23 November 2016

Dinovember 2016, Day 22

Unhappy that the tyrannosaurs were hogging the spotlight for short arms,
Gualicho convergently evolved a set of nubby didactyl grabbers of its own.
Name: Gualicho shinyae
Meaning: [Field Museum fossil preparator Akiko] Shinya's gualichu [a South American folkloric demon]
Time: Late Cretaceous, c 93 million years ago
Place: Patagonia
Size: uncertain, probably about 6-7 metres (19.7-23 feet) long
Type of Dinosaur: neovenatorid carcharodontosaur (oddball large carnivorous dinosaur)

Gualicho was named and described earlier this year. It's a rather bizarre South American predator known from only a partial skeleton. Its most striking feature is its arms, which have only two fingers and are very reduced in size, much like a tyrannosaur. In fact, Gualicho and its relatives, the Neovenatoridae, are of rather uncertain placement. Various features of their anatomy are reminiscent of the more birdlike tyrannosaurs, rather than the carcharodontosaurs they were initially thought to be related to. But further studies have suggested that the tyrannosaur-like features are products of that old rascal convergent evolution, and their underlying anatomy really does support a carcharodontosaur affinity. For now, the best answer is probably that neovenatorids are indeed carcharodontosaurs that occasionally developed tyrannosaur-like features, but several neovenatorids have been found recently and more work on these bizarre theropods will hopefully make their relationships more clear.

I still gave Gualicho a coat of simple feathers, as I think our best evidence is that (at least partial) feathery coverings are the original condition for dinosaurs, and that some groups lost these coverings. Even within some groups, I imagine there's probably variety in body coverings - even amongst living animals, lots of closely related species vary quite a bit in their hairiness/scales/whatever. The head and neck are necked and covered with caruncled skin, and the nubby arms themselves are bare too, and partially hidden in the shaggy feathers.

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