#ornitholithus

[mesozoicmarket]

A pair fossilized bird eggshell of a Gastornis sp. or the oospecies, Ornitholithus arcuatus from Bouches du Rhône, France. These Lower Eocene aged eggshells have a thickness of around 2 mm implying they were laid by giant birds like Gastornis which distinguishes it from smaller contemporary bird ootaxa like Ornitholithus biroi which has a 1mm thickness. The right specimen comes from Saint-Léger while the left comes from Saint-Antonin-sur-Bayon.

[a-dinosaur-a-day]

So, if Ornitholithus is a Gastornis egg, then why does it have its own scientific name? Is this a naming convention that I'm no aware of?

It can’t really be confirmed as a Gastornis egg, since it wasn’t found with a Gastornis skeleton; Gastornis is just the only contender in the region that COULD have laid an egg of such size and form. As such, it gets its own genus name, since it hasn’t been confirmed through association.

[a-dinosaur-a-day]

Ornitholithus

Ornitholithus is the eggs of the large Anseriform Gastornis, of fame from the Walking with Beasts program (though, Gastornis was actually probably an herbivore, unlike what that program suggests). Its eggs are known from the Late Paleocene in Spain and the early Eocene of France, and the eggs are quite huge, about 24 by 10 cm (leading to them being assigned to Gastornis, as no other large birds are known from that region and time). The shells themselves are 2.3 to 2.5 mm thick, making the egg about half as large as that of an ostrich and very different in shape from ratite eggs. 

Sources: 

Donaire, M., N. López-Martínez. 2009. Porosity of Late Paleocene Ornitholithus eggshells (Tremp Fm, south-central Pyrenees, Spain): Palaeoclimatic implications. Palaeogeography, Palaeoclimatology, Palaeoecology 279 (3-4): 147-159. 

https://en.wikipedia.org/wiki/Gastornis#Eggs

Shout out goes to @inculture-me!