Therizinosaurus

## TherizinosaurusScythe Lizard

* Adult
* Juveniles

* **Neck Length** of 2.2 meters (7 feet, 3 inches)
* **Arm Length** of 2.4 meters (8 feet)
* **Hand Claw Length** of 52 - 100 centimeters (1 foot, 8 inches - 3 feet, 4 inches), the longest claws of any animal
* **Leg Length** of 3 meters (10 feet)
* Fourth toe supports weight, unlike the vestigial fourth toes of other theropods.

***Therizinosaurus*** (Scythe Lizard) is a genus of therizinosaurid theropod dinosaur that lived in the Nemegt Formation, 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.

## Paleobiology

### Size and Physique

***“ An adult Therizinosaurus. It's huge, nearly 30 feet tall, and weighing five tonnes. ”***

― **David Attenborough**, *Forests*
*Therizinosaurus* is estimated to have reached up to 10 meters (33 feet) in length and 5 metric tons (5.5 short tons) in weight, making it one of the largest maniraptorans, and, along with its contemporary, the massive ornithomimosaur *Deinocheirus*, one of the largest maniraptoriforms. It is also one of the tallest theropods ever known, towering around 5 meters (13 - 16 feet) tall, or, according to Dr. Darren Naish, lead consultant of Prehistoric Planet, possibly even 7.4 meters (24 feet) tall. As a theropod, *Therizinosaurus* likely had several pneumatized (air-filled) bones to help reduce its mass.

The animal has a beak, a large belly to help process food, legs over 3 meters (10 feet) long, and 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*, an oviraptorosaur that lived in Mongolia 96 million years ago, had the longest necks of any theropod.

Unique to therizinosaurids 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. However, on Prehistoric Planet, *Therizinosaurus* is erroneously shown with the vestigial fourth toes of other conventional theropods.

### Feathers

While it is believed that *Therizinosaurus* still had feathers due to evidence of spine-like filaments on other related species, 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.

### Claws

***“ Their claws may look like daggers, but they're used more like salad servers... because these are plant-eaters. ”***

― **David Attenborough**, *Forests*
*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. 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. 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. 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.

### Prehistoric Planet's Depiction

On Prehistoric Planet, *Therizinosaurus* is depicted with thick plumage that comes in red and white, with larger feathers lining the forearms, a black tuft on top of the head (much like *Ornithomimus*), and dull yellow covering by the arms and legs. The juveniles, like most young theropods in the series, are depicted with a slightly different color scheme compared to the adults, with larger eyes and heads in proportion to their size. *Therizinosaurus* is also erroneously shown with its fourth toes raised off the ground, much like those of other theropods.

## Paleoecology

### Paleoenvironment

*Main: Nemegt Formation*

Main: Nemegt Formation

*Therizinosaurus* lived 70 million years ago in the Nemegt Formation, an area that would one day become the Gobi Desert in Mongolia. The formation shows evidence of a rich, humid environment with large river channels, tidal flats, and forests. However, the area 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*, and velociraptorine dromaeosaurids. Due to its great height of 5 - 7.4 meters (16 - 24 feet), *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, five-ton bite force, trying to do so would put the tyrannosaur within the striking range of the long, powerful clawed forearms of both animals.

During its cameo in 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. ”***

― **David Attenborough**, *Forests*
Regarding the care of their offspring, in Forests, juvenile *Therizinosaurus*, only six months old, 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.

### 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. ”***

― **David Attenborough**, *Forests*
While mostly known for its herbivorous preferences, therizinosaurs may have been opportunistic omnivores. In 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.

### Nocturnality

***“ For smaller creatures, it's safer to be out in the darkness than during the day. ”***

― **David Attenborough**, *Forests*
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), or this particular adult is not behaving normally, and is only wandering around in the night to get more food than usual.

## Appearances

### Deserts

In the fourth segment of Deserts, a temporary oasis formed by rain attracts several 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.

### Forests

In the sixth 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. ”***

― **David Attenborough**, *Forests*
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. ”***

― **David Attenborough**, *Forests*
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.

## Trivia

### Speculation

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.

## References

### General

1. ↑ 1.0 1.1 1.2 *The Princeton Field Guide to Dinosaurs*
2. ↑ 2.0 2.1 2.2 Holtz Dinosaur Genus Appendix
3. ↑ 3.0 3.1 Why sauropods had long necks; and why giraffes have short necks
4. ↑ 4.0 4.1 4.2 4.3 4.4 Hip heights of the gigantic theropod dinosaurs *Deinocheirus mirificus* and *Therizinosaurus cheloniformis*, and implications for museum mounting and paleoecology
5. ↑ 5.0 5.1 A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora)
6. ↑ 6.0 6.1 The Slothful Claw: Osteology and Taphonomy of *Nothronychus mckinleyi* and *N. graffami* (Dinosauria: Theropoda) and Anatomical Considerations for Derived Therizinosaurids
7. ↑ Functional space analyses reveal the function and evolution of the most bizarre theropod manual unguals
8. ↑ The Surprisingly Strong Arms of the Therizinosaur Dinosaurs

### Dr. Darren Naish

1. ↑ 1.0 1.1 1.2 The narration stating that *Therizinosaurus* is "30 feet high" (believed by some to actually mean "30 feet long") is not an error, for *Therizinosaurus* could exceed 7.4 meters (24 feet) in height when standing up as tall as it can.
2. ↑ 2.0 2.1 2.2 *Therizinosaurus* had claws that were about 1 meter (3 feet), the biggest claws of all time.
3. ↑ *Deinocheirus* lived somewhere cool, and dinosaurs may have been better at temperature control than big mammals.
4. ↑ Fossil evidence suggests that the juveniles of at least some theropods were independent and left the nest in a group.
5. ↑ Therizinosaurs may have opportunistically consumed fungi and fruits, and they might also be semi-omnivorous, especially the juveniles.
6. ↑ There was once a hypothesis in the 1990s that suggested that therizinosaurs were tree climbers, a view not supported in the modern day.