Cronopio dentiacutus is one of the very few mammal specimens to come out of South America from the era when dinosaurs ruled the Earth.

Tiny but toothy mammal unearthed

What the animal did with those impressive canines is not exactly clear

An extraordinary looking, mouse-sized, fossil animal is shedding new light on the ancient history of mammals.

With a thin snout, beady eyes and long canines, the creature would have looked remarkably like that fictional sabre-toothed squirrel of Ice Age movie-fame.
But Cronopio dentiacutus is one of the very few mammal specimens to come out of South America from the era when dinosaurs ruled the Earth.
The 100-million-year-old animal is reported in the journal Nature.

We know so little about the actual diversity of mammals that even some very wild guesses might come through; they might actually be present in the fossil record”

End Quote Prof Guillermo Rougier University of Louisville

It was discovered in sandstone sediments at Cipolletti, Rıo Negro Province, Argentina.

Those ancient river sediments reveal a lot about what the local environment was like in the Late Cretaceous, but scientists are struggling to pin down the details of Cronopio's lifestyle.
The animal displays a host of features that appear to have no parallel among living or extinct mammals, says Prof Guillermo Rougier from the University of Louisville, Kentucky, US.
"The back teeth, the molars, are the kind of teeth that you will find in an insectivore, an animal that eats insects of different kinds, and even very small invertebrates, or perhaps small lizards, which were present in the same place," he told BBC News.
"But we have no idea why he needed such huge canines. Those tusks are a big surprise."
It is possible Cronopio used them to skewer certain insect prey, but it is clear the canines could not have been deployed with much force.
The slender nature of the snout and of the teeth themselves mean that to have bitten down hard, or to have wrestled another creature with its mouth, would have invited almost certain injury.
Cronopio is what is termed a dryolestoid. These were a group of primitive, extinct mammals belonging to the lineage leading to modern marsupials and placental mammals.
They are known mainly from teeth and jaws found in North America and Europe from the Jurassic Period (145-200 million years ago). To now have relatively complete dryolestoid skulls form South America in the form of Cronopio is therefore a boon to scientists trying to study the spread and diversity of mammals through Earth history.

There are so few well-preserved South American mammals from the time of the dinosaurs

"In the northern continents, there is a longer tradition of palaeontology and so they are well represented," observed Prof Rougier.
"In South America, Africa and Australia - not so much work has been done proportionately, and so we know very little; and that's why Cronopio is so important.
"Instead of having a picture that is so heavily biased to what happened in the North, we're starting to get some information about what happened in the southern continents, and fortunately in this case the quality of the specimens is very good."
As to that likeness with Scrat, the acorn-obsessed squirrel in the animated Ice Age features films, Prof Rougier finds the association highly amusing.
"I remember when I saw the movie I thought, 'why have they done this ridiculous animal - there is no such thing?'. And then we find something that kind of looks like it. But it just goes to show - we know so little about the actual diversity of mammals that even some very wild guesses might come through; they might actually be present in the fossil record."

Archaeopteryx and the dinosaur-bird family tree 14 September 2011

Archaeopteryx and the dinosaur-bird family tree

14 September 2011

The first fossil skeleton specimen of Archaeopteryx lithographica was uncovered in 1861 and is looked after at the Natural History Museum. It shows a creature with both bird and dinosaur features.

The magpie-sized Archaeopteryx had bird and dinosaur features and helped show that birds evolved from dinosaurs. However, recent research in the journal Nature questions its position in the dinosaur-bird family tree.

Scientists know birds evolved from dinosaurs because many fossils have been found of ancient animals with both bird and dinosaur features, including the famousArchaeopteryx that lived 147 million years ago.

Painting of how Archaeopteryxmay have looked 147 million years ago © John Sibbick / Natural History Museum

Archaeopteryx had a feathered tail and wings with a flight feather arrangement just like modern birds. But it also had a long bony tail, teeth, and 3 fingers ending in claws, like dinosaurs. 

The first Archaeopteryx skeleton fossil was uncovered in 1861 in Solnhofen, Germany, and is looked after at the Natural History Museum. It provided the first evidence that helped demonstrate that modern birds descended from small meat-eating dinosaurs.

Along with researchers from all over the world, Museum scientists have studied the specimen ever since, and they have been able to reveal that it had hearing like an emu and a brain like a chicken.

Still a bird?

Close up of MuseumArchaeopteryx specimen showing the bird characteristic of a reversed perching toe. 

No other fossils of bird-like creatures older thanArchaeopteryx were known at the time, or for most of the time since this early discovery. So it became established as the earliest known bird. But is this still so?

Since the discovery of Archaeopteryx, many more fossils with combined dinosaur and bird features have been uncovered, especially in the last 10 years (with only 9 other Archaeopteryxfinds over the last 150 years).

In June, scientists revealed a new species from China that they say shows Archaeopteryx was not a bird at all.

Xing Xu from the Institute of Vertebrate Paleontology and Paleoanthropology, in Beijing, and colleagues, identified the feathered and chicken-sized Xiaotingia zhengi. It was very similar to Archaeopteryx, sharing features such as long and robust forelimbs, which the team says puts them together in the dinosaur group rather than with birds.

