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Discuss: Dale Husband’s hypothesis of bird evolution.
9 years ago
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Blog: Dale Husband’s hypothesis of bird evolution.
(1 comments) — Birds evolved from dinosaurs; among paleontologists there is no doubt about that now. Indeed, the forms of the earliest birds, Archaeopteryx, were so close to those of small theropod dinosaurs that some scientists (as well as myself) do not accept tha...  more


Anonymous
9 years ago

Michelle has received 244 new, 943 total stars from Care2 membersMichelle has been awarded 503 butterflies for taking action at Care2 Michelle M
I think your take on the theropods is right.
I cant' wait to see this theory tested. It seems like a good one to me, and I agree with you about archeopteryx. 

I am not sure what significance the lack of flight feathers in wings really has, though, because that's something that changes and evolves fairly fast.


Dale has received 81 new, 964 total stars from Care2 membersDale has been awarded 38 butterflies for taking action at Care2 Dale H.
Here's a related thread
Vertebrate Flight
Something interesting in the news...
9 years ago
Paleontologists Ponder Feather Evolution By MATT CRENSON, AP National Writer NEW YORK - A beautifully preserved fossil from southern Germany raises questions about how feathers evolved from dinosaurs to birds, two paleontologists argue in a study published Thursday. The 150 million-year-old fossil is a juvenile carnivorous dinosaur about 2 1/2 feet long that scientists named Juravenator, for the Jura mountains where it was found. It would have looked similar in life to the fleet-footed predators that menaced a young girl on the beach during the opening scene of "The Lost World," the second Jurassic Park movie. The fossil's exceptionally well-preserved bone structure clearly puts it among feathered kin on the dinosaur family tree. Because all of its close relatives are feathered, paleontologists would expect Juravenator to follow suit. But a small patch of skin on the creature's tail shows no sign of feathers. And the skin also doesn't have the follicles that are typical of feathered dinosaurs, said Luis Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles County. He and Ursula B. Gohlich of the University of Munich describe the fossil in Thursday's issue of the journal Nature. "It has a typical scaly dinosaurian skin," Chiappe said. The paleontologists believe Juravenator's closest known relative may have been a fully feathered dinosaur from China, Sinosauropterix. There are a number of possible explanations for Juravenator's nakedness. Feathers could have been lost on the evolutionary line leading to Juravenator after arising in an ancestor to both it and its feathered relatives. Or feathers could have evolved more than once in dinosaurs, cropping up in sister species at different times and places. It is also possible that this particular fossil of Juravenator, which appears to be a juvenile, only grew feathers as an adult or lost its feathers for part of the year. But there is another possibility as well, said Mark Norell, curator of paleontology at the American Museum of Natural History: It is entirely possible that Juravenator did have feathers, but they simply failed to fossilize. "Feathers are really just difficult things to preserve," Norell said. To support his hypothesis he pointed out that several fossils of the oldest known bird, archaeopteryx, lack feathers. Whether or not the new specimen raises interesting questions about how feathers — and thus birds — evolved, most experts do not see it as a challenge to the widely accepted view that modern birds are descended from dinosaurs.
Anonymous
9 years ago
Fossil birds like Diatryma are also found without feathers, but scientists reconstruct them with feathers because they are birds and all birds are known to have feathers today. Indeed, if not for the feather impressions found with some of the Archeopteryx fossils, we would have called it a dinosaur and never a bird at all. I think it is merely bias on the part of some of us that we assume all dinosaurs, including most theropods, had scaly skin and no feathers because of their reptilian skeletons. Because Archeopteryx had advanced flight feathers on its forelimbs, it is logical to conclude that theropods simular to it must also have had feathers, though not adapted for flight or even gliding.  The absence of feathers would merely mean that they were not preserved, not that they never existed. The same issue applies to fossils of early mammals, which are typically found without hair, but we do not therefore asssume that they were hairless, right?
9 years ago
That is very true Dale.
Anonymous
8 years ago

What's REALLY mind blowing is the idea that giant carnivorous dinosaurs like Allosaurus and Tyrannosaurus could have had a covering of FEATHERS instead of the scaly skin we have always assumed they had.

Indeed, it may violate conventional wisdom, but part of the nature of science is to challenge and overthrow such conventional wisdom if the evidence points to doing that....just as evolution itself overthrow creationism in the 19th Century.

