Pathology in a Permian parareptile: congenital malformation of sacral vertebrae

Paleobiological inferences from paleopathological occurrences in the Arctic ceratopsian Pachyrhinosaurus perotorum

As a key tool for understanding how animals lived in the past, paleopathology informs us about the lives and deaths of fossil animals. We identify paleopathologies within an assemblage of bones of the pachyrostran centrosaurine Pachyrhinosaurus perotorum, an Arctic ceratopsian. More than 1,000 bones of this dinosaur were collected from the Prince Creek Formation of North Slope, Alaska from fossil sites along the Colville River. Our survey shows the occurrence of paleopathology to be very low and comparable to other populations of horned dinosaurs from the lower latitudes, suggesting that the ancient Arctic environment did not impose intense hardships on these dinosaurs greater than in other environments, as expressed by paleopathological modification of the skeleton. This result may be due to the more equable mean annual temperatures in the Arctic region during the Cretaceous. Also of interest, the frequency of occurrence of paleopathology in the Arctic Pachyrhinosaurus population is very low compared to populations of fossil and historic quadrupedal artiodactyls that are recognized as long distance wanderers.

Rarity of congenital malformation and deformity in the fossil record of vertebrates - A non-human perspective

OBJECTIVE

A malformed pectoral joint of the middle Devonian antiarch fish Asterolepis ornata is described, and a survey of congenital malformations in the fossil record is provided.

MATERIALS

The specimen of A. ornata (MB.f.73) from Ehrman in Latvia, stored at the Museum für Naturkunde Berlin, Germany.

METHODS

A. ornata was macroscopically and radiologically investigated, and the overview on congenital malformation was based on an extensive literature survey.

RESULTS

In the deformed joint of A. ornata, the articular surfaces and muscle attachment sites are greatly reduced, indicating restricted mobility. Congenital malformations can be found since the middle Silurian and affect all groups of vertebrates, but they are rare. Teeth and the vertebral column are the most commonly affected anatomical regions, and the mechanisms causing these malformations probably remained the same through geological time.

CONCLUSIONS

Micro-CT of the deformed joint shows no disturbance of the normal trabecular pattern and no evidence of trauma or disease, suggesting a congenital hypoplasia, although an acquired deformity cannot be ruled out completely.

SIGNIFICANCE

Congenital malformations, even those that are rare, were part of the common history of vertebrates for more than 400 million years.

LIMITATIONS

Epidemiologic measures like incidence and prevalence usually cannot be applied to define rare diseases in the fossil record.

SUGGESTIONS FOR FURTHER RESEARCH

A broadly based analysis of species of fossil vertebrates with numerus recovered specimens (e.g. many bony fishes, amphibians, certain dinosaurs) might statistically affirm the occurrence of malformations and possible correlations with the paleoenvironment.

Investigation of a bone lesion in a gorgonopsian (Synapsida) from the Permian of Zambia and periosteal reactions in fossil non-mammalian tetrapods

While only distantly related to mammals, the anatomy of Permian gorgonopsians has shed light on the functional biology of non-mammalian synapsids and on the origins of iconic 'mammal-like' anatomical traits. However, little is known of gorgonopsian behaviour or physiology, which would aid in reconstructing the paleobiological context in which familiar mammalian features arose. Using multi-modal imaging, we report a discrete osseous lesion in the forelimb of a late Permian-aged gorgonopsian synapsid, recording reactive periosteal bone deposition and providing insights into the origins and diversity of skeletal healing responses in premammalian synapsids. We suggest that the localized lesion on the anterolateral (preaxial) shaft of the left radius represents acute periostitis and, conservatively, most likely developed as a subperiosteal haematoma with subsequent bone deposition and limited internal remodelling. The site records an inner zone of reactive cortical bone forming irregular to radial bony spicules and an outer, denser zone of slowed subperiosteal bone apposition, all of which likely occurred within a single growing season. In surveys of modern reptiles-crocodylians, varanids-such haematomas are rare compared to other documented osteopathologies. The extent and rapidity of the healing response is reminiscent of mammalian and dinosaurian bone pathologies, and may indicate differing behaviour or bone physiology compared to non-dinosaurian reptiles. This report adds to a growing list of putative disease entities recognized in early synapsids and broadens comparative baselines for pathologies and the evolution of bone response to disease in mammalian forebears. This article is part of the theme issue 'Vertebrate palaeophysiology'.

New tomographic contribution to characterizing mesosaurid congenital scoliosis

The presence of a pathology in the vertebral column of the early Permian mesosaurid specimen ZPAL R VII/1, being one of the oldest amniotic occurrences of congenital scoliosis caused by a hemivertebra, was recently recognized. Here we provide CT data to further characterize the phenomenon. The affected hemivertebra is wedged (incarcerated) between the preceding and succeeding vertebrae. The neural canal is misshapen but continuous and the number of dorsal ribs on each side of the specimen corresponds with the number of the vertebrae, documenting its congenital (homeobox-related) derivation.