When a young crocodile-like caiman snapped on the hind leg of a rag 13 million years ago near the Napo River in Peru, it left 46 tooth marks as evidence.
© Jorge A. González
Life reconstruction of the putative attack of a young to sub-adult Purussaurus on the ground lazy Pseudoprepotherium in a swamp of proto-Amazonia.
Now, investigators have been able to reconstruct the site of the attack after analyzing the hind leg bone of the unfortunate ground cover.
As an adult, this old caiman had a biting force of seven tons, more than four times the strongest bite ever measured in the animal kingdom according to previous research, study author Rodolfo Salas-Gismondi said in an email. He was not involved in the previous investigation. The youth Purussaurus who lazily attacked the ground had the biting power of a modern caiman, who was still powerful enough to break bones and fall.
© R. Salas-Gismondi
This is a large Purussaurus tooth found in the Pebas formation.
After the adult Purussaurus comes the next strongest bite of the modern saltwater crocodile, Crocodylus porosus, which has a biting force of 1.6 tons.
“The bite was so powerful that many teeth perforated the tibia and collapsed extensive parts of the cortical bone,” said Salas-Gismondi, a paleontologist at the BioGeoCiencias Lab of Universidad Peruana Cayetano Heredia in Lima, Peru. “The founders did not survive.”
© P. Baby
Rock outcrops along the Napo River are full of bones.
This fossil evidence is a rare glimpse into the relationship between predators and prey that once lived millions of years ago in the Amazon, as the area around the Amazon River in South America.
“The tibia discovered in the Peruvian Amazon is the first of a mammal that has crocodile tooth marks and is therefore crucial to understanding the dynamics of ancient ecosystems,” Salas-Gismondi said in an email.
“This is an unusual snapshot of the feeding behavior of the largest non-marine predator since the extinction of non-avian dinosaurs. We have recovered thousands of fossil bones from these Amazon locations and, to date, the tibia of the lazy the only bone with tooth marks we have discovered. “
The fossil record of the damaged tibia of the founders was discovered in 2004 by François Pujos, a research fellow and paleontologist who specializes in the evolution of foundations at the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales in Mendoza, Argentina.
© Pujos & Salas-Gismondi, 2020, Biology Letters
The tibia of the root glands contained 46 bite marks.
When he discovered rocks in the Pebas Formation along the Napo River in Peru, Pujos discovered that the rocks were full of bones.
He collected the tibia, intrigued by the tooth marks on the bone, but he and his researchers were not sure what could be causing the damage. Little was known then about the animals that lived in the area during the age of the land lot.
That fossil was stored at the paleontology department of vertebrate at the Museo de Historia Natural-UNMSM in Lima, where Salas-Gismondi is also a curator.
A research team, including French, Peruvian and American scientists, studied the Pebas Formation area for 15 years, and learned about the animals that once lived there by studying the bones they left behind.
Lakes and swamps served as the perfect habitat for ancient crocodiles and caimans between 11 million and 20 million years ago. And the research team realized that in 2019, they were “ready to know who killed this fundamentalist,” Salas-Gismondi said.
“We found that tooth marks in the tibia correspond to the anatomy and teeth of the top predator of the Pebas System, the giant caiman Purussaurus,” he said.
The study was published Tuesday in the journal Biology Letters.
Study the evidence
Purussaurus could reach 33 meters in length as an adult, but the researchers believe this was a boy about 13 meters long. And it was just the right place and time to fall out of the swamp and attack the lower hind leg of an unsuspecting ground cover that was probably foraging for plants along the coast.
This ground sloth was probably about 176 pounds, similar in size to modern capybaras, the largest modern living rodent in the world. Capybaras can be found in South America.
And the old sloth was no match for the biting power of the young Purussaurus, which left pits, scores and deep leaks in the leg bone of the sloth.
If the sloth had survived, there would have been evidence of bone regeneration.
The researchers did not rule out the possibility that the bite marks appeared shortly after death, because the Purussaurus broke off the carcass of the sloth.
The teeth of Purussaurus correspond to the marks found on the fossil bone, the researchers said. Other predators living in South America at the time included marsupials, crocodiles, and giant flightless birds. The birds had no teeth and the bite marks of marsupials do not match those on the bone. That the researchers analyzed teeth from the different species of ancient crocodiles and caymans to see which one fits best.
The strong, blunt cone-shaped teeth of Purussaurus corresponded to the deep, large leaks on the bone. Parts of the bone had collapsed even under the force of the bite.
Portrait of an old predator
Purussaurus were at that time the largest predators in this area.
Most crocodiles and alligators experience a change in diet as they grow. Newborns eat insects and spiders. As they grow, their biting power changes, which means that youth and adults have the ability to catch mammals and turtles.
With its massive biting power, Purussaurus was not limited by size when choosing its next meal. This is evidenced, along with the rooted tibia, by the fossil carcass of an old large turtle in the museum where Salas-Gismondi works.
This fossil shows that an adult Purussaurus took a 25-inch bite from the tortoise’s shell and amputated one of its hind legs. Unlike the founders, however, the tortoise survived on the basis of evidence of bone regeneration in the carapace.
Fossils found in the Amazon are difficult due to the dense tropical rainforest environment and heavy rainfall, but studying areas where ancient rocks are exposed may shed light on what ancient life was like in this area.
The researchers only get a month or so during the dry season to study these rocks before strong showers have the power to wash away the rocks and fossils.
“The good news is that every year a new window into the past opens up,” Salas-Gismondi said.
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