Rex and June the Baby T-Rex

## Rex and June

Rex and June are Tyrannosaurus Rex,

young, full of feathers. Rex and June like to play mischievously.
But it's very playful.

His father was Titan and his mother was Gaw.

## Information

***Tyrannosaurus*** is a genus of large theropod dinosaur. The species ***Tyrannosaurus rex*** (*rex* meaning "king" in Latin), often called ***T. rex*** or colloquially ***T-Rex***, is one of the best represented theropods. It lived throughout what is now western North America, on what was then an island continent known as Laramidia. *Tyrannosaurus* had a much wider range than other tyrannosaurids. Fossils are found in a variety of rock formations dating to the Maastrichtian age of the Upper Cretaceous period, 68 to 66 million years ago. It was the last known member of the tyrannosaurids and among the last non-avian dinosaurs to exist before the Cretaceous–Paleogene extinction event.

Like other tyrannosaurids, *Tyrannosaurus* was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to its large and powerful hind limbs, the forelimbs of *Tyrannosaurus* were short but unusually powerful for their size, and they had two clawed digits. The most complete specimen measures up to 12.3–12.4 m (40–41 ft) in length, but according to most modern estimates, *Tyrannosaurus* could have exceeded sizes of 13 m (43 ft) in length, 3.7–4 m (12–13 ft) in hip height, and 8 tonnes (7.9 long tons; 8.8 short tons) in mass. Although many other theropods likely rivaled *Tyrannosaurus* in size, it is still among the largest known land predators and is estimated to have exerted the strongest bite force among all terrestrial animals. By far the largest carnivore in its environment, *Tyrannosaurus rex* was most likely an apex predator, preying upon hadrosaurs, juvenile armored herbivores like ceratopsians and ankylosaurs, and possibly sauropods. Some experts have suggested the dinosaur was primarily a scavenger. The question of whether *Tyrannosaurus* was an apex predator or a pure scavenger was among the longest debates in paleontology. Most paleontologists today accept that *Tyrannosaurus* was both an active predator and a scavenger.

Specimens of *Tyrannosaurus rex* include some that are nearly complete skeletons. Soft tissue and proteins have been reported in at least one of these specimens. The abundance of fossil material has allowed significant research into many aspects of its biology, including its life history and biomechanics. The feeding habits, physiology, and potential speed of *Tyrannosaurus rex* are a few subjects of debate. Its taxonomy is also controversial, as some scientists consider *Tarbosaurus bataar* from Asia to be a second *Tyrannosaurus* species, while others maintain *Tarbosaurus* is a separate genus. Several other genera of North American tyrannosaurids have also been synonymized with *Tyrannosaurus*.

As the archetypal theropod, *Tyrannosaurus* has been one of the best-known dinosaurs since the early 20th century and has been featured in film, advertising, postal stamps, and many other media.

### Earliest finds

Teeth from what is now documented as a *Tyrannosaurus rex* were found in 1874 by Arthur Lakes near Golden, Colorado. In the early 1890s, John Bell Hatcher collected postcranial elements in eastern Wyoming. The fossils were believed to be from the large species *Ornithomimus grandis* (now *Deinodon*) but are now considered *T. rex* remains.

In 1892, Edward Drinker Cope found two vertebral fragments of a large dinosaur. Cope believed the fragments belonged to an "agathaumid" (ceratopsid) dinosaur, and named them *Manospondylus gigas*, meaning "giant porous vertebra", in reference to the numerous openings for blood vessels he found in the bone. The *M. gigas* remains were, in 1907, identified by Hatcher as those of a theropod rather than a ceratopsid.

Henry Fairfield Osborn recognized the similarity between *Manospondylus gigas* and *T. rex* as early as 1917, by which time the second vertebra had been lost. Owing to the fragmentary nature of the *Manospondylus* vertebrae, Osborn did not synonymize the two genera, instead considering the older genus indeterminate. In June 2000, the Black Hills Institute found around 10% of a *Tyrannosaurus* skeleton (BHI 6248) at a site that might have been the original *M. gigas* locality.

