Artist's impression of an ichthyosaur (Platypterygius). Ichthyosaurs had very obvious aquatic adaptations with an anatomy recalling that of a dolphin but with the caudal fin of a fish.
Credit: CNRS,/Université de Lyon 1/A. Beneteau
A close-up of the ichthyosaur snout showing the healed wounds.
Credit: Jo Bain, South Australian Museum
CARDIFF: A discovery of scars on the fossilised skeleton of an Australian ichthyosaur - a 120 million-year-old dolphin-like marine reptile - suggests that life might not have been easy in the ancient polar oceans.
Unearthed in a remote desert near the town of Marree in northern South Australia, the fossil provides a rare insight into the social behaviour of these large, extinct sea animals.
"Not much is really known about ichthyosaur behaviour, which is why rare evidence like these bite wounds are so important. Such finds have also rarely been reported in ichthyosaurs before", said co-author Benjamin Kear from the Palaeobiology Programme at Uppsala University in Sweden of the paper published in Acta Palaeontologica Polonica.
Prehistoric bite marks
Reaching speeds of up to 40 km/h, ichthyosaurs were high-speed pursuit predators that hunted small prey such as fish, squid-like animals, and even hatchling sea turtles. Adults of this particular kind of ichthyosaur, (Platypterygius), grew to about six metres and shared the cold Cretaceous polar seas with a diversity of plesiosaurs - long-necked marine reptiles that ranged from the size of a seal to the length of a bus.
Kear's discovery of the well preserved bite marks were made during the painstaking fossil cleaning and reassembly process with PhD student Maria Zammit, also from Uppsala University.
Looking at the non-lethal positioning and close spacing of the facial wounds, the researchers suggest they are the result of aggressive behaviour between members of the same species.
"Pathological traces on ancient fossilised bones and teeth give unique insights into the lives and social behaviours of extinct animals. This particular find suggests that ichthyosaurs might have engaged in aggressive behaviour with each other," said Kear. "Modern animals often fight over food, territory or mates, so we could expect that ichthyosaurs did the same."
A piece of the Australian story
Facial biting is a common social interaction observed in animals today and is often done to restrain an opponent's jaws. Evidence of advanced healing indicates that the animal survived the attack and lived on for some time afterwards.
Given the complex social behaviour in extant aquatic reptiles, researchers suggest the marks may be an indicator of conflict during courtship and mating, or combat over food, territory or social dominance. Similar behaviour has also been indicated in fossils of similar extinct aquatic reptile species. However as little is known about the ichthyosaur, which have no modern day relative, it can be difficult to infer behaviour from this rare sample.
"Marks like this could well have been made by other ichthyosaurs of the same species or by other large marine reptiles like a medium-sized pliosaur, and as they are not determinable to precise species they do not necessarily represent an indication of ichthyosaur behaviour," said John Long, an Australian palaeontologist from the Natural History Museum of Los Angeles County in the U.S., who was not involved in the study.
"They are still an interesting record of a marine reptile pathology, which are indeed rare in the fossil record and are an important peace of the puzzle that contributes to life in the Australian story," he added.
