Tiny Jurassic Mammals Were Picky Eaters
Pamela Gill/University of Bristol
Researchers digitally reconstructed the jawbones of 200-million-year-old mammals that lived during the Jurassic Period.
As paleontologists increasingly unearth evidence of feathers in prehistoric fossils, our conceptions of what dinosaurs looked like when they roamed the earth has gradually evolved.
Instead of the reptilian appearance we all recognize from childhood toys and films like Jurassic Park, many dinosaurs in fact more closely resembled birds, kind of like this recently discovered little guy, Eosinopteryx brevipenna, a flightless theropod dinosaur that roamed China during the Middle/Late Jurassic period.
Archaeopteryx, also known as Urvogel, the German word for "original bird" or "first bird," was first discovered in 1860 and later fossils of this species presented some of the earliest evidence of flight in these prehistoric animals.
An intermediate creature that was not quite dinosaur but not exactly a bird either when it lived 150 million years ago, Archaeopteryx had teeth, a long tail, and wings capable of flight with claws at the end for grabbing prey.
A century after the discovery of Archaeopteryx, paleobiologists increasingly found anatomical connections between birds and dinosaurs. In the 1970s, artists began to portray dinosaurs with feathers based on accumulating evidence.
Megapnosaurus, shown here, was another species with whom researchers began early to identify with feathers. A lightweight animal that could reach up to 10 feet in length and roamed Jurassic Zimbabwe, Megapnosaurus, also known as Syntarsus, traveled in packs and preyed on small reptiles and fish.
Many of the fossils unearthed that provided evidence of feathers had deteriotated over the eons they remained buried. It wasn't until 2010 that researchers identified color pigments in feathers from dinosaurs and early birds.
Sinosauropteryx, illustrated here, was a theropod dinosaur that had "simple bristles -- precursors of feathers -- in alternate orange and white rings down its tail," according to a description of the study's findings.
Given that so many feathered dinosaurs were in fact flightless, the purpose of the feathers has been a subject of debate. Some dinosaurs may have evolved feathers for social signaling; others had plumage to provide insulation.
In the cases of some dinosaurs, such as the two oviraptors, herbivores related to T. rex that lived during the Cretaceous period, researchers believe the feathers were used for mating displays, similar to modern-day peacocks and turkeys.
Jason Brougham/University of Texas
You might be fooled into thinking the animals in this illustration are something between a murder of crows and a band of blue jays. In fact they are Microraptors that lives more than 130 million years ago.
These four-winged, plumed dinosaurs were no larger than modern-day pigeons and sported iridescent tail feathers.
Researchers believe the shimmering plumage was likely used in mating and other social interactions.
Like the diversity among birds today, not all feathered dinosaurs were lightweight, agile animals. A massive tyrannosaur that lived in China until about 65 million years ago, Yutyrannus huali, meaning "beautiful feathered tyrant," grew up to 30 feet long and could weigh more than 3,000 pounds.
This titanic tyrannosaur, as it was described, significantly increases the size range for feathered dinosaurs.
In a stunning find published in the journal Science in 2011, paleontologists uncovered dinosaur feather preserved in amber that dated back some 79 million years ago.
This discovery provided scientists a new window into the evolution of feathers in terms of structure in the evolutionary timeline from dinosaurs to birds. Even shades of color remained well preserved in the amber.
In the Jurassic Period, when dinosaurs ruled the land, tiny mammals probably had to keep a low profile and survive by gobbling any insects they could find, but new research suggests these early mammals may have been pickier eaters than scientists previously thought.
The Jurassic lasted from about 201 million years ago to 145 million years ago. During this time, dinosaurs were in their heyday, but shrew-size mammals and their immediate ancestors were just starting to emerge.
The Jurassic is also when early mammals began developing better hearing and their teeth began evolving to enable more precise chewing. New techniques of fossil analysis have revealed that some of these mammals were not general insectivores as scientists had believed, but instead probably ate a unique and selective diet of insects. [In Photos: Mammals Through Time]
A team of researchers looked at 200 million-year-old mammal jawbones and teeth discovered in Glamorgan, in South Wales. Based on fossil analysis, the team determined that two of the earliest mammal groups, Morganucodon and Kuehneotherium, likely were discerning about the types of insects they ate.
"None of the fossils of the earliest mammals have the sort of exceptional preservation that includes stomach contents to infer diet, so instead we used a range of new techniques which we applied to our fossil finds of broken jaws and isolated teeth," study lead author Pamela Gill, a research associate in the School of Earth Sciences at the University of Bristol, in the United Kingdom, said in a statement. "Our results confirm that the diversification of mammalian species at the time was linked with differences in diet and ecology."
By examining the microscopic scratches and pits in the fossilized teeth, Gill and her colleagues determined that Morganucodonconsumed mostly harder and crunchier bugs like beetles, while Kuehneotheriumpicked softer insects like scorpion flies. This same technique is used to examine the teeth of present-day bats that feed on insects.
"This is the first time that tooth wear patterns have been used to analyze the diet of mammals this old," Mark Purnell, a professor of palaeobiology at the University of Leicester, in the U.K., said in a statement. "That their tooth wear compares so closely to bats that specialize on different kinds of insects gives us really strong evidence that these early mammals were not generalists when it came to diet, but were quite definite in their food choices."
The jaws of these mammals are only about 0.8 inches (2 centimeters) long, and many of the recovered fossils are broken into fragments. Gill and her colleagues used X-rays and CT scanning to examine the pieces of jawbone and teeth in detail.
The team then digitally reconstructed the jaws by using software to stitch the individual scans together. They also calculated the strength of the jaws using a technique called finite element modeling. This technique is the same one used to design artificial hip joints for humans. The researchers' analysis also showed that Morganucodonand Kuehneotheriumlikely used different methods to catch and chew their prey.
The study was published online today (Aug. 20) in the journal Nature.
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Image Gallery: Evolution's Most Extreme Mammals
In Photos: Wacky Fossil Animals from Jurassic China
The World's 5 Smallest Mammals