Articulated jaw really opens and closes!
Dimetrodon , meaning "two measures of teeth" is an extinct genus of non-mammalian synapsid that lived during the Cisuralian (Early Permian), around 295–272 million years ago (Mya). It is a member of the family Sphenacodontidae. The most prominent feature of Dimetrodon is the large neural spine sail on its back formed by elongated spines extending from the vertebrae. It walked on four legs and had a tall, curved skull with large teeth of different sizes set along the jaws. Dimetrodon was a quadrupedal, sail-backed synapsid. Most Dimetrodon species ranged in length from 1.7 to 4.6 m (6 to 15 ft) and are estimated to have weighed between 28 and 250 kg (60 and 550 lb). The largest known species of Dimetrodon is D. angelensis, around 4 m (13 ft) and the smallest is D. teutonis at 60 cm (24 in). The larger species of Dimetrodon were among the largest predators of the Early Permian, although the closely related Tappenosaurus, known from skeletal fragments in slightly younger rocks, may have been even larger at an estimated 5.5 metres (18 ft) in total body length. Although some Dimetrodon species could grow very large, many juvenile specimens are known.
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