28 March 2010

CSI: Crime Scene Investigation (in the Pliocene)

Four million years ago a Pliocene dolphin Astadelphis gastaldii died. Its skeleton was recovered, then stored in an Italian museum where it lied unstudied for more than a century... until some researchers decided to have a deep look at it. The result was amazing.

Carved into the old dolphin bones, researcher Giovanni Bianucci and his colleagues from the University of Pisa, Italy, found visible shark bite marks. By carefully studying the morphology and disposition of the tooth marks, the authors managed to attribute the bites to the predation of a single shark, most likely a Cosmopolitodus hastalis.

Then Bianucci and colleagues reconstructed what probably happened during the attack:
"… the shark attached from below, biting into the abdomen. Caught in the powerful bite, the dolphin would have struggled, and the shark probably detached a big amount of flesh by shaking its body from side to side. The bite would have caused severe damage and intense blood loss, because of the dense network of nerves, blood vessels and vital organs in this area. Then, already dead or in a state of shock, the dolphin rolled onto its back, and the shark bit again, close to the fleshy dorsal fin".
This study reveals how much can be inferred from skeletal remains, and offers a glimpse on ancient animal behaviour.

Silvia Bonizzoni

Drawing: Attack sequence as hypothesized by Bianucci et al.
A) the shark approached the prey; B) the shark bitted the abdomen of the dolphin; C) the dolphin, mortally injured, rolled to the left and the shark bitted adjacent to dorsal fin area.

For more information:

Bianucci G., Sorce B., Storai T., Landini W. 2010. Killing in the Pliocene: shark attack on a dolphin from Italy. Palaeontology 53(2):457–470.
Abstract - Shark bite marks, including striae, sulci and abrasions, in a well-preserved fossil dolphin skeleton referred to Astadelphis gastaldii (Cetacea, Delphinidae) from Pliocene sediments of Piedmont (northern Italy), are described in detail. The exceptional combination of a fossil dolphin having a significant part of the skeleton preserved and a large number of bite marks on the bones represents one of the few detailed documentations of shark attack in the past. Most bite marks have been referred to a shark about 4 m long with unserrated teeth, belonging to Cosmopolitodus hastalis, on the basis of their shape and their general disposition on the dolphin skeleton. According to our hypothesis, the shark attacked the dolphin with an initial mortal bite to the abdomen from the rear and right, in a similar way as observed for the living white shark when attacking pinnipeds. A second, less strong, bite was given on the dorsal area when the dolphin, mortally injured, probably rolled to the left. The shark probably released the prey, dead or dying, and other sharks or fishes probably scavenged the torn body of the dolphin.

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