On an unknown day millions of years ago, a prehistoric relative of the manatee was attacked by a hungry crocodile. After the crocodile killed the manatee's remains, they were eaten by a tiger shark. This anecdote about the prehistoric food chain is based on new fossil discoveries described in a study published August 29 in the Journal of Vertebrate Palaeontology. The results suggest certain similarities between the major players in the Miocene food chain and the organisms living on Earth today.
Prey, predator and scavenger
Scientists have found further evidence of animals eating each other in fossil records, which can tell them a lot about where organisms belong in prehistoric food chains. The mighty Megalodon fed on the snouts of sperm whales and may even have competed with great white sharks for resources. About 508 million years ago Tokummia catalepsis caught soft prey with claws that functioned like can openers.
In this new study, a team of paleontologists excavating in what is now northwestern Venezuela found the fossilized skull of a dugong sea cow from the extinct genus Culebratherium. The fossil is about 23 to 11.6 million years old and dates from the early to middle Miocene.
[Related: Meet the extinct sea cow that cultivated Pacific kelp forests.]
Some “conspicuous” deep tooth marks concentrated on the manatee's snout suggest that the crocodile first attempted to grab its prey by the snout in an attempt to suffocate it. Two other large marks indicate that the crocodile then probably performed a “death roll” while grabbing the manatee, a behavior still commonly seen in modern crocodiles.
The team also found a tiger shark's tooth in the manatee's neck. The entire skeleton was covered in shark bite marks, which the team believes show the remains were picked apart by scavengers. Modern tiger sharks are also known scavengers, eating just about anything.
“Today, when we observe a predator in the wild, we often find the carcass of the prey, attesting to its function as a food source for other animals as well; however, fossil finds of this are rarer,” said Aldo Benites-Palomino, study co-author and a paleontologist at the University of Zurich in Switzerland, in a statement. “We weren't sure which animals would serve this purpose as a food source for multiple predators. Our previous research has identified sperm whales being eaten by several shark species, and this new research highlights the importance of manatees within the food chain.”
Although fossil records provide evidence of interactions between predators and prey, they are usually broken fossils with traces whose meaning is not entirely clear. This makes it difficult to distinguish between traces of active predation and scavenger activity, according to Benites-Palomino.
“Our results represent one of the few examples of multiple predators targeting a single prey species and, as such, provide insight into food chain networks in this region during the Miocene,” said Benites-Palomino.
A “paleontological rescue operation”
The international team of researchers found the fossil in outcrops of the early to middle Miocene Agua Clara Formation south of the city of Coro, Venezuela. The remains included a fragmentary skeleton with a partial skull and eighteen associated vertebrae. The preservation of the fossil's cortical layer – which defined the structure of the brain's gray matter – also helped them observe such detailed evidence of prehistoric predators.
Study co-author and University of Zurich paleobiologist Marcelo R. Sanchez-Villagra called the discovery “remarkable,” in part because the fossil was found 62 miles (99 kilometers) from other fossils and because of the way they found it.
[Related: This tiger-sized, saber-toothed, rhino-skinned predator thrived before the ‘Great Dying.’]
“We first learned about the site through word of mouth from a local farmer who had noticed some unusual 'stones.' We were intrigued and decided to investigate,” Sanchez-Villagra said in a statement. “Initially, we were unfamiliar with the geology of the site and the first fossils we dug up were skull fragments. It took us a while to figure out what they were – remains of manatees, which look quite peculiar.”
The team consulted geological maps of the areas and studied the sediments in this new area, allowing them to determine the age of the rocks in which these fossils were exposed. It took several visits to the site to fully expose the remains, as these were relatively large animal remains.
“After finding the fossil site, our team organized a paleontological rescue operation, using extraction techniques with total protection of the shell,” said Sanchez-Villagra. “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 preparing and restoring the skull elements.”
