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A rare fossil has provided a snapshot of an exceptionally unlucky day for a prehistoric sea cow.
An extinct species of marine mammal resembling a manatee, a marine mammal, was swimming in the sea about 15 million years ago when it was preyed upon by two animals: a crocodile and a tiger shark. The latter left one of its teeth embedded in the sea cow’s body.
By analyzing the fossil discovered in Venezuela, researchers were able to figure out how the sea cow, which belongs to an extinct group of animals known as colibatherium, perished.
they StudyingThe study, published Thursday in the Journal of Vertebrate Paleontology, captures a moment in time that provides a unique look at how the food chain worked during the early to mid-Miocene epoch, 11.6 million to 23 million years ago.
“It is extremely rare to find evidence of two predators on a single specimen,” said Aldo Benitez Palomino, lead author of the study and a PhD student in the Department of Paleontology at the University of Zurich in Switzerland. “This explains why we should explore fossils in tropical regions like Venezuela.”
The fossilized remains—a partial skull and 13 vertebrae, or backbone—revealed three types of bite marks. Their shapes, depth, and orientation suggest they were made by two predators: a small to medium-sized crocodile and a tiger shark.
According to the study, the crocodile-like creature first attacked the dugong, taking deep teeth strikes to its snout, suggesting it tried to grab hold of that part of the dugong’s face to strangle it. Two other large, curved incisions suggest the crocodile dragged the dugong, tearing its flesh.
Lines and scratches on the fossil indicate that the crocodile performed a “death roll,” a spinning behavior to subdue prey that is also seen in living crocodile species.
“This type of mark only occurs as a result of biting incidents followed by tearing, rolling, or grasping,” the study authors noted.
The tiger shark, which has narrow, non-serrated teeth, then dismembered the sea cow. It can be difficult to distinguish between signs of active predation and dismemberment, but according to the study, the bite marks all over the sea cow’s body and their irregular distribution, along with the variation in depth, suggested to the researchers that this was typical of a scavenger like the tiger shark.
Scientists confirmed the shark’s identity by discovering an isolated tooth stuck in the sea cow’s neck, which belonged to an extinct species of tiger shark, Galeocerdo aduncus.
“I had to work as a forensic expert,” Bennetts-Palomino recalls.
However, the study noted that due to the fragmentary nature of the skeleton, other scenarios for the sea cow’s death could not be ruled out.
Dean Lummix, a paleontologist at the University of Bristol and the University of Manchester in the United Kingdom who was not involved in the research, said he agreed with the study’s findings but said it was difficult to distinguish between gregarious behavior and active predatory behavior.
“For example, it might not be unreasonable to think that the dugong was actually dead, perhaps floating and bloated, and then eaten by crocodiles and sharks at different times,” said Lumkes, author of “Freshwater Marine Animals.”Trapped in Time: Animal Behavior Discovered in 50 Stunning Fossils” Via email.
“Unless we have direct evidence of the dugong being inside the crocodile (as a last meal), or the crocodile and manatee dying during the attack, it is always rare to say with 100 percent certainty whether this was the result of an active hunting attack,” Lomax added.
Manatees at that point in time were probably up to five meters (about 16 feet) long, and their fatty tissue would have been a good source of food, Bennetts-Palomino said.
Today, crocodiles, killer whales, and sharks prey on dugongs and manatees, mostly targeting young ones because adults are harder to kill because of their size. It’s not clear exactly what kind of crocodile would have preyed on the dugong—it could have been an extinct caiman or a gharial, known for its long, thin mucus—but it would have been large—ranging from 4 to 6 meters (about 13 to 20 feet) long.
“There are several candidates,” Benitez Palomino added. “South America was a paradise for crocodiles at that time.”
A farmer south of the city of Coro, Venezuela, was the first to notice the remains of the sea cow at a site where fossils had never been discovered before.
“At first, we were not familiar with the geology of the site, and the first fossils we discovered were fragments of skulls,” Marcelo Sánchez-Villagra, one of the study’s authors, professor of paleobiology and director of the Institute and Museum of Palaeontology at the University of Zurich, said in a statement. “It took some time to determine what they were — dugong skulls, which look very strange.”
This rare discovery demonstrated the value of searching for fossils in “non-classical” South America, Bennetts-Palomino said.
“We’ve been going to the same fossil sites in North America and China for a long time, but every time we work in these new areas we keep finding new fossils.”
