|Feature Article - August 2014|
|by Do-While Jones|
Everyone “knows” something different about dinosaur evolution.
This article was inspired by two recent articles in the scientific literature about the metabolism of dinosaurs and the rate at which they evolved into birds. But before we start talking about dinosaur evolution, let me admit my personal bias on the subject, and why I can’t really take these stories too seriously.
On Christmas morning, 1954, I found an A.C. Gilbert chemistry set under the tree. I don’t still have that chemistry set (I wish I did!); but I am sure that if I repeated its experiments today, the results would still be the same as they were 60 years ago. What was true about chemical reactions then is still true today.
In those days, I also had lots of plastic dinosaurs. I knew all their names, and everything about them. I knew dinosaurs were stupid, slow, scaly cold-blooded reptiles. Kids today know that dinosaurs are smart, agile, hot-blooded feathered birds. It is amazing how much dinosaurs have evolved in just the past 60 years!
Evolutionists are quick to point out that “truth is progressive.” Yes, that’s true. Modern oscilloscopes are much more capable than the one I built in 1960; but my 1960 oscilloscope still works (as you can see in our Evolution for Intellectuals video). In real science, truth progresses as additional information is learned—but old truth is still true. Our knowledge of chemical reactions today greatly exceeds what the most brilliant chemist knew in 1954—but there’s nothing in a 1954 college chemistry textbook that isn’t true any more.
Opinions, on the other hand, do change. For example, the ACLU defended John Scope’s right to teach this “truth.”
The Races of Man. - At the present time there exist upon the earth five races or varieties of man, each very different from the other in instincts, social customs, and, to an extent, structure. These are the Ethiopian or negro type, originating in Africa; the Malay or brown race, from the islands of the Pacific; the American Indian; the Mongolian or yellow race, including the natives of China, Japan, and the Eskimos; and finally, the highest type of all, the Caucasians, represented by the civilized white inhabitants of Europe and America. [emphasis supplied] 1
Was it really a true, scientific fact that in 1914 the Caucasian race was the highest type of all human races? Or was that just an opinion?
With that in mind, do we really know much about dinosaurs—or are we deluding ourselves?
There was a time, not too long ago, when everyone knew dinosaurs were reptiles. But that changed at the end of the 20th century when Dr. Robert T. Bakker threw down the gauntlet by ending his dinosaur book with these two paragraphs:
As long as textbooks and museum labels unreflectively repeat the message, “Dinosaurs are reptiles,” it will be difficult to establish an intelligent debate about the true nature of dinosaur adaptations. Some of the orthodox paleontologists act as though dinosaurs must be assumed cold-blooded until their warm-bloodedness is proved beyond any reasonable doubt. That is at least highly unscientific. And it certainly represents “argument by definition”—dinosaurs are reptiles, reptiles are cold-blooded, therefore dinosaurs are cold-blooded.
A truly scientific skeptic would start by assuming neither cold-bloodedness nor warm-bloodedness, and then reevaluate the evidence without prior terminological bias. So as long as the Dinosauria remain stuck in the Class Reptilia, this type of analysis is nearly impossible. Let dinosaurs be dinosaurs. Let the Dinosauria stand proudly alone, a Class by itself. They merit it. And let us squarely face the dinosaurness of birds and the birdness of Dinosauria. When the Canada geese honk their way northward, we can say, “The dinosaurs are migrating, it must be spring.” 2
Bakker seems to us to be guilty of the crime he opposes. He wants to define geese as dinosaurs, therefore dinosaurs must be birds. Why not, as he suggests, let reptiles be reptiles, birds be birds, and dinosaurs be dinosaurs, each in a class by itself?
Bakker certainly is correct to recognize that classification is purely arbitrary, based on prevailing opinion. If the “feathered dinosaurs” discovered in China had been discovered in the 19th century, they no doubt would have been classified as birds because (duh) only birds have feathers. How do we know those feathered fossils aren’t the fossils of extinct birds—not dinosaurs? We don’t.
When dinosaur bones are dug up, they are the same temperature as the dirt they came out of. Therefore, one cannot measure the body temperature of the dinosaur directly—one must infer body temperature. Inference is nothing more than an educated guess. Inference isn’t as reliable as direct observation.
Here’s a summary of the debate:
Paleontologists have struggled for 50 years to determine whether dinosaurs were cold-blooded ectotherms like today's reptiles, making little effort to control their body temperatures, or [warm-blooded] endotherms, like most modern mammals and birds, which keep their body temperatures at a constant, relatively high set point. The answer greatly influences our view of dinosaurs, as endotherms tend to be more active and faster growing.
