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Palaeopathology part IV: What Death Can Teach Us About Life

Dr. Judith Pardo-Pérez is palaeontologist working on palaeopathologies in ichthyosaurs.

The Dino Doc

Have you ever stopped to think what happened with animals millions of years ago when no veterinaries were around (nor even evolved enough) to cure their diseases and injuries?

I am Judith Pardo, I come from Tierra del Fuego in the southern Chilean Patagonia, I am a paleontologist and, as veterinarians do with the animals in the present, I research on diseases from extinct animals… unfortunately a bit late to cure them.

In the Staatliches Museum für Naturkunde in Stuttgart (SMNS) I work specifically with ichthyosaurs. Why ichthyosaurs? Because the SMNS has one of the largest collections of these animals in the world recorded from the rich-in-fossils sediments of Southwest Germany and the areas around Stuttgart. The preservation of these ancient extinct animal is so magnificent that even part of the skin has been preserved. A perfect opportunity for me to study its bones in detail!

Temnodontosaurus in the exhibition gallery of the SMNS

Back to the past

182 millions of years ago (Early Jurassic), the area of southwest Germany was part of an inland sea formed due to rising sea levels and connected to the Tethys Ocean – a totally different landscape than the present. Baden-Württemberg was a diverse marine ecosystem, which included a rich fauna of invertebrates as well as vertebrates, such as marine reptiles and fishes. Among the reptiles, the most abundant and diverse were the ichthyosaurs: marine reptiles with long snouts, four paddles used for locomotion and steering in the water, a dorsal fin for stabilization and a caudal fin used for thrust generation. Five different genera of ichthyosaurs have been recorded in this area: Stenopterygius, Hauffiopteryx, Suevoleviathan, Eurhinosaurus and Temnodontosaurus. Adult sizes ranged from 2.5 up to more than 9 meters long, with Temnodontosaurus being the largest genus and the top-predator of this area. Through the fossil record was also possible to recover adults, juveniles, neonates and even gravid females, which are part of the historical collections of the SMNS museum, the Urwelt Museum Hauff in Holzmaden and the Paleontological collection of the University in Tübingen, among others. Using these beautiful ichthyosaur specimens I examined each bone of every specimen to see if we could identify abnormalities, and, lucky us, but poor ichthyosaur, we did.

Observing pathologies in the skull of a specimen of Temnodontosaurus from the Urwelt-Museum Hauff, Holzmaden. (picture courtesy of UMH)

How do I research palaeopathologies?

The study of pathologies allows us to recognize diseases and injuries in organisms. In fossils, its detection is limited to injuries observable in mineralized tissues (like bones), and helps to reconstruct aspects of an animal’s biology, ecology and behavior. There are pathologies described in Mesozoic dinosaurs, including reports of trauma and infection, however in marine reptiles these reports are rare, especially in ichthyosaurs.

For pathology detection we consider only bone alterations that show signs of healing, to differentiate them from other structures like non-healed broken or fractured bones, attachment of seafloor organisms to the bones, erosion during seafloor exposure, deformation caused during the fossilization process or damage incurred during excavation.

Healing process of bone. (from Pardo-Pérez et al., 2018b)

And you may be wondering how do we recognize pathologies in the ichthyosaurs? ­…

         Every bone that is broken and heals shows a record of this process. If you ever broke a bone you will have experienced the healing process. The process of healing in human bones can lasts from months to years to totally recover the original shape. This process has different stages and begins with hematoma formation and inflammation of the affected area, caused by the rupture of blood vessels and tendons. The next stage in the healing process starts with the development of the soft callus, which starts to unite the broken parts of the bone through the formation of cells that produce cartilage and connective tissues. After a few months the bony callus (hard callus) will be formed and here is when your doctor will show you with an X-ray test a clear prominence in the affected area of the bone. Finally, after a lot more time, the bone remodeling and arrangement of the bone fibers take place to recover it original shape.

