Extreme palaeontology

HIGH up in the mountains, the skeleton of a large meat-eating dinosaur is gradually emerging from the rocks. Nearby are some other early Jurassic fossils that have yet to be fully excavated - an allosaur, an unidentified predator and a herbivore. It sounds like a regular day in the field, but there's one big difference. This is Mount Kirkpatrick in the Transantarctic mountains, 4 kilometres above sea level and just 600 kilometres from the South Pole (see Map, page 38).

The skeleton, a cryolophosaurus or "frozen crested lizard", was discovered a decade ago. But the work is difficult and excruciatingly slow because sub-zero temperatures make machinery unreliable and fierce storms keep workers tent-bound for days at a time. Philip Currie, director of the Royal Tyrrell Museum in Drumheller, Alberta, Canada, spent a month at the site on his most recent visit and managed only six days of useful work.

Palaeontologists have a reputation as a rugged bunch, but sometimes even they are pushed to their limits. The dig on Mount Kirkpatrick is one of several recent expeditions that have braved extreme conditions to recover important finds. Dinosaur fossils have been found elsewhere in the Antarctic, as well as the high northern latitudes of Alaska and Greenland. They have been dug out of remote deserts and even war zones. Nowhere, it seems, is too remote or dangerous, as long as the dinosaur hunters bag another find.

And there is good reason to go to the ends of the Earth. Until recently, the best known fossil deposits, and consequently the best-studied dinosaurs, all came from parts of the northern hemisphere - western Europe, the western half of North America and east Asia. The rest of the world, particularly the southern continents and high latitudes, was relatively uncharted territory.

In recent years, palaeontologists have worked hard to put that right. Since 1992, the number of known dinosaur locations has increased considerably. Bones, footprints or eggs have been found at more than 1000 locations worldwide, up from about 650 in 1992 (see Tables, page 38). And in that time we have almost doubled the number of known genera of dinosaurs, from around 300 to more than 500.

Many of these new finds are in the traditional dinosaur heartlands- Yixian in China is a good example (see Dinotopia, page 40). But dinosaur palaeontology is an increasingly global discipline. In recent years important dinosaur deposits have been unearthed in almost every corner of the world, some in places that were previously off the map altogether - Ethiopia, Yemen, Ecuador, Uzbekistan and Siberia to name just a few.

There are still gaps palaeontologists would love to fill, notably the late Cretaceous period in Africa. But there is no doubt that this hugely expanded knowledge of dinosaur fossils has produced a much more complete picture of the dinosaur age.

One of the most pressing questions is what the world was like during the Cretaceous period, the apex of the age of dinosaurs. Take a look at the arrangement of the continents during the Mesozoic era and you can't help noticing two facts. First, for most of the dinosaur age, the continents were cemented together in a supercontinent called Pangaea. Then, in the late Jurassic, they split into two -Laurasia to the north and Gondwana to the south (see Timeline, page 44). Palaeontologists are only just starting to understand the implications of this continental drift for the dinosaurs.

For a couple of decades now, they have been coming round to the view that the dinosaur faunas of the northern and southern hemispheres also diverged dramatically

of Chicago. "It doesn't take too much thought to realise that the roots of these groups go back very, very far." In fact, it now looks as though most of the major dinosaur groups-both "northern" and "southern" - must have evolved and been widespread before the break-up of Pangaea. And new sites are constantly being opened up that will fill in pieces of the puzzle, though some are more challenging than others. Jeff Wilson of the University of Michigan in Ann Arbor, for example, has high hopes for a new location he has found in western Pakistan. Unfortunately it is not far from the Afghan border where Osama bin Laden is most likely hiding. "I'm not so keen to go there under the present circumstances," says Wilson. Meanwhile, Sereno has found a site that promises to fill that all-important gap at the end of the Cretaceous in Africa. The discovery is in north-eastern Niger, deep in the heart of the desert. "It's in the most forlorn, godforsaken place that takes days to get to, driving over sand seas," says Sereno. That is what he will be doing this autumn, and he is confident that it will be worth all the effort. The new site is a long stretch of good-looking rocky outcrops from the very end of the Cretaceous period. "There's some 200 to 300 miles of this stuff. I can't believe that somewhere in there are not some dinosaur bones." •

during the Cretaceous period, (New Scientist, 23 September 2000, p 22). The assumption was that during the Jurassic, species could, and did, roam across the globe. Specimens of that archetypal Jurassic predator allosaurus, for example, have turned up all over the world. In the Cretaceous, however, the picture changed. Up north, familiar and iconic beasts such as tyrannosaurus, triceratops, and the duck-billed hadrosaurs reigned. Down south in Gondwana it was a different story. The dominant animals were primitive throwbacks to the Jurassic: colossal meat-eaters, some with homs, known as abelisaurs and carcharodontosaurs, and even bigger, long-necked plant-eaters called titanosaurs. One of their number, argentinosaurus, which looked much like the Jurassic icon apatosaurus (formerly brontosaurus) on steroids, was the largest land animal that ever lived.

Funes Museum in Neuquen, Argentina.

The same holds true in what used to be the southernmost corner of Gondwana-Antarctica. In the past 10 years or so, northern-style armoured dinosaurs and duck-billed hadrosaurs have turned up in the late-Cretaceous rocks of the Antarctic Peninsula, along with more typically southern forms.

"Slowly but surely we keep finding these distinctive dinosaurs from the north and south on each other's territory," says Paul Sereno, a palaeontologist from the University

Most experts had assumed that these distinctive faunas evolved after Laurasia and Gondwana parted company. But recent discoveries are challenging that comfortable assumption "Southern" titanosaurs have recently been unearthed in the Cretaceous of Mongolia, Thailand, the US and Europe, and North America has yielded several specimens of a huge meat-eater that some think is the southern brute carcharodontosaurus.

Conversely, northern dinosaurs have been turning up in Gondwanan territory. Earlier this year Fernando Novas of Argentina's Museum of Natural Sciences in Buenos Aires described neuquenraptor, a nimble meat-eater from Patagonia (Nature, vol 433, p 858). Only a few fragments of bone are known, but they include a sickle-like claw that marks neuquenraptor as a member of an archetypal northern group from the late Cretaceous that includes velociraptor. Neuquenraptor is only the latest of several" northern" forms to turn up in South America, including duck-billed dinosaurs from Argentina. "I wouldn't be surprised to someday find a tyrannosaurus in South America," says Rodolfo Coria, a palaeontologist at the Carmen

Velociraptor, one of those exclusively "northern" dinosaurs that has recently turned up down south

Dinosaur territories old and new

0 0

Post a comment