Dinosaurs dug for mammalian prey

Mounting evidence suggests dinosaurs preyed upon our mammalian ancestors (Source: brotherxii/Flickr)

Larry O'Hanlon
Discovery News

Fossilised mammal burrows that appear to have been clawed out by a predator suggests dinosaurs dug into mammal dens to get furry morsels.

Since there were no large mammal predators 80 million years ago, the most likely candidates are theropod dinosaurs.

Making the connection even stronger is that claw marks in the burrows are a pretty good match to the claws of dinosaur fossils found in rocks nearby, though slightly later in time.

"It's pretty tight," says palaeontologist Professor Edward Simpson of Kutztown University of Pennsylvania. "We can't say whether it's a troodont or a velociraptor," because the claw bones of those found nearby have lost their nails, or cuticles. But otherwise the match is a good one, he says.

Simpson and his students have published their 'trace fossil' discovery - that is, fossilised evidence of animal behaviours rather than the animals themselves - in the August issue of the journal Geology.

"To me there is almost no doubt," says trace fossil expert Professor Anthony Martin of Emory University. "It's very good circumstantial evidence."

No actual mammal bones or teeth have been found, though the burrows match the complexity of those of other mouse- or shrew-like mammals of that time and their present-day counterparts.

The criteria for calling something a fossilised mammal burrow were laid out a few years ago in a separate paper by Martin.

Other evidence

With that criteria in mind, the team feels confident that they did find a mammal's subterranean abode. The researchers could go even further to make their case.

"One of the things we could do is to take the burrows and cut them up," says Simpson. There might be mammal teeth in them, which make an even stronger case.

But, he's hesitant to do that since it's a destructive process. There is also only a very small chance they will find any mammal bones or teeth.

So far Simpson and his students haven't even extracted the fossil burrow from the cliff in southern Utah in which it was found.

As for the dinosaur involved, it probably wasn't very big, judging by the claw marks in the burrows, says Martin.

Other evidence that has been reported to support the dinosaurs-bites-mammal story include the specialised jaw, teeth and skulls of some dinosaurs; mammal bones with bite marks; fossilised gut content; and faeces and trackways.

This case is different in that it points directly at how the dinosaurs hunted rather than just the fact that they ate mammals.

"This is an excellent example of how trace fossils can reveal animal behaviour," says Martin.

Dino demise supersized the mammals

Abbie Thomas
ABC

The demise of the dinosaurs kick-started a growth spurt in mammals that would see them become supersized within a mere 25 million years, new research has found.

The international team led by Felisa Smith from the University of New Mexico publish its findings today in the journal Science.

The mass extinction event at the end of the Cretaceous period, 65 million years ago, wiped out all the non-flying dinosaurs virtually overnight, as well as many other animals, plants and insects.
Suddenly there was room and resources for the mammals to flourish.

The researchers tracked how mammal body size changed over time by identifying the largest mammal from each geological period since the end of the Cretaceous. All major mammal groups including elephants, cats and horses were included.

For the extinct animals, often only fossil teeth were available. To work out how large the body might have been, researchers used modern day animals as a comparison. They calculated the ratio of tooth size to body size for these modern species, and then extrapolated this to extinct mammals.

When size was tracked over time, it was revealed that mammals eventually grew to a thousand times larger than they had been when they shared the Earth with dinosaurs.

The pinnacle of land mammal size was achieved by the bizarre Indricotherium, a hornless rhinoceros-like herbivore that lived around 34 million years ago. At 17 tonnes and standing five and a half metres at the shoulder, it would have dwarfed today's African elephant.

This pattern of increasing size in mammals after the demise of the dinosaurs repeated itself across all continents, including North America, Africa, Eurasia and to a lesser extent, South America, say the researchers.

So how did the dinosaurs keep the mammals at bay for so long?

Keeping mammals at bay

"It was most likely competition for resources [rather than direct predation]," says Dr Alistair Evans, a palaeontologist at Monash University in Melbourne and a co-author on the paper.

"The dinosaurs were there first, so they were able to fill the ecological niches very effectively, for example feeding on plants and carnivory: They could do it better than the mammals could," says Evans. "So there would have been limited opportunity for these smaller mammals to evolve into larger sizes."

