Mesosaur
| Mesosaurs Temporal range: Cisuralian, 299–272.3 Ma |
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| Mesosaurus | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | †Parareptilia |
| Order: |
†Mesosauria Seeley, 1892 |
| Family: |
†Mesosauridae Baur, 1889 |
| Genera | |
Mesosaurs ("middle lizards") were a group of small aquatic reptiles that lived during the early Permian period, roughly 299 to 270 million years ago. Mesosaurs were the first known aquatic reptiles, having apparently returned to an aquatic lifestyle from more terrestrial ancestors. However, just how terrestrial mesosaur ancestors had become remains uncertain; recent research cannot establish with confidence if the first amniotes were fully terrestrial, or only amphibious. Most authors consider mesosaurs to have been aquatic, although at least some of them may have been amphibious, rather than completely aquatic, as indicated by their moderate skeletal adaptations to an aquatic lifestyle. Similarly, their affinities are uncertain; they may be either the most basal sauropsids, or among the most basal parareptiles.
MESOSAURIDAE
MESOSAURIDAE
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