Therizinosaurus (Scythe Lizard) is a genus of therizinosaurid theropod dinosaur that lived in the Nemegt Formation of the Ömnögovi Province, an area in the northwest region of the Gobi Desert in southern Mongolia, 70 million years ago, during the Maastrichtian stage of the Late Cretaceous Period. It is recognized for possessing unguals that are a meter (3 feet, 4 inches) in length, the longest-known claws of any animal that ever lived.[6][DN 1]
Therizinosaurus is estimated to have reached up to 10 meters (33 feet) in body length, 1.5 meters (5 feet) in body width, and 5 metric tons (5.5 short tons) in mass, making it one of the largest maniraptorans, and, along with its contemporary, the massive ornithomimosaur Deinocheirus, and the Gigantoraptor, an oviraptorosaur that lived in Mongolia 96 million years ago, one of the largest maniraptoriforms. It is also one of the tallest theropods ever known, towering around 5 - 5.7 meters (16 feet - 18 feet, 8 inches) tall in its default stance, matching the height of an adult giraffe and the tallest azhdarchid pterosaurs like Quetzalcoatlus northropi and Arambourgiania.[1][2][3] Assuming that Deinocheirus stood more upright, however, it would reach up to 5.8 meters (19 feet), around 10.2 centimeters (4 inches) taller than Therizinosaurus by default.[1] According to Dr. Darren Naish, lead consultant of Prehistoric Planet, if Therizinosaurus tries rearing up as tall as possible, it can even reach a height of 7.4 meters (24 feet), justifying the reason why, in the sixth segment of Forests, it is said that an adult Therizinosaurus is "nearly 30 feet tall".[PhP 1][DN 3] Aside from Deinocheirus (assuming it had a more upright normal stance than thought), the only other theropod that surpasses Therizinosaurus in terms of default height is Gigantoraptor, which can grow up to 6.5 meters (21 feet, 4 inches) tall.[1]
Therizinosaurus stood on two legs over 3 meters (10 feet) long, reaching food with a neck at least 2.2 meters (7 feet, 3 inches) long based on comparisons with the cervical vertebrae of Nangshungiosaurus, a therizinosaur that lived around the same time in the Nanxiong Formation of southern China. This means Therizinosaurus, along with Deinocheirus and Gigantoraptor, had the longest necks of any theropod dinosaur.[4][5]
Unique to therizinosaurids (and the earlier, unrelated spinosaurids) are their tetrydactyl (four-toed) feet. Theropods generally walk on three toes, with their fourth toes reduced to useless dewclaws raised off the ground. In therizinosaurs, the fourth toes are functional and weight-bearing, a trait that likely evolved in response to the more upright posture adapted by therizinosaurs compared to other theropods.[7] However, on Prehistoric Planet, Therizinosaurus is erroneously shown with the vestigial fourth toes of other conventional theropods.
Claws[]
The claws of Therizinosaurus are the longest in the animal kingdom
“ Their claws may look like daggers, but they're used more like salad servers... because these are plant-eaters. ”
Therizinosaurus and Deinocheirus both possess arms that are 2.4 meters (8 feet) in length, the longest arms of any bipedal dinosaur. What sets Therizinosaurus apart from its contemporary, however, are its defining features, its unguals (claw bones), which measure around 52 - 100 centimeters (1 foot, 8 inches - 3 feet, 4 inches) in length, the longest claws known of any animal that ever existed.[5][6][DN 1] It is unknown what the true purpose of these claws are, for there have been studies arguing both for and against their supposed use in defense. Some studies suggest that they are merely decorative with no mechanical function, having only reached such lengths because of the animal's large size, which in turn extended the growth period of the claws.[8] Others argue that the arms, robust enough to generate significant forces, support the idea that the claws were involved in more physical usage, like the manipulation of food or actual defense and combat.[9] On Prehistoric Planet, their claws are used primarily as tools to get or manipulate food, with the juveniles using their claws to climb a tree (albeit clumsily) and get to a beehive, and an adult using its claws to swat the beehive down to the ground.
