Dinosaurs v. Mammals: The Final Conflict

[Razgovory]

What part of natural history is Dinosaurs vs mammals?

[Neil]

What part of natural history is Dinosaurs vs mammals?

Both dinosaurs and mammals are components of Earth's rich natural history.

[alfred russel]

Interesting.  I would have thought these kinds of dinosaurs would have suffered more from the fragility/brittleness of the bones than gained from the forced-pump breathing system, but obviously not.

However, this doesn't say that all dinos had this system.  OTOH, every one whose heart shapes have been fossilized appear to have had four-chamber hearts, so maybe they all had the breathing system as well.

In any case, i withdraw my objection; my info was out of date, it seems.

One of the arguments that dinosaurs had bird like respitory systems is the long necks many of the larger ones had. The problem being that mammalian respitory systems have limits on neck length because when we inhale the first air to enter our lungs is the air in the trachea that we have already used (the longer the neck-->the longer the trachea-->the higher the percentage of used air in our lungs). There was a group that analyzed this a few years ago and came to the conclusion that sauropods never could have been so large with a mammalian respitory system (and a reptilian would have been even worse) and it seems likely they had an avian system.

If sauropods had that type of breathing system, it would be good evidence that it was common if not universal in dinosaurs, as birds actually evolved from the theropods.

[Neil]

Although the sauropods were actually more closely related to the theropods than they were any other group of dinosaurs.

Do giraffes have problems with respiratory stress?

[alfred russel]

Although the sauropods were actually more closely related to the theropods than they were any other group of dinosaurs.

There are two orders of dinosaurs, and theropods and sauropods are in one. What is interesting is that their group was named for lizards, and the other was named for birds, as early on a relationship with birds was noticed in the other group. However, birds actually came from the order with the lizard name.

Do giraffes have problems with respiratory stress?

Obviously they work out okay, but they are much smaller than the larger dinosaurs.

[Queequeg]

That would help to explain why even the big mammals, like the Indricothere, didn't have the same kind of long necks as the Sauropods.

Interestingly, do we know when/why Dinosaurs developed such a massively superior breathing apparatus?  Clearly lizards don't, and I don't think Crocodiles do either, and it seems like a fair guess that Pterosaurs didn't, making that a probable advantage birds had.

[alfred russel]

That would help to explain why even the big mammals, like the Indricothere, didn't have the same kind of long necks as the Sauropods.

Interestingly, do we know when/why Dinosaurs developed such a massively superior breathing apparatus?  Clearly lizards don't, and I don't think Crocodiles do either, and it seems like a fair guess that Pterosaurs didn't, making that a probable advantage birds had.

There are three basic respitory systems for breathing air (ignoring those of amphibians and some fish): reptilian, mammalian, and avian. The most efficient (in terms of extracting oxygen from inhaled air) is the avian, and the least is reptilian. The avian system isn't necessarily ideal, though, because it requires the most space within the body (and the mammalian requires more than the reptilian).

I don't know why you would guess that pterosaurs wouldn't have an avian system. It seems more and more likely that an avian system was present in most dinosaurs, and an avian system tends to be both more efficient and lighter (which is important for flight). Although bats show flight is possible with a mammalian system, they are smaller than the larger pterasaurs and I don't know of any diapsids that have a mammalian system (which doesn't mean there aren't any). I don't know of anything that flies with a reptilian system.

[Queequeg]

Still doesn't really answer my original question.  How did the Avian-Dinosaur system come about?  Crocodiles, Pterosaurs and Dinosaurs aren't that that distant of relations; I'd think that modern crocodiles would at least have some remnants of the prototype avian respiratory system. 

[jimmy olsen]

Still doesn't really answer my original question.  How did the Avian-Dinosaur system come about?  Crocodiles, Pterosaurs and Dinosaurs aren't that that distant of relations; I'd think that modern crocodiles would at least have some remnants of the prototype avian respiratory system.

There was a much lower amount of oxygen in the mesozoic period, so a more efficient breathing mechanism was selected for.

[alfred russel]

Still doesn't really answer my original question.  How did the Avian-Dinosaur system come about?  Crocodiles, Pterosaurs and Dinosaurs aren't that that distant of relations; I'd think that modern crocodiles would at least have some remnants of the prototype avian respiratory system.

Two comments: first, we don't really know what aspects of a respiratory system any long extinct animal had. Respiratory systems consist of soft tissue that isn't preserved, so we have to make a lot of guesses. Some dinosaurs show evidence of avian like structures, and physiologically we think that other extant systems wouldn't work for some of them, so we guess that these had an avian like system. But ~200 million years of evolution separate the sauropods from the systems we see today.

Second, it is possible that the prototype avian respiratory system emerged after the divergence of crocodiles and dinosaurs/pterosaurs.

[DisturbedPervert]

What part of natural history is Dinosaurs vs mammals?

