Ancient sea cow attacked by both primitive crocodile and shark sheds new light on prehistoric food chains

A new study showing how a prehistoric sea cow was preyed upon by not one, but two different carnivores — a crocodilian and a shark — reveals clues about the ancient creatures’ predatory tactics and the broader food chain millions of years ago.

Published in the Journal of Vertebrate PaleontologyThese findings constitute one of the only examples of specimens of a creature attacked by two different predators during the Early to Middle Miocene epoch (23 to 11.6 million years ago).

The dugongine sea cow, belonging to the extinct genus Culebratherium, is thought to have been first attacked by the ancient crocodile and then devoured by a tiger shark (Galeocerdo aduncus) in what is now northwestern Venezuela.

“Visible” deep tooth impacts concentrated on the sea cow’s snout suggest that the crocodile first tried to grab its prey by the snout in an attempt to suffocate it.

Two more large incisions, with a round starting impact, show that the crocodile then dragged the sea cow and then tore it apart. The striations and cut marks on the fossils indicate that the crocodile likely performed a “death roll” while grabbing its prey, a behavior commonly seen in modern crocodiles.

A tiger shark (Galeocerdo aduncus) tooth found near the sea cow’s neck, along with shark bite marks seen throughout the skeleton, show how the creature’s remains were later dismantled by this scavenger.

The team of experts from the University of Zurich, the Natural History Museum of Los Angeles County, and the Venezuelan institutes Museo Paleontológico de Urumaco and the Universidad Nacional Experimental Francisco de Miranda, say their findings add to evidence that suggests the food chain millions of years ago behaved similarly to today.

“Today, often when we observe a predator in nature, we find the carcass of its prey which also demonstrates its function as a food source for other animals; but fossils are rarer.

“We didn’t know exactly which animals could serve as a food source for many predators. Our previous research identified sperm whales as food for several shark species, and this new study highlights the importance of manatees in the food chain,” says lead author Aldo Benites-Palomino from the Department of Palaeontology in Zurich.

“Although evidence for food chain interactions is not uncommon in the fossil record, it is mostly represented by fragmentary fossils with marks of ambiguous significance. It is therefore often difficult to distinguish between marks of active predation and those of scavenging.

“Our findings constitute one of the few records documenting multiple predators on a single prey item, providing insight into food chain networks in this region during the Miocene.”

The team’s discovery was made in outcrops of the Lower to Middle Miocene Agua Clara Formation, south of the city of Coro, Venezuela.

Among the remains, they found a fragmentary skeleton comprising a partial skull and eighteen associated vertebrae.

Describing the excavation, co-author, paleobiology professor Marcelo R Sanchez-Villagra, called the find “remarkable,” particularly because of where it was discovered, a site 100 kilometers from previous fossil finds.

“We heard about the site through word of mouth from a local farmer who had noticed some unusual rocks. Intrigued, we decided to investigate,” says Sanchez-Villagra, director of the Paleontological Institute and Museum in Zurich.

“At first, we didn’t know the geology of the site and the first fossils we discovered were pieces of skulls. It took us a while to determine what they were: skulls of sea cows, which have a rather particular appearance.

“By consulting geological maps and examining the sediments at the new site, 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 dig up a large portion of the vertebral column and, because these are relatively large animals, we had to remove a significant amount of sediment.

“The region is known for its evidence of predation on aquatic mammals, and one of the factors that allowed us to observe such evidence was the excellent preservation of the fossil’s cortical 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, using extraction techniques with full protection. The operation lasted about seven hours, with a team of five people working on the fossil. The subsequent preparation took several months, especially the meticulous work of preparation and restoration of the cranial elements.”