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A Collage of Cretaceous Coprolites

Coprolites, a fancy term for fossilized poo, are commonly highlighted by paleontologists for pure shock value and bad pun potential (“Protect Rare Coprolites: They’re an Endangered Feces!”). On a more pragmatic level, coprolites provide a wealth of information on diet, ecology, and environment. Yet, these fossils still usually land as Number Two (sorry) after more charismatic skeletal fossils. Today, a new PLOS ONE paper highlights an extraordinary sample of coprolites from the Las Hoyas locality of Spain, famed among many paleontologists for its gorgeous bird specimens (and other vertebrates) dating back more than 125 million years.

Coprolite with bones inside
This coprolite has a number of small bones inside, probably from a fish eaten by the coprolite creator. From Barrios-de Pedro et al. 2018, CC-BY.

The Las Hoyas locality is known as a Konservat-Lagerstätten–in other (less German) words, these rocks host absolutely jaw-dropping fossils. The very same factors that led to exceptional preservation of delicate birds, unusual non-avian dinosaurs, and countless fish may also have been associated with exceptional poo preservation. Researchers Sandra Barrios-de Pedro, Francisco José Poyato-Ariza, José Joaquı́n Moratalla, and Ángela D. Buscalioni undertook a detailed examination of more than 400 coprolites, cataloging their shape, size, chemistry, and enclosing rocks.

The key to the amazing coprolites (and indeed, many of the other amazing fossils of Las Hoyas) probably comes down to microbial mats. The rocks in this area preserve a freshwater ecosystem, probably originating as shallow bodies of water rich in carbonates. As these waters became even more shallow during dry spells, algal colonies (and other microscopic slimy things) formed on the muddy bottom. Other studies have shown that microbial mats create a perfect environment for preservation of delicate structures–whether those are skeletons of small fish, birds, lizards, or the poo they left behind while alive. This was probably the case during the Cretaceous of Spain, too!

Delicate coprolite
This delicate coprolite has exquisite preservation! From Barrios-de Pedro et al. 2018, CC-BY.

Numerous shapes and sizes of coprolites were recovered at Las Hoyas, many of which had a dominant calcium/phosphate composition and housed tiny bone fragments. All of this points towards carnivorous animals, such as fish and early crocodiles. As a paleontologist, this isn’t perhaps a huge surprise–carnivore coprolites tend to fossilize fairly well, and at the very least are easy to spot due to their sometimes high bone content. What is surprising, though, is how elaborate some of the coprolites are. Even the gentlest water currents can jostle apart delicate deuces, so the Las Hoyas feces were clearly buried quite quickly and with minimal disturbance.

Even with this first look at Las Hoyas coprolites, researchers have only scraped (wiped?) the surface. I’m hopeful that this will inspire more research into coprolites in other Mesozoic ecosystems, and that we’ll get even more info on these exquisite excretions.


Barrios-de Pedro S, Poyato-Ariza FJ, Moratalla JJ, Buscalioni ÁD (2018) Exceptional coprolite association from the Early Cretaceous continental Lagerstätte of Las Hoyas, Cuenca, Spain. PLoS ONE 13(5): e0196982.

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