Moraga, Calif. (Dec. 30, 2005) - Remains of a new species of marsupial discovered in the Netherlands provides fresh evidence of a northerly land bridge between North America and Europe during the Age of the Dinosaurs, according to a paper published in the December issue of the Journal of Mammalian Evolution. The paper's primary co-author is Dr. Judd Case, Dean of Science at Saint Mary's College of California.
The new species -- a herpetotheriid marsupial, an extinct group closely related to our own opossum -- was identified through a tiny tooth found in the Maastricht ENCI quarry in the Netherlands. Dr. Case, a paleontologist and marsupial expert, originally identified the specimen when he was shown a picture of the upper right molar by fellow co-author, Dr. James Martin of the South Dakota School of Mines and Technology.
According to the scientific paper, the new species is formally named Maastrichtidelphys meurismeti, meaning the "Maastricht marsupial of Meuris and Smet," to honor amateur collectors Roland Meuris and Frans Smet, who discovered the tooth.
The finding represents the first time a marsupial has been identified as living in Europe alongside the dinosaurs during the last period of the Mesozoic Era. The 66-million-year-old tooth fossil suggests that temporary, high latitude (polar) trans-Atlantic land bridges existed during this period, know as the Cretaceous. Until now, paleontologists assumed that these marsupials had not made the crossing from North America to Europe until some 10 million years after the extinction of the dinosaurs.
In a previous paper published in the January 2005 issue of the Journal of Mammalian Evolution, Dr. Case identified this same group of opossum-like marsupials living in North America in the Late Cretaceous period some 75 million years ago. Previously, opossum-like marsupials were thought to have originated in South America after the fall of the dinosaurs and then rapidly appeared in North America 55 to 37 million years ago. The finding of these marsupials first here in North America and now in Europe while the dinosaurs were still alive completely changes our ideas of when and where this group of marsupials originated.
Case and Martin collaborated on the paper with colleagues from the Natural History Museum in Maastricht (Natuurhistorisch Museum Maastricht), Netherlands, where the tooth, less than 2 millimeters in size, is on exhibit (under magnification), next to a life-size model of this new species.
To interview Dr. Case, please call him at (925) 631-4412.
View an online animation in English from the Natuurhistorisch Museum Maastricht:
Background information on the new
Cretaceous mammal Maastrichtidelphys
On the discovery:
In 2002, amateur collector Roland Meuris took a rock sample at the ENCI quarry near Maastricht to analyze this for small teeth. Fellow collector Frans Smet subsequently recognized a mammal tooth in that same sample -- the first mammal tooth from the Maastricht Cretaceous -- upon which he contacted the staff of the Natuurhistorisch Museum Maastricht.
Only in scanning electron microscopy does the small tooth, measuring 1.36 x 1.85 mm, reveal its true identity, because it is the details that count in describing and identifying mammal teeth. The placement of the various cusps, protuberances on the chewing surface, their height and differences therein, as well as the structure and position of "troughs" between the cusps are all characteristic features, allowing the identification of a species on the basis of a single tooth.
The first mammal from the Maastricht Cretaceous:
Never before had mammal teeth been recorded from the Maastricht Cretaceous. Maybe that does not come as a surprise, because many non-specialist books refer to the Cretaceous as the "Age of Dinosaurs," the Mesozoic. Although correct, the name "Age of Dinosaurs" is slightly misleading: even in those days mammals were already around, although they played a far more modest role and were far less impressive than dinosaurs, which often grew to gigantic size.
During the Cretaceous, all mammals were land-based; whales, which originate in the Eocene, only came into existence after the demise of mosasaurs, and bats did not yet exist. All remains of terrestrial animals in the Maastricht Cretaceous rocks thus, in principle, come from dead bodies transported by rivers into the sea.
The new find is about 66.1 million years old.
Mammals in the Age of Dinosaurs:
During the Cretaceous, mammals did not grow larger than the average household pet (i.e. a small dog or cat); most species did not even reach that size, as they were only of mouse- to rat-size. Smaller mammals have diminutive bones, delicate and fragile. Only under special conditions does any mammal skeleton stand a chance of being fossilized. As a result, our current knowledge of primitive mammals mainly derives from the study of teeth. Teeth are small, but very durable thanks to the enamel, which is why they are often the sole remains to be found of Cretaceous species. Maastricht is no exception.
Land bridge with North America:
A North American mammal present in the latest Cretaceous in Europe suggests that Maastrichtidelphys, or its direct ancestor, had managed to cross the North at that time. This sounds dramatic for a small marsupial, but the Atlantic Ocean in those days was half the width (at most) that it is today, and farther north there may have been a land bridge, via Greenland, during periods of low sea level. Around 71 million years ago and again four million years later, there were two intervals worldwide where sea level was particularly low. Above 70 degrees N, the "Thule" dispersal route may have been dry land; via islands in northern Canada, Baffin Island, Greenland, across the Faroes and Great Britain, Maastrichtidelphys may have reached the European mainland.
Were temperatures high enough to allow animals to cross? The best way to lower sea level is by turning water into ice. However, it is widely known that during the Cretaceous, climate was much better than today's climate, which makes the existence of polar ice caps unlikely. Except for land ice, we can also postulate movements along tectonic plates and activity of mid-ocean volcanic ridges that may have had an impact on sea level. More and more data on climate changes and sea level oscillations during the latest Cretaceous are becoming available; according to recent studies, the mean annual temperature at the poles was 6 degrees Celsius during the latest Cretaceous. If that scenario is correct, a crossing during summer months would have posed no problems whatsoever. The find of a few mammal hairs in Siberian amber, which oozed from trees some 70 million years ago at around 70 degrees N, makes such estimates even more plausible.
The discovery of this new mammal sheds more light on other finds of typically North American terrestrial animals in the European Cretaceous. After all, there are hadrosaur (duck-bill) dinosaurs in the Maastricht area, animals otherwise well represented in North America. Some snake remains from the uppermost Cretaceous in northwest Europe show similarities to North American boas. And, a single bone fragment of a carnivorous dinosaur from the Maastricht Cretaceous resembles the North American Dryptosaurus to some extent. Seen individually, these finds perhaps are not conclusive evidence to postulate a northerly land bridge during the latest Cretaceous, but taken together with the new mammal these finds become much more meaningful.
The description of Maastrichtidelphys has appeared in the scientific journal Journal of Mammalian Evolution. The complete reference is:
* Martin, J.E., Case, J.A., Jagt, J.W.M., Schulp, A.S. & Mulder, E.W.A. (2005). A new European marsupial indicates a Late Cretaceous high-latitude transatlantic dispersal route. Journal of Mammalian Evolution 12 (3-4): 495-511.
[a pdf file of this paper can be obtained from firstname.lastname@example.org].
* Jan. 4, 2006 - Tiny fossil tooth new evidence of land bridge to Europe (CanWest News Service, Edmonton Journal) - Link to Article
* Dec. 30, 2005 - Science Dean Identifies 66-million-year-old Marsupial (Contra Costa Times) - Saint Mary's College Dean of Science Judd Case discusses the discovery of a 66-million-year-old tooth belonging to a newly discovered, extinct species of marsupial in a front page article in the Contra Costa Times. Link to Article
Prior coverage of Dr. Case's discoveries can be found here.
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