An article published in the journal “Current Biology” describes a research on Waptia fieldensis (photo ©Verisimilus), an arthropod that lived about 508 million years ago, during the Cambrian period. The analysis of fossils of this ancient creature shows the presence of eggs with embryos preserved inside them. These eggs were protected by the mother’s body showing the most ancient traces of offspring care found so far.
Waptia fieldensis is the only species so far discovered of the Waptia genus. It was discovered already in 1909 by Charles D. Walcott in the famous Burgess Shale. Its shape resembles the shrimp’s, so much that in the course of past studies it was considered a primitive form of shrimp, but that idea was quickly abandoned. Today it’s considered an arthropod whose taxonomy is uncertain although it could be related to the crustaceans.
Jean-Bernard Caron, curator of invertebrate palaeontology at the Royal Ontario Museum and associate professor in the Departments of Earth Sciences and Ecology & Evolutionary Biology at the University of Toronto, Canada, and Jean Vannier at the Centre national de la recherche scientifique in Lyon, France, the authors of this study, discovered that five specimens of Waptia fieldensis hid their eggs under their carapace. These arthropods were equipped with a bivalve carapace, which means that it was divided into two parts. Under the anterior side the researchers found clusters of eggs.
These clusters are grouped into a single layer on each side of the specimen’s body. In some cases, the eggs are equidistant from each other while in others some are close to each other. It’s possible that this is due to differences in these specimens’ burial and movements during the burial. The maximum number of eggs preserved for specimen probably was 24.
The Waptia fieldensis’ eggs in some cases were more than 2 millimeters long. They can seem small but actually are relatively large for a creature that reached lengths of about 8 centimeters (about 3 inches). The researchers made a comparison with another arthropod species of the Cambrian, Kunmingella douvillei, which could have a large number of eggs but much smaller.
Fossils of Kunmingella douvillei are few million years older than those of Waptia fieldensis and show some kind of protection of the eggs, attached to its appendices. One key difference is that in Kunmingella douvillei’s fossil eggs no embryos were found. This suggests that Waptia fieldensis already had a strategy to improve the chances of survival of its offspring, protecting the eggs with its carapace.
In the past, other research showed signs of egg care in ostracods, a class of crustaceans, that lived in the upper Ordovician, about 450 million years ago. The study of Waptia fieldensis shows that some kind of parental care is even more ancient. The conclusions are that those are strategies that evolved for the first time very early in the history of complex life forms and that it happened a number of times.