My Prehistoric Saga: Dino Bios: Tyrannosaurus.

Tyrannosaurus rex (T. rex):

Time: 84-66 million years ago, Campanian-Maastrichtian of the late Cretaceous period.

Place: North America, Canada, and Mexico.

Size: 40-51 feet (12.2-15.5 meters). Maybe up to 66 feet (20.0 meters).

Weight: 7.4-9.7 tons (Based on CM 9380 and RSM 2523.8). Maybe more.

Diet: Carnivore.

Hello! Welcome to "Dino Bios!" This is a series that I created where we talk about dinosaurs. We're going to start off by talking about my favorite dinosaur: Tyrannosaurus rex!

Description:

Tyrannosaurus rex, or T. rex, which means "Tyrant lizard king" or "King of the tyrant lizards" (Smithsonian. "Fact Sheet: Tyrannosaurus rex," 2014) (Joseph Castro, 2017, p. 2), was the largest carnivorous theropod dinosaur of all time. It reached 40-70 feet in length (12.2-21.3 meters) and 7.4-9.7 tons in weight, possibly more. It carried a 5-6-foot long skull (1.47-1.829-meter), with jaws powerful enough to crush bones! Some herbivorous fossils with teeth marks, and bones found in T. rex's fossilized coprolite (dung) show that it could not only crush, but digest, bones as well (Gignac and Erickson, 2017, "Introduction" pg. 2, Figure 1, Table 1). T. rex gained its bone-crushing teeth at the age of 15 (Carr, 2020, "Growth categories," "Juveniles," "Large juveniles," "Dentition;" "Bite force and maturity;" "Tooth morphology" p. 2; "Skull and jaw strength" p. 6; "Conclusions" 21) (EurekAlert!, 2020, "New study: Tyrannosaurus rex size doesn't determine age," p. 5).

Carnivorous theropod dinosaurs had enamel in their teeth, so they must have had lips to cover and protect their teeth (Reisz and Larson, 2016, pg. 64-66) (Blake Eligh, 2016) (Mindy Weisberger, 2016) (Emanuela Grinberg, 2016) (Phys, 2016). Therefore, T. rex would have had lips covering its teeth. Interestingly, dinosaurs couldn't move their tongues (Mindy Weisberger, 2018) (ScienceDaily, 2018).

T. rex's eyes faced forward, allowing it to have binocular vision like a hawk. They were also the size of oranges, and sat on closer to the top of the animal's head. This allowed T. rex to have greater depth of vision (AMNH, 2019, "Mega-Predator T. rex Had Super Senses"). This isn't common in other theropods like the allosauroids (Allosaurus and Carcharodontosaurus) (Kent A. Stevens, 2006, "Abstract"). So, unlike what we were told in the Jurassic Park and World movies, T. rex's eyesight was really good. It would have seen you even if you were standing still. I think Paleontologist Jack Horner is responsible for creating this myth. In his book, The Complete T. rex, written in 1993 with fellow Paleontologist Don Lessem, he says that T. rex might've had good eyesight, but he doubts it (pg. 187-188). However, they give a description of T. rex's skull and show how it had binocular vision (pg. 185)... In two documentaries from the 1990's, PaleoWorld: The Legendary T. rex, and The Ultimate Guide: T-Rex, Horner says that T. rex had bad eyesight. One documentary from the 2000's, Valley of the T. rex, he says the same thing. Horner is the scientific consultant for the Jurassic series, so this seems to be where the concept of T. rex having bad eyesight came from.

T. rex's sense of smell was more advanced than other carnivorous theropods, and could have helped T. rex to hunt at night (John van Radowitz, 2008). Hughes and Finarelli (2019) says that T. rex had larger olfactory bulb and receptor repertoires than other extinct taxa studied in their paper. This would have helped T. rex to track prey or scavenge for carrion ("Discussion," "Inferred olfactory receptor repertoires of extinct taxa" p. 1-2).

T. rex's arms were originally thought to have been used for mating, since they were small for the animal's size but would have had surprisingly large muscle attachments (Osborn, 1906, pg. 290-291). Also, despite being short on its body, were the size of a full grown person's (Horner and Lessem, 1993, pg. 113). However, them seem to have been powerful. They could lift 400 pounds individually (Horner and Lessem, 1993, pg. 116) (Doug Hampton, 1990, p. 7) (Helen Thompson, 2014), and were capable of inflicting serious slashing (Steven M. Stanley, 2017, "Abstract") (Thad Morgan, 2017). It was previously suggested that the arms could have help T. rex to get up from the ground (Kent A. Stevens, 2005), but theropod dinosaurs couldn't put their palms on the ground to help them get up (Milner et al., 2009, "Abstract: Conclusions/Significance") (Eliza Strickland, 2009) (Thomas H. Maugh II, 2009). T. rex's arms could grab and injure prey (Doug Hampton, 1990) (Steven M. Stanley, 2017, "Abstract") (Thad Morgan, 2017), or for mating (Helen Thompson, 2014). In 2018, scientists stated that theropods, like T.rex, could bend their elbows and extend their palms inwards and upwards. This means that T. rex could extend its arms outwards and grab things (Laura Geggel, 2018). According to Kenneth Carpenter (2002), in most predatory theropods used their mouths first to grab prey first, and then they would grab their prey "in a 'bear hug'" with their hands. Even T. rex's small arms were used for predation (pg. 72, "Conclusion"). He even states that T. rex's arms were designed for using long ranges of motion, and for holding struggling prey close to it "until the jaws could be used to kill the prey" (pg. 69). In fact, T. rex's range of motion in its arms seems to be greater than other theropods' (pg. 68, "Biomechanical Analysis"). Text-figure 9 shows T. rex's, and other theropod's, range of motion for their hands (p. 69). Caneer et al., (2021) found T. rex arm marks in Colorado that suggests that it rose from a quadrupedal stance into a bipedal one using its arms (Abstract; pp. 29-30; p. 33 Figure 6, C; p. 35 Figure 8).

