Everything about Sauropterygia totally explained
Sauropterygia ("
lizard flippers") is a group of very successful aquatic
reptiles that flourished during the
Age of the Dinosaurs before they became
extinct. They are united by a radical adaptation of their
shoulder, designed to support powerful flipper strokes. Some later sauropterygians like the
pliosaurs developed a similar mechanism in their
pelvis.
The earliest sauropterygians appeared about 245
million years ago (Ma), at the start of the
Triassic period. Early examples were small (around 60 cm), semi-aquatic lizard-like animals with long limbs (
pachypleurosaurs), but they quickly grew to be several meters long and spread into shallow waters (
nothosaurs). The
Triassic-Jurassic extinction event wiped them all out except for the
plesiosaurs. During the
Early Jurassic these diversified quickly into both long-necked small-headed plesiosaurs proper, and short-necked large-headed
pliosaurs. Originally it was thought that Plesiosaurs and Pliosaurs were two distinct superfamilies that followed separate evolutionary paths. It now seems that these were simply morphotypes in that both types evolved a number of times, with some pliosaurs evolving from plesiosaur ancestors, and vice-versa.
Each morphotype filled a specific ecological role. The large pliosaurs, like the
Jurassic Rhomaleosaurus,
Liopleurodon and
Pliosaurus, and the
Cretaceous Kronosaurus and
Brachauchenius, were the
superpredators of the Mesozoic seas, around 7 to 12 meters in length, and filled a similar ecological role to that of
killer whales today. The long-necked plesiosaurs, meanwhile, included both those with medium-long necks, like the 3 to 5 meter-long
Plesiosauridae and the
Cryptoclididae, and the Jurassic and Cretaceous
Elasmosauridae, which evolved progressively longer and more flexible necks, so that by the middle and late Cretaceous the entire animal was over 13 meters in length (for example
Elasmosaurus), although as most of this was the neck, the actual body size was much smaller than that of the larger pliosaurs. These long-necked forms undoubtedly fed on fish, which they probably snared in their tooth-lined jaws with rapid lunges of the neck and head.
The sauropterygians thrived throughout the
Mesozoic. However, despite their success they became
extinct along with the
non-avian dinosaurs,
pterosaurs and
mosasaurs during the end Cretaceous
mass extinction.
Classification is difficult because the demands of the aquatic environment caused the same characteristics to evolve multiple times, illustrating
convergent evolution. While sauropterygians are considered
diapsids, they're also sometimes classified with
turtles. The bulky-bodied, mollusc-eating
placodonts may also be sauropterygians. In addition to the modifications of the shoulder, the group is also united by several modifications in their
skulls.
Taxonomy
Class Sauropsida (reptiles)
Further Information
Get more info on 'Sauropterygia'.
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