The snails that died associated with dinosaurs

Author: Julián Monge Nájera, Ecologist and Photographer

75 million years ago, huge herds of Maiasaura dinosaurs crossed the plains of Montana in the company of ankylosaurs, brachiceratops, gorgosaurs and … tiny snails.

Reconstruction of Maiasaura nest and young; Maiasaura (the “good mother dinosaur”) is thought to be the dinosaur that produced the dung in which many snails were preserved. Fuente: Keratops Yuta.

75 million years ago, herds of thousands of herbivorous dinosaurs (Maiasaura peeblesorum) crossed the plains of Montana in the United States. The only similar scene that we can see today is the large herds of wildebeest (Connochaetes spp.) that cross parts of Africa.

Just as herds of wildebeest travel accompanied by many other species; like zebras, gazelles, cheetahs and lions; the Maisaurs migrated with spectacular animals such as early birds, ankylosaurs, Brachiceratops, Bambiraptors and Gorgosaurs. But thousands of invertebrate species were also with them, including land snails and freshwater snails. 

Herds of herbivorous dinosaurs must have looked like these great herds of African wildebeest. Fuente: Bjørn Christian Tørrissen.

Just as herds of wildebeest travel accompanied by many other species; like zebras, gazelles, cheetahs, and lions; the Maisaurs migrated with spectacular animals such as early birds, ankylosaurs, Brachiceratops, Bambiraptors, and Gorgosaurs. But thousands of invertebrate species were also with them, including land snails and freshwater snails.

For reasons that are unknown, many snails died while feeding on the excrement of herbivorous dinosaurs, and thanks to their fossilization¹, we can now rebuild that relationship that ceased to exist tens of millions of years ago. In fact, just as the dinosaurs left, some of these snails are also extinct today, and the ones that still live are rare and usually only found in dark corners of the forests. (see Biography of a pond snail). 

In my sketchbook: Seven species of snails found inside fossilized dinosaur feces. The colors and bodies are based on current relatives, but are not known with certainty; and please remember: these are quick freehand sketches, not scientific illustrations.

These snails perished feeding on dinosaur feces that ended under the water in a stream, river, or flood plain. But dinosaur feces also fell on dry ground, and were also preserved there, nobody knows how with snails feeding inside. We know species of four genera¹. The most common was Megomphix, a snail the size of a human fingernail, whose descendants are still found, though rare, in the forests of Oregon and Washington. We do not know what they eat, or how they reproduce, or what their behavior and ecology are like. It is ironic that we know more about their now-extinct ancestors, which ate in the feces of dinosaurs; these snails certainly deserve to be studied in-depth and urgently to better understand how the life of their ancestor could have been. The same can be said of his companions, Polygyrella and Hendersonia. The fourth genus, Prograngerella, belongs to a totally extinct family and we know almost nothing about it.

Surprisingly, these dinosaurs not only ate live foliage but also fallen and half-decomposed branches, which provided them with microorganisms and invertebrates to supplement their diet². Among invertebrates from dinosaur feces, missing in the famous scene of the sick Triceratops from the film Jurassic Park, there were snails, crustaceans³, beetles¹ and cockroaches⁴; but, for me, the most fascinating are of course the snails, animals that saw the dinosaurs come and go, and probably will outlive our own species too.

*Edited by Zaidett Barrientos, Katherine Bonilla y Carolina Seas.

Originally published  in Blog Biología Tropical: 24 august 2020

REFERENCES

¹ Chin, K., et al. (2009). Opportunistic exploitation of dinosaur dung: fossil snails in coprolites from the Upper Cretaceous Two Medicine Formation of Montana. Lethaia, 42(2), 185-198.

² Chin, K. (2007). The paleobiological implications of herbivorous dinosaur coprolites from the Upper Cretaceous Two Medicine Formation of Montana: why eat wood?. Palaios, 22(5), 554-566.

³ Chin, K., et al. (2017). Consumption of crustaceans by megaherbivorous dinosaurs: dietary flexibility and dinosaur life history strategies. Scientific reports, 7(1), 1-11.

⁴ Vršanský, P., et al. (2013). Cockroaches probably cleaned up after dinosaurs. PloS one, 8(12), e80560.