### Skeleton discovery and naming

Barnum Brown, assistant curator of the American Museum of Natural History, found the first partial skeleton of *T. rex* in eastern Wyoming in 1900. Brown found another partial skeleton in the Hell Creek Formation in Montana in 1902, comprising approximately 34 fossilized bones. Writing at the time Brown said "Quarry No. 1 contains the femur, pubes, humerus, three vertebrae and two undetermined bones of a large Carnivorous Dinosaur not described by Marsh. ... I have never seen anything like it from the Cretaceous." Henry Fairfield Osborn, president of the American Museum of Natural History, named the second skeleton *T. rex* in 1905. The generic name is derived from the Greek words τύραννος (*tyrannos*, meaning "tyrant") and σαῦρος (*sauros*, meaning "lizard"). Osborn used the Latin word *rex*, meaning "king", for the specific name. The full binomial therefore translates to "tyrant lizard the king" or "King Tyrant Lizard", emphasizing the animal's size and presumed dominance over other species of the time.

Osborn named the other specimen *Dynamosaurus imperiosus* in a paper in 1905. In 1906, Osborn recognized that the two skeletons were from the same species and selected *Tyrannosaurus* as the preferred name. The original *Dynamosaurus* material resides in the collections of the Natural History Museum, London. In 1941, the *T. rex* type specimen was sold to the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, for $7,000. *Dynamosaurus* would later be honored by the 2018 description of another species of tyrannosaurid by Andrew McDonald and colleagues, *Dynamoterror dynastes*, whose name was chosen in reference to the 1905 name, as it had been a "childhood favorite" of McDonald's.

From the 1910s through the end of the 1950s, Barnum's discoveries remained the only specimens of *Tyrannosaurus*, as the Great Depression and wars kept many paleontologists out of the field.

### Resurgent interest

Beginning in the 1960s, there was renewed interest in *Tyrannosaurus*, resulting in the recovery of 42 skeletons (5–80% complete by bone count) from Western North America. In 1967, Dr. William MacMannis located and recovered the skeleton named "MOR 008", which is 15% complete by bone count and has a reconstructed skull displayed at the Museum of the Rockies. The 1990s saw numerous discoveries, with nearly twice as many finds as in all previous years, including two of the most complete skeletons found to date: Sue and Stan.

Sue Hendrickson, an amateur paleontologist, discovered the most complete (approximately 85%) and largest *Tyrannosaurus* skeleton in the Hell Creek Formation on August 12, 1990. The specimen Sue, named after the discoverer, was the object of a legal battle over its ownership. In 1997, the litigation was settled in favor of Maurice Williams, the original land owner. The fossil collection was purchased by the Field Museum of Natural History at auction for $7.6 million, making it the most expensive dinosaur skeleton until the sale of Stan for $31.8 million in 2020. From 1998 to 1999, Field Museum of Natural History staff spent over 25,000 hours taking the rock off the bones. The bones were then shipped to New Jersey where the mount was constructed, then shipped back to Chicago for the final assembly. The mounted skeleton opened to the public on May 17, 2000, in the Field Museum of Natural History. A study of this specimen's fossilized bones showed that Sue reached full size at age 19 and died at the age of 28, the longest estimated life of any tyrannosaur known.

Another *Tyrannosaurus*, nicknamed Stan (BHI 3033), in honor of amateur paleontologist Stan Sacrison, was recovered from the Hell Creek Formation in 1992. Stan is the second most complete skeleton found, with 199 bones recovered representing 70% of the total. This tyrannosaur also had many bone pathologies, including broken and healed ribs, a broken (and healed) neck, and a substantial hole in the back of its head, about the size of a *Tyrannosaurus* tooth.

In 1998, Bucky Derflinger noticed a *T. rex* toe exposed above ground, making Derflinger, who was 20 years old at the time, the youngest person to discover a *Tyrannosaurus*. The specimen, dubbed Bucky in honor of its discoverer, was a young adult, 3.0 metres (10 ft) tall and 11 metres (35 ft) long. Bucky is the first *Tyrannosaurus* to be found that preserved a furcula (wishbone). Bucky is permanently displayed at The Children's Museum of Indianapolis.

