Episode 194 – Alligators and Caimans

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They’re one half of the modern crocodilian family tree, and they’ve got an extensive and diverse fossil record going back to the Cretaceous. This episode, we explore Alligators and Caimans.

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The Alligatoroids

Among modern crocodilians, there are two main groups within the alligatoroid lineage: alligators and caimans.

Compared with their crocodile cousins, alligators and caimans tend to have more of an overbite and more U-shaped snouts, and they also lack the salt glands found in crocodiles and gharials.

There are two modern species of alligators: American alligators (Alligator mississippiensis, left) and Chinese alligators (Alligator sinensis, right).
Both images in the Public Domain [1, 2]
Caimans include several modern species native to South and Central America.
Top left: Smooth-fronted caiman (Paleosuchus trigonatus). Image by Factumquintus, CC BY-SA 3.0
Bottom left: Dwarf caiman (Paleosuchus palpebrosus). Image by Loury Cédric, CC BY-SA 4.0
Top right: Broad-snouted caiman (Caiman latirostris). Image by Dennis Jarvis, CC BY-SA 2.0
Second down on the right: Black caiman (Melanosuchus niger). Image by Jan Willem Kaptein, CC BY 2.0
Third down on the right: Yacare caiman (Caiman yacare). Image by Bernard DUPONT, CC BY-SA 2.0
Bottom right: Spectacled Caiman (Caiman crocodilus). Image by Berrucomons, CC BY-SA 3.0
Skeleton of a black caiman. Image by Ryan Somma, CC BY-SA 2.0

The earliest members of the alligatoroid lineage are known from the Cretaceous Period over 80 million years ago. These earliest species are quite similar to modern crocs, and they came in a variety of sizes and habits. True alligators and caimans arose by around 60 million years ago. Fossil alligators are known from North America and Eurasia, while fossil caimans are known from North and South America.

Two Cretaceous alligatoroids, among the earliest known.
Left: Skull of Leidyosuchus from Alberta. Image by Daderot, CC0 1.0
Right: Skeleton of the enormous Deinosuchus, known around the Western Interior Seaway. Image by Daderot, CC0 1.0
Paleogene alligatoroids.
Top: Skeleton of Diplocynodon, an alligatoroid known mainly from the Paleogene of Europe. Image by Ghedoghedo, CC BY-SA 3.0
Bottom: Skeleton of Allognathosuchus, an alligatorine from Eocene North America. Image by Ghedoghedo, CC BY-SA 3.0
Alligator prenasalis from Eocene South Dakota, the oldest known species in the genus Alligator. Image by Daderot, CC0 1.0
Skull of Mourasuchus, a giant caiman from Miocene South America. Scale bar = 20cm. Image from Cidade et al., 2017

Gigantic body sizes have evolved multiple times along the alligatoroid lineage, in genera such as Deinosuchus, Purussaurus, and Mourasuchus. The largest of these grew to over 30 feet (10 meters) long. Exactly how these giants’ lifestyles different from their modern cousins isn’t totally clear.

Learn More

Alligators and Caimans on the IUCN Red List
Crocodilian Species List, Crocodile Specialist Group
Crocodile Habitat Map

The feeding habits of the strange crocodylian Mourasuchus (technical, open access)
A systematic review of the giant alligatoroid Deinosuchus (technical, open access)

Anatomy, ontogeny, and evolution of the archosaurian respiratory system: A case study on Alligator mississippiensis and Struthio camelus (technical, open access)

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