Crocodylians

General Characters

• Large and powerful.

• Significant dermal armor.

• Dorsal scales fused to dermal bone on head.

• Together w/ birds, the sole remnants of the archosaurs.

• Have 4 chambered heart.

• Have complete secondary palate.

• No sperm storage.

General Characters

• Females exhibit parental care.– Females construct thermally beneficial nests.– Females guard nests.– Females assist young in emergence from eggs.

Alligatoridae

• Tropical americas in distribution.

• Restricted to fresh water.

• Lack lingual salt gland.

• Distinguishing characteristics:– mandibular teeth fit inside the upper jaw, so no

teeth are visible when the jaws are closed.– American alligators have a more rounded snout

than crocodiles.

Alligatoridae

• Alligator– 2 species

– warm temperate China and southeastern USA.

• Caimans– Caiman

– Melanosuchus

– Paleosuchus

– found in tropical Americas

Alligator mississipiensis

Caiman crocodylus

Paleosuchus trigonotus

Alligatoridae

• Thermal tolerance– Alligator mississipiensis can tolerate freezing

conditions … it does nothibernate.– Alligators lie with tails in deep warm water,

and snouts above the water line to breeth. Warmth of snout prevents water from freezing to snout.

Alligatoridae

• Habitats– Alligator mississipiensis occurs in lakes,

swamps, marshes, and rivers. 4m TL– Alligator sinensis is restricted to lakes and

rivers of lower Yangtse and coastal marshes. 3m TL. It is endangered.

– Caimans occupy all freshwater habitats.

Alligatoridae

• Caiman habitats:– Paleosuchus (1.5m TL): small rainforest

streams.– Caiman: large swamps, rivers, and lakes.– Melanosuchus (5m TL): large swamps, rivers,

and lakes.

Crocodylidae

• Distribution is worldwide in tropical freshwater and nearshore habitats.

• 4th mandibular tooth on each side lies exposed on the outside of the upper jaw when the mouth is closed.

• All have lingual salt glands (help maintain osmotic balance in marine habitats).

Crocodylidae• Crocodylinae– 3 genera: Crocodylus (10+

species), Osteolaemus, Mecistops.

– Crocodylus occurs worldwide. Often one species occupies freshwater while a second occupies estuarine and marine.

– In America, C. acutus is saltwater species and C. intermedius, C. moreletii, and C. rhombifer are freshwater.

– Osteolaemus is dwarf (2m) from W. Africa

• Tomistominae– Single species; Tomistoma

schlegeli - false gharial (4m TL).

– Lives in rivers and swamps of Malay peninsula and East Indies.

– Both first and 4th mandibular teeth lie outside closed mouth.

– As in true Gharails, narrow snout, and fish eating habit.

Gavialidae

• Only 1 species remaining, Gavialis gangeticus.

• Occurs only in upper reaches of the Indus, Ganges, Brahmputra, and Mahanandi rivers.

• Long slender snout, aids in piscivorous diet.

• 4th mandibular tooth and all anterior teeth are exposed when mouth is closed.

Gavialidae• Lower jaw symphisis extends backwards almost to

the end of the toothrow.

• Sexual size dimorphism:– males 3m TL when sexually mature.– Females 2.6m TL when sexually mature.– Adults rarely reach length greater than 4m– Greatest verified length is 6.45m.– Presumed greatest length is 8m.– Males have bulbous growth on snout, which increases in

size with age.