T. rex arm trace fossils (Caneer et al., 2021, p. 33 Figure 6, C):

Drawing of T. rex showing how it used its arms to sit down, or even get up from the ground (p. 35 Figure 8):

As for speed, T. rex could have either walked at 12-17 miles per hour (Sellers et al., 2017, "Abstract" and "Conclusion") (Sid Perkins, 2017, p. 11) (Ben Guarino, 2017, p. 4), or ran up to 18-29 miles per hour (Farlow et al., 1995, "Abstract," pg. 715) (Sellers and Manning, 2007, Table 1) (Igor Nesteruk, 2018, pg. 46). What seems to have helped T. rex in hunting was pack-hunting and agility. T. rex seems to have hunted in packs led by females (Ben Schaub, 2018). Second, the tail of T. rex seems to have made it more agile while it was in motion (Persons and Currie, 2011, "Abstract") (Jeanna Bryner, 2011) (Snively et al., 2018, pg. 3) (Laura Geggel, 2018). In fact, it seems to have been more agile than other carnivorous theropods (Snively et al., 2018, pg. 63) (Larson and Carpenter, 2008, pg. 382). Tyrannosaur feet were designed to make quick turns (pg. 382), and they seem to have been faster than their prey (pg. 381). Even though T. rex was heavy, this doesn't mean that it was slow (Snively et al., 2018, pg. 46). It seems more likely now that T. rex could have ran up to 20-plus miles per hour, was surprisingly athletic, and used packs to help it hunt for food. However, Dececchi et al., (2020) says that theropods over 1000 kg would not be able to run fast, despite their different limb lengths. Instead, they were speed-walkers (Dececchi et al., 2020, "Abstract;" "Discussion," "Getting up to speed" p. 3; "Why tyrannosaurids?" p. 2) (EurekAlert, 2020). Young tyrannosaurs were surprisingly fast ("Results," "Relative leg length" p. 1). For the adult tyrannosaurs, T. rex was estimated to have ran up to 18 km/h (12 miles per hour), but it could do this for a long time (The Canadian Press, 2020). Pack-hunting was also suggested to help T. rex take down prey (The Canadian Press, 2020) (Dececchi et al., 2020, "Discussion," "Why tyrannosaurids?" p. 2-3). In summary, T. rex seems to have moved at 12 miles per hour. It still would have been fast, and agile, enough to capture prey.

To my surprise, 12 miles per hour is pretty fast. Take a look at this:

An African elephant can reach a speed of 13.2 mph (5.9 m s-1) (Hutchinson et al., 2006, pg. 3814 Table 1). An Asian elephant can run up to 8.3-15.2 miles per hour (University of London Royal Veterinary College, 2003, "Are fast moving elephants really running?") (Hutchinson et al., 2006, "Summary;" pg. 3814 Table 1). It seems that T. rex can run just as fast as an African elephant! In fact, depending on how large an individual is, T. rex could have, possibly, moved faster. Asian elephants are smaller than the African elephants, weighing up to 7,700-15,000 pounds (3.9-7 tons) (Denver Zoo, "Asian Elephant: Physical Description"). African elephants weigh 4-24,000 pounds (2-12 tons) (Sea World, "All About Elephants: Physical Characteristics: Size") (Elephants for Africa, "Elephant Facts: Facts about Elephant Size"). A 7-ton T. rex could have been as fast as an Asian elephant, moving up to 8.3-15.2 miles per hour. A 9-plus-ton T. rex could have moved at 13 miles per hour, as stated previously.

T. rex would have reached its maximum size at age 19 *(Erickson et al., 2004, pg. 773) (ScienceDaily, 2004) (Carr, 2020, Figure 12, Table 14, "Abstract," "Conclusions" 22) (Laura Geggel, 2020, p. 1), but "Sue" didn't stop growing until the age of 22 (Cullen et al., 2020, Supplementary Materials, pg. 22 Table S3). Perhaps most T. rexes ceased to grow at 19, but the maximum age for T. rex seems to be 22. It reached sexual maturity around 13-15 years of age (Carr, 2020, "Conclusions" 23). In 2018, it was stated that T. rex's intelligence would have been equal to a chimpanzee's, after recent studies on its brain were conducted. This was stated by paleontologist Steven Brusatte (Jaqueline Ronson, 2018) (Columbia Magazine, 2018, "Book Expert: 'The Rise and Fall of Dinosaurs'").

There has been a long debate as to whether or not T. rex had feathers. In Bell et al., (2017), it was stated that T. rex had scales predominately along its body (neck, pelvis, and tail, and based on other tyrannosaurs, the abdomen, and thoracic/middle section of body) ("Results: (a) Description"), but it might have had feathers along its dorsum (its back, according to Merriam Webster) ("Discussion" p. 1). The arms might've been covered in feathers too. A good example of this is from The Real T-Rex with Chris Packman.

T. rex with Feathers ("Tristan Otto" Specimen from The Real T-Rex with Chris Packman):

In Benton et al., (2019), it is said that tyrannosauroids would have had "tufts of filaments" ([?]Figure 7):

It seems that T. rex was, at least, partially covered in some kind of feather-like structures along its back, and probably the arms.

Specimens and Size:

1. UCMP 119853:

Figure came from Carpenter (1982) (p. 128 Figure 5; A is labial/lateral view, B is distal/posterior/back view).

At 8 mm in height, this is the smallest specimen of T. rex found to date. It was first described by Carpenter in 1982, and I wrote a paper on it at the beginning of the year (2023). It showed that T. rex's tooth morphology didn't change during ontogeny.

I wrote a paper on the specimen:
https://www.academia.edu/96575022/A_Baby_Tyrannosaurus_rex_Premaxillary_or_First_Maxillary_Tooth

2. BHI 6439:

Pic belongs to Hiroshi Kato (2018) (from Twitter).

At 23 feet long (7.0 meters), this is, what I consider to be, a baby T. rex specimen (probably 8 or 9 years of age). The lingual bar covering the first two alveoli, only 13 alveoli/teeth present, and the first tooth being incisiform, shows that T. rex's dentary morphology and tooth count doesn't decrease during ontogeny. This is decisively different from the cf. Dryptosaurus specimen "Jane," which was 22 feet (6.7 meters) long. "Jane" had the lingual bar covering the first alveoli, had 17 teeth present, and the first tooth was not incisiform.

I wrote a description of the specimen:
https://www.academia.edu/105502160/A_Description_of_the_Baby_T_rex_Specimen_BHI_6439

3. UCRC-PV 1:

Pic belongs to Larson (2018) (from Twitter).

Another baby specimen. At 26 feet (8.0 meters) long, this specimen's arm morphology was identical to the adults'. The manual phalanx 1-1 is short, as seen in other T. rex specimens like TCM 2001.90.1 ("Bucky"), MOR 980, and others. cf. Dryptosaurus specimens BHI 6437 had an elongated manual phalanx 1-1, as seen in the holotype specimen of Dryptosaurus.

4. CM 9380 (Holotype):

The original/holotype skeleton of T. rex is CM 9380. This specimen was 42 feet long (12.9 meters), and weighted 7.4 tons. It was a female.

5. FMNH PR 2081 (Formerly BHI 2033) ("Sue"):

BHI 2033/FMNH PR 2081, or "Sue," is the most complete specimen of T. rex known. She's 45 feet long (13.6 meters) and weighed up to 9.3 tons. At 28-33 years of age, "Sue" is also one of the oldest. "Sue's" skull is 166.6 cm long, and Gignac and Erickson (2017) stated that "Sue's" skull generated 17,769-34,522 thousand newtons of bite force (Table 1). That's the weight of three cars (AMNH, 2019, "Mega-Predator T. rex Had Super Senses")!

Fun fact: Despite her name, it's not known for sure if "Sue" was definitely a female (Peter Larson, 1994) or a male (Christopher Brochu, 2003, pg. 129).

Six other (good) specimens of T. rex rival "Sue" in age or size:

6. UCMP 118742:

Figure is from Witmer (2019) (Figure 6).

