Paleontoriano

A Triceratops may have been the last dinosaur standing, according to a new study that determined a fossil from Montana's Hell Creek Formation is "the youngest dinosaur known to science."

The Triceratops, described in the latest Royal Society Biology Letters, dates to 65 million years ago, the critical period of time associated with the Cretaceous-Tertiary (K-T) extinction event that wiped out all non-avian dinosaurs and many other animals and plants.

Since this rhinoceros-looking, three-horned dinosaur lived so close to the mass extinction moment, it could negate an earlier theory that dinosaurs gradually died out before 65 million years ago.

"Our paper suggests that dinosaurs did not go extinct prior to the impact," lead author Tyler Lyson told Discovery News. "The fact that this dinosaur is so close to the K-T boundary lends support to the idea that they went extinct as a result of a meteorite impact."

Lyson, a researcher in Yale University's Department of Geology and Geophysics, and his team discovered the remains of the Triceratops, including its over 1.5-foot-long horn, just 5 inches below the pollen-calibrated K-T boundary at Camel Butte, a hill at the Hell Creek Formation in southeastern Montana.

By studying the region's geological layers, the scientists can see how dinosaurs suddenly disappeared after the catastrophic event, which Lyson and many other experts believe was a meteorite strike that directly hit Earth at Mexico's Yucatan Peninsula.

Lyson said that "we don't fully understand the kill mechanism," but other researchers "have a proposed a nuclear winter, while others have proposed a thermal pulse."

The prior theory that dinosaurs gradually died out before 65 million years ago was often based on what is known as the "3-meter gap," which referred to an apparent geological zone devoid of dinosaur fossils before the K-T event.

The Hell Creek Triceratops, however, was not only found within that 3-meter region, but it also exists at the upper reaches of it, proving that at least one dinosaur and presumably more were still alive when the meteorite blasted into Chicxulub, Mexico.

Co-author Stephen Chester of Yale's Department of Anthropology told Discovery News that the Camel Butte site is important both because it has "the most recent dinosaur specimen" and "because we are finding a great diversity of small mammals that are first documented directly after the extinction event."

Chester continued, "Although the K-T mass extinction event is mainly known for the disappearance of the non-avian dinosaurs, it is also an extremely important event in mammalian evolution because once the dinosaurs vanished, mammals underwent a large adaptive radiation and began occupying diverse ecological niches in the Paleocene."

These mammals included condylarths, which were hoofed animals proposed to be ancestral to some modern orders of hoofed mammals. They also included multituberculates, which Chester described as being "extinct rodent-like animals with a very specialized dentition."

It remains unclear why certain mammals, turtles and other animals survived the K-T extinction event, but Lyson explained that species with generalist, rather than specialized, diets tended to fare better, as did smaller animals and water dwellers.

Kirk Johnson is vice president of Research & Collections and chief curator at the Denver Museum of Nature & Science.

Johnson told Discovery News that he agrees the Triceratops is indeed "the last known non-avian dinosaur of the Cretaceous." He said, "The 3M Gap is a weak concept to begin with," and that his own work on plants and insects supports the idea that the meteor impact was the "direct and immediate cause of habitat destruction and extinction of more than 50 percent of North American plant and insect species."

The feathered dinosaur Sinornithosaurus

Non-avian feathered dinosaurs might have spent much of their time nibbling off insects and scratching themselves, suggests a new study that proposes certain dinosaurs were the first animal hosts of lice.

“Our analysis suggests that both bird and mammal lice began to diversify before the mass extinction of dinosaurs," principal investigator Kevin Johnson was quoted as saying in a University of Illinois at Urbana-Champaign press release. “And given how widespread lice are on birds, in particular, and also to some extent on mammals, they probably existed on a wide variety of hosts in the past, possibly including dinosaurs."

That view is strengthened in the journal paper itself. The researchers write: "These data give an early- to mid-Cretaceous origin (115 - 130 million years ago) for lice, which suggests that these parasites probably infested feathered theropod dinosaurs."

