Imagine a typical day 100 million years ago in Zhejiang Province, southeastern China. Bulky, long-necked, herbivorous sauropods set a deliberate pace across the landscape in the shadow of an ancient chain of volcanoes. Bizarre beaked and feathered therizinosaurs rest in the shade, their hands with enlarged claws folded wing-like at their sides. Large and small varieties of herbivorous, bipedal ornithopods kick up mud in the shallows of a small lake, some leaving tracks as they make their way along the shoreline. A curious mother oviraptorosaur eyes a turtle sliding silently into the water. These animals and more have left skeletal remains and other evidence of their past existence, including eggs and footprints, in layers of Cretaceous-aged rock now scattered across more than 40 sedimentary basins in Zhejiang Province.
Presumably, all of the animals described above laid eggs, and as avid readers of this blog now know, a tremendous diversity of fossil eggs has been unearthed in Zhejiang in recent years, as China’s growth has propelled a profusion of construction and development projects that lay bare new exposures of Cretaceous bedrock before human eyes. The difficulty in understanding this abundance of fossil eggs comes in attempting to figure out which dinosaurs or other animals laid all of the different kinds of eggs. Only eggs with preserved embryonic bones inside, which are exceedingly rare and not currently known from Zhejiang Province, can provide a confident identification of the parent. Thus, scientists are faced with a dilemma when attempting to make sense of fossil egg diversity: how can eggs be named and organized when the identity of the egg-layer remains a mystery?
The answer lies in utilizing parataxonomy. Parataxonomy is a separate and parallel system of classification for some fossils that aims to avoid making potentially erroneous assignments of eggs or trace fossils (like footprints and burrows) to an organism already known from skeletal remains. Two examples of what parataxonomy seeks to circumvent are the cases in which the eggs of both Oviraptor and Troodon were originally misidentified as the eggs of other species of dinosaurs before Oviraptor and Troodon embryos were found within those same egg types. Parataxonomy allows for a standard set of names to be applied to eggs and trace fossils that facilitates communication among researchers. Fossil eggs have their own branch of parataxonomy, called ootaxonomy, within which eggs have traditionally been given oogenus names ending in “-oolithus,” which means “egg stone.” This is the reason for all of the daunting, tongue-tying names for egg types, including Spheroolithus, Dendroolithus, Dictyoolithus, Faveoloolithus, and Macroelongatoolithus (a name as long as the 40+ cm eggs themselves).
My topic of study on the current trip to China, in addition to more precisely determining locality and associated geologic information for the eggs examined during the 2010 trip, is to document the range of egg types present in the large collection of eggs housed at the Zhejiang Museum of Natural History. I hope to further understand the relationships of these various egg types to one another and to eggs with known embryos through a method of hypothesizing evolutionary relatedness called cladistics. The eggs of Zhejiang are well suited to contribute to such a study because of the great diversity of egg types preserved in a relatively small geographic area and housed in one museum collection. Because bones are not usually as abundant as eggs in the Zhejiang formations, understanding this staggering amount and variety of eggs may play an important role in reconstructing the fauna of the vanished realm of mid-Cretaceous China.
Blog post by Danny Barta