In the summer of 2000, crews organized by Jack Horner discovered five *Tyrannosaurus* skeletons near the Fort Peck Reservoir. In 2001, a 50% complete skeleton of a juvenile *Tyrannosaurus* was discovered in the Hell Creek Formation by a crew from the Burpee Museum of Natural History. Dubbed Jane (BMRP 2002.4.1), the find was thought to be the first known skeleton of a pygmy tyrannosaurid, *Nanotyrannus*, but subsequent research revealed that it is more likely a juvenile *Tyrannosaurus*, and the most complete juvenile example known; Jane is exhibited at the Burpee Museum of Natural History. In 2002, a skeleton named Wyrex, discovered by amateur collectors Dan Wells and Don Wyrick, had 114 bones and was 38% complete. The dig was concluded over 3 weeks in 2004 by the Black Hills Institute with the first live online *Tyrannosaurus* excavation providing daily reports, photos, and video.

In 2006, Montana State University revealed that it possessed the largest *Tyrannosaurus* skull yet discovered (from a specimen named MOR 008), measuring 5 feet (152 cm) long. Subsequent comparisons indicated that the longest head was 136.5 centimetres (53.7 in) (from specimen LACM 23844) and the widest head was 90.2 centimetres (35.5 in) (from Sue).

### Footprints

Two isolated fossilized footprints have been tentatively assigned to *T. rex*. The first was discovered at Philmont Scout Ranch, New Mexico, in 1983 by American geologist Charles Pillmore. Originally thought to belong to a hadrosaurid, examination of the footprint revealed a large 'heel' unknown in ornithopod dinosaur tracks, and traces of what may have been a hallux, the dewclaw-like fourth digit of the tyrannosaur foot. The footprint was published as the ichnogenus *Tyrannosauripus pillmorei* in 1994, by Martin Lockley and Adrian Hunt. Lockley and Hunt suggested that it was very likely the track was made by a *T. rex*, which would make it the first known footprint from this species. The track was made in what was once a vegetated wetland mudflat. It measures 83 centimeters (33 in) long by 71 centimeters (28 in) wide.

A second footprint that may have been made by a *Tyrannosaurus* was first reported in 2007 by British paleontologist Phil Manning, from the Hell Creek Formation of Montana. This second track measures 72 centimeters (28 in) long, shorter than the track described by Lockley and Hunt. Whether or not the track was made by *Tyrannosaurus* is unclear, though *Tyrannosaurus* is the only large theropod known to have existed in the Hell Creek Formation.

A set of footprints in Glenrock, Wyoming dating to the Maastrichtian stage of the Late Cretaceous and hailing from the Lance Formation were described by Scott Persons, Phil Currie and colleagues in 2016, and are believed to belong to either a juvenile *T. rex* or the dubious tyrannosaurid *Nanotyrannus lancensis*. From measurements and based on the positions of the footprints, the animal was believed to be traveling at a walking speed of around 2.8 to 5 miles per hour and was estimated to have a hip height of 1.56 m (5.1 ft) to 2.06 m (6.8 ft). A follow-up paper appeared in 2017, increasing the speed estimations by 50–80%.

## Description

### Size

*T. rex* was one of the largest land carnivores of all time. One of the largest and the most complete specimens, nicknamed Sue (FMNH PR2081), is located at the Field Museum of Natural History in Chicago. Sue measured 12.3–12.4 m (40.4–40.7 ft) long, was 3.66–3.96 meters (12–13 ft) tall at the hips, and according to the most recent studies, using a variety of techniques, maximum body masses have been estimated approximately 8.4–8.46 metric tons (9.26–9.33 short tons). A specimen nicknamed Scotty (RSM P2523.8), located at the Royal Saskatchewan Museum, is reported to measure 13 m (43 ft) in length. Using a mass estimation technique that extrapolates from the circumference of the femur, Scotty was estimated as the largest known specimen at 8.87 metric tons (9.78 short tons) in body mass.

