tyrannosaurus rex had feathers -- 12/23/20

Today's selection -- from The Story of the Dinosaurs in 25 Discoveries by Donald R. Prothero. Our understanding of the dinosaur Tyrannosaurus rex has developed significantly in recent decades:

"[From the initial discovery of a fossil skeleton in 1900,] Tyrannosaurus became one of the most popular of the dino­saurs and was a cultural icon. It first appeared in the 1918 silent film Ghost of Slumber Mountain and later in the 1925 stop-motion version of The Lost World (based on the 1912 novel by Sir Arthur Conan Doyle). Tyrannosaurs made an appearance in the original 1933 version of King Kong and in the 2005 Peter Jackson remake. They have appeared in everything from movies to TV shows (for example, the 'Sharptooths' of the Land Before Time series and Barney the Dinosaur on PBS Kids TV). Tyrannosaurus rex was the star and the major villain of the first four Jurassic Park/Jurassic World movies. It has been featured in parade floats and turned into thousands of items of merchandise. There was even a rock band called 'T. rex.' It is hard not to be impressed by a huge predator, towering over visitors to the museum. The late paleontologist Stephen Jay Gould said that his first sight of this skeleton at age five both terrified him and inspired him to become a paleontologist.

"In the 114 years since it was first discovered and described, a lot has been learned about Tyrannosaurus rex, The most obvious change is the posture of the dinosaur, as can be seen in the changing position of the mounted skeletons. The original American Museum mount that Osborn supervised depicted it as very reptilian, dragging its tail and walking in a tripodal pos­ture.

Restoration showing partial feathering

"During the Dinosaur Renaissance in the 1970s and 1980s, paleontolo­gists began to rethink bipedal dinosaur posture. It made more sense that they were active, fast-moving predators, with their bodies balanced on their hind legs in a bird-like stance. This configuration was confirmed by the fact that large theropod trackways never show tail drag marks, and some theropods (such as Deinonychus) have a stiffening network of elongate extensions of their vertebrae preserved in their tails. (This is similar to the ossified trusswork of tendons in duck-billed dinosaurs, and the long exten­sions of the vertebrae in sauropods.) During the 1970s, paleontologists studying the original, upright Tyrannosaurus rex mounts realized that the pose was impossible. It would cause their limbs to become disjointed, the tail to bend to an impossible degree, and weaken the joint between the skull and neck. When the American Museum revamped their dinosaur halls in 1992, they remounted their Tyrannosaurus rex (Brown's fourth specimen), which Osborn had put in the kangaroo pose in 1915, with the spine in the horizontal position (only 77 years later). Thanks to the Jurassic Park book by Michael Crichton, and the movie by Steven Spielberg in 1993, most people are now familiar with this horizontally balanced version of Tyrannosaurus rex (figure 14.3B), and the archaic, tail-dragging version seen on many toys and sculptures and images looks odd to us.

"The size estimates of Tyrannosaurus rex have also changed over time.

"Currently, the largest known relatively complete skeleton is in the Field Museum of Natural History (figure 14.4) and is nicknamed 'Sue' (after Sue Hendrikson, who discovered it). It measures 3.66 meters (12 feet) at the hips and is 12.3 meters (40 feet) in length, and the number of tail verte­brae is not a guess (as we saw with many incomplete dinosaurs, such as the sauropods, in chapter 10). This is the longest preserved Tyrannosaurus rex fossil we have -- there's a good chance that some individuals were larger. Given that the maximum length of known specimens is not guesswork, it's surprising that there are a wide range of weight estimates. Over the years the weight numbers have been as low as 8.4 metric tonnes (9.3 tons) to 14 metric tonnes (15.4 tons), but most modern estimates place it between 5.4 metric tonnes (6 tons) and 8 metric tonnes (8.8 tons). A study by Packard and colleagues in 2009 tested the methods used to estimate the dinosaur weights on elephants of known weight and argued that most of This is a common pattern among some birds and mammals that have high infant mortality rates, then rapid growth to adult size, and finally high death rates as adults due to battles over mating and the stresses of reproduction.

"Many scientists have tried various methods to see if Tyrannosaurus rex shows sexual dimorphism (differences in males and females), but no study has been convincing so far. Only one specimen has been conclusively demonstrated to be female as it had medullary tissue in a number of bones. This bone tissue is only found in female birds that are laying eggs; they lay down spongy porous medullary tissue in their bones as they divert calcium to their eggs and embryos.

"One of the most significant changes in how we think about Tyrannosau­rus concerns its body covering. For almost a century, it was rendered as a big scaly reptile, a lizard on steroids. The only known skin impressions of Tyrannosaurus preserve a mosaic of small scales. In the 1990s, discoveries in China produced many fossils of dinosaurs, birds, and mammals with soft tissues preserved, especially in lake shales, which are low in oxygen and formed in stagnant water. These produced a small tyranno­saur called Dilongparadoxus, which clearly showed filamentous feathers or fluff on its body. When a larger tyrannosaur, Yutyrannus halli, was found in China, it too was covered with a coat of feathers. Given that these animals are very closely related to Tyrannosaurus rex and all other tyrannosaurs, it is extremely likely that the iconic dinosaur of the five Jurassic Park movies was not the scaly lizard that the movie makers created but a bird-like crea­ture with a coating of down or at least feather tufts over much of its body. Of course, by the second movie (Jurassic Park: The Lost World), the filmmak­ers stopped listening to paleontologists and continued to show all the dino­saurs as scaly lizard-like creatures, without adding feathers to any of them. This was truly sad for many of us in paleontology. The original novel and movie was up to date with the current state of dinosaur research in the early 1990s, but they abdicated their efforts to keep the movies current and just gave the audience the scaly monsters they had come to expect."

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Donald R. Prothero


The Story of the Dinosaurs in 25 Discoveries: Amazing Fossils and the People Who Found Them


Columbia University Press


Copyright 2019, Donald R. Prothero


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