Episode 48 is all about Therizinosaurus, the inspiration for Indominus Rex in Jurassic World.
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In this episode, we discuss:
- The dinosaur of the day: Therizinosaurus
- Name means “scythe lizard”
- Theropod that lived in the late Cretaceous
- Only one species, Therizinosaurus cheloniformis
- Fossils found in Mongolia, and first thought to be turtle-like (cheloniformis means “turtle-formed); only a few bones found, including large hand claws
- A joint Soviet-Mongolian fossil expedition found the first Therizinosaurus bones in 1948, in Mongolia
- Russian paleontologist Evgeny Maleev in 1954, who thought it was a turtle-like reptile that used its claws to get seaweed; the holotype only has claws
- Maleev thought it used its forelimbs for swimming and claws to “cut aquatic vegetation”
- More fossils were found, which included more claws and parts of forelimbs (Rinchen Barsbold described in 1976)
- Altangerel Perle described another specimen in 1982, which had hindlimbs
- In 1970, Anatoly Konstantinovich Rozhdestvensky said Therizinosaurus was a dinosaur, not a turtle
- It was controversial about what type of dinosaur Therizinosaurus was (some thought it was a carnosaur, others thought it had a killing claw like a deinonychosaur)
- In 1970 Therizinosaurus classified as some type of theropod
- In northern China, related species were found which helped paleontologists figure out more about Therizinosaurus
- Identified as a segnosaurid when Segnosaurus and Erlikosaurus was found (in Asia)
- Segnosaurids are herbivorous theropods with long arms, long necks, and big bellies
- The segnosaurid group name eventually changed to therizinosaur (more on that later)
- Fossils of Alxasaurus and Beipiaosaurus were found, which were determined to be in the same group as Therizinosaurus, showed that Therizinosaurus probably had a bird-like pelvis, and gave details about the feet and skulls. Found that therizinosaurs were more advanced, herbivorous maniraptoran theropods
- Therizinosaurids are theropods (but herbivores)
- Theropods usually only used three toes when standing and walking, but therizinosaurs used four toes
- Now scientists base Therizinosaurus looks on related therizinosaurids. It probably had a small skull, long neck, and a wide body. Probably bipedal
- Probably had long forelimbs (8 ft or 2.5 m or even up to 11.5 ft or 3.5 m)
- Gregory S Paul estimated in 2010 that the largest Therizinosaurus would have been 33 ft (10 m) long and weighed 5 tons (based on largest known therizinosaurs and maniraptorans)
- Closely related to Velociraptor, based on shape of wrist and hip bones
- Looks a lot like ornithomimid Deinocheirus (because of claws)
- Therizinosaurus had large claws, larger than most therizinosaurs, and were probably 3.3 ft (about 1 m) long; they have the longest claws of any known animal
- Claws were straight, but tapered into a point
- Claws may have been used for display (show reproductive maturity)
- Males may have fought each other with claws (like how ceratopsians battled with horns)
- Claws may have also been a deterrent for predator Tarbosaurus bataar (looking fearsome)
- Other dinosaurs that lived around Therizinosaurus included Avimimus, Conchoraptor, Alioramus (tyrannosaur) and Nemegtosaurus (titanosaur)
- Possibly used its large claws to pull down tree branches
- Claws may have been used to pull down vegetation (in which case, would have been a picky eater)
- Therizinosaurus was probably an herbivore, based on other therizinosaurs, but it’s unclear what it ate
- No Therizinosaurus skull found, but most of its relatives had small, leaf-shaped teeth and were herbivores
- Some scientists think it ate insects, (used claws to rip into termite nests)
- Some therizinosaurs may have been omnivores
- Some therizinosaurs had feathers, such as Beipiaosaurus, from China
- Unclear if Therizinosaurus had feathers (much larger than Beipiaosaurus)
- In 2013, a nest of therizinosaur eggs were found (17 clutches in the Gobi Desert), which may show they were somewhat social
- The eggs found had no embryos, which may mean they all hatched and the babies left with their parents
- The adults of the eggs were estimated to weigh 1100lb or 500 kg
- Can see a life-sized Therizinosaurus statue in Poland, along with Allosaurus, Diplodocus, Iguanodon, and more, in Jurapark
- Can see Therizinosaurus and Tarbosaurus battling in Chased by Dinosaurs, a documentary from 2002
- Can also see Therizinosaurus in BBC’s Walking With Dinosaurs: Inside Their World
- Therizinosaurus will be in a future update of ARK Survival Evolved (game); it will be large and slow but tamed and trained for players to ride and use for defense
- Indominus Rex was first inspired by how Therizinosaurus looked, according to Jack Horner in an interview with Yahoo Movies (due to big, grasping arms)
- Therizinosauridae means “reaper lizards”
- They are advanced theropods (herbivores and omnivores)
- Lived in the Cretaceous
- Found in Mongolia, China, and U.S.
- Therizinosaurs had long necks, wide torsos, and walked on four toes in a similar way to basal sauropodomorphs
- They had unique hip bones that pointed backwards, and made paleontologists originally think they were like the “bird-hipped” ornithischians
- They also have large claws on their hands, and could reach far forward with their forelimbs (farther than other theropods), which makes scientists think they were mostly herbivores
- They may have used their claws to grasph at branches, similar to a sloth
- Beipiaosaurus skin impressions show primitive down-like feathers, similar to Sinosauropteryx (compsognathid)
- Some theroziniosaurs were relatively small, like Beipiaosaurus (7.3 ft or 2.2 m long), but others were large (Therizinosaurus was the largest)
- Because therizinosaurus was such an incomplete find, and had a whole bunch of strange features that were akin to theropods, prosauropods and ornithischians, scientists at first grouped therizinosaurs as segnosaurs. They also thought they were semi-quadrupedal because prosauropods were semi-quadrupedal. However, this is impossible because of their bird-like wrists.
- In the mid 1990s, scientists found Alxasaurus, which was more like a typical theropod. Alxasaurus and Therizinosaurus were part of the segnosaur group, which made more scientists accept that these dinosaurs were herbivorous theropods, descended from carnivorous theropods
- Then more primitive dinosaurs in the same group were found, including Beipiaosaurus in 1999 and Falcarius in 2005 (which was described as a missing link between carnivorous maniraptoran theropods and herbivorous therizinosaurs
- Therizinosaurs had skulls similar to sauropods and teeth and jaws that made them herbivores
- The group Segnosauria was named an infraorder of theropoda in 1980. But now they’re considered a specialized group within theropoda, and a synonym of Therizinosauridea (Therizinosaur named first, so the group took the new name once scientists realized it was part of the same group, and Segnosaurs became synonymous with Therizinosaurs)
- In 1954, Maleev named the superfamily Therizinosauroidea, but it only had Therizinosaurus at the time. Then scientists found it was an advanced segnosaur, and renamed the group (partly because Therizinosauroidea was older, partly because Segnosauria was associated with the idea that they were related to prosauropods, which was discredited)
- Not much is known about therizinosaur behavior
- CT scans in 2012 of the therizinosaur Erlikosaurus showed it had a large brain, good balance, and good sense of hearing and smell, which could have helped avoid predators, find food, and engage in social behavior
- Fun fact: Noise-making equipment of most animals don’t fossilize, and outside of dinosaurs like Parasaurolophus that appeared to use a resonant chamber we don’t know what they sounded like. According to the Tate Geological Museum from Casper College: “Tyrannosaurus rex might have hissed like a snake, chirped like a bird, or bellowed like an alligator during the mating season or been completely silent like many modern reptiles.”