Not every adult *Tyrannosaurus* specimen recovered is as big. Historically average adult mass estimates have varied widely over the years, from as low as 4.5 metric tons (5.0 short tons), to more than 7.2 metric tons (7.9 short tons), with most modern estimates ranging between 5.4 metric tons (6.0 short tons) and 8.0 metric tons (8.8 short tons).

### Skull

The largest known *T. rex* skulls measure up to 1.54 meters (5 ft) in length. Large fenestrae (openings) in the skull reduced weight, as in all carnivorous theropods. In other respects *Tyrannosaurus*'s skull was significantly different from those of large non-tyrannosaurid theropods. It was extremely wide at the rear but had a narrow snout, allowing unusually good binocular vision. The skull bones were massive and the nasals and some other bones were fused, preventing movement between them; but many were pneumatized (contained a "honeycomb" of tiny air spaces) and thus lighter. These and other skull-strengthening features are part of the tyrannosaurid trend towards an increasingly powerful bite, which easily surpassed that of all non-tyrannosaurids. The tip of the upper jaw was U-shaped (most non-tyrannosauroid carnivores had V-shaped upper jaws), which increased the amount of tissue and bone a tyrannosaur could rip out with one bite, although it also increased the stresses on the front teeth. The teeth of *T. rex* displayed marked heterodonty (differences in shape). The premaxillary teeth, four per side at the front of the upper jaw, were closely packed, *D*-shaped in cross-section, had reinforcing ridges on the rear surface, were incisiform (their tips were chisel-like blades) and curved backwards. The *D*-shaped cross-section, reinforcing ridges and backwards curve reduced the risk that the teeth would snap when *Tyrannosaurus* bit and pulled. The remaining teeth were robust, like "lethal bananas" rather than daggers, more widely spaced and also had reinforcing ridges. Those in the upper jaw, twelve per side in mature individuals, were larger than their counterparts of the lower jaw, except at the rear. The largest found so far is estimated to have been 30.5 centimeters (12 in) long including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur yet found. The lower jaw was robust. Its front dentary bone bore thirteen teeth. Behind the tooth row, the lower jaw became notably taller. The upper and lower jaws of *Tyrannosaurus*, like those of many dinosaurs, possessed numerous foramina, or small holes in the bone. Various functions have been proposed for these foramina, such as a crocodile-like sensory system or evidence of extra-oral structures such as scales or potentially lips, with subsequent research on theropod tooth wear patterns supporting such a proposition.

### Skeleton

Life restoration showing scaly skin with sparse feathering, and lipped jaws

Skeletal reconstruction of specimen "Sue"

The vertebral column of *Tyrannosaurus* consisted of ten neck vertebrae, thirteen back vertebrae and five sacral vertebrae. The number of tail vertebrae is unknown and could well have varied between individuals but probably numbered at least forty. Sue was mounted with forty-seven of such caudal vertebrae. The neck of *T. rex* formed a natural S-shaped curve like that of other theropods. Compared to these, it was exceptionally short, deep and muscular to support the massive head. The second vertebra, the axis, was especially short. The remaining neck vertebrae were weakly opisthocoelous, i.e. with a convex front of the vertebral body and a concave rear. The vertebral bodies had single pleurocoels, pneumatic depressions created by air sacs, on their sides. The vertebral bodies of the torso were robust but with a narrow waist. Their undersides were keeled. The front sides were concave with a deep vertical trough. They had large pleurocoels. Their neural spines had very rough front and rear sides for the attachment of strong tendons. The sacral vertebrae were fused to each other, both in their vertebral bodies and neural spines. They were pneumatized. They were connected to the pelvis by transverse processes and sacral ribs. The tail was heavy and moderately long, in order to balance the massive head and torso and to provide space for massive locomotor muscles that attached to the thighbones. The thirteenth tail vertebra formed the transition point between the deep tail base and the middle tail that was stiffened by a rather long front articulation processes. The underside of the trunk was covered by eighteen or nineteen pairs of segmented belly ribs.