He says, the researchers found that larger animals evolved whenever the Earth got cooler. A big body helps conserve heat, last longer without food and travel further to find it.

But mammals can't keep growing forever. The researchers say that mammal body size will always be limited by environmental temperatures and available land area.

Being big also means slower reproduction rates and a certain vulnerability to changes in the environment.

"We're talking over tens of millions of years, but it may be that if the world gets warmer in the future, the larger mammals may well go extinct again, because they are adapted to cooler climates," says Evans.

How the world's biggest mouth evolved

Blue whales are the largest creatures that have ever lived (Source: Carl Buell)

Anna Salleh
ABC

An Australian palaeontologist has figured out a missing step in the evolution of giant filter-feeding mouths characteristic of blue whales.

Dr Erich Fitzgerald from Museum Victoria in Melbourne reports his argument in today's issue of Biology Letters.

"You could fit an average garden-variety kombi van in the mouth of a blue whale," says Fitzgerald, adding that blue whales are the largest animal ever known to inhabit the earth.
They have no teeth but, like other such whales, live on a diet of krill and other marine organisms that they filter out from seawater, using bristles on the roof of their mouths, called baleen.
Central to this baleen whale filter-feeding system is a cavernous mouth with a wide upper jaw and an elastic lower jaw that can open up wide to allow more than the whale's own bodyweight in sea water to enter in one gulp.

"[Modern baleen whales] have extremely mobile lower jaws, which is quite frankly bizarre because no other mammals have that sort of specialisation," says Fitzgerald.

This elastic lower jaw, in which the left and right hand sides are able to stretch apart, was until now believed to be a feature of all baleen whales, even fossil ones.

Scientists have long wondered how ancestral baleen whales, which used their teeth to catch large prey (like killer whales do) evolved into toothless filter feeders.

"This is a huge evolutionary jump," says Fitzgerald.

He now believes he has found the evolutionary missing link in the story.

Missing link

Fitzgerald has found the first fossil evidence of a toothed baleen whale that has no elastic lower jaw.
The newly-described jaw belonged to a tiny 25 million-year-old primitive baleen whale called Janjucetus hunderi, which was at most just three metres long, the size of a bottlenose dolphin.

"This is the clearest evidence yet that the earliest baleen whales could not filter feed and that's interesting because it had previously been thought that all baleen whales were filter feeders," says Fitzgerald.

He first analysed and named this creature in 2006, but at that stage he only had an incomplete lower jaw.

Fitzgerald then came across missing lower jaw bones in the collection of an amateur fossil hunter, by the name of Brian Crichton, who originally found them in the 1970s on a beach near Torquay in Victoria.

These new bones showed that the two halves of the lower jaw bone in Janjucetus hunderi were fused, and unable to open up to allow filter feeding.

Yet, Fitzgerald had previously found the animal had evolved another feature thought to be essential for the filter feeding - a wide upper jaw that creates a large space inside the mouth.

So why did this toothed whale evolve a wide upper jaw?

Suction feeding

Fitzgerald finds a clue in the mouths of modern dolphins, which also lack an elastic lower jaw. Those with really wide upper jaws feed by sucking in large individual prey, he says.

"They generate a vacuum [helped by the wide upper jaw] and hoover up fish and squid, sucking them in through a relatively small opening at the front of their mouths," says Fitzgerald.

"I argue that the big mouth of baleen whales possibly originally evolved to enhance the ability to generate suction."

He says it would be less of an evolutionary leap to go from baleen whales that catch large prey with their teeth to those that suction feed, than directly to those that filter feed of lots on tiny organisms.
After being decimated by past whaling the numbers of blue whales remain low with only about 10,000 individuals left, mainly in the Southern Ocean, says Fitzgerald.

Although they are now protected, he says they remain under threat due to changes in the ocean ecosystem that may affect levels of krill.

Mammals 'thrived despite dinosaurs'

Multituberculate mammals like this evolved teeth that were suited to eating flowering plants, researchers say (Source: Jude Swales/Burke Museum of Natural History and Culture)

Anna Salleh
ABC

Mammals did not need the dinosaurs to die off in order to thrive, new research on fossil teeth suggests.