This specimen is known as being either a 16-year old sub-adult, or perhaps an adult specimen. Either way, it was 45 feet long (13.8 meters).

7. RSM 2523.8 ("Scotty"):

"Scotty," at 22-30-plus years of age, is 46 feet long (14.1 meters) and weighed 9.7 tons.

8. MOR 980 ("Peck's rex," "Rigby rex," "T. rex imperator"):

This specimen was stated to have been larger than "Sue," then smaller, then back to "rivaling" "Sue" in length. From my own measurements, it seems like MOR 980 exceeded "Sue" in length, reaching 47 feet (14.3 meters).

9. LACM 23844:

Another well-known specimen. It reached 47 feet (14.3 meters), like MOR 980.

10. BMNH R7794/(?)NHMUK R7994 (Formerly AMNH 5866/"Dynamosaurus imperiosus"):

This is technically the original holotype specimen of T. rex, but it was labelled as "Dynamosaurus imperiosus" instead... Under CM 9380 in the same paper... The early bird catches the worm. Anyway, this specimen was 50 feet (15.2 meters).

11. NMMNH P-1013-1/NMMNH P-3698 ("Elephant Butte T. rex"): ("Elephant Butte T. rex"):

This specimen is based on a semi-complete dentary. Based on the dentary/tooth row length up to the 4th alveolus, it was 51 feet (15.5 meters) (at best). This is the largest (relatively good) specimen to date.

12. UCMP 137538 IV-2 (Longrich et al., 2010):

Based on a pedal phalanx IV-2, this specimen was touted all over the internet as being larger than "Sue." People nowadays say that it was either the same size as, or smaller than, "Sue." However, using my own measurements for both specimens, UCMP does come out being longer than "Sue." It reached 59 feet (17.9 meters).

13. MOR 1126 ("Celeste rex;" "C. rex"):

Photo came from Smith (2000).

This specimen was stated by paleontologist Dr. Jack Horner to have been larger than "Sue." Mysteriously, there hasn't been a full description of this specimen yet... A figure of a pedal phalanx II-2 from the specimen was put in the same paper that featured UCMP 137538 (Longrich et al., 2010). Based on a comparison with "Sue," this specimen would've been 64 feet long (19.6 meters).

14. YPM VP 057488(A):

Figure 5 from Dalman (2013).

This specimen came out of nowhere. It's a pedal phalanx II-2 that's larger than "Sue," according to sizes obtained by Dalman (2013), Brochu (2003), and myself! Compared to "Sue's" pedal phalanx II-2, this individual was 66 feet long (20.0 meters).

Weight:

T. rex is officially the heaviest theropod of all time. "Sue" weighed 9.3 tons and "Scotty" weighed 9.7 tons (Petersons IV et al., 2019).

Vocals:
In 2018, a documentary called, The Real T.rex with Chris Packham, tried to give the most accurate depiction of the "tyrant lizard king" to date. In the documentary, they explained that T. rex was more closely related to birds and crocodilians, who don't roar like T. rex has often been depicted doing (ex. Jurassic Park). Crocodilians, in particular, make low frequency sounds, and T. rex's ears were designed to pick up those sounds. Therefore, it would have had a low frequency-type roar. T. rex has been depicted as roaring like a mammal, but T. rex would have sounded like a bird or crocodilian, mainly a crocodilian. The researchers in the documentary gave the T. rex a modified Chinese Alligator vocal, and it resulted in sounding like a demon out of hell... or the Jaws theme song.

In my opinion, I think T. rex would have sounded like an American alligator, since both of them lived in North America. However, it would have been an even deeper version of the alligator's vocals. Other candidates I think would be good are the cassowary and emu. In fact, I think T. rex's roar could have been a combination of all three of these.

Alligator Vocals 1:

Alligator Vocals 2:

Cassowary Vocals:

Interestingly, it's been noted since 2009 that dinosaurs, in general, didn't seem to make vocal sounds. Phil Center (2009) says, "Acoustic displays by non-avian dinosaurs were therefore probably non-vocal," ("Abstract"). However, he notes that his hypotheses might be reaffirmed or changed in the future ("The big picture," p. 7). It seems that his hypotheses remained the same though.

Time and Place:
T. rex lived 84-66 million years ago, during the Campanian-Maastrichtian of the late Cretaceous period (Connor, 1992, pg. 12) (White et al., 1998, "Introduction": Depositional Setting") (Wilson, 2005, "Abstract," "Chronostratigraphic Framework" pg. 57) (Woodward, 2005, Chapter 2 Part 2: "Tectonic Setting" pg. 6) (Urban and Lamanna, 2006, pg. 231-232) (Dalman et al., 2018, pp. 125-126, 136) (Arens and Allen, 2014, pg. 175) (Wich, 2014, "Abstract") (NPS, "Fossils of the 2018 National Fossil Day Artwork," 2018) (Leslie et al., 2018, "Paleoclimate and Depositional Environments" pg. 6). It lived in North America (Sampson and Loewen, 2005) (Sebastian G. Dalman, 2013, "Abstract:) (McClain et al., 2018, "Abstract," pg. 165) (New Mexico Museum of Natural History and Science, "New Mexico: The Tyrannosaur State") (Sullivan and Lucas, 2015, pg. 112-114) (Lozinsky et al., 1984, pg. 73) (John W. Hoganson, 2012) (Serrano-Branas et al., 2014, pg, 164, Table 3) (Dalman et al., 2021, Geological Settings, para. 3; Figure 20 C), and Canada (Persons IV et al., 2019, "Introduction" pg. 657) (Berry, 2008, p. 12).

T. rex was discovered in the Campanian-age Two Medicine (81-75 million years old) (Dalman et al., 2018, pp. 125-126, 136), or Judith River (75 million years old) Formations in Montana (Urban and Lamanna, 2006, pg. 231-232), the Campanian-Maastrichtian-aged Naashiobito Member of the Ojo Alamo Sandstone (73-68 million years old) (Lucas et al., 1987, pg. 40 Figure 3 "E," pg. 46 "Age of the Naashiobito Member of the Kirkland Shale) (*Lucas et al., 2009, Figure 1, "Magnetostratigraphy" p. 5), and the Maastrichtian-aged Javelina Formation (70-66 million years old) in Texas (*Lehman, 1991, "Abstract;" back up in Kelson et al., 2018, Figure 1) (*Woodward, 2005, Chapter 2 Part 2: "Tectonic Setting" pg. 6) (*Lehman et al., 2006, "Abstract") ((?)Jasinski and Sullivan, 2011, p. 213) (Wich, 2014, "Abstract") (NPS, 2018, "Fossils of the 2018 National Fossil Day Artwork") (*Leslie et al., 2018, "Results": "Detrital Sanidine Dating" pg. 8-9), the Lance Formation of Wyoming and Montana (68-66 million years ago) (*Connor, 1992, pg. 12) (Sebastian G. Dalman, 2013, "Abstract"), the Hell Creek Formation of Montana, North and South Dakota (68-66 million years ago) (*White et al., 1998, "Introduction": Depositional Setting") (*Wilson, 2005, "Abstract," "Chronostratigraphic Framework" pg. 57) (*Arens and Allen, 2014, pg. 175) (Larson, 1994, pg. 139), the Frenchman Formation of Canada (Persons IV et al., 2019, "Introduction" pg. 657), the North Horn Formation of Utah (Sampson and Loewen, 2005), the McRae Formation of New Mexico (Lozinsky et al., 1984, pg. 73), and the Lomas Coloradas Formation of Mexico (Serrano-Branas et al., 2014, pg. 164, Table 3). One mature skeleton was discovered in Colorado, and was dated to 71 Ma (Berry, 2008, pp. 12-13). Another specimen, named cf. Tyrannosaurus sp., came from the Hall Lake Formation of New Mexico, aged 73.2 Ma (Dalman et al., 2021, Geological Setting, para. 3; Figure 20 C). This specimen seems to be NMMNH P-1013-1 (Larson and Carpenter, 2008, pp. 17-18).

