Dinosaur Dreaming

2001 Research report

Tom Rich

Since 1994, when Lesley Kool, Pat Vickers-Rich, and I first went to Patagonia to search for fossils, our objective there has remained the same: to try and find fossils that would tell us whether or not land animals during the Early Cretaceous actually went between Australia and South America.

Why we think this might have been so was based on reconstructions of the continents at that time. With Australia then firmly joined to East Antarctica, and South America close to the West Antarctic Archipelago, the only barrier to such interchange would appear to have been the high latitude of Antarctica and the water gaps within the West Antarctic Archipelago. For although West Antarctica today (that part of the continent in the western longitudes) appears on a map to be solid land, if all the ice there melted, it would be a series of large islands much like the Indonesian region.

Over the years, mostly what was found by us in Patagonia were isolated bones of the giant sauropods along with a few specimens of large theropods. Missing entirely were the small dinosaurs so characteristic of the same aged rocks in Victoria. Because we do have the very rare remains of large dinosaurs in Victoria, fist-sized fossils that obviously come from elephant-sized animals, we know that the larger dinosaurs were here. However, because of the way they were buried in small stream channels incapable of transporting entire large bones, the evidence for such dinosaurs in Victoria is rare indeed. So the differences we see between Argentina and Australia, probably mostly owe to different burial mechanisms, not necessarily differences in the animals that were living in the two regions 115 million years ago.

Be that as it may, on that first trip in 1994, a site almost instantly dubbed "Turtle Town" was found in Patagonia. Loaded with turtle remains, the site was unlike the pattern so typical of the Early Cretaceous in Patagonia in that there were smaller vertebrates preserved there. We have just learned from Eugene Gaffney of the American Museum of Natural History, New York, that the skull of one of the turtles collected at Turtle Town shows a remarkable resemblance to the turtle Otwayemys that was collected from Dinosaur Cove. So, after all the effort put into Argentina since that first trip in 1994, a payoff for that is beginning to emerge.

A colleague, Elizabeth Smith, working on the fossils from Lightning Ridge that are about the same age as those from Dinosaur Cove, has been told by Dr. Gaffney that a turtle skull she has from the Ridge is very similar to both Otwayemys and the one to be named from Chubut. So turtles are linking the three regions together. Elizabeth will visit our collection later this year to make direct comparisons.

The discovery on December 3rd 2000 of two additional mammal jaws, each far more complete than any ever previously recovered from Flat Rocks, came at a most propitious time. When they were found, a paper had been submitted to the scientific journal Nature describing the third species of mammal to be recognised at Flat Rocks. The specimens on which that paper was based were much less complete than the two December jaws. The two jaws could have been one or both of the previously described mammals from Flat Rocks.

But that did not prove to be the case, for they were clearly the same species as the new one being described. However, because the editorial process was so far along, we hesitated to withdraw the paper and redo it. But when another five months had passed and the editor at Nature could still not make up his mind exactly what he wanted us to do to make our paper "acceptable" for publication, we withdrew it. Then a frantic period ensued when Peter Trusler put in long, hard hours painting an exquisite illustration of one of the December jaws that would become the name-bearer (or holotype) of the new species instead of one of the far less complete specimens found previously.

To do this and keep to the schedule we wanted to meet (in order to have the new species available for addition to a book by colleagues overseas about the mammals that lived alongside the dinosaurs) Peter at times slept just two hours a night and that was on the floor of his studio so he could complete the illustration on time. The publication did appear a week ahead of schedule in early June, just seven months after the holotype was found, and so it will be included in the forthcoming book, to be published in late 2002.

The new mammal was named Bishops whitmorei. This was to honour two people at the National Geographic Society who supported Pat and Tom's efforts for years. They did this because they felt that if the National Geographic supported them over the long haul, eventually the birds and mammals that lived alongside the dinosaurs - always Pat and Tom's primary goals - would be found.

Even though Tom had long given up on ever finding mammals, they did not. And they were right. Bishops is in honour of the late Barry Bishop, for many years chairman of the Committee for Research and Exploration of the National Geographic Society, the arm of the organisation that dispenses funds for research. whitmorei is in honour of Barry's offsider, Frank Whitmore. Although in his mid-80s, Frank is still an active palaeontologist with about four papers currently in press concerning his favourite topic, fossil whales.

Bishops whitmorei is placed in the same family as the first mammal to be described from Flat Rocks, Ausktribosphenos nyktos. However, while about the same size, Bishops is more advanced in a number of features. These features make it more like typical placental mammals, the group which both have been assigned to by Tom and his coauthors. In this, they are a definite minority, for most vertebrate palaeontologists are quite certain that whatever these ausktribosphenids are, they are not placentals.

That difference of opinion has led to a lively debate in the scientific journals, which still continues and shows no sign of abating. It is that debate and the ramification of its outcome, whatever it may be, to the most basic ideas we have about the origin of mammals, that adds zest to the scientific results emerging from all the hard work and long hours at Flat Rocks. As even the opponents of the idea readily admit, the mammals being found at Flat Rocks are amongst the most interesting of Mesozoic age being uncovered anywhere in the Southern Hemisphere at the moment.

The willingness of one of the placental sceptics (Richard Cifelli of the University of Oklahoma) to be quoted saying that, may well have been the reason that the Australian Research Committee has committed funds to the Dinosaur Dreaming project. This will provide a salary for Lesley Kool and a partial salary for a second preparator to continue the preparation of the fossils at Flat Rocks for the next five years. That increase in preparation time by the second person should result in even more interesting fossils turning up much more quickly.

After the "Rookies Day" discovery, things went rather quietly in the fossil mammal business at Flat Rocks. But the completeness of those two specimens made it a hard act to follow. However, Gerry Kool was a man up to the job. What Gerry did was to find another mammal new to the site and new to science. But it was not just another mammal. The reason we knew - even before Lesley had performed one of her remarkable feats of fossil preparation - that Gerry had found a new mammal was because of its size.

Tiny though Ausktribosphenos nyktos and Bishops whitmorei are, Gerry's jaw is even smaller. It is only half to two-thirds the size of these other species. As yet, Gerry's jaw is unnamed. In part this is because there has not been time to describe and analyse it. But also because we are all hoping that as was the case with B. whitmorei, more complete material of the same species as Gerry's jaw will be found. Just how much smaller mammals at Flat Rocks could have been, we do not know. However, Gerry's jaw is getting close to the size of one of the smaller shrews, the smallest of living mammals.

While more mammal jaws will always be welcome at Flat Rocks, it is doubtful that more of them will ever provide the evidence to decide one way or the other whether the ausktribosphenids are true placental mammals or a group of mammals quite unrelated to the placentals. If that debate is ever resolved to the satisfaction of most of the present disputants, it will probably come about because of the discovery of a partial skull.

While in New York at the American Museum of Natural History at the end of May, Tom had with him two skull fragments. Experts on fossil mammals there all agreed that these fragments belonged to mammals but which one, they had no idea. From their size being significantly greater than the ausktribosphenids, it is likely that they belong to the other group of mammals known to occur in the Australian Mesozoic, the egg-laying monotremes.

Although not giants today, compared with most Mesozoic mammals, monotremes such as the Lightning Ridge Steropodon and Kollikodon, were amongst the largest mammals of their day. What these specimens are, though intriguing in itself, is not their greatest importance. What they unequivocally demonstrate is that at the Flat Rocks site, skull material of mammals can be preserved. This means that in working towards eventually recovering skull material of the ausktribosphenids, we have not set ourselves an unrealistic objective, rare those such fossils might be at the site.