While it is believed that Therizinosaurus still had feathers due to evidence of spine-like filaments on other related species,[DN 1] it is debated as to whether large maniraptoriforms like Therizinosaurus itself and the contemporary Deinocheirus had a full coat of feathers as depicted on the show, or were only sparsely covered in feathers to prevent overheating given their large sizes. It's been argued that, since they lived in an environment understood to be cool, and dinosaurs may have been better at temperate control compared to big mammals, it is possible that Deinocheirus - and, by extension, the similar Therizinosaurus - had thick, feathery integument.[DN 4]
On Prehistoric Planet, Therizinosaurus is depicted covered in thick red plumage with black and white stripes and accents. The head has a black, hair-like tuft of feathers on top (similar to the show's depiction of Ornithomimus), and two sideburn-like black parts on the sides of its head (separated by a white stripe). Its shoulders and the top edges of its arms are white, while two black stripes run down the arm. The bottom edge of the arms have large, white feathers with dark, horizontal stripes and red tips. Most of the legs and tail are covered in black plumage. The animal is not completely covered in feathers, as the gray scales of its face and feet are left bare.
The juveniles, like most young theropods in the series, are depicted with a slightly different coat pattern compared to the adults (though they already share a similar color scheme), with larger eyes and heads in proportion to their size. Therizinosaurus is also erroneously shown with its fourth toes raised off the ground, similar to those of other theropods.
The Ömnögovi is the largest aimag (province) of Mongolia, found in the south of the country, in the northeast portion of the Gobi Desert. Within this aimag is an area called the Nemegt Basin, known locally as the "Valley of Dragons" due to its rich fossil content. It encompasses three formations showing the states the area underwent throughout the Late Cretaceous, namely, the Djadochta (75 - 71 million years old), Barun Goyot (72 - 71 million years old), and Nemegt (70 million years old) Formations. Therizinosaurus lived in the last of the three formations, which showed evidence of a rich, humid environment with large river channels, tidal flats, and forests. However, the Nemegt Formation is also known to have undergone periodic droughts, and there is precedence for arid regions much like the Gobi Desert today existing in Mongolia during those times, thus justifying the depiction of Therizinosaurus living in or at least traveling through a vast desert environment.
Paleofauna[]
Therizinosaurus would have coexisted with similarly-large creatures like Tarchia, Barsboldia, Nemegtosaurus, Opisthocoelicaudia, and other, larger titanosaurs that may potentially rival Argentinosaurus in size. It also shared its habitat with small animals like Mononykus, Prenocephale, velociraptorine dromaeosaurids, oviraptorosaurs, and troodontids. Due to its great height of 5 - 7.4 meters (16 - 24 feet),[DN 3]Therizinosaurus would have been able to feed from relatively higher trees than some herbivores, and it would have been an intimidating sight to behold, being among the tallest and heaviest non-sauropod dinosaurs in the area alongside the large ornithomimosaur Deinocheirus. Even a large Tarbosaurus (the apex predator of the region) would not have been able to bite any higher than the belly or thigh of an adult Therizinosaurus or Deinocheirus, and, though it has a tremendous, bone-crushing bite force, trying to do so would put the tyrannosaur within the striking range of the long, powerful clawed forearms of both animals.[5]
During its cameo in the fourth segment of Deserts, Therizinosaurus is shown to be tolerant of other herbivorous species around it. It also shows a bit of curiosity or surprise when it stopped drinking to briefly regard a Mongolian Titan that came down to drink close to it. Prehistoric Planet does not depict Therizinosaurus interacting with large carnivores or others of its kind, but it may have used its robust limbs and long claws to intimidate or even fight other creatures in hostile encounters.
Parental Habits[]
“ These Therizinosaurus hatched just six months ago. Barely three feet long, they are only a tenth of their adult size. ”
Regarding the care of their offspring, in the sixth segment of Forests, juvenile Therizinosaurus, only six months old (about as long as the claws of a fully-grown adult Therizinosaurus, only barely coming up to an adult's foot in height), were shown wandering together without a parent guarding over them, implying that they were left to fend for themselves at a very early age, or at least, earlier than other theropods, with the young forming small groups to increase their chance of survival, much like Antarctopelta. Fossil evidence does indicate that some theropods were independent from an early age and left the nest in a sibling group.[DN 5]
Feeding Preferences and Adaptations[]
“ Bees usually build their nests beyond the reach of ground-dwellers, but this one is lower than most. And it's too good to miss. Unlike most dinosaurs, young Therizinosaurus can climb, although they're not exactly experts. ”
While mostly known for its herbivorous preferences, therizinosaurs may have been opportunistic omnivores.[DN 2] In the sixth segment of Forests, juvenile Therizinosauruses are shown climbing trees clumsily to reach a beehive for a midnight snack of honey. This climbing ability is based on an old hypothesis published in the 1990s, an idea that is admittedly not supported today.[DN 6]
The beak of Therizinosaurus likely exerted a low bite force based on how therizinosaurs decreased their bite force as they evolved, relegating the mouth to merely stripping and cropping vegetation rather than actively grinding and mashing their meals,[10] while their large belly did most of the food processing.
