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A rare fossil has shed light on a particularly unlucky day for a prehistoric manatee.
The now extinct species of dugong, a manatee-like 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 in the manatee’s body.
By analyzing the fossil, which was discovered in Venezuela, the researchers were able to piece together how the manatee, which belonged to an extinct group of animals known as Culebratherium, was lost.
Their study, published Thursday in the Journal of Vertebrate Paleontology, captures a moment in time that provides a unique insight into how the food chain worked in the Middle Miocene Epoch 11.6 million to 23 million years ago.
“It is extremely rare to find evidence of two predators on one specimen,” said lead study author Aldo Benites-Palomino, a doctoral student in the Department of Paleontology at the University of Zurich in Switzerland. “It shows why we should be searching for fossils in tropical regions like (Venezuela).
Anatomy of an attack
The fossilized remains – a partial skull and 13 vertebrae or backbone – revealed three types of bite marks. Their shape, depth and orientation suggested that they were made by two predators: a small to medium-sized crocodile and a tiger shark.
The crocodile-like creature first attacked, according to the study, with a deep tooth impact in the sea cow’s snout, suggesting that it tried to grasp this part of the dugong’s face to kill it. Two other large curved incisions show that the crocodile dragged the sea cow, tearing her flesh.
Streaks and slashes on the fossil indicated that the croc performed a “death roll,” a spinning behavior to detect prey that is also seen in living crocodile species.
“This type of mark is only made by biting events followed by rubbing, rolling or biting actions,” the study authors noted.
Then, the sea cow was picked apart by a tiger shark, which has narrow, non-serrated teeth. It can be challenging to distinguish between marks of active predation and scavenging, but according to the study, bite marks all over the manatee’s body and the irregular distribution along with the variation in depth suggest to researchers that the behavior of a scavenger like a tiger. shark.
The scientists confirmed the shark’s identity by finding a detached tooth lodged in the manatee’s neck that belonged to an extinct species of tiger shark, Galeocerdo aduncus.
“I had to work as a forensic scientist,” Benites-Palomino said.
However, the study noted that given the nature of the skeletal fragments — other cases of the manatee’s death could not be ruled out.
Dean Lomax, a paleontologist at the University of Bristol in the United Kingdom and the University of Manchester who were not involved in the research, said he agreed with the study’s findings but said it is difficult to distinguish between scavenging and active prey behaviour.
“For example, it may not be unreasonable to think that the dugong was already dead, it may have been swimming and (was) thriving, and the crocodile and sharks were eating (dispersed) by different times,” Lomax said. , the author of “Locked in Time: Animal Behavior Discovered in 50 Surprising Fossils,” via email.
“Unless we have the direct evidence of the dugong inside the croc (as a final meal), or the croc and dugong dying mid-attack, it is always very rare to say 100% whether this was a definitive result of active attack over. scavenging,” said Lomax.
Chance of fossil discovery
Sea cows at that point could be as much as 5 meters (about 16 feet) long, Benites-Palomino said, and their fatty tissue would be a good food source.
Today, dugongs and manatees are preyed upon by crocodiles, orcas and sharks, mainly targeting the young as adults are difficult to kill due to their size. It is not clear exactly what kind of crocodile would have preyed on the manatee — it may have been an extinct type of caiman or gharial, which had a long, thin snout, but it would have been large — 4 to 6 meters (approx. on 13 metres). to 20 feet) long.
“There are several candidates. South America was a paradise for crocodiles at that time,” Benites-Palomino added.
A farmer south of the city of Coro, Venezuela, first noticed the remains of a manatee in a place where fossils had not been found before.
“At first, we were not familiar with the geology of the site, and the first fossils we found were parts of skulls. It took us a while to find out what they were – manatee skulls, which look very strange,” said Marcelo Sánchez-Villagra, study co-author and professor of paleobiology and director of the Palaeontological & Museum Institute at the National University of Ireland. Zurich, in a statement.
Benites-Palomino said the rare discovery showed the value of fossil hunting in “non-classical” South America.
“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 always find new fossils.”
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