Photo Credit: Kelley Watson

A tent at a field camp on Vega Island in March 2011 where paleontologists recovered numerous Cretaceous-age fossils. The Naze of James Ross Island, where bits of dinosaur fossils were recovered, is visible in the background.

Ross MacPhee and his field parties have been blinded by snowstorms, nearly blown off an island by hurricane-force winds, and stymied by pack ice in the pursuit of Cretaceous-age fossils from Antarctica.

Third time’s a charm? Try the fourth.

“We did quite well,” MacPhee said of his most recent expedition to a series of islands off the Antarctic Peninsula where he and fellow paleontologists recovered a couple hundred fossils of marine reptiles, birds, fishes, plants and even a few tantalizing fragments from what appears to be two different dinosaurs.

But the big prize — Cretaceous mammalian fossils that could bolster theories about vertebrate dispersal through the southern hemisphere — still eluded him.

“All the biogeographical indications are that mammals had to have been there,” said MacPhee, a curator in the mammalogy department at the American Museum of Natural History in New York City.

Before wandering to its present position and entering into a deep freeze nearly 40 million years ago, Antarctica was sandwiched between South America and Australia as part of the former supercontinent Gondwana. Even as the continent separated, land bridges likely persisted between the southern continents for millions of years, offering plenty of opportunity for animals to traverse across the bottom of the world.

MacPhee is particularly interested in the history of Australian marsupials, believing that their ancestors emerged in South America and traveled across Antarctica to Australia sometime in the neighborhood of 80 million years ago. He is even of the mind that it’s just possible that some critters might have first sprung up in Antarctica and spread out to the north.

“It’s surprising to me that we got no evidence this time because we were able to hit one area called Sandwich Bluff on Vega,” said MacPhee, referring to a rock outcrop on Vega Island that has proven to be a rich treasure trove for Cretaceous-age fossils.

Part of the challenge, of course, is that most of Antarctica, even those areas above the Antarctic Circle where the researchers visited, is covered by ice and snow. That limits fossil hunting to the few bald spots of exposed rock.

A further complication is the type of rock outcrops that exist on the James Ross Island group located off the tip of the Antarctic Peninsula. The sediments were laid down in a marine setting, meaning fossils from any land vertebrates would have had to get some help getting there, such as being washed into seashore by a river.

“[Mammal fossils are] going to be rare because of the type of deposits we have to look in. We’re not looking in conventional terrestrial-style basins,” MacPhee noted.

Paleontologist Joe Sertich was also hoping to find some faunal connections between Antarctica and the remainder of Gondwana. But Sertich is interested in Cretaceous-age dinosaurs and crocodiles that might have migrated through Antarctica from other parts of the ancient supercontinent.

“Antarctica is thought to be a potential link between South America, Madagascar and India,” explained Sertich, curator of vertebrate paleontology at the Denver Museum of Nature and Science . He said one theory of vertebrate dispersal posits that some animals bypassed Africa, instead traveling from South America to Madagascar and India via Antarctica.

“We’re looking for clues as to how they were connected — if they were,” Sertich said. “Anything would be significant.”

The team spent most of its field season at a camp on Vega Island, a small island north of James Ross Island that had previously yielded one of the most significant finds in bird evolution. This discovery offered the first evidence that modern birds existed alongside non-avian dinosaurs at the end of the Cretaceous, a geological period of time that lasted from about 145.5 to 65.5 million years ago.

“Antarctica is really a remarkable place to study the origins of modern birds, because the only undoubted members of modern bird groups that have been found from the Age of Dinosaurs come from the James Ross Island Group,” noted Matthew Lamanna , a member of the expedition whose research interests include Cretaceous dinosaurs from the southern continents and the evolution of birds.

“The origin of birds from non-avian dinosaurs is now well-established. If we want to look at the next step in bird evolution … the next step in the chain from something that looks like a Velociraptor to something that looks like a goose, then Antarctica is a great place to go,” added Lamanna, assistant curator of vertebrate paleontology at Carnegie Museum of Natural History in Pittsburgh.

Julia Clarke , another member of the latest expedition, led a team that six years ago reported that close relatives of at least one order of modern birds co-existed with dinosaurs. The new species, Vegavis iaai, was collected on Vega Island in 1992 by scientists from Argentina, but it was Clarke and her U.S. and Argentine team that re-examined the material more than a decade later.

It offered some of the best fossil evidence to date that the modern bird divergence — the spread of some of today’s bird groups — occurred before the mass extinction of non-avian dinosaurs about 65 million years ago.

Lamanna said the team recovered about 20 isolated bird bones and one or more partial skeletons in rock concretions. Analysis is just now under way, but he said the group is “encouraged” by what it collected.

“Every bird fossil we found appears very advanced, consistent with being a member of a modern group,” he said.

A short visit to an area called the Naze on James Ross Island turned up a few non-avian dinosaur fragments from the Late Cretaceous as well. Among the finds was a tooth from a carnivore and a toe bone that may have belonged to a two-legged herbivore.

“We’re very optimistic about the Naze. If we get another opportunity to go to Antarctica, we’re going to make the Naze one of our major targets,” Lamanna said.

The expedition — MacPhee’s fourth in as many years — was the final one of this grant from the National Science Foundation’s Office of Polar Programs . However, the group has put in a proposal to return, encouraged by the number of fossils expedition members were able to collect in just over two weeks.

The best specimens found by the expedition came from a group of marine reptiles known as plesiosaurs, including two partial skeletons, one of which may prove to be a new species. Plesiosaurs have been found previously around the island group, including a nearly complete skeleton of a juvenile long-necked (elasmosaurid) plesiosaur, which was discovered in early 2005. [See previous article: Team reveals juvenile plesiosaur fossil in the Dec. 4, 2006 issue of The Antarctic Sun , page 3.]

“It’s an indication that at least the waters around Antarctica at that time [during the Late Cretaceous] were just vibrant with all kinds of life,” said MacPhee, who will return to the region once again in January 2012 with Argentine colleagues to continue the search for his elusive marsupials.

“It does sound a bit quixotic,” he conceded, but argued that evolutionary theory demands that the evidence should be there. “It would be astounding if after years and years nobody finds anything.”