Titanosaurid Egg Containing Cocoons of Wasps Discovered
In a scenario not out of place in a television detective series, scientists have carefully examined the fossilised remains of insects preserved inside a seventy-million-year-old dinosaur egg, to try to piece together the story of how this egg was broken and what it can tell them about the role of insects in dinosaur dominated food chains. The fossil forensics have been conducted upon the egg of a huge, long-necked Cretaceous plant-eater known as a titanosaur. These creatures were some of the largest land-living animals of all time, but their eggs are surprisingly small given the fact that these animals could grown to upwards of thirty metres in length and weigh perhaps as much as ten elephants.
Exceptionally preserved fossils of insect cocoons have allowed researchers in Argentina to describe how wasps played an important role in food webs devoted to consuming rotting dinosaur eggs. The research is published in the scientific journal Palaeontology.
The approximately 70 million year old eggs, from gigantic titanosaur sauropod dinosaurs were discovered in 1989 in the Patagonia region of Argentina, well known for yielding fossils of sauropod dinosaur eggs and even embryonic dinosaurs. Only recently it was discovered that one of the broken eggs contained tiny sausage-shaped structures, 2-3 cm long and 1 cm wide. The structures closely resembled fossilised insect cocoons, and were most similar in size and shape to the cocoons of some species of modern wasp.
Pictures show the bottom half of the broken sauropod egg, the cocoons of wasps can be made out and the coin provides scale. Each wasp cocoon is approximately 2 cm long.
There are many records of fossilised dinosaur eggs, and even several records of fossil cocoons, but, as author Dr Jorge Genise of the Museo Argentino de Ciencias Naturales stated:
“This is the first time that these cocoons are found closely associated with an egg.”
This fossils provides a rare insight into the role played by insects and how they interacted with the Dinosauria.
Dr Genise went onto state the results of their forensic examination indicate that:
“Wasps probably participated in the food web, mostly composed of scavenging insects, which developed on the rotten egg.”
Such creatures make-up of carrion communities – spiders, beetles and other creatures populating rotting organic matter, today modern forensic police scientists use insect and other scavenger evidence to try to date corpses, as any viewer of the CSI franchise would know. The work done by the researchers on the dinosaur egg is more familiar to us from the screens of crime scene investigation documentaries.
The numbers and different types of creatures indicate the length of deposition and the time since death. In this particular CSI, it appears that the dinosaur egg was broken by force, and subsequent fractures in the egg shell allowed scavenging creatures to feed upon the contents. At egg sizes of around 20 cm, this represents a sizeable amount of yolk! Other creatures later appeared to feed not upon the egg contents, but on the initial scavengers themselves. The wasps represent the top of the food web, and could have been feeding on insects or spiders gorging on rotting egg contents.
These scavengers also played an important role in cleaning up nest sites. Palaeontologists believe that some dinosaurs revisited nest sites year after year to lay new clutches of eggs. Carrion communities were essential to removing decaying material in advance of new nesting seasons. This new discovery gives us an insight into the murky world of insect communities that thrived at the feet of gigantic dinosaurs.