Invasive/Rare Species:
Very few fossils of Tyrannosaurus/T. rex have been found from the Campania-era formations of North America. This seems to be due to a possible hypothesis/theory that T. rex was an invasive species from Asia. According to paleontologists Dr. Thomas Carr and Steven Brusatte, T. rex is closely related to Zhuchengtyrannus and Tarbosaurus, and a land bridge between Asia and North America opened up 67 million years ago. This would have allowed T. rex to enter into North America. However, the presence of Tyrannosaurus/T. rex fossils from the Campanian seems to show that T. rex appeared a lot earlier than that.

However, I have another idea in mind. T. rex might have been around during the Campanian, but it was a rare predator. Other tyrannosaurids like Gorgosaurus and Daspletosaurus were very abundant during the Campanian, and there were other tyrannosaurs like Bistahieversor, Appalachiosaurus, Teratophoneus, and Lythronax. These tyrannosaurs would have been the top predators during the Campanian, and since Tyrannosaurus fossils are very rare in the Campanian, it seems that T. rex might have been a "hidden predator" during this time. However, when the Maastrichtian came along, T. rex might have driven the other tyrannosaurs into extinction, since it was bigger. This was also hinted by other paleontologists in 2016. Two other tyrannosauroids, Albertosaurus and Dryptosaurus, also lived during the Maastrichtian, but T. rex was the top predator. The decline in the number of different tyrannosaur genus during the Maastrichtian might seem to point towards this as well.

In conclusion, it seems that the genus Tyrannosaurus, perhaps the species Tyrannosaurus rex in general, appeared during the Campanian of North America, 84-72 million years ago. This is much older than the 68-66-million-year time frame that T.rex is usually given. Also during the Campanian, T. rex seems to have been a rare genus of tyrannosauroid, but it would become the top predator when the Maastrichtian came around, seemingly kicking other tyrannosauroids into extinction in the process.

Ontogeny:
After an extensive investigation, here's a summary of the traits that T. rex had during ontogeny:

1. T. rex doesn't show any signs of increasing, and then decreasing, in tooth count during ontogeny. In fact, it shows the opposite. T. rex's tooth count seems to have stayed the same, or even increased. For example: "Stan" had 11 teeth in its maxilla and 13 teeth in its dentary, but "Samson" had 13 teeth in its maxilla and 15 teeth in its dentary. "Stan" is 18 years old, while "Samson" is 23. The small fluctuations in tooth counts is a result of individual variation, and variation is not too vast from specimen to specimen.

2. The nasals had very few, and small, rugosities on it, even when the individual was 14 years old. This is seen in LACM 23845. The rugosities seem to have grown larger, and increased in number, when the individual grew to be a subadult. This is seen in "Stan."

3. T. rex's maxilla had a wide maxillary fenesta (hole) in its antorbital fossa throughout its lifetime. It did not change shape during ontogeny.

4. The maxillary strut grew from being weak during a young age to being very prominent and deep in adulthood, and the maxillary fenestra was closer in position to the strut rather than the antorbital fenestra. It did not change position during ontogeny.

5. Maxillary strut is circular, and straight, in the beginning. This is near the front of the maxilla, and doesn't change during ontogeny. The strut is so straight at the beginning that a straight line could be drawn through it, cutting it in half.

6. The first maxillary tooth is probably slightly incisiform when the species was a baby, but it is still serrated and they are located on the lateral/side views of the tooth, unlike in Nanotyrannus', Dryptosaurus', and Gorgosaurus'. Nanotyrannus' is either unserrated, or very lightly serrated, and there are ridges on the lateral/side views of the tooth. These ridges are not on T. rex's first maxillary tooth, and this is evident in baby specimens. Tarbosaurus' was the same. Gorgosaurus' first maxillary tooth was identical to Nanotyrannus'.

7. The lingual bar in the interior/medial side of the dentary covered the first two alveoli/teeth throughout its lifetime.

8. The teeth were always wide without any sign of changing shape (extremely blade-like to extremely thick) during ontogeny.

9. T. rex's lacrimal horn, or cornual process, was probably, or not, present when it was 4, as seen in "Baby Bob." However, it may have appeared around the animal's juvenile stage, as seen in RSM P.2990.1. When the animal turned 14, the lacrimal horn disappeared. This is seen in LACM 23845.

10. The arms started out small and grew during ontogeny. They didn't start out large and then shrink. This is seen in the juvenile specimens LACM 23845 and UCRC-PV 1.

11. The manual phalanx 1-1 started small and skinny during ontogeny, as seen in UCRC-PV 1, "Bucky," and , and MOR 980. It was similar to Albertosaurus' and Daspletosaurus'. Over time, the bone grew to be thicker but not that much taller, as seen in the adult specimen MOR 980. The largest manual phalanx 1-1 is about 10 cm long, and it belongs to "Scotty" (Persons IV et al., 2019, p. 669).

12. The manual unguals (hand claws) were small but thick throughout T. rex's lifetime, contrary to Nanotyrannus' which were longer.

13. T. rex's femur and the tibia were either about the same lengths, or the tibia was slightly longer, when it was a baby and a juvenile, as demonstrated by "Baby Bob," LACM 23845, and MOR 009. At best, the tibia was barely and longer than the femur during this time in its life.

14. The skull was shorter than the femur for baby-juvenile specimens, as seen in "Baby Bob" and LACM 23845.

15. The skull grew larger than the femur when the animal became a subadult, as seen in "Stan"

16. The femur grew larger than the tibia when T. rex became a subadult, as seen in USNM 6183 and "Stan."

17. T. rex reached maturity (stopped growing) at the age of 19, as indicated by an EFS marker in "Sue" (Erickson et al., 2004, p. 773 Figure 1 C).

