Dinosaur Feathers Found in Amber

Many outlets are reporting the find in Myanmar of perfectly-preserved dinosaur feathers in Amber.  From the Washington Post:

The amber hunters who dug up the segment in Burma (Myanmar) assumed the encased remains were vegetation, making the amber valuable when carved into jewelry. It probably did not occur to them that their discovery could be a dinosaur tail with secrets to tell. But a Chinese paleontologist named Xing Lida, perusing a Burmese amber market in 2015 for objects of scientific interest, recognized the amber’s true value.

“With the new specimen from Myanmar, we finally get that association between identifiable bones and feathers preserved in exquisite detail,” said Ryan McKellar of the Royal Saskatchewan Museum in Canada, a paleontologist and an author of the study, in an email to The Washington Post. Lida, McKellar and their Chinese and Canadian colleagues published an analysis of the tail on Thursday in the journal Current Biology.

How do we know it is from a dinosaur and not a bird?

X-ray images revealed that no ancient bird grew this tail. The tail tip belonged to a two-legged dinosaur called a theropod. “We can tell that this specimen came from a theropod dinosaur because the tail is flexible and the vertebrae articulate with each other, instead of being fused together to form a solid rod — which is a characteristic of modern birds and their closest relatives,” McKellar said. Specifically, the researchers hypothesized the animal was a type of dinosaur called a coelurosaur, and likely a juvenile.

Image Credit: A rendition of the coelurosaur. (Chung-tat Cheung and Yi Liu)

This further cements the link between the late Cretaceous theropods and early birds. More pieces of the puzzle.

More Feathered Dinosaurs

Science Daily has a story on the discovery of more feathered dinosaurs. From down in the story:

Theropods are bipedal, mostly carnivorous dinosaurs. In recent years, scientists have discovered that many extinct theropods had feathers. But this feathering has only been found in theropods that are classified as coelurosaurs, a diverse group including animals like T. rex and birds. Sciurumimus -- identified as a megalosaur, not a coelurosaur -- is the first exception to this rule. The new species also sits deep within the evolutionary tree of theropods, much more so than coelurosaurs, meaning that the species that stem from Sciurumimus are likely to have similar characteristics.

Once again, we are seeing that, in response to changing climate, some dinosaurs are evolving feathers to keep warm. The writer alludes to this at the end of the quote. It is likely that the ancestors of both branches of theropods will have rudimentary feathers. The coelurosaurs simply took it and ran with it.

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Where Did the Cretaceous Birds Go?

As evidence continues to pile up supporting the theropod dinosaur-to-bird transition, the question has arisen: where did all of the Cretaceous birds that did not give rise to modern birds go?  Science Daily has this report:

Now a team of paleontologists led by Yale researcher Nicholas Longrich has provided clear evidence that many primitive bird species survived right up until the time of the meteorite impact. They identified and dated a large collection of bird fossils representing a range of different species, many of which were alive within 300,000 years of the impact.
"This proves that these species went extinct very abruptly, in terms of geological time scales," said Longrich. The study appears the week of Sept. 19 in the journal Proceedings of the National Academy of Sciences.

Aside: the next time I see a scientist use the word “prove” I am going to strangle them. Scientists don't prove anything. They provide support for a hypothesis or they reject a hypothesis.  Onward.  The common consensus about the dinosaur extinction is that it was, in large part, caused by a huge meteorite that fell to earth toward the end of the Cretaceous in the Yucatan Peninsula.

The crater reflecting this impact is 110 miles across and, while it probably wasn't the entire cause of the dinosaur extinction, it wiped out a good chunk of 'em.The article continues:

Yet modern birds are very different from those that existed during the late Cretaceous, Longrich said. For instance, today's birds have developed a much wider range of specialized features and behaviors, from penguins to hummingbirds to flamingoes, while the primitive birds would have occupied a narrower range of ecological niches. "The basic bird design was in place, but all of the specialized features developed after the mass extinction, when birds sort of re-evolved with all the diversity they display today," Longrich said. "It's similar to what happened with mammals after the age of the dinosaurs."

Another piece of the puzzle!

Bernard Wood and Terry Harrison on Early Human Origins

Bernard Wood and Terry Harrison, two of the preeminent scholars in the study of human origins think that we are assimilating too many fossils into our family tree. In an article in PhysOrg, the author writes:

The paper, "The evolutionary context of the first hominins," reconsiders the evolutionary relationships of fossils named Orrorin, Sahelanthropus and Ardipithecus, dating from four to seven million years ago, which have been claimed to be the earliest human ancestors. Ardipithecus, commonly known as "Ardi," was discovered in Ethiopia and was found to be radically different from what many researchers had expected for an early human ancestor. Nonetheless, the scientists who made the discovery were adamant it is a human ancestor.

Wood and Harrison have a point here. One of the things that we castigate those that are unfamiliar with evolutionary theory about is “unilineal” thinking—that you can have transitional forms in the fossil record that do not reflect direct ancestry but “collateral” ancestry. This is especially true in the transition from the late theropod dinosaurs to birds. Yet, because we are talking about our own lineage, we tend to slip into a unileal way of thinking. Witness the brouhaha about Ida last year. Everyone wanted to roll her into the human fossil line even though there was no concrete evidence of such.