A 1993 study compared Therizinosaurus to the extinct odd-toed ungulate Chalicotherium, which convergently evolved similarly features like the long, clawed arms and massive body. It's been suggested that Therizinosaurus may have been able to sit on its pelvis while feeding, and that, unlike Chalicotherium, which had claws more suited to hook branches, Therizinosaurus instead used its claws to push foliage. As a mammal with comparatively more advanced teeth and muscles as well as a more developed brain, Chalicotherium is reasonably assumed to be more precise in its movements than Therizinosaurus.[11]
Three juvenile Therizinosaurus are shown walking through the forest at night. While it is stated to be due to smaller creatures avoiding threats that they may encounter during daytime, an adult Therizinosaurus was also shown walking through the forest that night. It is unknown if this means that the adults are also nocturnal, cathemeral (active in irregular intervals during day and night, which is supported by the fact that Therizinosaurus was seen in the fourth segment of Deserts, which occurs during the day), or this particular adult is not behaving normally, and is only wandering around in the night to get more food than usual.
In the fourth segment of Deserts, a temporary oasis formed by rain attracts numerous animals of every kind from many miles away. While not spoken of or focused on, a few Therizinosauruses are briefly seen among the congregating animals. Unlike the Nemegtosaurus and Mongolian Titans, which suck the water up, or the Barsboldia, which lap the water with their tongues, theropods like Therizinosaurus, Mononykus, and Tarbosaurus (as well as Tyrannosaurus, which was shown drinking in a similar manner in Freshwater) are depicted as drinking by scooping water with its lower jaw. One Therizinosaurus, shown in a more close-up shot, briefly stops drinking water to stand up and glance at a Mongolian Titan that came down to drink close to it.
In the sixth, penultimate segment of Forests, on the floor of a forest in Central Asia, fungi of all kinds begin to sprout in the middle of the night, feeding and flourishing on long-dead trees, producing an eerie green glow, their bioluminescence attracting insects to help spread their spores.
As the sauropods of the forest sleep, their pneumatized skeletons amplifying their snores, a trio of six month-old Therizinosaurus wander around in search of food, briefly feeding on some surrounding plants before finding a beehive up on a tree. Two of them successfully scale the tree while the third one watches from the ground.
“ Angry bees produce a Mexican wave to warn intruders to keep away... or suffer the consequences. ”
The bees begin forming a warning signal on their hive as they begin swarming the juveniles. However, these youngsters press on, and one takes a bite out of the hive, provoking the bees into assaulting them. The juveniles fall from the tree as the bees continue to swarm them.
Soon after, the three juveniles, sensing a large presence coming close, scurry away and hide. The three juveniles watch in awe as the majestic giant, an adult Therizinosaurus, walks in and briefly nibbles on the beehive. When the bees try to attack it, the adult knocks the beehive down to the ground with a single swat of its claws, and bites off most of the hive.
“ At last, a little treat, and a few more stings. ”
Once the adult went on its way, the juvenile Therizinosaurus trio emerged once more to feast on what remained of the hive, with the remaining bees trying to sting them to no avail.
Subject The evolutionary means and efficient systems that let sauropods attain their massive sizes.
Experts Professor Paul Barrett, Dr. Susannah Maidment
Near the end of the Uncovered segment "How Did Dinosaurs Get So Big?", stock footage from the fourth segment of Deserts is shown, featuring a Mongolian Titan drinking water alongside a Therizinosaurus, a herd of Barsboldia, and a few Mononykus, with a pair of Tarchia in the background. Although its cameo appearance is not given further elaboration, Therizinosaurus itself could be seen as an example of dinosaurs gaining not only massive body sizes, but also large body features. In the case of Therizinosaurus, its large size keeps its neck out of reach from the jaws of Tarbosaurus (which can only reach up to the animal's belly and thighs),[5] and its great size increased its claw length through peramorphic growth (extended growth period).[8]
Trivia[]
Concept art by Dr. Darren Naish revealed that there was an idea for an encounter between a pair of Tarbosaurus and a pair of Therizinosaurus in the forests of the Nemegt Formation.[DN 7]
It is unknown how exactly dinosaurs drank water. Prehistoric Planet chose to depict various types of dinosaur drinking water in different ways, with theropods shown scooping up water with their lower jaws rather than lapping it with their tongues or sucking it up. In the fourth segment of Deserts, Mononykus, Therizinosaurus, and Tarbosaurus drink water in this manner, and Tyrannosaurus is later depicted doing the same in the second segment of Freshwater.