Bones are structures that give support to our body, and their function and composition are the same in humans, dogs, whales and ichthyosaurs, therefore the healing process is also the same. However, in fossils we can only recognize the two last stages of the healing process: the hard callus and bone remodeling. The recognition of healing in fossilized bones is a sign that the animal did not die from the trauma or disease, and can help us to reconstruct the history of its life and behaviour.

Using a flashlight and my pocket loupe I checked in detail 39 specimens of Temnodontosaurus deposited in different collections from Germany to identify damage to the bones. I took measurements of the jaws and limbs elements to estimate the total length of the specimens that are not totally preserved to control for growth stages (e.g., adults vs. juveniles). I recorded the state of preservation of the bones and preparation of the material, to differentiate the pathological alterations from other structures not related to trauma or disease.

Together with my colleague from the SMNS Dr. Erin Maxwell and colleagues from Berlin, Sweden, and Chile we analyzed the results and discussed how much a large top-predator was affected by pathologies, what kind of pathologies were the most represented, and which anatomical unit of the skeleton was the most likely to be affected by a pathology.

The results

Our results show that the most frequent type of pathology in Temnodontosaurus was traumatic injury, affecting mainly the skull and ribs, followed by a few cases of fusion of finger bones in the front paddle.

Temnodontosaurus trigonodon, SMNS 15950. Pathologies were observed in the skull (fiber remodeling) and in the ribs (broken and healed with callus developed). (Modified from Pardo-Pérez et al., 2018a)

But how we interpret these traumas in the skeleton of an ichthyosaur if they are now extinct? To understand the possible causes of the pathologies of ichthyosaurs, we compared the pathologies seen in ichthyosaurs with those reported in marine mammals, such as whales and dolphins.

Fusion of bones observed in the anterior margin of one of the forefins of Temnodontosaurus trigonodon from the Geological and Paleontological collection of the University Tübingen.

Since aggressive interactions with members of the same species are relatively common in apex predators, the hypothesis is that most of the pathologies observed in Temnodontosaurus were caused by members of the same species during aggressive encounters, such as battles for territory or mates. Interestingly no injuries were detected in the vertebral column of Temnodontosaurus, or in the pelvic girdle and hind fin, although these injuries have often been reported for other marine reptiles and mammals (mosasaurs, plesiosaurs, and whales). The absence of pathologies in the vertebral column of Temnodontosaurus indicates functional differences on the axial skeleton, possibly related to the large intervertebral spaces and the quantity of soft tissue between the vertebrae, which may have protected the vertebral column from articular diseases and injury.

Remodeled and healed areas in the skull of Temnodontosaurus trigonodon from the Geological and Paleontological collection of the University Tübingen, possibly caused after an aggressive encounter with a conspecific.

Significance of this research

This research represents the first systematic study of palaeopathologies in marine reptiles, and provides an atlas of pathologies that can be used and extrapolated to other extinct animals. The next step of our palaeopathological research is to analyze the pathologies observed in the different species of ichthyosaurs from southwest of Germany using variables that may have affected on their frequency: (1) growth stages (adults vs. juveniles), (2) adult body size (e.g., large species compared to small ones) and (3) the stratigraphic horizons where the fossils were found.


References

Pardo-Pérez, J. M., Kear, B., Gómez, M., Moroni, M & Maxwell, E. E. 2018. Ichthyosaurian palaeopathology: Evidence of injury and disease in fossil ‘fish lizards’. Journal of Zoology. 304 (1): 21-33. https://doi.org/10.1111/jzo.12517

Pardo-Pérez JM, Kear BP, Mallison H, Gómez M, Moroni M, Maxwell EE (2018) Pathological survey on Temnodontosaurus from the Early Jurassic of southern Germany. PLoS ONE 13(10): e0204951. https://doi.org/10.1371/journal.pone.0204951

Pardo-Pérez, Judith & Kear, Benjamin & Maxwell, Erin. (2019). Palaeoepidemiology in extinct vertebrate populations: factors influencing skeletal health in Jurassic marine reptiles. Royal Society Open Science. 6. 190264. 10.1098/rsos.190264. https://doi.org/10.1098/rsos.190264

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