THE T. REX:
The Tyrannosaurus rex specimen has already been partially excavated, and the material that has been cleaned up is on display at the KU Natural History Museum. So far, the consists of the left maxilla, lacrimal, jugal, and postorbital, the nasal, the right dentary, several cervical ribs, the furcula, a few vertebrae, fragments of the pubis and ischium, and several bones from the hind limbs. Based on measurements of the dentary, this individual was between 14 and 16 years old. This age estimate is also supported by the fact that the teeth are shorter in proportion to body size than in older T. rex specimens. This probably means that it would have hunted smaller prey - given that juvenile T. rex had proportionally longer hindlimbs and a lighter overall build than adults, they may have been better equipped for tackling more swift-moving herbivores.
Additionally, a cross-section of the femur shows what may be evidence of medullary bone - though it could also be due to some sort of pathology such as an infection. If upon closer analysis it does turn out to be evidence of medullary bone, this would give us another T. rex specimen of known (ie confirmed) sex. In T. rex specimens, there are two distinct morphotypes, called the 'gracile' and 'robust' morphs. Some have argued that this represents sexual dimorphism, with the robust morphotype representing the females, but due to the fact that it is nearly impossible to determine the sex of a fossil animal in normal circumstances this has been an issue of debate. However, given that [provided that the medullary bone presence is confirmed] both confirmed female T. rex are of the robust morphotype, this could be solid evidence that the morphotypes represent the two sexes (though a sample size of 2 is not going to give a great level of certainty). Since there are many other dinosaur species showing the same pattern of 'gracile' and 'robust' morphotypes, understanding the cause of this dichotomy in T. rex could allow us to apply that knowledge to other species.
A secondary reason why the presence of medullary bone in this specimen would be significant is due to its age. Since medullary bone is only found in birds that are gravid (eggs not laid yet) or have recently laid eggs, this would indicate that the animal reached sexual maturity before it was finished growing.
The specimen also shows evidence of past injury - there is a raised, roughened area on the left tibia, providing evidence of possible infection or disease. However, whether or not this played a role in the death of this individual is uncertain. Closer inspection and excavation/cleaning of more skeletal material may give us a better idea, and may even reveal additional pathologies - only time will tell!
The Tyrannosaurus rex specimen has already been partially excavated, and the material that has been cleaned up is on display at the KU Natural History Museum. So far, the consists of the left maxilla, lacrimal, jugal, and postorbital, the nasal, the right dentary, several cervical ribs, the furcula, a few vertebrae, fragments of the pubis and ischium, and several bones from the hind limbs. Based on measurements of the dentary, this individual was between 14 and 16 years old. This age estimate is also supported by the fact that the teeth are shorter in proportion to body size than in older T. rex specimens. This probably means that it would have hunted smaller prey - given that juvenile T. rex had proportionally longer hindlimbs and a lighter overall build than adults, they may have been better equipped for tackling more swift-moving herbivores.
Additionally, a cross-section of the femur shows what may be evidence of medullary bone - though it could also be due to some sort of pathology such as an infection. If upon closer analysis it does turn out to be evidence of medullary bone, this would give us another T. rex specimen of known (ie confirmed) sex. In T. rex specimens, there are two distinct morphotypes, called the 'gracile' and 'robust' morphs. Some have argued that this represents sexual dimorphism, with the robust morphotype representing the females, but due to the fact that it is nearly impossible to determine the sex of a fossil animal in normal circumstances this has been an issue of debate. However, given that [provided that the medullary bone presence is confirmed] both confirmed female T. rex are of the robust morphotype, this could be solid evidence that the morphotypes represent the two sexes (though a sample size of 2 is not going to give a great level of certainty). Since there are many other dinosaur species showing the same pattern of 'gracile' and 'robust' morphotypes, understanding the cause of this dichotomy in T. rex could allow us to apply that knowledge to other species.
T. rex femoral cross-section, showing possible medullary bone (light colored center of the bone).
A secondary reason why the presence of medullary bone in this specimen would be significant is due to its age. Since medullary bone is only found in birds that are gravid (eggs not laid yet) or have recently laid eggs, this would indicate that the animal reached sexual maturity before it was finished growing.
The specimen also shows evidence of past injury - there is a raised, roughened area on the left tibia, providing evidence of possible infection or disease. However, whether or not this played a role in the death of this individual is uncertain. Closer inspection and excavation/cleaning of more skeletal material may give us a better idea, and may even reveal additional pathologies - only time will tell!
THE LOCALITY:
The locality is fluvial mudstone, likely representing a curve in a river - it is likely that the T. rex was carried downstream after death. In the same locality, a femur attributed to an Ornithomimosaur has been uncovered, though it is not known whether or not there is more material from the specimen since the site where the femur was found has not been excavated any further. I do hope that at some point someone does more digging to see if there is more material, as it could potentially be a specimen of Ornithomimus velox, which is currently only known from a few ankle bones. As more work is done on the layer, there may be yet more fossils uncovered.
In the pictures, the fossil-bearing layer is visible as a purplish-brown layer of rock. This summer, we will be working with awls and brushes from the level of the shovel (see attached photo) to the cliff face.
As I've said, I'm super excited for this amazing opportunity, and I hope that this post about the specifics of the expedition has gotten you excited as well!
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