The Bizarre Therizinosaurids such as Nothronychus

There are a great many different types of dinosaur, ranging from tiny crow-sized species up to the huge leviathans such as the Sauropods.  One particular group of these incredible creatures has proved particularly difficult to classify and study.  This is because their fossils are exceptionally rare and they seem to have possessed a mixture of characteristics – a sort of dinosaur made up from features of other dinosaurs.  We are referring to the unusual Therizinosaurids, a rare, exclusively Cretaceous group which is still not well understood today, despite the first of their kind (Therizinosaurus), being named and described more than fifty years ago.

These dinosaurs seem to show a mixture of meat-eating and plant-eating characteristics, the name Therizinosaur means “scythe lizard”, a reference to the huge claws on each of their fingers (three-fingered hands).  The technical term for these hand claws is manual ungual.  The claws are long, slightly curved and in the case of Therizinosaurus, the largest member of this group discovered to date; the fossilised claws are over 70 cm long.  In life they would have been covered with a horny sheath, so they in reality would have been even longer.  It has been suggested that these claws may have been used to help break open termite mounds, indicating that these animals were insectivores, however, the more favoured theory at present is that the claws were used to pull branches down in a giant-sloth like manner and these creatures were largely vegetarian.

Incidentally, Therizinosaurus has a number of unique characteristics amongst Therizinosaurs, so much so that it may be reclassified into its own group – the Segnosaurs.

Illustration of a Typical Therizinosaur (Nothronychus)

Picture Credit: Everything Dinosaur

To view a model of a Therizinosaur (model of Nothronychus) you can visit the Everything Dinosaur website: Dinosaur Toys for Boys and Girls – Dinosaur Models

Nothronychus shows the features that characterise this particular group of dinosaurs.  The small head, with leaf-shaped teeth in the jaws (indicating a plant-eating diet), a long neck, powerful arms with the three-fingered hands and long claws.  The body was quite stocky and these animals although members of the Theropoda (Saurischian dinosaurs), have a swept back hip girdle more reminiscent of the plant eating Ornithischian group.

Nothronychus would have been up to 6 metres long and represents the first member of this group to be found outside Asia.  Two partial specimens have been discovered in the western USA.  Nothronychus means “sloth like claws”, as the scientists that named and described this animal thought that it resembled a ground sloth with its upright stance, big belly and enormous claws.

Scientists still debate about the taxonomic position of this bizarre and unusual group, although most artists depict these animals covered in simply proto-feathers, indicating warm-blooded creatures with a need to keep insulated.  They really are most peculiar animals and as such many a palaeontologist has remarked that they are like a dinosaur designed by a committee.

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