Here's my four growth charts for T. rex's and juvenile Dryptosaurus' ("Nanotyrannus") femur and tibia lengths:

As you can see, three out of four of the charts state that the juvenile Dryptosaurus specimens ("Nanotyrannus") are either outside, or way below, T. rex's growth in terms of femur and tibia lengths. All trendlines are linear. The growth trendline (R^2) for the first chart is 0.941 for T. rex's femur, and 0.777 for the tibia. Dryptosaurus' is 0.998 for the femur, but 1 for the tibia. The second chart shows 0.888 for T. rex's femur, and 0.648 for the tibia. Dryptosaurus' femur is 0.998 again, but 1 for the tibia. The third chart shows 0.932 for T. rex's femur, and 0.8 for its tibia. Dryptosaurus' femur is 0.893, and its tibia is 0.887. A more positive result this time. For the fourth and final chart, T. rex's femur is 0.888, and the tibia is 0.648. Dryptosaurus' femur is 0.883, and its tibia is 0.887.

This is not good if the juvenile Dryptosaurus specimens ("Nanotyrannus") were juvenile T. rexes.

Dryptosaurus (Blue) vs. T. rex (Red) Ontogeny Chart:

Note: In the Dryptosaurus chart, the 7.3-meter specimen is the actual Dryptosaurus holotype. No age has been assigned to this specimen, but it has been stated as being an adult in Brusatte et al., (2011).

The trendline (linear) (R^2) for Dryptosaurus is 0.775. The trendline for T. rex is 0.962. A 7-year old Dryptosaurus (CMNH 7541) was 1.4 meters shorter than a 4-year old T. rex ("Baby Bob"). I obtained a length of 7.0 meters for BHI 6439, which would place this specimen in between a 4-14-year old individual. However, this specimen would probably have been only slightly older than "Baby Bob," since I got a length of 6.0 meters for that specimen. So, a baby T. rex would have been the same size as a juvenile Dryptosaurus. An adult Dryptosaurus (the actual holotype of Dryptosaurus), at 7.3 meters in length, is completely dwarfed by two 14-year old T. rex specimens ('Tinker" and LACM 23845). This leads me to conclude that an actual juvenile T. rex would be two, or more, meters longer than an adult Dryptosaurus.

Update (3/5/22):

Chart 3 (Featuring all the T. rex specimens listed here):

Note: T. rex specimen BHI 6439's age is unknown, so it is left blank. This is still the same for the Dryptosaurus holotype.

The trendline (linear) (R^2) for Dryptosaurus is still 0.775, but the trendline for T. rex is down to 0.908. Still a large difference between the two species, and the results from my first ontogeny chart still ring true.

For more information, check out these two posts below:
Link 1:

https://psdinosaurs.blogspot.com/2021/08/evidence-of-subadult-nanotyrannus.html

Link 2:

https://psdinosaurs.blogspot.com/2021/11/my-ontogenetic-growth-series-for-t-rex.html

Prey:
T. rex Hunting Triceratops:

The prey that T. rex hunted was some of the deadliest, and largest, animals that ever roamed the planet. These animals included Triceratops (23-30 feet; 7.0-9.2 meters), Ankylosaurus (18-20 feet; 5.5-6.1 meters), Denversaurus (18 feet; 5.5 meters), Edmontosaurus (30-62 feet; 9.0-18.9 meters), Pachycephalosaurus (10 feet; 3.0 meters), Struthiomimus (16 feet; 4.9 meters), and Alamosaurus (70-225 feet; 21.2-68.5 meters). These creatures had body armor, long tails, and size for defense. However, T. rex had the intelligence, jaw and arm strength, agility, and numbers to take on some of the most dangerous prey. Triceratops had a frill and horns for protection. However, Krauss and Robinson (2013) suggested that T. rex could kill a Triceratops by using a technique called "cow-tipping." T. rex would have to knock the Triceratops onto its side, and then go in for the kill ("Abstract"). Funny enough, this was shown in Jurassic Park when the T. rex knocked the visitor car over with Lex and Tim in it, and tried to do so again in a chase scene with a Jeep.

Edmontosaurus had a tail, and its size, for protection. However, Kenneth Carpenter (2001) describes an Edmontosaurus skeleton with a puncture wound from a T. rex in its tail vertebra. The hadrosaur managed to escape (pg. 139-143).

Update 10/16/20: Tanke and Rothschild, 2014 say was caused by another Edmontosaurus, not a T. rex. If it was being hunted by a T. rex, then the wound would be even worse. Heck, the animal would probably be dead altogether ["Abstract," "Discussion" pp. 8-13]).

Alamosaurus was the largest animal in T. rex's environment. Each-hunting more than likely was the only option for T. rex if it tried to hunt Alamosaurus. Pachycephalosaurus had a dome on the top of its head made of solid bone. It has been controversial as to how this animal may, or might not, have used its dome-covered head, but it does seem to have been used for combat (Peterson and Vitto, 2012, "Abstract," "Discussion") (Peterson and Longrich, 2013, "Abstract"). Struthiomimus had long legs for running. It seems likely that juvenile Tyrannosaurus hunted these two animals, since they were faster than the heavier adults (Aylin Woodward, 2020).

Usually, it is said that only the young, sick, or old animals would get taken down by predators. This is true, since they are unable to get away faster, or defend themselves better, than healthier animals. Also, if an individual weighs too much, then they were probably left alone by predators. This is mainly due to the possibility that the predator's health could have been in jeopardy. This was studied among birds of prey by Genovart et al., (2010) ("Abstract").

It has been debated whether or not T. rex was an obligate scavenger. However, Carbone et al., (2011) says that T. rex, along with other huge predatory dinosaurs, "would have been unable to compete as obligate scavengers and would have primarily hunted large vertebrate prey, similar to many large mammalian carnivores in modern-day ecosystems" ("Abstract").

Alamosaurus vs. T. rex from Riley Black (2009):

Enemies:

Aside from T. rex itself, T. rex's enemies consisted of a large dromeosaur called Dakotaraptor (13-17 feet; 3.8-5.2 meters), the tyrannosauroids Dryptosaurus (24 feet; 7.3 meters) and Appalachiosaurus (24-25 feet; 7.3-7.6 meters), the tyrannosaurids Teratophoneus (23 feet; 7.0 meters), Gorgosaurus (28 feet; 8.5 meters), Bistahieversor (29 feet, 8.9 meters), Daspletosaurus (25-31 feet; 7.7-9.4 meters), Lythronax (31 feet; 9.5 meters), and Albertosaurus (31-32 feet; 9.5-9.6 meters). Another enemy was the pterosaur, Quetzalcoatlus (52 feet; 15.7 meters).

Links:
Original Papers:
Osborn (1905) (pg. 262):
http://digitallibrary.amnh.org/bitstream/handle/2246/1464//v2/dspace/ingest/pdfSource/bul/B021a14.pdf?sequence=1&isAllowed=y
Osborn (1906):

http://digitallibrary.amnh.org/bitstream/handle/2246/1473/B022a16.pdf;jsessionid=A5E2CEC741C29C429F5CF67FEEF543BA?sequence=1
Name Meaning:
Smithsonian. "Fact Sheet: Tyrannosaurus rex." 2014:
https://www.si.edu/newsdesk/factsheets/tyrannosaurus-rex
Joseph Castro (2017) (P. 2):
https://www.livescience.com/23868-tyrannosaurus-rex-facts.html#:~:text=The%20name%20Tyrannosaurus%20rex%20means,means%20%22king%22%20in%20Latin.