Evolutionary biologist Dr Alistair Evans, of Monash University in Melbourne, and colleagues, report their findings today in the journal Nature.

Until now, most scientists believed it took the extinction of the dinosaurs, around 66 million years ago, before mammals were able to develop, says Evans. But his latest research suggests this is not the case.

Before the death of the dinosaurs, the most common mammals were multituberculates - so called because of their teeth.

"Many of the multituberculates have very bumpy teeth and each of the bumps are called a tuberculate," says Evans. "It's a very long name for 'bumpy teeth'".

Evans and colleagues carried out a comprehensive survey of teeth from about 48 multituberculate species held in fossil collections around the world.

They used software normally used to analyse land topography to create high-resolution 3D images of the teeth.

By analysing the complexity of the teeth bumps, Evans and colleagues were then able to map the evolution of multituberculates.

170 million years ago, their teeth were very simple but about 90 million years ago - long before the dinosaurs died off - their teeth started getting more complex.

Previous research has shown that increasing complexity in teeth enables animals to shift from eating insects and other meat to plant material.

Plants are easier to come by, but they also take longer to digest so a shift to herbivory is also generally associated with an increase in body size. Larger animals have a lower relative metabolic rate and have the time to digest slowly.

Significantly, Evans and colleagues found the increase in multituberculate teeth complexity coincided with the evolution of flowering plants.

"There's a nice correlation there between the ecological dominance of flowering plants and the rise of herbivory in multituberculates," says Evans.

At the same time multituberculates increased in size from that of a mouse to a beaver, also supporting the move to herbivory.

Evans and colleagues think these changes gave multituberculates a way of thriving even during the time of dinosaurs.

"We think it might be because they were exploiting this new food source that perhaps dinosaurs weren't using as much as they could have," says Evans.

These changes also gave multituberculates an evolutionary head start compared to other mammals, meaning they were able to do better than others once the dinosaurs did go extinct.

Multituberculates maintained an edge over other mammals for another 30 million years after the dinosaur extinction, and only died out 35 million years ago, due to competition from primates and rodents.

Persuasive

Curator of Vertebrate Palaeontology at Museum Victoria, Dr Tom Rich describes the research as "a new and imaginative approach" to quantifying the adaptation of the multituberculates.

"The authors show quite persuasively that the widely held conventional view that mammalian evolution was 'held back' until the non-avian dinosaurs became extinct is a generalisation that does not hold in detail," he says.

Rich says although there are literally thousands and thousands of multibuerculate fossils in museum collections from sites in the Northern Hemisphere, there is just one specimen known from Australia.
"But we've got one so we know they were here, too! That's all it takes," he says.

New Horned Dinosaur: Two-Ton Plant-Eater Lived 78 Million Years Ago in Montana

Artist's rendering of Medusaceratops. (Credit: Copyright Luis Rey)

Science Daily (May 30, 2010) — Michael J. Ryan, Ph.D., a scientist at The Cleveland Museum of Natural History, has announced the discovery of a new horned dinosaur, Medusaceratops lokii. Approximately 20 feet long and weighing more than 2 tons, the newly identified plant-eating dinosaur lived nearly 78 million years ago during the Late Cretaceous period in what is now Montana. Its identification marks the discovery of a new genus of horned dinosaur.

Ryan, curator and head of Vertebrate Paleontology at the Museum, published his findings on the new genus in the book, "New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium," available from Indiana University Press. Ryan was the book's lead editor.

Medusaceratops belongs to the Chasmosaurinae subfamily of the horned dinosaur family Ceratopsidae. The other subfamily is Centrosaurinae. The specimen is the first Campanian-aged chasmosaurine ceratopsid found in Montana. It is also the oldest known Chasmosaurine ceratopsid.

The new dinosaur was discovered in a bonebed on private land located along the Milk River in North Central Montana. Fossilized bones from the site were acquired by Canada Fossil, Inc., of Calgary, Alberta, in the mid-1990s. The company consulted with Ryan and his colleagues to identify material from the site. At first, the scientists could not make a positive identification.

