Tomistoma.–The general configuration of the skull and snout is that of Gavialis, but the nasal bones are long and reach the premaxillaries, although not the nasal groove, thereby separating the maxillaries. The first and fourth mandibular teeth fit into notches of the upper jaw, while most of the others fit into pits between the teeth of the upper jaw. About twenty upper and eighteen lower teeth on each side.
T. schlegeli, the only species, reaches a length of 15 feet; it inhabits the rivers and swamps of Borneo, Malacca, and Sumatra. Fossil specimens of Tomistoma have been found in the Miocene of Malta and Sardinia. Gavialosuchus of the Miocene of Hungary is closely allied.
Fam. 5. Atoposauridae.–The few members of this family, Atoposaurus, Alligatorium, and Alligatorellus, lived in the Upper Oolitic period of France, and were small, about one foot in length. The vertebrae are amphicoelous. The nasal groove is divided by a prolongation of the nasal bones. The head is short, and in its general shape rather like that of a lizard.
Fam. 6. Goniopholidae, in the Purbeck and Wealden of Europe and the corresponding level of North America. The vertebrae are amphicoelous. The choanae are still elongated but are situated between the palatines and pterygoids. The premaxillaries are rather large, and each sends a broad triangular process between the nasal and maxillary. The nasals are broad and are well separated from the nasal groove. The splenials help to form the mandibular symphysis.
Goniopholis.–The general configuration of the skull is rather like that of Crocodilus vulgaris. There is a pair of deep notches in the upper jaw for the reception of the lower canine teeth. G. simus and G. crassidens in England and continental Europe, and others in Colorado, were large-sized Crocodiles, some with a skull 2 feet in length. The dermal armour consisted of a pair of dorsal rows, a thoracic and an abdominal shield, composed as in the Teleosauridae of six to eight longitudinal sutured rows.
Fam. 7. Crocodilidae.–Beginning in the Upper Cretaceous period of Europe and North America, many forms of Crocodiles, Alligators, and Caimans existed in the Tertiary period in America, Europe, and India; persisting in Europe until the Plistocene. The vertebrae are procoelous. The choanae are completely surrounded by the pterygoids. The nasals reach the nasal groove, except in Crocodilus cataphractus. The orbits are larger than the small supratemporal fossae, and always continuous superficially with the lateral temporal fossae, the postfronto-jugal bridge not reaching the surface. The dorsal armour consists of more than one pair of longitudinal rows, while the ventral armour is much reduced in thickness or absent.
Diplocynodon.–Common in the Oligocene and Miocene of Europe, e.g. D. hastingsiae. The skull resembles that of the Alligators, but has a pair of lateral notches in the premaxilla for the reception of the third, and sometimes also of the fourth mandibular tooth. The ventral armour is still rather strong.
Crocodilus.–The fourth mandibular tooth fits, as a rule, into a notch in the upper jaw. The other teeth are more or less interlocked with those of the other jaw. The fifth upper tooth is the largest. The nasal bones form the posterior border of the nasal groove, but do not extend into it as a septum. The bony scutes of the dorsal shield are keeled, and stand closely together, being rarely united by suture; and they form from four to six principal rows.
Crocodiles have occurred since the Upper Chalk in Europe; many species existed in the Tertiary epoch in Europe and North America, decreasing in numbers in the Pliocene and disappearing with the beginning of the Plistocene. About ten recent species are known, and these have now a somewhat scattered distribution; namely, three species in Africa, one of them extending into Syria; three in tropical America and the West Indian Islands; the rest in the Malay, Indian, and North Australian countries.
C. palustris.–The "Mugger" of India. The premaxillo-maxillary suture is transverse, as in the Alligators. The adults retain the five teeth in each half of the premaxilla. The mandibular symphysis is short, extending only to the level of the fourth or fifth tooth. The snout is stout, rather broad; the top of the head is rough but without any ridges. The upper and lower jaw each contain nineteen teeth on either side. The nuchal scutes, six in number, are packed closely together, the four biggest forming a square. Four smaller scutes are arranged in a curved line on the occiput. The dorsal shield is composed of four, sometimes of six rows of larger scutes, of which the central pair is the broadest. The fingers are webbed at the base; the outer toes are broadly webbed, and the outer edge of the hind-limbs is turned into a serrated fringe. The general colour of the upper parts is dark olive-brown; the young are pale, with black spots. The length of twelve feet is considered a fair average size for a large specimen.