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Oldest known crocodiloid eggs discovered in Portugal

150 million years ago, Portugal was a completely different place to now. While much of the beautiful landscapes still existed, the animals living there were alien compared to those living there now. Ecosystems were dominated by a dizzying array of weird dinosaur species, along with the ancestors of modern groups like mammals, amphibians, and crocodiles.

Fossils from the Late Jurassic of Portugal are very common. Some of the greatest discoveries are those of early crocodile-ancestors, collectively called crocodylomorphs. While dinosaur eggs have been fairly common among the fossilised remains of these animals, crocodylomorph eggs have rarely been found or studied, until now.

Global distribution of fossil crocodiloid eggs. Russo et al., 2017.

Russo and colleagues discovered and recently reported several new occurrences of ‘crocodiloid’ egg from the ancient Portuguese rocks, together representing two different and previously unknown types of egg.

Now, the naming and identification of eggs is a bit different to normal fossils. Their remains are called ootaxa, instead of just taxa, and these are broken down into oofamilies, oogenera, and oospecies. This comes from the Greek term “oolithus”, which literally means “stone egg”.

One clutch of 13 fossilised eggs were like nothing the researchers had seen before, and distinct enough for them to create the new name Suchoolithus portucalensis for them. Some of the other material they found was similar to an existing genus, and newly named as Krokolithes dinophilus. The latter oospecies name is due to the occurrence of these eggshells with dinosaur nests and eggshells, which suggests an interesting ecological nesting association between dinosaurs and crocodylomorphs here. For example, the crafty crocs might have hidden their nests among those of theropods to trick the larger predators into thinking they were there own, and therefore not eating them.

Both different types of egg were also of different sizes, which suggests that they were laid by females of different sizes and species too. This is really cool, as it supports a lot of recent evidence that different species of crocodylomorphs, often of vastly different lifestyles, often co-existed alongside each other in the Late Jurassic of Europe. This is called ‘sympatry’, and is a way of different but closely-related species sharing an ecosystem by taking on different ecological roles within it.

These eggs also represent the oldest known crocodylomorph eggs in the fossil record. What is remarkable about this is that over 150 million years of evolution, the structure of these eggs seems to have changed very little compared to modern crocodylians, while the egg-layers themselves have often changed quite a bit – crocodylomorphs were quite the evolutionary explorers.

Despite crocodiloid eggs being first identified in the 1930s and 1940s, and even with the advance of modern chemical imaging and analytical techniques, this conservatism seems to be the rule for all remains that have since been discovered. As the saying goes, if it ain’t broke, don’t fix it!

Crocodiles and their ancestors remain a huge success story in reptile evolution, and it seems that their eggs might have been a big part of that.

Full disclosure: I was one of the peer reviewers for this paper.

Reference

Russo J, Mateus O, Marzola M, Balbino A (2017) Two new ootaxa from the late Jurassic: The oldest record of crocodylomorph eggs, from the Lourinhã Formation, Portugal. PLoS ONE 12(3): e0171919. doi:10.1371/journal.pone.0171919 (link)

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