For the first 150 years after their discovery, dinosaurs were considered ectotherms like today's reptiles. Ectothermy makes some sense: “It requires much less energy from the environment,” explains Roger Seymour, a zoologist at the University of Adelaide in Australia. But it has drawbacks, too: “The animal cannot feed in cold conditions and has a much more limited capacity for sustained, powerful activity, even if warmed by the sun,” he says.
Beginning in the late 1960s, researchers put forward the then-heretical idea of dinosaurs as endotherms, and evidence for this has accumulated. Annual growth rings in dinosaur bones suggest fast, energy-hungry developmental rates. Birdlike air sacs may have boosted their respiratory efficiency, suggesting rapid movements. And isotopic data from fossils suggest higher body temperatures (Science, 22 July 2011, p. 443).
Giant endotherms pose their own puzzles, however, such as the huge quantities of food needed to sustain them. An endothermic Tyrannosaurus rex “would probably have starved to death,” Grady says. 3
Originally, it was inferred that dinosaurs had to have been cold-blooded because they were so big they could not possibly eat enough food to nourish their huge bodies. Although not mentioned in the quote above, there is also a “heat shedding” problem with large warm-blooded animals. Big warm-blooded animals produce lots of internal heat when moving, with proportionally less surface area to allow that heat to escape. (Elephants have big ears, which act as radiators, and hippos spend lots of time in cool water for this reason.) Therefore it was logically concluded that dinosaurs could not have been warm-blooded.
On the other hand, it was inferred that dinosaurs had to have been warm-blooded because a large cold-blooded animal could not absorb enough heat from the environment to remain active, especially in cold weather. Snakes are long and skinny because that shape provides a better surface-to-volume ratio than any fat dinosaur shape. Therefore it was logically concluded that dinosaurs could not have been cold-blooded. But they had to have existed because their bones are real, so they must have been one or the other. What’s the right answer? It is a matter of opinion, which has changed over time.
As we have already mentioned, dinosaur names reveal a bias. When I was a child, the two best-known dinosaurs were Brontosaurus and Tyrannosaurus rex, both of which were (as their names implied) slow, cold-blooded lizards.
He [Othniel Charles Marsh] named the new species Brontosaurus excelsus, meaning "thunder lizard", from the Greek brontē/βροντη meaning "thunder" and sauros/σαυρος meaning "lizard", and from the Latin excelsus, "highest, sublime", referring to the greater number of sacral vertebrae than in any other genus of sauropod known at the time.
The finds—the largest dinosaur ever discovered at the time and nearly complete, lacking only a head, feet, and portions of the tail—were then prepared for what was to be the first mounted display of a sauropod skeleton, at Yale's Peabody Museum of Natural History in 1905. The missing bones were created using known pieces from close relatives of Brontosaurus. Sauropod feet that were discovered at the same quarry were added, as well as a tail fashioned to appear as Marsh believed it should, as well as a composite model of what he felt the skull of this massive creature might look like. This was not a delicate Diplodocus-style skull (which would later turn out to be more accurate), but was composed of "the biggest, thickest, strongest skull bones, lower jaws and tooth crowns from three different quarries", primarily those of Camarasaurus, the only other sauropod for which good skull material was known at the time. This method of reconstructing incomplete skeletons based on the more complete remains of related dinosaurs continues in museum mounts and life restorations to this day. In 1979, two Carnegie researchers replaced the skull on the museum's skeleton with the correct head found in a quarry in Utah in 1910. 4
So, technically, Brontosaurus never existed. It was really mostly Apatosaurus bones with a Camarasaurus skull. All of them were “saurus.”
Historically, museums have not been as forthcoming as we might wish when it comes to distinguishing which parts of the skeleton were found in-situ, and which parts are assumed to have existed, but were not found. Of course, all of the paintings are artists’ conceptions, which may or may not be accurate.
The movie Jurassic Park came out in 1993 (21 years ago) so, today, every high school student has lived his or her entire life with the image of a Velociraptor firmly in mind.
Velociraptor (commonly shortened to "raptor") is one of the dinosaur genera most familiar to the general public due to its prominent role in the Jurassic Park motion picture series. In the films it was shown with anatomical inaccuracies, including being much larger than it was in reality and without feathers. 5
The original meaning of the word “raptor” was, “bird (such as an eagle or hawk) that kills and eats other animals for food.” 6 But now, because of the movie, the second definition for “raptor” is, “a small or medium-sized dinosaur that ate other animals.” 7
Because dinosaurs are now commonly assumed to be birds, the recently discovered feathered dinosaurs tend to have names containing the word “raptor” rather than “saurus.” Their names imply warm-bloodedness.
So, what’s the truth? Were dinosaurs cold-blooded reptiles or warm-blooded birds? Here’s what the experts now say,
Were dinosaurs ectotherms or fast-metabolizing endotherms whose activities were unconstrained by temperature? To date, some of the strongest evidence for endothermy [warm-bloodedness] comes from the rapid growth rates derived from the analysis of fossil bones. However, these studies are constrained by a lack of comparative data and an appropriate energetic framework. Here we compile data on ontogenetic growth for extant and fossil vertebrates, including all major dinosaur clades.
