Shaking Up the Dinosaur Family Tree

Mar 27, 2017

By Nicholas Wade

For more than a century, the placement of dinosaurs on the branches of their family tree has been based on the shape of their hips.

This classification has now been radically challenged by proponents of a new tree which, if accepted, swaps large subfamilies around, sheds new light on dinosaurs’ evolution and suggests they may have originated not in South America, as widely assumed, but perhaps in some Northern Hemisphere locality such as Scotland.

A Victorian paleontologist, Harry Seeley, declared in 1888 that dinosaurs should be divided into the bird-hipped (Ornithischia) and the lizard-hipped (Saurischia) categories that have been accepted ever since.

Under this system, the heavily armored stegosaurs and ankylosaurs are placed on the Ornithischian branch of the family tree. The Saurischian branch includes both sauropods like the herbivorous diplodocus, and theropods like the meat-eating tyrannosaurs.

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2 comments on “Shaking Up the Dinosaur Family Tree

  • The following entry in Wikipedia, Ornithoscelida, gives a clear and succinct outline of the Ornithoscelida hypothesis put forward by Matthew Baron, David Norman and Paul Barrett. It will be interesting to see what palaeontologists as a whole end up doing with it.

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  • I see a new discovery in Africa, has taken the roots of the tree back in time – and found another “missing link”!

    Early dinosaur relative walked like a croc

    New fossils found in 2015 help fill gaps in our knowledge of how Teleocrater looked

    One of the earliest relatives of dinosaurs had some features we associate today with crocodiles and alligators, a study suggests.

    Many palaeontologists have wondered what the earliest dinosaur relatives looked like, as the fossil record in this time period is sparse.

    Some assumed they walked on two legs, looking a bit like miniature dinosaurs.

    But the newly described creature walked on four legs like a croc, the journal Nature reports.

    The 2-3m (7-10ft) carnivorous animal, unearthed in southern Tanzania, lived some 245 million years ago during the Triassic Period.
    It pre-dated the earliest dinosaurs.

    Prof Paul Barrett, from London’s Natural History Museum, one of the authors on the new paper, said: “This is a little animal that we call Teleocrater. It’s not very big…it probably would have weighed about the same as the average family dog.”

    Teleocrater rhadinus appeared just after a large group of animals known as archosaurs split into one branch that led to dinosaurs (and, eventually, birds) and another branch that led to today’s alligators and crocodiles.

    Its anatomy combines features present in the last common ancestor of these groups, such as a crocodilian-like ankle joint, with some features considered characteristic of dinosaurs.

    The first fossils belonging to Teleocrater were discovered in 1933 in Tanzania. They were studied at London’s Natural History Museum in the 1950s. But these specimens were missing crucial bones, such as the ankle.

    Therefore, scientists at the time could not tell whether they were more closely related to crocs or to dinosaurs.

    The new specimens were uncovered in the East African country in 2015, resolving some of those outstanding questions. They show that it is one of the earliest members of the archosaur family tree and that it walked like a crocodylian.

    Sterling Nesbitt, one of the new study’s authors from Virginia Tech in Blacksburg, US, said: “The discovery of Teleocrater fundamentally changes our ideas about the earliest history of dinosaur relatives.”

    But he added: “It also raises far more questions than it answers.”

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