A unique new fossil discovered in Jordan has given researchers fresh insight about a prehistoric sea lizard called prognathodon, as it is the first fossil to show the shape of the lizard's tale, suggesting that it swam like a shark.
The prognathodon was a huge, fearsome predator that hunted in Earth's oceans during the late Cretacious period, roughly between 65 and 80 million years ago. They could grow up to 12 metres long, and although they lived their entire lives in the ocean, they were air-breathers, and it's thought that they evolved on land first and adapted to life at sea. This species is sometimes called the 'T-rex of the seas' ('sea rex'?). Just one look at fossils of the species' skull, with its powerful, tooth-filled maw, and it's easy to see why.
Up until now, the various prognathodons fossils found by researchers over the past 200 years or so only showed the fossil bones, which tapered off towards the end of the tail. With no further information available, reconstructions gave it a long, thin tail, similar to that of an alligator or crocodile.
Now, though, a new fossil discovered in Jordan in 2008 was examined in 2011 by Johan Lindgren, a professor at Lund University in Sweden. He found a preserved soft-tissue imprint in the rock around the tail of the fossil, and this imprint that showed off nearly its entire shape. Rather than long and thin, it was actually shaped like an upside-down shark's tail. This find gives a long-overdue update the look of this lizard, changing its flatter, more rectilinear shape to a more streamline form, similar to the dolphin-like ichthyosaurs that preceded prognathodon, and more like modern-day sharks and whales.
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Since these giant lizards started out on land and evolved to be more adapted to living in the water, Lingdren points out that this species is one of the best examples of large-scale evolution, as prognathodon changed its appearance to adapt to the new environment.
(Images courtesy: Johan Lindgren/Stefan Sølberg, Royal Tyrrell Museum)
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