200-million-year-old fossil poop reveals ecosystem and critters of the past in India

Bone-bearing coprolites from the Upper Triassic of India: ichnotaxonomy, probable producers, and predator–prey relationships

Summarized by Sarah Arias Madrigal, a third-year geology student at the University of South Florida. She plans to one day become an earth science teacher. She enjoys dancing and playing spike ball in her free time.

Point of the paper: Coprolites (fossilized feces) from the Late Triassic (237–201 million years ago), from the Tiki Formation of India were studied to understand who made the feces, using ichnotaxonomy (i.e., classifying an animal based on trace fossil, in this case coprolites), their diet and feeding behavior, selection of prey, physiology, and their paleoecosystem (the prehistoric environment in which an ecological community lived).

What data were used?: Coprolites were collected near the village of Tiki, India. The most common body fossils in this area, among other animal bones, were an extinct group of amphibians called Metoposaurus. They were mostly aquatic with flattened heads). Fossils of this animal were found with a mix of other animal bones. 170 coprolites were examined, of which 30 were spiral coprolites (feces produced by prehistoric fish that pass through spiral intestines) and 140 were non-spiral coprolites.

Methods: The coprolites were examined both macroscopically (by hand) and under a microscope. Many coprolites were sectioned to examine the internal morphology (i.e., the structure, shape, form of an animal or plant). Thin sections were also made (thin slice of rock placed on glass) and examined using scanning electron microscopy (SEM).

Results: The external and internal details of the coprolites were important in identifying its producer. The composition of the coprolite and undigested pieces included in it directly reflected the food material the producer ate, which in turn helps in identifying the producer of the poop.. Fish scales were visible on the surface of the spiral coprolites, indicating that it ate fish. The components of the non-spiral coprolites varied drastically within each different specimen where undigested food, waste matter, gas escape structures and cracks were present. By knowing the body fossils present in the fossil beds of the Tiki Formation, scientists matched the coprolites to these fossils as being the probable poo producers. The spiral coprolites seemed to have come from elongate streamline fishes (called saurichthyids) and lungfishes, as well as extinct sharks. The turn counts (meaning, the number of spiral turns in the coprolite caused by the shape and muscle action of the intestine) of the spiral coprolites can tell scientists the depth of where each fish likely lived. Fish that lived in open ocean waters, nearer to the surface (pelagic), typically show higher turn counts. Fewer turn counts indicate the fish likely lived in deep waters at the sea bottom (benthic). However, using turn count is difficult since coprolites can be found broken or incomplete. The non-spiral coprolites seem to have come from tetrapods (four-limbed animals, like vertebrate land animals today). Specifically identifying the exact species to a non-spiral coprolite is difficult, as many different tetrapods can produce very similar coprolites. The best approach in identifying the coprolites produced by tetrapods was by looking at the cross-sectional geometry of a coprolite which is unique to an animal’s anal structure, also called a cloaca. Most of the non-spiral coprolites contained calcium phosphatic skeletal fragments, suggesting they were carnivorous. Calcium phosphate is what makes up the teeth and bones of all animals with backbones, or vertebrate. Carnivores eat vertebrate, therefore when remains of calcium phosphate fragments are found, this is indicative of an animal that eats other animals. Cross sectional geometries of the coprolites, along with the shape of the coprolites, whether the coprolite experienced shrinkage/cracking, and the state of the undigested pieces found in the coprolite allowed for conclusions of the animals that made the the non-spiral coprolites. These include prehistoric reptiles closely related to crocodilians, dinosaurs, and birds. 

The figure is sectioned into 7 microscopic images, labeled A through F, each showing different types of inclusions in spiral coprolite samples. Images A,B, and C depict fish scales imbedded within the surface of an orange-colored coprolite. This reveals the diet of the producer of this coprolite as well as their role within the prehistoric ecosystem. Image D depicts a black and white SEM image with a circled cluster of fish scales lined up parallel to each other. This a characteristic of spiral coprolites, where inclusions are usually aligned parallel to coprolite layers. Image E shows a black and white SEM image of a coprolite with arrows pointing at 2 mucosal folds. The folds are notable as sectional ridges running parallel to each other within the coprolite. Image F shows the last black and white SEM image with an arrow pointing to a singular tooth imbedded within a spiral coprolite. This is another example of how inclusions reflect the food material the producer ate and its diet. The last image has arrows pointing towards skeletal fragments and remains imbedded within an orangish coprolite. Scale bars represent 0.5 millimeters for A-C, 500 micrometers for D, 1 milliliter for E,G and 100 micrometers for F.
Different types of inclusions in samples of spiral coprolites. A–C, clusters of fish scales on the external surface of coprolite. D–F, SEM images of inclusions: D, cluster of fish scales (circled); E, mucosal folds (arrows), which are folds within the lining of an animal’s intestine with is reflected on a coprolite. ; F, an isolated tooth (arrow); G, skeletal remains (arrows) on the external surface. Fish scales and bones in coprolite reveal the coprolite producers’ diet and role in the food chain. Scale bars represent 0.5 millimeters for A-C, 500 micrometers for D, 1 milliliter for E,G and 100 micrometers for F.

Why is this study important?: Studying extinct fish, reptile, and amphibian coprolites of the Triassic Tiki Formation further reveals the intestinal and anal structure of these animals, each animals’ digestive strategy for survival, feeding behavior, and habitat they likely lived in. Undigested food remains in the coprolites also provide a look at the food chain and predator-prey interaction at that time. Without the soft tissue preservation of these prehistoric animals, coprolites allow for a reconstruction of the intestinal structures of aquatic animals. 

Broader Implications beyond this study: Studying older coprolites can reveal the time in which fish evolved a spiral intestinal valve, and what factors, such as palaeoecological, paleoclimatic, etc. that drove particular fish species to develop and retain it to this day.

Citation: Rakshit, Ray, S., & Marchetti, L. (2022). Bone‐bearing coprolites from the Upper Triassic of India: ichnotaxonomy, probable producers and predator–prey relationships. Papers in Palaeontology8(1). https://doi.org/10.1002/spp2.1418