A new skeleton of Tyrannosaurus rex is coming to the National Museum of Natural History and excitement is mounting. The fossil is from a large T. rex – one of the biggest discovered. It also is unusually complete, making it especially interesting to scientists. In fact, dozens of scientific articles have already been published using data from this specimen, and there is a lot more to be learned from it.
If you found yourself thinking when you read the previous paragraph that “unusually complete” means “incomplete,” you are right. Incompleteness is a fact of life when dealing with vertebrate fossils, including dinosaurs. This is because animal skeletons usually are gnawed by predators or scavengers or at least partly broken down by other natural processes before they can begin to fossilize. To make matters worse, erosion, which exposes long-buried fossils by wearing away the rock that holds them, destroys fossils as well. It’s not uncommon for a paleontologist to find parts of a skeleton in an eroding hillside and realize that many more bones might have been recovered if the site had been found sooner. As a consequence, our understanding of extinct animals is usually pieced together from more than one (often many) separate discoveries.
T. rex is a great example of this. Henry Fairfield Osborn, who named the species, published a scientific report in 1906 based on three partial skeletons discovered in Wyoming and Montana between 1900 and 1905. Incomplete in different ways, the specimens contributed different information to Osborn’s description. One preserved the jaws and parts of the skull, a neck vertebra, a dozen more vertebrae from the back, bones from the pelvis, a few huge foot bones, an enormous left femur (thigh bone), and a shoulder blade and upper arm bone, both surprisingly small (Osborn described them as “absurdly reduced as compared with the femur.”) The bones of the second specimen included a full set of vertebrae from the neck, and the third preserved both tibiae, adding information about the lower legs. Osborn wrote, “Taken together … they afford knowledge of a considerable part of the skull and of practically the entire skeleton excepting the bones of the fore arm and manus (hand) and the caudal (tail) vertebrae.”
Information about the tail followed quickly with the 1908 discovery of a specimen that boasted 18 vertebrae from the tail (the total number of tail vertebrae in T. rex remains unknown to this day because no intact tail has been found), but the arms and hands remained the subject of speculation for decades. Scientists assumed that they would have been like those of similar bipedal meat eating dinosaurs, and when the first skeletal mounts of T. rex were displayed, they included sculpted arms and three-fingered hands modeled on the known arm and hand bones of Allosaurus. Allosaurus lived about 90 million years before T. rex – too long a separation to consider them close relatives -- so when Gorgosaurus, a species of tyrannosaur that lived a mere 10 million years earlier, was found to have sported two-fingered hands, skeletal mounts with two fingers became the norm.
A nearly full set of arm and hand bones from T. rex finally came to light in 1988 with the discovery of our new specimen by Kathy Wankel, a Montana rancher. Shortly afterward, a second specimen preserving arm and hand bones was discovered and excavated in South Dakota. (The second skeleton, nicknamed “Sue,” is on exhibit at the Field Museum in Chicago.) The new fossils confirm the two-fingered hands and provide evidence that the arm and hand bones, although small, were strongly built and supported large muscles. It’s clear that they did something important, but there isn’t yet consensus among scientists as to what that was.
The Department of Paleobiology is looking forward to hosting the Nation’s T. rex. The individual bones of this fossil will be fully assembled in a lifelike pose for the first time when it takes center stage in our new National Fossil Hall. Our researchers will take advantage of having the bones “in house” to make new discoveries about how this massive creature lived and died.
Read an earlier post in which Matthew Carrano, our Curator of Dinosauria, wrote about how we will mount the T. rex for exhibit.
Read Henry Fairfield Osborn’s 1906 paper, quoted in this post: Tyrannosaurus, Upper Cretaceous Carnivorous Dinosaur (Second Communication.) Bulletin of the American Museum of Natural History, Volume 22: 281-296.
Visit the National Fossil Hall webpage at 9 a.m. on April 15th, 2014 to watch a live webcast of the Nation’s Tyrannosaurus rex arrival ceremony, learn how the T. rex made its journey to Washington, and catch a first-ever glimpse of the fossil in the museum’s Rotunda! The T. rex will be one of the stars of our new National Fossil Hall which opens in 2019. Before it can go in the new exhibit, it needs special care. Come visit the Rex Room between April 15th and October 20th to see us studying, conserving, photographing, and 3D-scanning its bones – and dozens of other fossils being prepared for the new exhibition.
Visit the Deep Time at the Smithsonian facebook page for updates on all aspects of the National Fossil Hall renovations.