and Antón, 1997; Janis et al., 1998), and most extinct forms have larger canines than in modern lions and tigers (Figure 10.38(d, e)). The sabre-toothed cats of North America and Europe are remarkably similar to the unrelated marsupial sabre-tooths of South America (see p. 315), which share specific predatory adaptations: the lower jaw can be dropped very low; the sabre, up to 150 mm long, has a backwards curve; and it is flattened like a knife blade, rather than being round. Modern cats diversified in the Pleistocene, and some, such as the European cave lion (see Box 10.10), are extinct.

The most famous sabre-toothed cat, Smilodon, fed on the carcasses of elephants and other large herbivores in the late Pleistocene. It probably used its sabres for cutting out chunks of flesh from its prey, rather than stabbing (Akersten, 1985). Smilodon attacked a vulnerable young elephant, say, by sinking its teeth in superficially, closing the jaws and levering a chunk of flesh off using its powerful neck muscles (Figure 10.38(e)). The prey was left to bleed to death. Huge collections of Smilodon and other large carnivores, such as coyote,

American lion, bobcat, puma and lynx, have been found in the Rancho La Brea tar pits in California, USA. These carnivores have signficantly more broken teeth than are found in living large carnivores, and this indicates that late Pleistocene carnivores were competing more actively for prey (Van Valkenburgh and Hertel, 1993). The massive canines of Smilodon were not damaged more often than the other teeth and this confirms that it did not simply stab its prey. When the abundant large elephants, rhinoceroses, wild cattle and the like died out at the end of the Pleistocene, the sabre-tooths also disappeared.

The second carnivore group, the caniforms, includes the dogs (Canidae) and the arctoids, the bears, raccoons, weasels and seals. A typical early dog, Hesperocy-on (Figure 10.38(f)),has long limbs and digitigrade feet (only the toes touch the ground), but it was probably not a fast runner. The weasels (Mustelidae) and raccoons (Procyonidae) are known first from the early Miocene and late Oligocene respectively. The amphicy-onids, extinct medium- to very large dog-like animals, are best known from the upper Eocene to upper Miocene of North America, with representatives also in Africa and Eurasia. The bears (Ursidae) arose in the late Eocene and they were particularly successful in the northern hemisphere. Early forms were rather dog-like. The large extinct Pleistocene cave bear of Europe is

0 0

Post a comment