I was wrong, it was on the Science Channel, not History

http://www.youtube.com/watch?v=YIKlplx11n4

[Neil]

There are two orders of dinosaurs, and theropods and sauropods are in one. What is interesting is that their group was named for lizards, and the other was named for birds, as early on a relationship with birds was noticed in the other group. However, birds actually came from the order with the lizard name.

Yeah.  At some point, the pubic boot turned itself back.

Obviously they work out okay, but they are much smaller than the larger dinosaurs.

Their necks are terribly long though.  I wonder what the upper limit is.

[jimmy olsen]

Two comments: first, we don't really know what aspects of a respiratory system any long extinct animal had. Respiratory systems consist of soft tissue that isn't preserved, so we have to make a lot of guesses. Some dinosaurs show evidence of avian like structures, and physiologically we think that other extant systems wouldn't work for some of them, so we guess that these had an avian like system. But ~200 million years of evolution separate the sauropods from the systems we see today.

Second, it is possible that the prototype avian respiratory system emerged after the divergence of crocodiles and dinosaurs/pterosaurs.

However, paleontologist have made found soft tissue remains in the last ten years that have lead to great breakthroughs.

T. Rex Soft Tissue Found Preserved
Hillary Mayell
for National Geographic News
March 24, 2005

A Tyrannosaurus rex fossil has yielded what appear to be the only preserved soft tissues ever recovered from a dinosaur. Taken from a 70-million-year-old thighbone, the structures look like the blood vessels, cells, and proteins involved in bone formation.

Most fossils preserve an organism's hard tissues, such as shell or bone. Finding preserved soft tissue is unheard of in a dinosaur-age specimen.

"To my knowledge, preservation to this extent—where you still have original flexibility and transparency—has not been noted in dinosaurs before, so we're pretty excited by the find," said Mary H. Schweitzer, a paleontologist at North Carolina State University in Raleigh.

The findings may provide new insights into dinosaur evolution, physiology, and biochemistry. They could also increase our understanding of extinct life and change how scientists think about the fossilization process.

"Finding these tissues in dinosaurs changes the way we think about fossilization, because our theories of how fossils are preserved don't allow for this [soft-tissue preservation]," Schweitzer said.

Uncovering T. Rex

For three years scientists from the Museum of the Rockies in Bozeman, Montana, excavated the T. rex from sandstone at the base of the nearby Hell Creek formation. The dinosaur was relatively small and around 18 years old when it died.

"The dinosaur was under an incredible amount of rock," said Jack Horner, a curator of paleontology at the museum. "When it was collected, the specimen was very far away from a road, and everything had to be done by helicopter.

"The team made a plaster jacket to get part of the fossil out, and it was too big for the helicopter to lift. And so we had to take the fossil apart.

"In so doing, we had to break a thighbone in two pieces. When we did that, it allowed [Schweitzer] to get samples out of the middle of the specimen. You don't see that in most excavations, because every effort is made to keep the fossil intact," said Horner, a co-author of the study.

A certain amount of serendipity lead to the discovery.

Because the leg bone was deliberately broken in the field, no preservatives were added. As a result, the soft tissues were not contaminated.

The museum, which is a part of Montana State University, has a laboratory that specializes in cellular and molecular paleontology (the study of prehistoric life through fossil remains).

The study authors also looked at several other dinosaur fossils to see whether there was something unique about this particular T. rex fossil.

"There's nothing unique about the specimen other than the fact that it's the first that's been examined really well," Horner concluded. Other dinosaurs, in other words, are probably similarly preserved.

Soft Tissues

Schweitzer's background is in biology, and she performed a number of tests on the fossils that are common medical practices today.

The paleontologist and her colleagues removed mineral fragments from the interior of the femur by soaking it in a weak acid. The fossil dissolved, exposing a flexible, stretchy material and transparent vessels.

The vessels resemble blood vessels, cells, and the protein matrix that bodies generate when bones are being formed.

"Bone is living tissue, is very active tissue, and has its own metabolism and has to have a very good blood supply," Schweitzer said.

"So bone is infiltrated with lots and lots of blood vessels in its basic structure. When bone is formed, it's formed by cells that are specific for bone, that secrete proteins like collagen and form a matrix."

Further chemical analysis might enable the scientists to answer long-standing questions about the physiology of dinosaurs. For instance, were they warm-blooded, cold-blooded, or somewhere in between?

If protein sequences can be identified, they can be compared to those of living animals. This might allow a better understanding of how different groups of animals are related.

The find may potentially change field practices, perhaps by encouraging more scientists to reserve parts of fossils for cellular and molecular testing.

And once tested, the proteins definitely seem similar to avian proteins.

http://news.nationalgeographic.com/news/2007/04/070412-dino-tissues.html

Dinosaur Soft Tissue Sequenced; Similar to Chicken Proteins
Scott Norris
for National Geographic News
April 12, 2007

Ancient collagen—the main protein component of bone—has been extracted from the remains of a 68-million-year-old Tyrannosaurus rex, according to two new reports.

The new studies provide strong support for the hotly debated claims that organic material previously extracted from the T. rex's leg bone is original dinosaur soft tissue that somehow escaped fossilization.