Time:
Campanian:
https://psdinosaurs.blogspot.com/2019/12/did-tyrannosaurus-appear-during.html
Urban and Lamanna (2006) (PP. 231-232):
https://www.researchgate.net/publication/270582382_Evidence_of_a_giant_tyrannosaurid_Dinosauria_Theropoda_from_the_Upper_Cretaceous_Campanian_of_Montana
Dalman et al., (2018) (PP. 125-126, 136):
https://www.researchgate.net/publication/328676947_TYRANNOSAURID_TEETH_FROM_THE_UPPER_CRETACEOUS_CAMPANIAN_TWO_MEDICINE_FORMATION_OF_MONTANA
Dalman et al., (2021) (Geological Setting, para. 3; Figure 20 C):
https://www.sciencedirect.com/science/article/abs/pii/S0195667121002822
Larson and Carpenter (2008) (PP. 17-18):
https://www.google.com/books/edition/Tyrannosaurus_Rex_the_Tyrant_King/5WH9RnfKco4C?hl=en&gbpv=1&dq=Hall+Lake+Formation+Tyrannosaurus&pg=PA7&printsec=frontcover
Campanian-Maastrichtian:
Lucas et al., (2009) (Figure 1, "Magnetostratigraphy" p. 5):
https://palaeo-electronica.org/2009_2/199/199.pdf
Link 2:
https://www.yumpu.com/en/document/read/13877844/palaeontologia-electronica-robert-m-sullivan
Link 3:
http://webcache.googleusercontent.com/search?q=cache:52FfhPLynTIJ:nebula.wsimg.com/374609f962db54145b03444879d7dcba%3FAccessKeyId%3D7A0F80A288FF44894815%26disposition%3D0%26alloworigin%3D1+&cd=11&hl=en&ct=clnk&gl=us
Maastrictian:
Lucas et al., (1987) (Pg. 40 Figure 3 "E," pg. 46 "Age of the Naashiobito Member of the Kirkland Shale):
https://books.google.com/books?id=28kOM7jNJLsC&pg=PA46&lpg=PA46&dq=Naashoibito+Member+age&source=bl&ots=4JFXGDKTDL&sig=ACfU3U1arvE7J0YOU6XYdIlT-dUcQJcaLQ&hl=en&sa=X&ved=2ahUKEwiomuaD_ZHrAhXAl3IEHSdoDP0Q6AEwAHoECAoQAQ#v=onepage&q=Naashoibito%20Member%20age&f=false
Lehman et al., (1991) ("Abstract"):
https://www.sciencedirect.com/science/article/abs/pii/003707389190047H?via%3Dihub
Connor (1992) (P. 12):
https://pubs.usgs.gov/bul/1917i/report.pdf
Larson (1994) (P. 139):
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010028790.pdf
White et al., (1998) ("Introduction": Depositional Setting"):
https://www.jstor.org/stable/3515280?seq=1
Wilson (2005) ("Abstract," "Chronostratigraphic Framework" p. 57):
https://www.researchgate.net/publication/226509400_Mammalian_Faunal_Dynamics_During_the_Last_18_Million_Years_of_the_Cretaceous_in_Garfield_County_Montana
Woodward (2005) (Chapter 2 Part 2: "Tectonic Setting" p. 6):
https://ttu-ir.tdl.org/handle/2346/1091
Urban and Lamanna (2006) ("Introduction," P. 231):
https://www.researchgate.net/publication/270582382_Evidence_of_a_giant_tyrannosaurid_Dinosauria_Theropoda_from_the_Upper_Cretaceous_Campanian_of_Montana
Lehman et al., (2006) ("Abstract"):
https://www.tandfonline.com/doi/abs/10.1671/0272-4634(2006)26%5B922%3AFIUAFT%5D2.0.CO%3B2

Berry (2008):
https://geoinfo.nmt.edu/publications/periodicals/nmg/30/n1/nmg_v30_n1_p12.pdf
Abstract:
https://www.semanticscholar.org/paper/Evidence-for-aTyrannosaurus-rex-from-southeastern-Osborn-Berry/a81db8a7fff4af4b8f1c3e994e3fba90516facce
Jasinski and Sullivan (2011) (P. 213):

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.694.3557&rep=rep1&type=pdf

Link 2:

https://books.google.com/books?id=fugoCgAAQBAJ&pg=PA213&lpg=PA213&dq=javelina+formation+u-pb+dating&source=bl&ots=KZkjxhphVt&sig=ACfU3U1m_uZLp44nhdaKwpncDEw2unczpA&hl=en&sa=X&ved=2ahUKEwj81-Sy45HrAhXThHIEHWHTCSwQ6AEwB3oECAcQAQ#v=onepage&q=javelina%20formation%20u-pb%20dating&f=false

