Fossil crocodile discovered with remains of another crocodile in its abdominal cavity

José Tadeu Arantes/Agência FAPESP/DICYT A previously unknown specimen of fossil crocodile, with the remains of another crocodyliform specimen in its abdominal cavity, has been discovered in the General Salgado region of northeastern of São Paulo State.

This is the first time that the abdominal contents of a fossil crocodile have been unequivocally identified, proving that these animals sometimes preyed on individuals of other species of the same group. A detailed description of the finding has been published in the scientific journal PLOS One.

The discovery is the topic of the master’s thesis by Pedro Lorena Godoy, who is a FAPESP scholarship holder. Godoy was advised by Max Cardoso Langer, an associate professor in the Biology Department of the University of São Paulo, Ribeirão Preto campus.

“We consider this to be one of the most significant paleontological findings made in Brazil in recent years because, on a global scale, it is the first reliable report of stomach contents in a fossil crocodile and the first evidence of predation between different species of extinct crocodiles,” Langer told Agência FAPESP.

The animals were excavated from rocks in the so-called Adamantina Formation, which extends over western São Paulo State and the Minas Triangle, and which dates back to the Cretaceous, nearly 70 million years ago. The predator, which measured approximately two meters long, received the name Aplestosuchus sordidus (“filthy gluttonous crocodile”).

It was classified in the subgroup Baurusuchus, which includes other species of carnivorous terrestrial crocodiles. The remains were identified as a specimen belonging to the subgroup Sphagesaurus, which are smaller animals that were omnivorous or herbivorous.

Although important, the discovery of a new crocodyliform species (the clade Crocodyliformes includes modern crocodiles and their extinct relatives) is not, in itself, spectacular. There are several records of other species of the same group in the region. “What was new was the discovery of the animal’s stomach contents,” Langer said.

These types of traces, discovered once before, were found to be so altered by the digestive process that they barely allowed scientists to determine whether they were indeed the remains of animals consumed by their predators.

The current discovery, however, found sufficiently whole and identifiable parts. “We found four skull bones and teeth, which are the most resistant materials of the skeleton, and we were able to categorize these findings into the subgroup Sphagesaurus,” said Langer.

In addition, this was the first time that an extinct crocodyliform species was determined to be predaceous. Although rare, this type of predation is known to occur in some modern crocodiles; for example, it occurs in the marine crocodile of Australia, a contemporary reptile that measures more than four meters in length. This carnivore, which devours any type of animal found in its habitat and constitutes a threat to humans as well, may also feed on freshwater crocodiles. However, among extinct species, such intragroup predation had not been determined.

The table above, prepared by the researchers and published with the PLOS One article, shows the principal components of vertebrate fauna of the Adamantina Formation during the period in question. The figures in black correspond to subgroups of Crocodyliformes, number 9 (baurusuchids) corresponds to the predator subgroup, and number 14 corresponds to the prey (sphagesaurids).

Figure 7 corresponds to the subgroup Trematochampsidae, whose features were practically identical to those of modern crocodiles: an elongated snout with nasal openings above and short paws, both of which are anatomical features typical of aquatic animals. A comparison of figures 7 and 9 allows us to easily observe the predominantly terrestrial features of the predator that were found: a shorter snout with nasal openings toward the front and elongated paws.

The table also shows (in gray) three types of dinosaurs: a large bipedal carnivore (figure 1), a large quadruped herbivore (figure 13) and a small bipedal carnivore (figure 15). Curiously enough, although such animals inhabited the Adamantina Formation, the number of dinosaur fossils found to date is much smaller than the number of crocodyliform fossils.

The researchers still cannot fully explain this imbalance. “It may be because of environmental factors or some adaptive advantage that the Crocodyliformes had with regard to the dinosaurs,” Langer conjectured.