New Research Shows Dinosaur Eggs Directly Correlate to Modern Bird Eggs

Fossilized Spanish eggs show a strong link between Theropoda and Aves

Paleontologists have been aware for some time of the close anatomical links between certain members of the lizard-hipped dinosaurs known as Theropoda and modern birds. A large body of evidence has been collected to show that certain types of dinosaurs, such as the Dromaeosauridae, the raptors, were closely related to Aves (birds). Scientists know, for example, that many small carnivorous theropods, such as members of the Dromaeosauridae, dinosaurs like Microraptor and Sinornithosaurus, were covered in feathers, but there are also striking similarities between the skeletons of birds and the fossilized bones of this type of dinosaur. .

Dinosaur/Bird Link Theory Almost as Old as the Science of Paleontology

The link between dinosaurs and birds is not a new theory in paleontology. Of course, there have been a number of surprising discoveries made of feathered dinosaurs, most notably in the Lower Cretaceous strata of Liaoning province (north China). It was people like Thomas Henry Huxley who first proposed the dinosaur/bird link.

Huxley’s study of Archeopteryx

Thomas Henry Huxley was an English biologist and an ardent supporter of Darwinism. When Sir Richard Owen purchased a nearly complete specimen of Archeopteryx (A. lithographic) in the 1860s, Huxley used this fossil to support Darwin’s theory of natural selection and declared the Archeopteryx specimen a “transitional fossil” between reptile and bird evolution.

But dinosaur eggs don’t look like bird eggs, do they?

However, one of the gaps in our knowledge about the relationship between certain members of Dinosauria and the Order Aves, referred to the shape and composition of the eggs that these types of creatures lay. Several different shapes and sizes of dinosaur eggs are known from the fossil record, but the fossil eggs attributed to theropods do not closely resemble the shape of a modern bird egg, like the type of egg a chicken would lay. Typically, a small meat-eating dinosaur would produce relatively elongated eggs, not the ovoid shape we’re used to when seeing a bird egg.

The discovery of the remains of dinosaur eggs in northeastern Spain may change all that, as these eggs resemble those of a modern bird.

Spanish dinosaur eggs scramble existing dinosaur theories

Nieves López Martínez, a paleontologist at the Complutense University of Madrid (Spain), with a doctorate in geology and biology, had been investigating the strange ovoid and asymmetrical fossil eggs that had been found in the Montsec area of ​​Lleida in the north. -East of Spain. Unfortunately, she passed away in December 2010. Her work and that of her colleague Enric Vicens, a paleontologist at the Universitat Autonoma de Barcelona (Spain), have just been published. Her extensive research provides strong evidence linking theropod dinosaurs to modern birds, as the eggs found in Spain are very similar in shape and composition to those of modern birds.

late cretaceous “raptors” eggs

The eggs were extracted from two excavations, located on both sides of the Terradets pass. The strata in this part of Spain represent sediments deposited at the end of the Cretaceous (Campanian and Maastrichtian faunal stages). Several different types of dinosaurs are known from this stratum: ornithopods, theropods, and titanosaurs. The geological record of this part of Spain is very important, as it provides scientists with an idea of ​​the flora and fauna that existed in Europe at the end of the Age of Dinosaurs.

Although scientists can’t determine exactly what type of dinosaur lays the eggs, they have postulated that they were produced by a troodontid, a type of dinosaur closely related to birds. Troodonts were small, agile, bipedal predators. Egg fossils, consisting of many fragments plus some complete eggs, have been given the scientific name of Pyrenean sankofa. The generic name is related to an ancient bird symbol showing a bird looking over its back with an egg that has just fallen from its mouth. The species name is related to the fact that the fossils were found in a part of the southern Pyrenees mountain range.

Spain seventy million years ago

Approximately seventy million years ago, this part of Spain was a low-lying coastal area with many shallow lagoons fringed by lush, dense forests. Several dinosaur egg fossils have been found in this area, there seem to be several different types of ugly dinosaur eggs on the raised beaches that made up this coastal area, but most of the fossil eggs found to date are large, rounded. Titanosaurus eggs. These eggs are very different, measuring just three inches tall and with a diameter of about four inches. The egg shell is about the same thickness as a chicken egg. The scientists measured the fossilized eggshell and found it to be around 0.27mm thick.

Fossil eggs under the microscope

Sectional analysis of eggs that had been preserved intact showed that a substantial air pocket was present at the widest end of the egg. Such air pockets are found in modern bird eggs. If you take a chicken egg and place it in water, a fresh egg will sink but have some degree of buoyancy. Buoyancy is provided by a small air space contained within the egg. The air sac allows the organism inside the egg to breathe during the last phases of its development before hatching.

Spanish eggs, a “missing link” between dinosaurs and birds

Such oval-shaped, asymmetrical eggs are extremely rare in the Cretaceous fossil record. The Spanish researchers related the shape of their eggs to that of a bird from the Late Cretaceous whose fossils have been found in South America. The research team postulated that this bird and its dinosaur laid eggs that were intermediate between the eggs of modern birds and the eggs laid by extinct non-avian theropods.

microscopic differences

A microscopic analysis of the fossil eggshell of Pyrenean sankofa revealed significant differences in shell structure compared to that of a modern bird’s egg. The eggshell of birds and most reptiles is composed almost entirely of calcium carbonate, the structure of the crystals and the way they are arranged in a bird’s egg differ from that seen in the internal structure of the eggshell attributed to S. pirnenaica.

Some dinosaurs, like birds, had only one oviduct.

The shape of an egg is largely dictated by the physiology of the organism that lays those eggs. The asymmetry in bird eggs is related to the fact that birds only have one oviduct, so they can only form one egg at a time. Most dinosaur nests show that eggs were laid in pairs, indicating that these animals had two oviducts. Scientists believe that modern birds lost the second oviduct as an evolutionary response to the need to lighten their bodies for more efficient powered flight. The asymmetric shape of the Spanish dinosaur eggs suggests that Pyrenean sankofa it also possessed a single oviduct.

This fossil evidence strongly supports the theory that certain dinosaur clades were very closely related to birds. Parts of Dinosauria and Aves are closely related phylogenetically.

Extrapolating from this evidence, the next time you eat a boiled egg, you’re technically eating the egg of a creature closely related to a dinosaur, or given where these fossil eggs were found, would you prefer a Spanish omelette?