This does not mean that Sahelanthropus, Orrorin and Ardipithecus are not transitional. It just means that there is no direct evidence that they are ancestral to the human line. In the article, Wood and Harrison write:

There is no reason why higher primate evolution in Africa in the past ten million years should not mirror the complexity observed in the evolutionary histories of other mammals during the same time period. Nor is there any reason, especially with the lessons from Ramapithecus and Oreopithecus fresh in the minds of researchers, to assume that hominins should not be prone to the same limitations and uncertainties of phylogenetic analysis as other fossil primates.¹

This does not make them any less worthy of study or of producing excitement in the palaeoanthropological community.

¹Wood B., Harrison T. (2011) The evolutionary context of the first hominins. Nature 470:347-352.
10.1038/nature09709

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More on the Microraptor Specimen

Reuters has a story on the discovery of the microraptor with four wings (see the post below this one):

"This finding suggests that birds are likely to be descended from a kind of small-sized four-winged dinosaur about 160 million years ago," Xu said.

"It is a link between more typical theropods (dinosaurs which moved around with two rear limbs) and birds. It lived around a time period ... that we expected for birds' ancestor."

In a statement, the researchers said: "Long feathers cover the arms and tail, but also the feet, suggesting that a four-winged stage may have existed in the transition to birds."

The transition from dinosaurs to birds is still poorly understood because of the lack of well-preserved fossils, and many scientists say bird-like dinosaurs appear too late in the fossil record to be the true ancestors of birds.

It seems to be clear that a whole series of theropods were moving in the direction of flight. Which one got there first is still not known. We likely do not have enough information of the collateral ancestry of birds.

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Tyrannosaurus Rex and Trichomonosis: The Dinosaur to Bird Avalanche of Evidence Continues

The Chicago Sun-Times has an article on what may have killed the famous Tyrannosaur named Sue, which currently resides in the Field Museum. According to the story, by David Newbart:

Theories abound on what led to the demise of the Field Museum’s most famous specimen: shortly after the Tyrannosaurus rex was found, some wondered if a series of holes in the back of her massive skull were bite marks suffered during a ferocious battle with another meat-eating dinosaur.

But researchers have honed in on a culprit far smaller: a throat infection caused by a single-celled organism.

Writing in Tuesday’s edition of the online journal of Public Library of Science One, researchers from the University of Wisconsin and elsewhere theorize that the parasitic infection could have led to an autoimmune response that eventually could have led Sue to starve to death 67 million years ago.

Now the punch line: the infection shows evidence of being caused by the Trichomonosis bacteria which is found in only one other sub-class: birds. Given all of the other palaeontological evidence that the the theropod dinosaurs and Aves share a common ancestry, what are the odds they would share the same kind of infection by chance?

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More on Limusaurus inextricabilis

InSciences has an expanded article on the discovery of the beaked dinosaur with the more avian-like hand structure:

The newly discovered dinosaur's hand is unusual and provides surprising new insights into a long-standing controversy over which fingers are present in living birds, which are theropod dinosaur descendants. The hands of theropod dinosaurs suggest that the outer two fingers were lost during the course of evolution and the inner three remained. Conversely, embryos of living birds suggest that birds have lost one finger from the outside and one from the inside of the hand. Unlike all other theropods, the hand of Limusaurus strongly reduced the first finger and increased the size of the second. Drs. Clark and Xu and their co-authors argue that Limusaurus' hand represents a transitional condition in which the inner finger was lost and the other fingers took on the shape of the fingers next to them. The three fingers of most advanced theropods are the second, third and fourth fingers--the same ones indicated by bird embryos--contrary to the traditional interpretation that they were the first, second and third.

The article will appear in the June 18 issue of Nature.

Another Bird-Dinosaur Link

Yahoo news is reporting an incredible fossil find in China:

A young dinosaur that fatefully wandered into a mudpool around 155 million years could help explain the mysterious evolution of birds, says the world's most famous fossil-hunter.

A team led Xing Xu, a Chinese dino expert with scores of astonishing finds to his name, uncovered the fossilised remains of a small, exceptional dinosaur in the Shishugou Formation in western China's Junggar Basin.

The creature is the only known beaked herbivorous therapod -- the family of two-legged dinosaurs that were notorious meat-eaters -- from the Jurassic era, they report in Nature, the London scientific journal.

But that is apparently not what is getting everybody's attention. It is the feet:

A widely-accepted theory is that birds emerged from small therapod dinosaurs, developing wings from reptilian forelimbs. The earliest known bird, Archaeopteryx, lived around 150 million years ago.

But in the late 1990s, evidence came forward that appeared to punch a hole in the bird-dino idea. Therapods have digits corresponding to the first, second and third digits -- the thumb, index and middle finger -- on a human hand.

But scientists discovered that in bird embryos, all five digits start to emerge, yet only the second, third and fourth digits survive to develop into the wing structure. The first and outer digits disappear.

In other words, the 1-2-3 of dino digital orthodoxy ran into the 2-3-4 of avian digital reality. There was no way that bird's wings could have developed this way, said critics. They claimed either theropods were not the forerunners of birds -- or else theropods and birds shared some pre-dino common ancestor.

But the new study shows that Limusaurus, startlingly, has a greatly-reduced first digit, while its second, third and fourth digits are far more fully developed. This could be a sign of a process by which digit use shifted, with ceratosaurs as a sort of halfway house, argues Xu.

It could be that this was just one of many different variants of late non-avian, early avian theropods. Another piece of the puzzle.