Fossils of an extinct sea cow – a marine mammal related to manatees – have captured a predatory event that happened millions of years ago. Tooth marks left on the animal’s bones reveal it may have been attacked by a crocodile. Furthermore, a tooth and more bone bite marks indicate sharks then scavenged the remains of the sea cow. Scientists revealed this glimpse of the ancient food chain on August 29, 2024. The attack occurred during the Miocene Epoch, 11.6 to 23 million years ago, in what is now modern-day Venezuela.
The scientists published their peer-reviewed results in the Journal of Vertebrate Paleontology on August 28, 2024.
Scientists occasionally find evidence of predation and scavenging of marine mammals on fossils. For example, there are fossilized bones of seals, walruses, and whales showing teeth marks from predators such as sharks.
This new finding, however, is remarkable because it’s a rare case in the fossil record of multiple predators feeding on a single prey.
Scientists studying the sea cow fossils – a partial skull, some back vertebrae and ribs – found bite marks from a crocodile and sharks all over the bones. They used that evidence to try to reconstruct what happened to the sea cow many millions of years ago. There were deep tooth impacts on the sea cow’s snout, suggesting the crocodile grabbed the snout to try to suffocate the sea cow. Additional markings suggest the crocodile may have then dragged the sea cow before tearing into it.
Furthermore, a tiger shark’s tooth was found near the sea cow’s neck. There were even more markings on the skeleton indicating that sharks had bitten into the carcass, scavenging what was left of it.
The food chain, the scientists observed, was very much like it is in the wild today. The paper’s lead author, Aldo Benites Palomino of the University of Zurich, said:
Today, often when we observe a predator in the wild, we find the carcass of prey which demonstrates its function as a food source for other animals too, but fossil records of this are rarer.
We have been unsure as to which animals would serve this purpose as a food source for multiple predators. Our previous research has identified sperm whales scavenged by several shark species, and this new research highlights the importance of sea cows within the food chain.
The fossils were near the city of Coro in northwestern Venezuela. Marcelo R. Sanchez Villagra, also with the University of Zurich, talked about the discovery:
We first learned about the site through word of mouth from a local farmer who had noticed some unusual ‘rocks.’ Intrigued, we decided to investigate.
Initially, we were unfamiliar with the site’s geology, and the first fossils we unearthed were parts of skulls. It took us some time to determine what they were: sea cow remains, which are quite peculiar in appearance.
By consulting geological maps and examining the sediments at the new locality, we were able to determine the age of the rocks in which the fossils were found.
Excavating the partial skeleton required several visits to the site. We managed to unearth much of the vertebral column, and since these are relatively large animals, we had to remove a significant amount of sediment.
The region is known for evidence of predation on aquatic mammals, and one factor that enabled us to observe such evidence was the excellent preservation of the fossil’s cortical layer [hard outer layer], which is attributed to the fine sediments in which it was embedded.
After locating the fossil site, our team organized a paleontological rescue operation, employing extraction techniques with full casing protection.
The operation took about seven hours, with a team of five people working on the fossil. The subsequent preparation took several months, especially the meticulous work of preparing and restoring the cranial elements.
In the skull, in the area corresponding to the sea cow’s snout, the scientists found shallow round punctures. The shape of those marks indicate they came from the teeth of a crocodile. (See images labeled “A” and “B” below.)
The next type of bite marks they saw were punctures with a dragging effect. This showed the crocodile bit deeply into the sea cow, tearing violently into it. (See the image labeled “C” below.)
There was a third category of bite marks, long narrow grooves with a triangular-shaped cross section. These came from the teeth of sharks. They showed how the sharks bit into the bone and dragged their teeth as they tore out flesh from the sea cow. Scientists could not identify the shark species based on teeth marks alone. But, luckily, one of those sharks left a tooth near the sea cow’s neck. It was a tiger shark (Galeocerdo aduncus).
Bottom line: The fossil remains of a sea cow from the Miocene Period reveal bite marks that suggest it was attacked by a crocodile and subsequently scavenged by sharks.
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