Therizinosauridae
| Therizinosaurids Temporal range: Late Cretaceous, 94–66 Ma Possible Early Jurassic record |
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| Reconstructed skeleton of Nothronychus mckinleyi | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Order: | Saurischia |
| Suborder: | Theropoda |
| Superfamily: | †Therizinosauroidea |
| Family: |
†Therizinosauridae Maleev, 1954 |
| Type species | |
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Therizinosaurus cheloniformis Maleev, 1954 |
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| Genera | |
| Synonyms | |
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Segnosauridae Perle, 1979 |
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Segnosauridae Perle, 1979
Enigmosauridae Barsbold & Perle, 1983
Nanshiungosauridae Dong & Yu, 1997
Therizinosauridae ("reaper lizards") is a family of theropod dinosaurs whose fossil remains have been dated to the Mid-to-Late Cretaceous period (100 to 70 mya). Even though representative fossils have only been found throughout China, Mongolia, and the United States, the range of Therizinosauridae was believed to have spanned much of the supercontinent of Laurasia at its height.
Therizinosauridae was named after the large, claw-bearing ungual found on the manus of members in the group. This feature has led to little insight about the ecology of the family, and the purpose of the claw remains unknown. Other notable aspects of the physiology of these animals include a modified pelvis, robust hind-limbs, and a highly derived, nearly avian inner-ear. Moreover, the larger superfamily of Therizinosauroidea is believed to be the earliest group in which simple feathers have been documented.
Research into therizinosaurids has also focused on uncovering more about the unique ecology and paleobiology of the family. A fair portion of modern research has concentrated on the feeding-patterns of these reptiles, as they are considered to be the best regarded candidate for the emergence of herbivory within Theropoda. While many closely related taxa are carnivorous, it is thought that the members of Therizinosauroidea, including Therizinosauridae, diverged and adopted either an herbivorous or omnivorous lifestyle.
The current scientific consensus is that therizinosaurids evolved from small, bird-like maniraptorans, and thus they fall within the coelurosaurian clade called Maniraptora. Most studies have concluded that within Maniraptora, Therizinosaurians were the first of five major groups to diverge.
The family Therizinosauridae was coined by Evgeny Maleev in 1954 to contain the enigmatic Therizinosaurus cheloniformis, which Maleev originally thought to be a species of giant "turtle-like lizard." It was long considered a strange, probably carnivorous, species. Relatives of Therizinosaurus were later found but not recognized as such for some time. These more complete specimens were herbivores, and had a bizarre mixture of what looked to early researchers like a mix between ornithischian and "prosauropod" dinosaurs. Collectively, these were included in the family Segnosauridae, or "slow lizards", due to their heavy bodies, short legs, and presumably slow, ground sloth-like lifestyle. Subsequent studies found that segnosaurids were neither prosauropods nor ornithischians, but actually bizarre theropods, and that the previously enigmatic Therizinosaurus was also a member of this group. Since the family Therizinosauridae was named earlier than Segnosauridae, the later name became a junior synonym of the former, despite the fact that Therizinosaurus was a new addition to the segnosaurid group.
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