Arens and Allen (2014) (P. 175):
https://books.google.com/books?id=chKDAgAAQBAJ&pg=PA173&lpg=PA173&dq=A+florule+from+the+base+of+the+Hell+Creek+Formation+in+the+type+area+of+eastern+Montana:+Implications+for+vegetation+and+climate&source=bl&ots=Kjk3INQAlf&sig=ACfU3U3H7qwv1qDhZFPttjd8fFtHKzcL2A&hl=en&sa=X&ved=2ahUKEwiot9u5l_7qAhVjYTUKHcoYDv0Q6AEwAnoECAoQAQ#v=onepage&q=A%20florule%20from%20the%20base%20of%20the%20Hell%20Creek%20Formation%20in%20the%20type%20area%20of%20eastern%20Montana%3A%20Implications%20for%20vegetation%20and%20climate&f=false
Link 2:
https://www.researchgate.net/publication/279980306_A_florule_from_the_base_of_the_Hell_Creek_Formation_in_the_type_area_of_eastern_Montana_Implications_for_vegetation_and_climate
Wich (2014) ("Abstract"):
https://www.sciencedirect.com/science/article/pii/S0195667114000500
NPS. "Fossils of the 2018 National Fossil Day Artwork." 2018:
https://www.nps.gov/articles/fossils-of-the-2018-national-fossil-day-artwork.htm
Leslie et al., (2018) ("Paleoclimate and Depositional Environments" Pg. 6):
https://www.researchgate.net/publication/326054859_Revised_age_constraints_for_Late_Cretaceous_to_early_Paleocene_terrestrial_strata_from_the_Dawson_Creek_section_Big_Bend_National_Park_west_Texas
Link 2:
https://webcache.googleusercontent.com/search?q=cache:fkAz7KbDpU4J:https://osf.io/utrsb/download/+&cd=3&hl=en&ct=clnk&gl=us
Kelson et al., (2018) (Figure 1):
https://www.researchgate.net/publication/328235438_Warm_Terrestrial_Subtropics_During_the_Paleocene_and_Eocene_Carbonate_Clumped_Isotope_D_47_Evidence_From_the_Tornillo_Basin_Texas_USA
Persons IV et al., (2019) ("Introduction" pg. 657):
https://onlinelibrary.wiley.com/doi/epdf/10.1002/ar.24118?tracking_action=preview_click&r3_referer=wol&show_checkout=1
International Chronostratigraphic Chart (2020):
https://stratigraphy.org/timescale/
International Commission of Stratigraphy Website:
https://stratigraphy.org/news/130
Locations:
North America:
Lozinsky et al., (1984) (Pg. 73):
https://geoinfo.nmt.edu/publications/periodicals/nmg/6/n4/nmg_v6_n4_p72.pdf
Sampson and Loewen (2005):
http://www.bioone.org/doi/abs/10.1671/0272-4634(2005)025%5B0469:TRFTUC%5D2.0.CO%3B2
Link 2:
https://www.jstor.org/stable/4524461?seq=1
Link 3:
https://www.tandfonline.com/doi/abs/10.1671/0272-4634%282005%29025%5B0469%3ATRFTUC%5D2.0.CO%3B2
John W. Hoganson (2012):
https://www.dmr.nd.gov/ndgs/documents/newsletter/2012JULY/TheOccurrenceofTyrannosaurusrex.pdf
Sebastian G. Dalman (2013) ("Abstract"):
http://www.bioone.org/doi/abs/10.3374/014.054.0202
Serrano-Branas et al., (2014) (Pg, 164, Table 3):
https://www.academia.edu/6608485/Tyrannosaurid_teeth_from_the_Lomas_Coloradas_Formation_Cabullona_Group_Upper_Cretaceous_Sonora_México
Link 2:
https://www.researchgate.net/publication/261218484_Tyrannosaurid_teeth_from_the_Lomas_Coloradas_Formation_Cabullona_Group_Upper_Cretaceous_Sonora_Mexico
Sullivan and Lucas (2015) (Pg. 112-114):
https://www.researchgate.net/publication/299592501_Cretaceous_vertebrates_of_New_Mexico
McClain et al., (2018) ("Abstract," pg. 165):
https://www.researchgate.net/publication/324653356_Tyrannosaur_cannibalism_A_case_of_a_tooth-traced_tyrannosaurid_bone_in_the_Lance_Formation_Maastrichtian_Wyoming
New Mexico Museum of Natural History and Science ("New Mexico: The Tyrannosaur State"):
http://www.nmnaturalhistory.org/online-exhibits/new-mexico-tyrannosaur-state
Canada:
Persons IV et al., (2019) ("Introduction" pg. 657):
https://onlinelibrary.wiley.com/doi/epdf/10.1002/ar.24118?tracking_action=preview_click&r3_referer=wol&show_checkout=1
Size:
https://psdinosaurs.blogspot.com/2018/05/tyrannosaurus-rex-specimen-sizes.html
Link 2:
https://psdinosaurs.blogspot.com/2019/08/size-calculations-for-tyrannosaurus-rex.html
Link 3:
https://psdinosaurs.blogspot.com/2018/11/how-big-was-sue-fmnh-pr-2081.html
Link 4:
https://psdinosaurs.blogspot.com/2018/10/calculations-for-largest-theropods.html
Skull Sizes:
https://psdinosaurs.blogspot.com/2019/08/size-calculations-for-tyrannosaurus-rex.html
Link 2:
https://psdinosaurs.blogspot.com/2018/05/tyrannosaurus-rex-specimen-sizes.html
Link 3:
https://psdinosaurs.blogspot.com/2018/10/calculations-for-largest-theropods.html
Jaw Power:
Gignac and Erickson (2017) ("Introduction" pg. 2, Figure 1, Table 1):
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5435714/
AMNH (2019) ("Mega-Predator T. rex Had Super Senses"):
https://www.amnh.org/explore/news-blogs/on-exhibit-posts/t-rex-super-senses
Carr (2020) ("Growth categories," "Juveniles," "Large juveniles," "Dentition;" "Bite force and maturity;" "Tooth morphology" p. 2; "Skull and jaw strength" p. 6; "Conclusions" 21):
https://peerj.com/articles/9192/
EurekAlert! "New study: Tyrannosaurus rex size doesn't determine age." 2020. P. 5:
https://www.eurekalert.org/pub_releases/2020-06/p-nst060220.php
Lips:
Reisz and Larson (2016) (Pg. 64-66):
https://cansvp.files.wordpress.com/2013/08/csvp-2016-abstract-book-compressed.pdf
Blake Eligh (2016):
https://www.utoronto.ca/news/did-dinosaurs-have-lips-ask-university-toronto-paleontologist
Mindy Weisberger (2016):
https://www.livescience.com/54912-did-t-rex-have-lips.html
Emanuela Grinberg (2016):
https://www.cnn.com/2016/05/22/world/dinosaur-lips-teeth-study/index.html
Phys (2016):
https://phys.org/news/2016-06-dinosaurs-lips.html
Tongue:
Mindy Weisberger (2018):
https://www.scientificamerican.com/article/t-rex-couldnt-stick-out-its-tongue/
ScienceDaily (2018):
https://www.sciencedaily.com/releases/2018/06/180620150129.htm
Sense of Smell:
John van Radowitz (2008):
https://www.independent.co.uk/news/science/sense-of-smell-helped-t-rex-hunt-at-night-977432.html
Hughes and Finarelli (2019) ("Discussion," "Inferred olfactory receptor repertoires of extinct taxa" p. 1-2):
https://royalsocietypublishing.org/doi/10.1098/rspb.2019.0909
Arms:
Osborn (1906) (Pg. 290-291):
http://digitallibrary.amnh.org/bitstream/handle/2246/1473/B022a16.pdf;jsessionid=A5E2CEC741C29C429F5CF67FEEF543BA?sequence=1
Horner and Lessem (1993) (Pg. 113 and 116):
https://books.google.com/books?newbks=1&newbks_redir=0&id=KPwoAQAAMAAJ&dq=horner+and+lessem+the+complete+t.rex&focus=searchwithinvolume&q=
Doug Hampton (1990) (P. 7):
https://www.latimes.com/archives/la-xpm-1990-06-24-mn-630-story.html
Helen Thompson (2014):
https://www.smithsonianmag.com/science-nature/five-things-we-dont-know-about-tyrannosaurus-rex-180951072/
Steven M. Stanley (2017) ("Abstract"):
https://gsa.confex.com/gsa/2017AM/webprogram/Paper297346.html
Thad Morgan (2017):
https://www.history.com/news/there-was-a-dangerous-purpose-behind-t-rexs-tiny-arms
Kent A. Stevens (2005):
http://ix.cs.uoregon.edu/~kent/paleontology/Tyrannosaurus/RexSit.html
Milner et al., (2009) ("Abstract: Conclusions/Significance"):

