It is rare for paleontologists to document vital processes of organisms that lived millions of years ago. This difficult task requires finding ichnofossils (recorded signals of the activity of living things in the past). Among these, the most common are the ichnites, or footprints; but you can also find coprolites, or fossilized feces.
In a work published this week in the journal PLoS ONE, paleobiologists from the Autonomous University of Madrid (UAM), in collaboration with the Geological and Mining Institute of Spain (IGME), provide new information on the Lower Cretaceous coprolites of the Cuenca de Las Hoyas site, so far not studied.
As described by experts, in the biota of the Las Hoyas deposit not only are corporeal fossils of plants and animals being documented. A great diversity and abundance of fossilized feces, generally of medium size (between 1 and 5 centimeters), is also being discovered.
“So far we have cataloged more than 1,500 specimens of coprolites. It is one of the best documented and complete records in the world referring to a continental wetland from the Lower Cretaceous, ”the UAM researchers say.
“Within this set - they add - we have managed to characterize up to 12 different types of coprolites, taking into account their morphology. We have also elaborated a dichotomous key to specify its shapes, the geometry of its ends and its symmetry ”.
The fossils were studied with non-destructive techniques. The researchers analyzed the chemical composition of the matrix using EDX analysis, noting that it is composed primarily of calcium phosphate. This would indicate that the producers of the coprolites were carnivores, in part due to the breakdown of the apatite that is part of the bones.
"According to their forms, and sometimes also because of their content, it can be said that the producers of certain coprolites were predators of vertebrates, since a good part of these ichnofossils contain small bone fragments," say the experts.
“What's more,” they add, “a large part of the bones included in the coprolites are from fish, so it can be ensured that the producers were mostly fish eaters. This means that the predators that produced these fecal masses could have been other fish, crocodiles, salamanders or even turtles ”.
Researchers are trying to understand why coprolites are so abundant in the Las Hoyas deposit. Preservation in this site is associated with the presence of microbial mats, capable of protecting the remains and favoring fossilization.
By estimating the relative abundance of coprolites in the sediment layers associated with the periods of greatest growth of the microbial mats, the percentage of coprolites in these is up to twenty times higher than in those periods with less development or even without these microbial mats.
One of the researchers' conclusions is that fossil feces allow proposing different types of eating strategies. Thus, they suggest that 126 million years ago it was possible to distinguish between less efficient digestive processes and less aggressive acid-enzymatic contents, and more efficient digestive strategies that would give rise to stools in which hardly any bone inclusions appear and more degraded.
"This evidence will help us to accurately characterize the trophic relationships of this Cretaceous ecosystem, for which it is necessary to contrast different levels of information. This publication provides the first evidence to assess, according to the sample studied, that less efficient digestive processes were dominant in this ecosystem ”, conclude the experts.
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