Paleontologists have found the fossil remains of a shark that lived 115 million years ago and is estimated to be eight meters in size. This suggests that the lineage of giant sharks evolved much earlier than expected, still in the age of dinosaurs. This discovery was described in a study published on the 25th in the scientific journal Communications Biology from the Nature group.
The discoveries include five vertebral centers from a species from the order Lamnidae, a group that includes several fossils and 15 current species, such as the great white shark (Carcharodon carcarias(and the basking shark)Citorhinus maximus). Laminids vary in size, with some reaching ten metres, and live in environments influenced by the tides (coastal zone) to the neritic zone (beyond the continental shelf).
The vertebrae were found in the Darwin Formation (Bathurst Island Group), at Casuarina Beach, in the suburb of the municipality of Darwin, in the Northern Territory of Australia. Their age is estimated to be late Aptian (about 115 million years).
Benjamin Kerr, senior curator at the Swedish Museum of Natural History and coordinator of the study, said it is believed from other fossil records that laminaria appeared 100 million years ago. But the new fossil changes this.
“The modern lineage of sharks has its evolutionary history as giant predators 115 million years ago, in the age of dinosaurs. This anticipates previous records by more than 15 million years and uniquely links the first large sharks to higher-latitude, colder-water oceanic environments,” he said. Boundby email.
To arrive at the approximate size of the animal, the researchers conducted a statistical analysis comparing measurements of different laniform sharks, obtained from fishing databases and scientific collections, with Darwin’s vertebrae, which range in size between 11.4 cm and 12.6 cm in diameter. The comparison indicated that the total length ranged between 6 and 8 meters and a weight of up to three tons. The great white shark, which can reach five meters long and weigh up to 3.4 tons, has vertebrae with a diameter of 8 cm at their centres.
“Previous body size estimation approaches typically used extrapolations based on measurements of teeth and/or spine center,” explains Kerr. “We obtained a new dataset that combined snout-tail length, gross weight, and spine dimensions for a variety of living species of platypus, and then used a rigorous statistical approach to compare the body size of both Darwin’s shark and a variety of geologically younger giant fossil sharks known from the age of dinosaurs.”
One of the fossils compared is the largest shark ever found Otodus megalodonIt became extinct 3.6 million years ago and its estimated size ranges between 15 and 20 metres. The authors state that in cases of very large sharks, a predictive model makes estimating body size difficult based on vertebrae alone, but tooth and bone sizes can help determine differences within a species. In the case of Darwin’s fossil, they are still hoping to find other fossil remains (such as teeth) in the same formation that would help confirm this body size.
“This approach took into account the effects that different shark body shapes can have on predicting the body size of these extinct species,” says the paleontologist.
According to the authors, previous studies of the Darwin Formation suggest a shallow-water, high-latitude ecosystem with a much cooler climate than that found in Australia today. Scientists say they believe the presence of lamellars in this region may be the result of a condition known as mesothermia, which is the regulation of body temperature in cold water, a fact that would explain gigantism.
In addition to sharks, the Darwin Formation is known to contain the remains of other large aquatic vertebrates, including reptiles, but laminids are the main marine predators in that area, as no giant marine reptiles have been found in the formation, suggesting that sharks may have occupied this ecological niche.
“This discovery reveals that the habitat (of the Darwin Formation) was a cooler water environment, which is fundamental to the co-evolution of large body size and mesotherm, which was clearly beneficial for sharks specializing as predators in such environments,” the researcher says.