Now, for the first time, scientists have obtained partial protein sequences from the soft tissue remains.

"The sequences are clearly from T. rex," said John Asara of Harvard Medical School in Cambridge, Massachusetts, who led one of the studies.

In addition, both studies found similarities between the dino sample and the bone collagen of chickens, providing molecular support for the hypothesis that modern birds are descended from dinosaurs.

Until now the dino-bird connection has been entirely based on physical similarities in fossils' body structures (related: "Earliest Bird Had Feet Like Dinosaur, Fossil Shows" [December 1, 2005]).

In a related study, a team led by Mary Higby Schweitzer of North Carolina State University conducted tests that also revealed the presence of collagen in the T. rex remains.

In one experiment, antibodies that normally react in the presence of chicken collagen reacted strongly to the dinosaur protein, suggesting a similar molecular identity.

Multiple Tests

For the protein sequencing study, Asara's team isolated seven fragmentary chains of amino acids—the building blocks of proteins—from the T. rex specimen.

The results are by far the oldest such data ever recovered. Previously, the earliest protein sequence data came from a 300,000-year-old mammoth specimen.

Asara's team extracted the amino acids using a highly refined version of the analytical technique known as mass spectrometry.

They also used the technique to isolate more than 70 amino acid
sequences from a mastodon thought to be between 160,000 and 600,000 years old.

Comparing the dino and mastodon samples to data from modern animals allowed the team to identify sequences that link the ancient amino acids to modern collagen.

Schweitzer and colleagues independently used a variety of chemical and molecular tests to identify the preserved collagen.

Both of the new studies, which will appear in tomorrow's edition of the journal Science, were conducted using the same unusual T. rex remains Schweitzer and others first described in 2005.

In that report the researchers described the seemingly inexplicable preservation of soft tissues—including branching blood vessels and bone matrix—in a T. rex fossil from Wyoming.

Some experts were immediately skeptical, saying that preservation of organic material over such a vast period of time should not be possible.

"The accepted viewpoint is that collagen, like other organic molecules, will degrade relatively rapidly, so that after a maximum of about a hundred thousand years nothing will remain," Schweitzer acknowledged.

But when conditions for preservation are just right, she said, "degradation rates may differ from predictions. Data from both [new] papers suggest that original protein may be preserved."

Burden of Proof

Hendrik Poinar is an expert in fossil proteins and DNA at McMaster University in Ontario, Canada.

Like others in the field, he had questioned whether Schweitzer's 2005 report made a sufficiently strong case that the preserved tissues came from a T. rex and were not the result of more recent contamination.

The new studies have him more convinced.

"I'd have to say, I'm more optimistic about it than I was previously," Poinar said. "Now the burden of proof is on the skeptics."

One self-proclaimed skeptic is Christina Nielsen-Marsh, an expert on ancient bone proteins at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

"I would love it to be true," she said of the new T. rex findings. "But I do have serious doubts. I know of no other research group that has been able to extract—let alone sequence—indigenous proteins from fossils older than a million years.

"Based on what we presently understand, these T. rex sequences make no sense at all," Nielsen-Marsh said.

"That doesn't mean they are wrong. But if they are right, then we all need to rethink how molecules survive in the geological environment."

Schweitzer and her collaborators, including paleontologist John Horner of Montana State University, agree that their discovery should prompt such a rethinking, which could lead to changes in how fieldwork is conducted.

In a Wednesday teleconference, the researchers said several factors may help explain the unusual protein preservation in the T. rex fossil.

The size and density of some dinosaur bones, they said, may help shield internal structures from decay. And bones preserved in dry sandstone may resist degradation better than those trapped in moist soil layers.

Horner said that a central lesson is that paleontologists need to dig deeper to find exceptionally well-preserved fossils.

"If we spend time getting as deep into the sediment as we can, I think we're going to find that many specimens are like this," Horner said.

"This summer we're sending out a major expedition, going worldwide looking for exquisite preservation."

Extensive Sequences

On the laboratory side, Harvard's Asara said, researchers should expect further improvements in analytical techniques, facilitating the recovery of protein sequences from very old remains.

Previous beliefs that proteins rarely if ever survive beyond a few hundred thousand years have now been proven false, he said.

"The mastodon [analysis] revealed a lot of protein," Asara said. "We can now get extensive sequences from species half a million years old, if they are very well preserved."

The researchers said that obtaining more ancient sequences should lead to a powerful new synthesis of paleontology and molecular biology.

"We can now begin [to study] evolutionary relationships between modern and extinct organisms at the molecular level," Asara said.

[Neil]

Still doesn't really answer my original question.  How did the Avian-Dinosaur system come about?  Crocodiles, Pterosaurs and Dinosaurs aren't that that distant of relations; I'd think that modern crocodiles would at least have some remnants of the prototype avian respiratory system.

Crocodilians are archosaurs, not dinosaurs.  Only dinosaurs and their close relatives seem to have that adaptation.

[alfred russel]

Tim, that really isn't the same thing.