Medusaceratops had giant brow bones more than 3 feet long over each eye, and a large, shield-like frill off the back of its skull adorned with large curling hooks. Medusaceratops lokii means "Loki's horned-faced Medusa," referring to the thickened, fossilized, snake-like hooks on the side of the frill. It was named after Loki, the Norse god of mischief, because the new dinosaur initially caused scientists some confusion.

"At first we couldn't figure out what we had," said Ryan. "Some of the material looked as if it came from a form related to Centrosaurus, a centrosaurine noted for having short brow horns. The rest of the pieces had giant brow horns similar to Triceratops, a chasmosaurine. That's one of the problems with bonebeds -- even though you can collect a large amount of material, much of it is broken and all of it is disarticulated, so the story is rarely clear cut."

Eventually Ryan found a complete articulated skull of a centrosaur with long brow horns in southern Alberta of what appeared to be the new animal from Montana, and named it Albertaceratops in 2007. At that time, he assumed he was looking at a stray that had literally crossed the international border millions of years ago.

After reexamining the Montanan material more recently, Ryan realized that at least some of the material in the Montana bonebed was not Albertaceratops. Some of the elements were much larger than any other horned dinosaur from the same time period, including Albertaceratops. And even though Albertaceratops and Medusaceratops are superficially very similar, the shape and number of the hooks and ornaments along the edge of the frill actually puts them in separate horned dinosaur groups, with Medusaceratops being a chasmosaur.

"Although the ornamentation on the frill is pretty spectacular, it probably was not used for defense against predators; rather it was more likely prehistoric "bling" used to attract a mate," said co-author Anthony Russell, Ph.D., professor of biological sciences at the University of Calgary in Alberta.

"Medusaceratops is the oldest member of the Chasmosaurinae in North America and shows that the group, like its most famous member, Triceratops, had long brow horns and were fairly large when they first evolved," said Ryan. "But later chasmosaurs that are just a bit younger than Medusaceratops tend to have much shorter horns and have much smaller, lighter bodies.

"Here we have something almost the size of Triceratops, but 10 million years before it lived," Ryan said. "T. rex was not around yet, so what was Medusaceratops squaring off against? That's one of the things we're now looking for in Alberta."

The research was originally conducted when Ryan was a Ph.D. candidate working with Dr. Russell at the University of Calgary in Alberta, Canada. Much of the material, including the holotype, is now in the collection of the Wyoming Dinosaur Center in Thermopolis, Wyoming, with other material curated at the Royal Tyrrell Museum in Drumheller, Alberta.

Amazing Horned Dinosaurs Unearthed on 'Lost Continent'; New Discoveries Include Bizarre Beast With 15 Horns

Artist's rendering of two new species of dinosaur -- Utahceratops gettyi and Kosmoceratops richardsoni -- discovered in the Grand Staircase-Escalante National Monument of southern Utah. (Credit: Courtesy of Utah Museum of Natural History)

ScienceDaily (Sep. 22, 2010) — Two remarkable new species of horned dinosaurs have been found in Grand Staircase-Escalante National Monument, southern Utah. The giant plant-eaters were inhabitants of the "lost continent" of Laramidia, formed when a shallow sea flooded the central region of North America, isolating the eastern and western portions of the continent for millions of years during the Late Cretaceous Period.

The newly discovered dinosaurs, close relatives of the famous Triceratops, were announced in PLoS ONE, the online open-access journal produced by the Public Library of Science.

The study, funded in large part by the Bureau of Land Management and the National Science Foundation, was led by Scott Sampson and Mark Loewen of the Utah Museum of Natural History (UMNH) and Department of Geology and Geophysics, University of Utah. Additional authors include Andrew Farke (Raymond Alf Museum), Eric Roberts (James Cook University), Joshua Smith (University of Utah), Catherine Forster (George Washington University), and Alan Titus (Grand Staircase-Escalante National Monument).

The bigger of the two new dinosaurs, with a skull 2.3 meters (about 7 feet) long, is Utahceratops gettyi (U-tah-SARA-tops get-EE-i). The first part of the name combines the state of origin with ceratops, Greek for "horned face." The second part of the name honors Mike Getty, paleontology collections manager at the Utah Museum of Natural History and the discoverer of this animal. In addition to a large horn over the nose, Utahceratops has short and blunt eye horns that project strongly to the side rather than upward, much more like the horns of modern bison than those of Triceratops or other ceratopsians. Mark Loewen, one of the authors on the paper, likened Utahceratops to "a giant rhino with a ridiculously supersized head."