Anonymous
8 years ago
A recent challenge to my hypothesis of bird evolution comes from the discovery, via analysis of the molecular evidence I advocated in the blog above, that tinamous are actually the ratites' closest living relatives. If this is correct, then it may be that the tinamous, which have keeled sternums and can fly for short distances, are an example of parallel evolution with the galliformes, the group that chickens and the turkey belong to. The galliformes are not related to the tinamous or ratites at all, but are closer in ancestry to all the more "modern" birds. The molecular evidence does confirm, however, that the ratites are indeed a genuine clade of their own.
Fossil Solves Mystery of Dinosaur Finger Evolution
5 years ago

http://news.yahoo.com/s/livescience/20090617/sc_livescience/fossilsolvesmysteryofdinosaurfingerevolution

Bird wings clearly share ancestry with dinosaur "hands" or forelimbs. A school kid can see it in the bones. But paleontologists have long struggled to explain the so-called digit dilemma.

Here's the problem: The most primitive dinosaurs in the famous theropod group (that later included Tyrannosaurus rex) had five "fingers." Later theropods had three, just like the birds that evolved from them. But which digits? The theropod and bird digits failed to match up if you number the digits from 1 to 5 starting with the thumb. Theropods looked like they had digits 1, 2 and 3, while birds have digits 2, 3 and 4.

That mismatch failed to support the widely accepted evolutionary link between dinosaurs and birds.

Now, newly described fossilized hands from a beaked, plant-eating dinosaur, called Limusaurus inextricabilis, reveal a transitional step in the evolution of modern wings from dino digits. The finding could resolve a debate over which fingers ultimately became embedded in the wing.

"Limusaurus is another one of those discoveries that makes one excited to be a paleontologist," said Matthew Lamanna of the Carnegie Museum of Natural History in Pittsburgh, who was not involved in the new study. "The discovery of a toothless, plant-eating Jurassic ceratosaur, from Asia of all places, is something that nobody in our field ever expected."

The remains of the dinosaur were discovered in the Junggar Basin of Xinjiang, in northwestern China. The deposits date back some 159 million years.

"This new animal is fascinating in and of itself, and when placed into an evolutionary context it offers intriguing evidence about how the hand of birds evolved," said James Clark of George Washington University. He and several colleagues have described the theropod dinosaur in the June 18 issue of the journal Nature.

Jack Conrad, vertebrate paleontologist at the American Museum of Natural History in New York, calls the finding a "spectacular discovery." Conrad was not involved in this current research.

Part 2
5 years ago

The dinosaur was a ceratosaur, which is the group name for the earliest theropods. The largest known ceratosaur, Ceratosaurus nasicornis, boasted a length of up to 25 feet (8 meters), and showed off a prominent nasal horn. (L. inextricabilis had no crest or horn.)

Stretching no more than 5 feet (1.5 meters) from nose to tail tip, the newly described dinosaur had a toothless beak for nibbling plants.

However, it was the dinosaur's hand that especially caught the attention of Clark and his colleagues. It sheds light on a longstanding question over which fingers are present (albeit in a modified form) in the wings of living birds. And since nearly all paleontologists think that birds derived from a group of theropods some 150 million years ago, remains of such dinosaurs can provide the most full-proof evidence of how that transition from hand to wing occurred.

Here's the digit dilemma in more detail: Again, the most primitive theropods had five digits or fingers. Remains from theropods that are more recent, evolutionarily speaking, show these dinosaurs had three fingers. And until now, scientists have suspected those digits were the inner three (starting with the thumb with respect to our hands). But embryos of living birds suggest the wings are made up of the middle digits, with the inner- and outer-most digits missing. So there's a discrepancy.

The digit arrangement of L. inextricabilis, which Clark says is an evolutionary intermediate between the most primitive five-fingered dinosaurs and the three-fingered ones, matches up with birds' wings. The specimen had the three most central fingers (considered the second, third and fourth digits on a five-digit hand, counting the thumb as the first digit) while an inner, first finger or thumb was reduced to what Clark called "a nub."

With the new discovery, the transition from a five-fingered forelimb to three digits in birds' wings makes sense: Basically, the middle three digits persisted and became modified as part of the wings of modern birds.

"It's not going to stop the debate," Clark said during a telephone interview. But, he added, "no one can argue this isn't an important addition."

For Conrad, the finding just about nails the coffin shut. "I would say it resolves the debate," Conrad said. "It's the best evidence we could hope to have to resolve the debate."

As for how the dinosaur used its "hands," the scientists aren't sure. Meat-eating theropods like T. rex used their hands for grasping prey, but L. inextricabilis was a plant-eater.

"Based on its morphology, we are sure its hands are not for grasping as in most other theropods," lead researcher Xing Xu, of the Institute of Vertebrate Paleontology and Paleoanthropology in China, told LiveScience. "One possibility is that they may have been adapted for assisting the animal when it rose from a prone position to standing, providing important muscular assistance and momentum at the start of the maneuver."

Part 3
5 years ago

This research was funded in part by the National Geographic Society, National Science Foundation Earth Science Division, Chinese National Natural Science Foundation, Jurassic Foundation and the Hilmar Sallee bequest.

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