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0004591

Eliza Strickland (2009):

https://www.discovermagazine.com/planet-earth/dinosaur-handprints-show-it-could-hold-a-basketball-not-dribble

Thomas H. Maugh II (2009):

https://www.latimes.com/archives/la-xpm-2009-mar-04-sci-dinohands4-story.html

Laura Geggel (2018):
https://www.livescience.com/63858-t-rex-dinosaur-arms.html
Kenneth Carpenter (2002):
https://www.researchgate.net/publication/225366451_Forelimb_biomechanics_of_nonavian_theropod_dinosaurs_in_predation

Caneer et al., (2021):

https://www.researchgate.net/publication/348002331_TRACKS_IN_THE_UPPER_CRETACEOUS_OF_THE_RATON_BASIN_POSSIBLY_SHOW_TYRANNOSAURID_RISING_FROM_A_PRONE_POSITION

Eyes:
https://psdinosaurs.blogspot.com/2018/05/t-rex-hunter-and-scavenger-solved.html
AMNH (2019) ("Mega-Predator T. rex Had Super Senses"):
https://www.amnh.org/explore/news-blogs/on-exhibit-posts/t-rex-super-senses
Kent A. Stevens (2006) ("Abstract"):
https://www.researchgate.net/publication/228671730_Binocular_vision_in_theropod_dinosaurs
Speed:
Farlow et al., (1995) (Pg. 715) (22 miles per hour/10 meters per hour):
https://eurekamag.com/pdf/008/008239134.pdf
Sellers and Manning (2007) (Table 1):

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2279215/

Larson and Carpenter (2008) (Pg. 381):
https://books.google.com/books?id=5WH9RnfKco4C&pg=PA382&lpg=PA382&dq=t.+rex+pes+length&source=bl&ots=08cLY-1FQx&sig=ACfU3U1gS-kNQzhAzQt7kPoaiXYPQVpx3w&hl=en&sa=X&ved=2ahUKEwjN_Lm2zJPqAhUvRzABHZX3DsAQ6AEwFHoECBQQAQ#v=onepage&q=t.%20rex%20pes%20length&f=false
Sellers et al., (2017) ("Abstract" and "Conclusion"):
https://peerj.com/articles/3420/

Sid Perkins (2017) (P. 11: 17 mph):
https://www.google.com/amp/s/www.sciencenewsforstudents.org/article/t-rex-may-not-have-been-able-run-it-was-still-pretty-fast/amp

Ben Guarino (2017) (P. 4: 12 mph):
https://www.google.com/amp/s/www.washingtonpost.com/news/speaking-of-science/wp/2017/07/19/tyrannosaurus-rex-couldnt-run-but-it-was-a-speedy-walker/%3foutputType=amp

Igor Nesteruk (2018) (Pg. 46) (21-29 miles per hour):
https://www.researchgate.net/publication/324248024_Tyrannosaurus_Rex_Running_Estimations_of_Efficiency_Speed_and_Acceleration
Dececchi et al., (2020):
https://www.researchgate.net/publication/336117841_The_fast_and_the_frugal_Divergent_locomotory_strategies_drive_limb_lengthening_in_theropod_dinosaurs
EurekAlert (2020):
https://www.eurekalert.org/pub_releases/2020-05/p-trw051320.php
The Canadian Press (2020):
https://www.kamloopsthisweek.com/news/research-says-t-rex-was-built-for-long-distances-not-sprints-1.24134506

Man Running at 12 Miles Per Hour:

https://www.youtube.com/watch?v=Rx_A919BQDs
University of London Royal Veterinary College. "Are fast moving elephants really running?." 2003. ("Overview") (Date given in "History"):

https://www.rvc.ac.uk/research/research-centres-and-facilities/structure-and-motion/projects/are-fast-moving-elephants-really-running

Hutchinson et al., (2006) ("Summary;" pg. 3813; pg. 3814 Table 1):

https://jeb.biologists.org/content/jexbio/209/19/3812.full.pdf?ijkey=R5QSJxWz2U03bqn&%2520keytype=finite

Link 2:

https://jeb.biologists.org/content/209/19/3812
Denver Zoo. "Asian Elephant." "Physical Description":

https://www.denverzoo.org/wp-content/uploads/2018/09/Asian-Elephant.pdf

Sea World. "All About Elephants." "Physical Characteristics." "Size":

https://seaworld.org/animals/all-about/elephants/characteristics/

Elephants for Africa. "Elephant Facts." "Facts about Elephant Size":

https://www.elephantsforafrica.org/elephant-facts/

Packs:
Ben Schaub (2018):
https://www.cbc.ca/natureofthings/features/the-fierce-t-rex-hunted-in-female-led-packs
Agility:
Persons and Currie (2011) ("Abstract"):
https://www.researchgate.net/publication/49683186_The_Tail_of_Tyrannosaurus_Reassessing_the_Size_and_Locomotive_Importance_of_the_M_caudofemoralis_in_Non-Avian_Theropods
Jeanna Bryner (2011):
https://www.livescience.com/11207-rex-declared-faster-inspection-rump.html
Snively et al., (2018):
https://peerj.com/preprints/27021.pdf
Peer-Reviewed:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6387760/
Laura Geggel (2018):
https://www.livescience.com/64019-turning-tyrannosaurs-t-rex.html
Larson and Carpenter (2008) (Pg. 382):
https://books.google.com/books?id=5WH9RnfKco4C&pg=PA382&lpg=PA382&dq=t.+rex+pes+length&source=bl&ots=08cLY-1FQx&sig=ACfU3U1gS-kNQzhAzQt7kPoaiXYPQVpx3w&hl=en&sa=X&ved=2ahUKEwjN_Lm2zJPqAhUvRzABHZX3DsAQ6AEwFHoECBQQAQ#v=onepage&q=t.%20rex%20pes%20length&f=false
Age:
My Ontogenetic Growth Stage for T. rex:

https://psdinosaurs.blogspot.com/2021/11/my-ontogenetic-growth-series-for-t-rex.html

Erickson et al., (2004) (pg. 773):
http://www.miketaylor.org.uk/tmp/lovejoy/Erickson-et-al_04_tyrannosaurid-growth.pdf
Science Daily (2004):

https://www.sciencedaily.com/releases/2004/08/040812053920.htm
Carr (2020) (Figure 12, Table 14, "Abstract," "Conclusions" 22 and 23):
https://peerj.com/articles/9192/
Laura Geggel (2020) (P. 1):
https://www.livescience.com/tyrannosaurus-rex-size-age.html

Cullen et al., (2020):
"Abstract":

https://royalsocietypublishing.org/doi/10.1098/rspb.2020.2258
Supplementary Materials:

https://rs.figshare.com/collections/Supplementary_material_from_Osteohistological_analyses_reveal_diverse_strategies_of_theropod_dinosaur_body-size_evolution_/5195306
Katie Hunt (2020):

https://www.cnn.com/2020/11/24/world/dinosaur-growth-t-rex-study-scn/index.html