Second of the new species is Kosmoceratops richardsoni (KOZ-mo-SARA-tops RICH-ard-SON-i). Here, the first part of the name refers to kosmos, Latin for "ornate," and ceratops, once again meaning "horned face." The latter part of the name honors Scott Richardson, the volunteer who discovered two skulls of this animal. Kosmoceratops also has sideways oriented eye horns, although much longer and more pointed than in Utahceratops. In all, Kosmoceratops possesses a total of 15 horns -- one over the nose, one atop each eye, one at the tip of each cheek bone, and ten across the rear margin of the bony frill -- making it the most ornate-headed dinosaur known. Scott Sampson, the paper's lead author, claimed that, "Kosmoceratops is one of the most amazing animals known, with a huge skull decorated with an assortment of bony bells and whistles."

Although much speculation has ensued about the function of ceratopsian horns and frills -- from fighting off predators to recognizing other members of the same species or controlling body temperature -- the dominant idea today is that these features functioned first and foremost to enhance reproductive success. Sampson added, "Most of these bizarre features would have made lousy weapons to fend off predators. It's far more likely that they were used to intimidate or do battle with rivals of the same sex, as well as to attract individuals of the opposite sex."

The dinosaurs were discovered in Grand Staircase-Escalante National Monument (GSENM), which encompasses 1.9 million acres of high desert terrain in south-central Utah. This vast and rugged region, part of the National Landscape Conservation System administered by the Bureau of Land Management, was the last major area in the lower 48 states to be formally mapped by cartographers. Today GSENM is the largest national monument in the United States. Sampson added that, "Grand Staircase-Escalante National Monument is now one of the country's last great, largely unexplored dinosaur boneyards."

For most of the Late Cretaceous, exceptionally high sea levels flooded the low-lying portions of several continents around the world. In North America, a warm, shallow sea called the Western Interior Seaway extended from the Arctic Ocean to the Gulf of Mexico, subdividing the continent into eastern and western landmasses, known as Appalachia and Laramidia, respectively. Whereas little is known of the plants and animals that lived on Appalachia, the rocks of Laramidia exposed in the Western Interior of North America have generated a plethora of dinosaur remains. Laramidia was less than one-third the size of present day North America, approximating the area of Australia.

Most known Laramidian dinosaurs were concentrated in a narrow belt of plains sandwiched between the seaway to the east and mountains to the west. Today, thanks to an abundant fossil record and more than a century of collecting by paleontologists, Laramidia is the best known major landmass for the entire Age of Dinosaurs, with dig sites spanning from Alaska to Mexico. Utah was located in the southern part of Laramidia, which has yielded far fewer dinosaur remains than the fossil-rich north. The world of dinosaurs was much warmer than the present day; Utahceratops and Kosmoceratops lived in a subtropical swampy environment about 100 km from the seaway.

Beginning in the 1960's, paleontologists began to notice that the same major groups of dinosaurs seemed to be present all over this Late Cretaceous landmass, but different species of these groups occurred in the north (for example, Alberta and Montana) than in the south (New Mexico and Texas). This finding of "dinosaur provincialism" was very puzzling, given the giant body sizes of many of the dinosaurs together with the diminutive dimensions of Laramidia. Currently, there are five giant (rhino-to-elephant-sized) mammals on the entire continent of Africa. Seventy-six million years ago, there may have been more than two dozen giant dinosaurs living on a landmass about one-quarter that size.

Mark Loewen asks, "How could so many different varieties of giant animals have co-existed on such a small chunk of real estate?" One option is that there was a greater abundance of food during the Cretaceous. Another is that dinosaurs did not need to eat as much, perhaps because of slower metabolic rates more akin to those of modern day lizards and crocodiles than to those of mammals and birds. Whatever the factors permitting the presence of so many dinosaurs, it appears that some kind of barrier near the latitude of northern Utah and Colorado limited the exchange of dinosaur species north and south. Possibilities include physical barriers such as mountains, or climatic barriers that resulted in distinct northern and southern plant communities. Testing of these ideas have been severely hampered by a dearth of dinosaurs from the southern part of Laramidia. The new fossils from GSENM are now filling that major gap.

