South Dakota School of Mines News
FOR IMMEDIATE RELEASE
December 29, 2005
Contact: Breanna Bishop, 394-6082
NEW FOSSIL MAMMAL FROM EUROPE RELATED TO THOSE IN SOUTH
DAKOTA INDICATES NEW TRANSATLANTIC DISPERSAL ROUTE DURING
THE AGE OF DINOSAURS
A mammal whose origins are in South Dakota has been identified in Europe in
the type Maastricht of the Netherlands. Dr. James E. Martin, Museum of
Geology, South Dakota School of Mines and Technology, identified the mammals
as a relative of living opossums while conducting research funded by the
National Science Foundation. The marsupial tooth represents a mammal new to
science, is 66 million years old, and is most similar to those found in the Late
Cretaceous time (~70 million years) in western South Dakota. The European
relative indicates these mammals were able to disperse across a heretofore
unknown, northern high-latitude trans-Atlantic route. Such teeth had not been
found before because the Netherlands was under salt water at the end of the
Age of Dinosaurs. Evidently, remains of this small pouched mammal had floated
out to sea, sunk, and was preserved against all odds.
Until now, paleontologists had assumed that these marsupials had not made the
crossing from North America until the Eocene, some 10 million years after the
extinction of dinosaurs. The new fossil suggests that already during the end of
the Cretaceous (end of the Age of Dinosaurs) that temporary trans-Atlantic land
bridges existed. The new find thus fundamentally changes our views on the
distribution of animals at the end of the Age of Dinosaurs.
Two amateur collectors, Roland Meuris and Frans Smet, from the Netherlands
discovered the tooth, and when paleontologists at the Natural History Museum of
Maastricht showed a photograph to Martin, he recognized its significance. The
find of this new marsupial species has just been published in the scientific
journal, Journal of Mammalian Evolution. The new species is named after the
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South Dakota School of Mines and Technology
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amateurs and is termed Maastrichtidelphys meurismeti, which means the
“Maastricht opossum of Meuris and Smet.”
The South Dakota School of Mines Museum of Geology that sponsored much of
this research is a major center for the study of fossils, both in the Northern Great
Plains and worldwide. Although the Museum possesses vertebrate fossils from
around the world, specimens from South Dakota comprise a majority of the
collections, and based upon this library of specimens, Martin was able to
recognize the uniqueness of the Maastricht mammal. In addition to the extensive
research collections, the museum is also a major contributor to the South Dakota
School of Mines and Technology’s Paleontology Program which is widely
recognized for its Paleontology graduate degree and research expertise in
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Background information on the new Cretaceous mammal
On the discovery
In 2002, amateur collector Roland Meuris took a rock sample at the ENCI cement
quarry near Maastricht, Netherlands, to analyze this for small shark 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 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
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 the Maastricht is composed of
rocks laid down in a seabed, not laid down in terrestrial enviornments where
marsupials are normally found. Also, the ��Age of Dinosaurs’ is a term used for a
time period, 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. Therefore, all remains of
terrestrial animals in the Maastricht Cretaceous rocks come from dead bodies
transported by rivers into the sea.
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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 mostly 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. Of necessity, our current knowledge
of primitive mammals is primarily derived from the study of teeth. Teeth are
small, but very durable thanks to their enamel covering. Therefore, they are
often the sole remains to be found of Cretaceous mammal species. The
Maastricht marsupial is no exception.
New species, formal publication
In the newest issue of the Journal of Mammalian Evolution the new find is
formally named, Maastrichtidelphys meurismeti, the ‘Maastricht opossum
(didelphid) of Meuris and Smet’. To describe the fossil, the Natuurhistorisch
Museum Maastricht sought the help of two American experts of Mesozoic
mammals, Professor James E. Martin of the South Dakota School of Mines and
Technology (Rapid City), and Professor Judd Case of St Mary’s College
(Moraga, CA). During Martin’s visit to Maastricht in 2003, right after the discovery
of the tooth, he recognized it as one of a herpetotheriid marsupial – an
unexpected occurrence in the Maastricht Cretaceous.
Herpetotheriids are a group of opossum-like marsupials, which came into being
in North America during the Cretaceous. The oldest representatives of these
marsupials come from Meade County, South Dakota. A detailed comparison
with the structure, position and height of cusps, and many other features of the
Maastrichtidelphys molar with other Late Cretaceous and Early Paleogene
mammals, suggests that Maastrichtidelphys is a close ally of the North American
marsupial, Nortedelphys described by Case and others in 2004.
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
Atlantic. This sounds dramatic for a small marsupial, but the Atlantic Ocean in
those days was half the width (at most) of today’s Atlantic Ocean, and further
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.
But: 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 polar ice caps unlikely. Except for land ice, we can also
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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 ca 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 then, make such estimates even
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-billed) dinosaurs in the Maastricht area, animals otherwise
well represented in North America. Some snake remains from the uppermost
Creatceous 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 were 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.
Martin and Case have already postulated a similar dispersal route across the
southern continents to get marsupials from North America to Australia. Their find
of a duck-billed dinosaur in Antarctica whose occurrences are common in South
Dakota suggest a southern route as well as the northern. Therefore, a world-wide
drop in sea level at the end of the Age of Dinosaurs may have allowed
greater dispersal throughout the world than previously recognized.
The description of Maastrichtidelphys appears 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 vol. 12, Nos. 3/4, 495-511.
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