Johnson, an ornithologist with the State Natural History Survey at the university, and his colleagues came to the dino-lice conclusion after constructing a partial family tree for lice. They did this by comparing the DNA sequences of genes from 69 present-day louse lineages. Changes in gene sequence are believed to be a reliable measure of relatedness among different species in the same basic animal group. Because these changes accumulate over time, they can also be used to create a rough timeline of the evolution of related groups of organisms.

The lice family tree indicates the wingless insects were around long before dinosaurs bit the ultimate dust 65 million years ago.

While anyone who has dealt with lice, such as head lice on kids, knows how tenacious and hearty these insects can be, it is still surprising to learn that lice have been around for so long. The oldest fossils found so far that resemble modern bird and mammal groups are less than 65 million years old, Johnson explained. That's what led to the prior belief that major bird and mammal lineages -- as well as their body-dwelling insects -- appeared only after the dinosaurs went extinct.

But the lice DNA findings indicate that modern birds and mammals were already around when the non-avian dinosaurs died out. The researchers can see that because each louse species evolves specialized traits to suit a particular host animal. Wing lice, for example, have long bodies that allow them to insert themselves between the barbs in a feather and thus evade preening. Gopher lice have grooves in the tops of their heads that clasp onto a single shaft of hair.

These specialized traits make it hard for lice to shift to other hosts. As a result, their evolutionary history coincides very closely with that of their hosts. This history provides evidence of the existence of mammals and birds before 65 million years ago.

“Lice are like living fossils," explained co-principal investigator Vincent Smith, who was a former postdoctoral researcher in Johnson’s lab and is now at the Natural History Museum in London. “The record of our past is written in these parasites, and by reconstructing their evolutionary history, we can use lice as markers to investigate the evolutionary history of their hosts.”

If dinosaurs did indeed have lice, as the researchers strongly suspect, Johnson said, "maybe birds just inherited their lice from dinosaurs."

Furrows preserved in 565-million-year-old rocks are now the first evidence that some of Earth's earliest and mysterious living things had muscles to move themselves -- and so were truly animals.

That means muscles may have evolved earlier and been part of a long evolutionary fuse that led to the so-called "Cambrian Explosion," 30 million years later, of the many lineages of marine animals still found in the oceans today.

"If you saw (these furrows) in rocks the same age as dinosaurs, you'd say it was something crawling alongthe sea floor," said Duncan McIlroy of Memorial University in Newfoundland, Canada. "But when it's this old you have to be very cautious about it."

The so-called Ediacarans are the earliest complex organisms before the Cambrian Explosion, and debate continues over what the Ediacarans looked like and even, what they were.

When McIlroy's doctoral student Alex Liu sent him pictures of the furrows he'd found in Precambrian, deep-sea rocks near Mistaken Point, Newfoundland, McIlroy was pretty certain they were from an animal. But because they were from rocks dated to a time before true animals are thought to have evolved, it required a bit more work to make the case, he told

So McIlroy, Liu and Martin Brasier carefully reviewed all the things known to paleontologists which could possibly create track marks -- both living and non-living. In the end, they found themselves back where they started.

"It needs to have had muscles to push and create the ridges in the tracks," McIlroy explained, referring to the fine, crescent-shaped structures in the furrows. So it had to be some kind of animal.

To further test this idea, the researchers went so far as to grind up rocks from the same location and recreate the mud of the 565-million-year-old seabed. Then they dropped a modern sea anemone onto it. The result was a similar trail, McIlroy said, made by the anemone moving about, trying to find a firmer, rockier place to settle down.

"The other question that remains to be answered is who is making these," said trace fossil expert Whitey Hagadorn of Amherst College. At the moment there are no candidates among the strange and mysterious soft-bodied creatures that inhabited the seas of the Ediacaran period, just before the Cambrian.

The great irony of the discovery, said Hagadorn, is that it was made at a location and in rocks that have been studied by literally thousands of geologists for more than a century.

"This stuff happens all the time in geology," Hagadorn told Discovery News. "Until you know what to look for, you won't see it."

Now that the discovery has been made, it would not be surprising if other people start recognizing similar features in other Ediacaran rocks elsewhere.

"That will be the proof of the pudding," agreed McIlroy, "if others start finding other trails."