Therizinosaur
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 Therizinosaur
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Therizinosaurs (includes Segnosauria (Barsbold & Perle), a name that has now been dropped) were theropod dinosaurs and members of the clade Therizinosauria. Therizinosaur fossils have been found in Early through Late Cretaceous deposits in Mongolia, the People's Republic of China and Western North America. Various features of the forelimbs, skull and pelvis unite them quite comfortably, both as theropods and, as Maniraptora, close relatives to birds.
Among the most striking characteristics of therizinosaurs are the enormous claws on their hands, which reached lengths of three feet and earned them the nickname "Scythe-Claw" (in fact, therizinosaur is Greek for "scythe lizard"). Since the therizinosauroid Beipiaosaurus was feathered, it is likely that all the therizinosaurs were. Although they are classified as theropods, specifically maniraptors, therizinosaurs had skulls similar to those of sauropods and the shape of their teeth and jaws make it likely that they were herbivores. The unusual range of motion in therizinosaur forelimbs, which allowed them to reach forward to a degree other theropods could not achieve, also supports the idea that they were mainly herbivorous. Therizinosaurs may have used their long reach and strongly curved claws to grasp and shear leafy branches, in a manner similar to the prehistoric ground sloths (Burch, 2006).
The relation between the more derived therizinosaurids and other theropods has been greatly elucidated by the find of the primitive therizinosauroid Falcarius in 2005: "Falcarius utahensis seems to represent an intermediate stage between a carnivorous and herbivorous form (and) is the missing link between predatory dinosaurs and the bizarre plant-eating therizinosaurs" BBC.
The name Therizinosaur is derived from the Greek therizo meaning 'to reap' or 'to cut off' and sauros meaning 'lizard'. The name Segnosaur is derived from Latin segnis meaning 'slow' or 'sluggish' and Greek sauros meaning 'lizard'.
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[edit] Taxonomy
Barsbold and Perle named the group Segnosauria as an infraorder of Theropoda in 1980, though this name has fallen into disuse due to its association with the now discredited idea that these animals were relatives of prosauropods.[1]
The clade Therizinosauria is defined as the most inclusive group containing Therizinosaurus but not Ornithomimus, Oviraptor, Shuvuuia, Tyrannosaurus, or Troodon (Sereno, 2005).
The superfamily Therizinosauroidea, established by Maleev in 1954 and defined as a clade by Clark in 2004 (as the last common ancestor of Therizinosaurus and Beipiaosaurus and all its descendants), is a larger group also containing those therizinosaurs that are too basal to belong to Therizinosauridae. One of the former is perhaps Falcarius, discovered in 2005. Another is, by definition, Beipiaosaurus. Zhang et al. (2001) had previously defined this clade as all dinosaurs closer to Therizinosaurus than to other coelurosaurs. This earlier definition, however, defines the same group as the pre-existing Therizinosauria, so many paleontologists, including Sereno (2005), prefer Clark's definition.
[edit] Classification
- Therizinosauria
- ?Eshanosaurus
- ?Thecocoelurus
- Falcarius
- Superfamily Therizinosauroidea
- Beipiaosaurus
- Erliansaurus
- Neimongosaurus
- Nothronychus
- Family Alxasauridae
- Family Therizinosauridae
[edit] Phylogeny
Cladogram after Barsbold & Maryanska (1990), Keesey (1996-2001), Xu et al. (1999), Xu et al. (2002), and Kirkland et al. (2005).[1]
| Therizinosauria (=Segnosauria, Segnosaurischia) |
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[edit] References
- Burch, S. (2006). "The range of motion of the glenohumeral joint of the therizinosaur Neimongosaurus yangi (Dinosauria: Theropoda)." Chicago Biological Investigator, 3(2): 20. (Abstract).
[edit] External links
- Therizinosauroidae - UCMP, Berkeley
- Therizinosauria
- Evo Wiki (Uses creative commons license. Can not be wholesale copied into Wikipedia.)
