An international team of palaeontologists have found how a meat-eating species of dinosaurs, that share many similarities with birds, lost their fingers.
The fossil specimens of “Xiyunykus pengi” and “Bannykus wulatensis”, discovered in China, are an enigmatic group of theropods known as alvarezsaurs.
Their bodies were found to be slender, with a bird-like skull and many small teeth instead of the usual large, sharp cutting teeth of their meat-eating relatives.
“Alvarezsaurs are weird animals. With their strong, clawed hands and weak jaws, they appear to be the dinosaurian analogue to today’s aardvarks and anteaters,” said Jonah Choiniere, Associate Professor at the Wits University in South Africa.
However, “the new fossils have long arms and show that alvarezsaurs evolved short arms only later in their evolutionary history, in species with small body sizes. This is quite different to what happens in the classic example of tyrannosaurs, which have short arms and giant size,” said co-author Professor Roger Benson from Britain’s Oxford University.
According to the researchers, the alvarezsaurs did not always look this way. Early members of the group had relatively long arms with strong-clawed hands and typical meat-eating teeth. Over time, they evolved into dinosaurs with mole-like arms and a single claw.
Bannykus and Xiyunykus are important because they show transitional steps in the process of alvarezsaurs adapting to new diets, the researchers said, in the paper published in the journal Current Biology.
The new Alvarezsaurian dinosaurs are among the most bizarre groups of theropods, with extremely short, robust forelimbs with a single functional claw and gracile, bird-like skulls and hind limbs.
Some may be familiar with mythical sea monsters. For example, Scotland’s infamous Loch Ness Monster “Nessie,” and Giganto — fictional beasts of comic book fame. But millions of years ago, real-life sea monsters lived and thrived in what we now call the South Atlantic Ocean.
South Atlantic Ocean basin
As the continents of South America and Africa separated millions of years ago, scientists say a fantastic array of ferocious predators and other lifeforms colonized the newly formed body of water off the coast of Angola.
That diverse collection of marine reptiles included mosasaurs (aquatic lizards), plesiosaurs (which exhibited broad flat bodies, large paddlelike limbs, and typically a long flexible neck and small head), and the more familiar giant sea turtles.
But a catastrophic asteroid that hit earth 66 million years ago wiped most of them out, according to scientists.
Today, thanks to a project called Projecto PaleoAngola among Angolan, American, Portuguese and Dutch researchers, paleontologists have been able to visit the coastal cliffs of Angola to excavate and study what remains of these giant animals.
“We knew that there were fossils there, we just didn’t know how good they would be,” says Louis Jacobs, collaborating curator and professor emeritus of paleontology at Southern Methodist University in Dallas, Texas.
“Nobody had been there, so this was a vast, unknown terrain and we wanted to get there.”
A 72-million year-old ecosystem
What the team of paleontologists discovered was a treasure trove, giving them an unprecedented look into a strange yet familiar ecosystem.
In addition to mosasaurs, plesiosaurs and sea turtles, there were fossilized remains of a variety of fish and other marine life forms.
While mosasaurs have been known to exist on all continents and are relatively common in certain places, this particular sample is the largest collection of southern hemisphere mosasaurs known, according to the paleontologists.
“It’s certainly the best locality for these kinds of animals in sub-Saharan Africa and it could be one of the best in the world,” Jacobs said.
Rediscovering a lost world
Eleven authentic fossils from Angola’s ancient seas, full-size reconstructions of a mosasaur and an ancient sea turtle are on display for the first time in a new exhibit at the Smithsonian’s National Museum of Natural History in Washington, titled “Sea Monsters Unearthed: Life in Angola’s Ancient Seas.”
There are also 3-D scanned replicas of mosasaur skulls, and photo-murals and video vignettes transport visitors to field sites along Angola’s modern rugged coast, where Projecto PaleoAngola scientists unearthed the fossil remains from this lost world.
Jacobs, who was part of a team of scientists and students at SMU that helped prepare the fossils for the Smithsonian exhibit, says any visitor “can look and see and compare how the ecosystem and its animals of the cretaceous of 72 million years ago are similar to ecosystems today in the same general areas.”
“The species are different, but the ecological jobs of the species are very similar,” he added.
Michael Polcyn, senior research fellow at SMU, pointed out an example in the exhibit.
Standing in front of a fossil skull and partial skeleton of a mosasaur, he described the reptile as an “optimized fish eater.”
“You see the long narrow snout, the interlocking teeth — this would be similar to what you would see in the ocean today, in a dolphin for instance,” he said.
He gestured to a graphic posted on the display case depicting a rough toothed dolphin which it described as “the analog for the animal in the modern ecosystem.”
Another great example of diversity within that ancient ecosystem is the hardshell-eating mosasaur, Polcyn said, which preyed on large oysters which were almost a meter (three feet) across.
“They were really big, so to crack an oyster three feet across you needed the dentition and the musculature to do that, and that’s what you see here in these very strange mushroom-shaped teeth that you see in this animal,” Polcyn explained.
Within the same ecosystem was another example of a top predator, the Prognathodon kianda. Its full-scale skeleton on display in the museum is almost eight meters long.
In addition to top predators like the monster-like mosasaur, the exhibit also includes fossils of gentler creatures; small fish and an ancient giant sea turtle.
“We have a snapshot of this moment in time 72 million years ago that has preserved all of these animals that were living together in one place,” Polcyn said.
The big dig
Jacobs says the fossil find in Angola was a big deal for a number of reasons:
“First of all because it’s going into a country that never really had a heritage of fossils,” he said. “It basically was unknown at the level that we are opening it up.”
“Fossils,” he says, “instill a sense of pride in what’s in the country, and it provides something to use for education, and it builds science. And the way it builds science is because every country has fossils, so every country has something to offer, so every country is a piece of the puzzle and the Angola piece is now there.”
Michael Polcyn agrees that unearthing this cache of ancient fossils has been a huge breakthrough on a number of fronts.
“From a purely scientific point of view it gives us an incredible window into an ecosystem 72 million years ago that is relatively complete,” he says. “From a very human point of view this really shows the people of Angola, and the people of the world, what incredible resources we have in our natural environments.”
And lastly, he says, “These fossils are the patrimony of Angola, these are their heritage, and for us to be able to bring them to the Smithsonian and ultimately back to Angola, on a very personal level, is a thrill for us.” (VOA)