During the past decade, crews from the University of Utah and several partner institutions (e.g., the Utah Geologic Survey, the Raymond Alf Museum of Paleontology, and the Bureau of Land Management) have unearthed a new assemblage of more than a dozen dinosaurs in GSENM. In addition to Utahceratops and Kosmoceratops, the collection includes a variety of other plant-eating dinosaurs -- among them duck-billed hadrosaurs, armored ankylosaurs, and dome-headed pachycephalosaurs -- together with carnivorous dinosaurs great and small, from "raptor-like" predators to mega-sized tyrannosaurs (not T. rex but rather its smaller-bodied relatives). Also recovered have been fossil plants, insect traces, clams, fishes, amphibians, lizards, turtles, crocodiles, and mammals, offering a direct glimpse into this entire ancient ecosystem. Most remarkable of all is that virtually every identifiable dinosaur variety found in GSENM turns out to be new to science, offering dramatic confirmation of the dinosaur provincialism hypothesis. Many of these animals are still under study, but two have been previously named: the giant duck-billed hadrosaur Gryposaurus monumentensis and the raptor-like theropod Hagryphus giganteus.

Utahceratops and Kosmoceratops are part of a recent spate of ceratopsian dinosaur discoveries. Andrew Farke, another of the paper's authors, stated, "The past year has been a remarkable one for horned dinosaurs, with several new species named. The new Utah creatures are the icing on the cake, showing anatomy even more bizarre than typically expected for a group of animals known for its weird skulls."

Clearly many more dinosaurs remain to be unearthed in southern Utah. "It's an exciting time to be a paleontologist," Sampson added. "With many new dinosaurs still discovered each year, we can be quite certain that plenty of surprises still await us out there."

Gigantic fossils of ‘Predator X’ found in the Arctic

A massive pliosaur has been found in the Arctic archipelago of Svalbard. The creature’s estimated bite was over 10 times more powerful than that found in any modern animal – and four times the bite of a T-Rex

The giant fossilised Jurassic-era marine reptile was found on the Norwegian Arctic archipelago of Svalbard. The sea monster, nicknamed “Predator X”, is a 15-metre-long pliosaur with enormous jaws. The power of its bite would make even T-Rex look feeble, as reported by Reuters quoting scientists from the Natural History Museum of Oslo University.

“With a skull that's more than 10 feet long you'd expect the bite to be powerful, but this is off the scale,” said Joern Hurum, an associate professor of vertebrate paleontology who led the international excavation in 2008.

Pliosaurs are carnivorous marine reptiles from the Jurassic and Cretaceous eras. Some of their species appear to be the largest marine reptiles to have ever existed

The Museum’s scientists reconstructed the predator’s head and, with the help of colleagues from Florida State University, estimated the bite power by comparing it with the similarly-shaped jaws of alligators. Their results were astonishing: “The calculation is one of the largest bite forces ever calculated for any creature,” they said.

Predator X's bite was over 10 times more powerful than in any modern species of shark, crocodile or alligator. Moreover, it was four times the bite of the famous T-Rex – a giant terrestrial meat-eating dinosaur.

The scientists reconstructed the reptile, which belongs to a new species of pliosaur, from a partial skull and 20,000 fragments of skeleton. It had impressive 30cm-long teeth and a body weight of approximately 45 metric tons. Being similar in length to the largest pliosaur species to date found on Svalbard in 2007, Predator X is distinguished by having larger bones.

The scientists believe that the first fossilised pliosaur was big enough to chomp on a small car. Predator X could more likely crush a Hummer, said Dr. Harum, referring to General Motors' massive 4x4.

Unlike its enormous body size, the pliosaur had a small brain shaped like that found in a great white shark, as revealed by Patrick Druckenmiller of the University of Alaska.

Pliosaurs are closely related to plesiosaurs and are characterized by having a much shorter neck and elongated head. Both had four huge flippers to propel themselves. Different species ranged in length from 4 to 15 metres, preying on squid-like animals, fish, and other marine reptiles, including ichthyosaurs and other plesiosaurs.