Theropod paleopathology is the study of injury and disease in theropod dinosaurs. In 2001, Ralph E. Molnar published a survey of pathologies in theropod dinosaur bone that uncovered pathological features in 21 genera from 10 theropod families. Pathologies have been seen on most theropod body parts, with the most common sites of preserved injury and disease being the ribs and tail vertebrae. The least common sites of preserved pathology are the weight-bearing bones like the tibia, femur and sacrum. Most pathologies preserved in theropod fossils are the remains of injuries, but infections and congenital deformities have also been documented. Pathologies are less frequently documented in small theropods, although this may simply be because the larger bones of correspondingly larger animals would be more likely to fossilize in the first place.
Identification Paleontologist Ralph Molnar has observed that genuine injuries and illnesses in theropod remains can be distinguished from scavenging traces because pathological bones should show signs of healing, while damage to a carcass after death would not. He also notes that the location of a potential pathology on the body can help determine whether the apparent injury was inflicted before or after death. He reasons that body parts like hands and feet lacked enough soft tissue to be attractive to scavengers, so apparent injuries to sites like digits and metapodials were more likely to be injuries received in life than to be traces of post mortem feeding. Molnar also cautioned fellow researchers that when unusual fusions between, or asymmetry of the skull bones are found it means the individual in question was probably just suffering from advanced age rather than specific illness.
History of research Scientific documentation of pathologies in theropod bones goes all the way back to the first description of a large theropod. Nevertheless, Ralph Molnar contends that despite the long history of recognized pathologies in theropod dinosaurs the topic had been almost completely overlooked in the scientific literature. For most of the ensuing 200 years paleopathologies were only noted when scientists describing new species were concerned that such abnormalities would complicate comparisons between different kinds of theropod for classification purposes. Even when paleontologists mentioned pathologies in their research they typically didn't try to ascertain their causes. This inattention towards theropod paleopathology kept science in the dark about the subject and many pathological specimens probably went completely unnoticed. By 2001, 13 species in 13 genera had reported pathologies. That year, Ralph Molnar performed a comprehensive review of the subject and found pathologies in 21 genera from 10 families.
Affected taxa
Primitive saurischians The Herrerasaurus ischigualastensis specimen PVSJ 407 had a pit in a skull bone, with two more pits on the lower jaw. Paul Sereno and Novas thought that they were obtained in a fight with another Herrerasaurus due to their size and differing directions of penetration. A short-lived non-fatal infection left the bone around these puncture wounds swollen and porous.
Primitive theropods
One Dilophosaurus wetherilli specimen has a left humerus that is smaller than its right one. This asymmetry may have been a congenital deformity brought on by environmental stress during development. Another specimen bears both a possible abscessed humerus and injured vertebra. Coelophysis rhodesiensis specimens, on very rare occasions, show signs of healed fractures in the tibia and metatarsus. An asymmetrical sacral rib has also been documented in this species. Like the D. wetherilli specimen mentioned above, this asymmetry was likely a congenital deformity caused by stress experience during development.
Ceratosaurs The holotype specimen of Ceratosaurus nasicornis, USMN 4735, was found with its second, third, and fourth left metatarsals fused. Whether or not this fusion was pathological or normal for the species became controversial when Baur in 1890 speculated that the fusion was the result of a healed fracture. A later analysis by Darren Tanke and Bruce Rothschild supported Baur's contention. An unidentified species of Ceratosaurus preserved a broken and subsequently further worn tooth. A stress fracture in a single Ceratosaurus toe bone has also been discovered.
Megalosauroids A Megalosaurus rib figured in 1856 and 1884 publications by Sir Richard Owen is swollen at the point where it would have articulated with its vertebra. The Monolophosaurus jiangi specimen IVP 84019 had its 10th and possibly 11th neural spines fractured. The tenth neural spine is fused to the eleventh. A series of parallel ridges on one of the specimens' dentaries may represent tooth marks.
Allosauroids A Poekilopleuron bucklandii individual preserves three different kinds of documented pathologies. The first is a tail vertebra with an exostosis ankylosing the chevron of one vertebra to the centrum of the next. The second is a phalanx, probably belonging to the animal's foot, that shows three low, irregular exostoses. Lastly, a phalanx that probably belong to the animal's hand exhibits a short round callus. A British bombing raid near the end of the Second World War destroyed the specimen, thus it is impossible to study the causes of these pathologies. The Allosaurus jimmadseni specimen MOR 693 exhibits at least 14 separate bone pathologies. The animal had multiple broken bones in its hands and feet, including fractures in the first phalanx of the first finger, first and third segments of the first and third toes and the third and fifth metatarsals. The head of the first phalanx of the third toe also contained a possible involucrum. Multiple pathologies were also observed in five ribs and cervical vertebrae 6, thoracics (3rd, 8th, 13th) and chevron of the second tail vertebra. The right scapula, gastralia and ilium were also affected, with the ilial fracture suggesting overhead impact. The left scapula and fibula of an Allosaurus fragilis specimen catalogued as USNM 4734 both have healed fractures. The specimen USNM 8367 preserved several pathological gastralia which preserve evidence of healed fractures near their middle. Some of these fractures produced false joints because they didn't heal well.
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