Image source: Noiel / Shutterstock
- Normal geological evidence isn't precise enough to confirm paleontologists' suspicions.
- The new fossils find is covered by a fine veneer of red sand deposited in a single season.
- Scientists can infer whose eggs they were.
Paleontologists suspected that some dinosaurs nested in colonies, but it was impossible to know for sure. Yes, they'd often found what appeared to be groups of fossilized eggs. But did these egg "clutches" date from the same time, or had they gradually accumulated in a popular nesting area?
An unusual layer of sediment recently found in the Gobi desert appears to finally answer this question: At least one group of dinosaurs definitely nested and protected their clutches as a colony. A report of the find was published Jul 15 in Geology.
Why paleontologist have been wondering
Crocodiles lay eggs together in nests that they guard and protect as a colony. There are also a variety of modern birds that do this: seabirds such as auks and albatrosses, wetland birds like herons, and even some blackbirds and swallows. As descendants of dinosaurs, experts have wondered how far back this goes. Since the first dinosaur eggs were unearthed in France in 1859, paleontologists have been finding them in hundreds of locations around the world, and in 1978, the first evidence of a nesting colony was discovered in western Montana. Such clutches contain anywhere from 3 to 30 eggs.
Dating of such fossils is typically imprecise, however. A layer of rock covering a find may take millions of years to lay down, and can only suggest approximate ages of individual fossils. Though radiocarbon dating using Carbon-12 isotopes has a margin of error of just decades, that's still not quite close enough to establish that the eggs were actually contemporaneous.
The thin red line
The Gobi desert is the site of countless dinosaur fossils
Image source: Galyna Andrushko / Shutterstock
It took some extraordinary good luck to finally solve the riddle. In 2015, a group of paleontologist including some from Canada's Royal Tyrrell Museum and the University of Calgary came across a large deposit of dinosaur eggs in China's southeast Gobi Desert, in the Javkhlant formation. There were 15 nests and over 50 eggs about 80 million years old in a 286 square-meter formation.
What made the find so unusual, and ultimately dispositive, was the thin veneer of red rock, likely deposited in a single breeding season, that covered all of the eggs. It's believed to be sand deposited by flooding from a nearby river. "Because everything is relatively undisturbed, it likely wasn't a massive flood," says François Therrien. Adds Darla Zelenitsky, another co-author, "Geologically, I don't think we could've asked for a better site." Equally compelling, some 60 percent of the eggs had already hatched and had the red sand inside them.
This "was a demonstration that all of these clutches were actually a true dinosaur colony and that all those dinosaurs built their nests in the same area at the same time," asserts Therrien.
Whose eggs were they?
A mock-up, not real hatchlings.
Image source: Jaroslav Moravcik/Shutterstock
The find also offered up some insights into who these eggs belonged to. The texture and thickness of the eggs suggests their parents were non-avian theropods, a group that includes velociraptors. Not that these particular theropods were necessarily so fleet of foot.
"These animals were relatively big," Therrien tells CBC News, "They were around seven to nine meters in length, so way too big to fly. And they would have been covered with feathers, but very primitive types of feathers… hairy and light. They would not have had wings and would have been unable to fly." Such dinosaurs had, he adds, "a long neck, small head, but they have very, very large hands and very, very long claws on their four limbs," likely for defense.
The scientists were also able to infer something about the dinosaurs' parental behavior by comparing the rate of successful hatches to modern animals such as crocodiles and birds that guard their eggs. The survival rate strongly suggests that the colony protected their progeny throughout the incubation and hatching process, rather than abandoning them. Says Therrien, "If we compare that to modern animals, we see a very high hatching success like that around 60 percent among species where one or several parents guard in their colony. Basically, if the adults leave — abandoned the nest — we have a much lower hatching success because the eggs either get trampled or get predated upon."
"Sometimes you can extract a fascinating and detailed story about the ecology and behavior of these animals simply by looking at the rocks themselves," he notes.
Image source: Sereno, et al
Mind & Brain
- A powerful MRI combined with modeling software results in a totally new view of the human cerebellum.
- The so-called 'little brain' is nearly 80% the size of the cerebral cortex when it's unfolded.
- This part of the brain is associated with a lot of things, and a new virtual map is suitably chaotic and complex.
Just under our brain's cortex and close to our brain stem sits the cerebellum, also known as the "little brain." It's an organ many animals have, and we're still learning what it does in humans. It's long been thought to be involved in sensory input and motor control, but recent studies suggests it also plays a role in a lot of other things, including emotion, thought, and pain. After all, about half of the brain's neurons reside there. But it's so small. Except it's not, according to a new study from San Diego State University (SDSU) published in PNAS (Proceedings of the National Academy of Sciences).
A neural crêpe
A new imaging study led by psychology professor and cognitive neuroscientist Martin Sereno of the SDSU MRI Imaging Center reveals that the cerebellum is actually an intricately folded organ that has a surface area equal in size to 78 percent of the cerebral cortex. Sereno, a pioneer in MRI brain imaging, collaborated with other experts from the U.K., Canada, and the Netherlands.
So what does it look like? Unfolded, the cerebellum is reminiscent of a crêpe, according to Sereno, about four inches wide and three feet long.
The team didn't physically unfold a cerebellum in their research. Instead, they worked with brain scans from a 9.4 Tesla MRI machine, and virtually unfolded and mapped the organ. Custom software was developed for the project, based on the open-source FreeSurfer app developed by Sereno and others. Their model allowed the scientists to unpack the virtual cerebellum down to each individual fold, or "folia."
Study's cross-sections of a folded cerebellum
Image source: Sereno, et al.
A complicated map
Sereno tells SDSU NewsCenter that "Until now we only had crude models of what it looked like. We now have a complete map or surface representation of the cerebellum, much like cities, counties, and states."
That map is a bit surprising, too, in that regions associated with different functions are scattered across the organ in peculiar ways, unlike the cortex where it's all pretty orderly. "You get a little chunk of the lip, next to a chunk of the shoulder or face, like jumbled puzzle pieces," says Sereno. This may have to do with the fact that when the cerebellum is folded, its elements line up differently than they do when the organ is unfolded.
It seems the folded structure of the cerebellum is a configuration that facilitates access to information coming from places all over the body. Sereno says, "Now that we have the first high resolution base map of the human cerebellum, there are many possibilities for researchers to start filling in what is certain to be a complex quilt of inputs, from many different parts of the cerebral cortex in more detail than ever before."
This makes sense if the cerebellum is involved in highly complex, advanced cognitive functions, such as handling language or performing abstract reasoning as scientists suspect. "When you think of the cognition required to write a scientific paper or explain a concept," says Sereno, "you have to pull in information from many different sources. And that's just how the cerebellum is set up."
Bigger and bigger
The study also suggests that the large size of their virtual human cerebellum is likely to be related to the sheer number of tasks with which the organ is involved in the complex human brain. The macaque cerebellum that the team analyzed, for example, amounts to just 30 percent the size of the animal's cortex.
"The fact that [the cerebellum] has such a large surface area speaks to the evolution of distinctively human behaviors and cognition," says Sereno. "It has expanded so much that the folding patterns are very complex."
As the study says, "Rather than coordinating sensory signals to execute expert physical movements, parts of the cerebellum may have been extended in humans to help coordinate fictive 'conceptual movements,' such as rapidly mentally rearranging a movement plan — or, in the fullness of time, perhaps even a mathematical equation."
Sereno concludes, "The 'little brain' is quite the jack of all trades. Mapping the cerebellum will be an interesting new frontier for the next decade."