Museum specimen showing the fossil tail of 147-million-year-oldArchaeopteryx that shows the bird-like feather and dinosaur-like long bony tail.

Dr Paul Barrett, Museum dinosaur expertsays, ‘The June research shows just how fine the line between birds and non-avian dinosaurs really is’.

Species that have a mixture of features, and are hard to place in one group or another, are known as transitional forms, sometimes incorrectly called a ‘missing link’. Their fossils provide a record of significant steps in the evolution of new features.

Although Archaeopteryx and X. zhengi had some bird-like features, the researchers say they had more features that put them in the group Deinonychosauria, which includesMicroraptor and Velociraptor, rather than in the bird group Avialae.

So, does the whole bird family tree need re-arranging? 

Not according to Barrett. ‘Xiaotingia does not necessitate a major re-writing of early bird evolution, but shows that the evolution of many of the detailed anatomical features that changed during the origin of birds may have been slightly more complex than previously thought.’

Dr Angela Milner, Museum dinosaur expertcomments. ‘This recent research in no way diminishes the scientific and historical importance of Archaeopteryx.

‘Thomas Henry Huxley [pioneering biologist and educator] pointed out in 1868 that it was the first fossil to provide a snapshot of evolution in action between two major groups, dinosaurs and birds, and a clear demonstration that birds are the descendents of small meat-eating dinosaurs.

Another bird-like branch?

If Archaeopteryx is not a direct ancestor of birds, why does it have bird-like features and where does it sit in relation to the transition of dinosaurs to birds?

Archaeopteryx could be on another branch of the dinosaur family tree with bird-like feathers and skeletal features evolving in another closely related dinosaur group, suggests Barrett.

‘Maybe Archaeopteryx wasn't on the direct ancestral line to birds, but was part of an early experimentation in how to build a bird-like body.’

Overall bird origin picture

The overall picture of birds descending from meat-eating dinosaurs is firmly established. Now scientists need to rearrange the details of the early stages in the bird evolutionary tree.

Barrett adds, ‘As the authors of the June paper note, the evidence suggesting thatArchaeopteryx is not a bird is fairly equivocal and new analyses or new animals could very easily change this picture.

‘In reality what we now have are a set of animals incredibly close to bird origin – unsurprisingly these are very similar to each other, to birds and to other small meat-eating dinosaurs. As they are so similar, it becomes exceptionally difficult to disentangle their relationships accurately.’

Milner concludes, ‘The fact that Archaeopteryx may represent one of many early flying experiments rather than being the direct ancestor of modern birds is no surprise at all.

‘It is only now that Archaeopteryx can be assessed in the context of all the recent discoveries in China which provide so much more information.

Stromatolite colony found in Giant's Causeway

The discovery was made at the Giant's Causeway

In a small grey puddle tucked into a corner of the world famous Giant's Causeway, scientists have made an extraordinary find.

A colony of stromatolites - tiny structures made by primitive blue-green algae.

Stromatolites are the oldest known fossils in the world.

The tiny algae or bacteria that build them are also thought to be the most ancient life form that is still around today, after more than three billion years.

What makes the discovery in Northern Ireland so remarkable is that until now these structures have been found mainly in warm and often hyper saline waters which discourage predators.

The stromatolites in the Giant's Causeway are in a tiny brackish pool, exposed to the violence of waves and easy prey to the animals that are already living amongst them.

Stromatolites are formed by blue-green algae that excrete carbonate to form a dome-like structure. Over thousands of years these build up into a hard rock that continues to grow.

Stromatolite fossils have been dated as far back as three and a half billion years.

The colony at the Giant's Causeway on Northern Ireland's wind-swept north coast was found by accident.

Scientists from the School of Environmental Sciences at the nearby University of Ulster were looking for very different geological formations when Professor Andrew Cooper spotted the stromatolites.

'Puzzling'

"I was very surprised", explained Professor Cooper.

"I was walking along with a colleague looking at something else. Out of the corner of my eye I spotted these structures which, had I not seen them before in my work in South Africa, I probably wouldn't have known what they were."

The colony is very young, just a layer thick, so it's recently formed. One thing that is puzzling scientists is why its chosen this spot.

"There is some unusual set of circumstances that occurs just here that doesn't occur even 10 metres away along the beach," said Professor Cooper.

"So whatever it is, it's very special to this particular time and space."

One clue could be the myriad of shells in the grass banks just about the tiny pool. Rain water is leaching through the ground and the shells, dissolving out calcium carbonate and carrying to the stromatolites.

Stromatolites' appearance on this planet is seen as a turning point in the earth's evolution

The blue-green algae that form the stromatolites helped create our present atmosphere by breaking down carbon dioxide and excreting oxygen. Their appearance on this planet is seen as a turning point in the earth's evolution.

While living examples are thought to be rare, it could be that we haven't found them because we aren't looking for them.

"The chances are that they may be more widespread than we actually know", explained Professor Cooper.

"Geologists have spent a lot more time studying the ancient stromatolites that are two billion years old than we have spent on living stromatolites.

"So this is an important site where we can look at the circumstances in which stromatolites actually occur."

News of the find is only starting to leak out but its expected to start a frenzied search around the coast of Ireland to see if there is more of this primitive organism to be discovered.

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