Our results find that mass-independent growth rates in dinosaurs were intermediate to, and significantly different from, those of endothermic and ectothermic taxa (table S2). Although some dinosaur growth rates overlap with high-power ectotherms or low-power endotherms, they cluster closest to energetically and thermally intermediate taxa, such as tuna. 8
How long is it going to take the general public to accept the idea that dinosaurs were not cold-blooded lizards or warm-blooded birds of prey, but were actually tepid-blooded fish?
Of course, there is an obvious size and weight difference between dinosaurs and birds.
Most paleontologists agree that birds are descended from dinosaurs. How did such large terrestrial or aquatic animals evolve into small feathered fliers? Lee et al. used two large databases of theropod morphology to explore possible evolutionary patterns that may have driven this dramatic transformation (see the Perspective by Benton). They found no clear pattern of miniaturization across the entire clade of Theropoda. However, several lines of evidence suggested that the lineage leading to birds underwent sustained miniaturization. Within that lineage, body sizes decreased and species evolved faster. They also developed ecological and morphological innovations linked to smaller body sizes. 9
Dr. Lee and his colleagues went looking for an explanation of how big, heavy dinosaurs could have evolved into little, light birds. “They found no clear pattern.” Could that be because it didn’t happen? Perish that unthinkable thought!
Such a big change happened in such a short time! That proves “species evolved faster.” (Or, maybe it proves that it didn’t happen at all.)
Because birds live different kinds of lives in different environments than dinosaurs did, they “developed ecological innovations” in order to survive there. Because birds are smaller than dinosaurs, they had to evolve “morphological innovations” in order to survive.
In other words, “It happened because we think it happened.” That’s not science!
Birds evolved from dinosaurs, but how long did this evolutionary transition take? Twenty years ago, it was widely assumed that the first bird—Archaeopteryx, which lived in the Late Jurassic (see the photo)—evolved its feathers, wings, and ability to fly within just 10 million years or so. Since then, it has become clear that most of the 30 or more characteristics that distinguished the small, flying Archaeopteryx from ground-dwelling, carnivorous dinosaurs (theropods) emerged much earlier. On page 562 of this issue, Lee et al. provide evidence for sustained miniaturization for 50 million years before Archaeopteryx evolved (see the graph). 10
Nevertheless, there remain many intriguing questions regarding size and anatomical evolution along the bird stem lineage. Theropods were typically large to gigantic, but small body size characterized all taxa near the origin of forewing-powered flight in birds. 11
Our study quantifies rates of evolutionary innovation in dinosaurs using 1549 (data set 1) and 421 (data set 2) skeletal and other anatomical traits distributed across the entire body. A clear pattern emerges: Branches along the bird stem undergo substantially faster morphological evolution than those of the rest of the tree. 12
In other words, the evolutionary change in size from T. rex to hummingbird happened a lot faster than the rate of normal evolution! Really? It took a huge grant of money to a team of PhDs to figure that out? And what really is the evidence? The evidence is nothing more than the fact that birds today are smaller than prehistoric dinosaurs coupled with the unwarranted assumption that birds evolved from dinosaurs.
Earlier in this essay we said, “there’s nothing in a 1954 college chemistry textbook that isn’t true any more.” We did not (and could not) say, “there’s nothing in a 1954 dinosaur book that isn’t true any more” because the “truth” about dinosaurs is changing all the time.
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Hunter, Civic Biology, 1914, the book Scopes was accused of using.
2 Bakker, The Dinosaur Heresies, Zebra Books, 1986, page 462.
3 Balter, Science, 13 June 2014, “Dinosaur metabolism neither hot nor cold, but just right”, pp. 1216-1217, http://www.sciencemag.org/content/344/6189/1216.full
8 Grady, et al., Science, 13 June 2014, “Evidence for mesothermy in dinosaurs”, pp. 1268-1272, http://www.sciencemag.org/content/344/6189/1268.full?sid=7e54c5b2-3efc-4c7a-ab3f-0383a14b2bf8
9 Vignieri, Science, 1 August 2014, “Turning large dinosaurs into small birds”, p. 526, http://www.sciencemag.org/content/345/6196/526.2.full?sid=f2bacd9e-ed1d-4632-b4b4-e7a64768d7cd
10 Benton, Science, 1 August 2014, “How birds became birds”, pp. 508-509, http://www.sciencemag.org/content/345/6196/508.full
11 Lee, et al., Science, 1 August 2014, “Sustained miniaturization and anatomical innovation in the dinosaurian ancestors of birds”, pp. 562-566, http://www.sciencemag.org/content/345/6196/562.full