Smithsonian.com

A figure of the "London specimen" of Archaeopteryx discovered in 1861. From the Catalouge of Fossil Birds in the British Museum (Natural History), 1891.

Among the many recurring themes on this blog, the evolution of birds from feathered maniraptoran dinosaurs is probably the most prevalent. Hardly a month goes by without a new study relevant to this major evolutionary transition, and as paleontologists discover more they continue to find that many traits once thought to be exclusive to birds were widespread among dinosaurs. Yet this understanding has only coalesced within the last 15 years. For over a century, the early evolution of birds remained a mystery, and numerous suggestions were made about avian origins.

For much of the past 150 years, how the first birds evolved and what sort of animals they originated from depended upon whom you asked. The English anatomist Thomas Henry Huxley proposed that there was a step-by-step transition from small dinosaur-like creatures through flightless birds (like ostriches) to flying birds, whereas his colleague Harry Govier Seeley vehemently disagreed and believed that birds had evolved from pterosaurs. The idea that birds had an aquatic origin—either evolving from swimming dinosaurs or becoming adapted to life in the sea before taking to the air—was also espoused by several naturalists. But one of the most amusing ideas I have yet encountered was an article by W.T. Freeman printed in an 1897 issue of Gentleman’s Magazine.

Freeman had developed his own peculiar way of looking at the history of life. A creationist, but of a different sort than today’s religious fundamentalists, he thought that there was a clear succession of organisms over time in which there were distinct species incapable of evolving into something else. As evidence for this, Freeman cited the fact organisms created near-perfect copies of themselves through reproduction. No organism gave birth to a different species, and even when two species interbred—an inappropriate interaction Freeman deemed “perverted”—the hybrid never became established as a new species.

Within this creationist system, Freeman believed he had found an explanation for Archaeopteryx. Recognized by many naturalists as an early bird with reptilian characteristics such as teeth and a long, bony tail, Archaeopteryx was regularly used as evidence that birds had indeed evolved from reptiles. (“Everything has, or has had, a definite purpose in life,” Freeman wrote, “and the archaeopteryx lived its life in order to bring bliss to the soul of the evolutionist.”) But Freeman took a different view. The mish-mash of bird and reptilian characters indicated that Archaeopteryx was nothing more than a sign of ancient indiscretions:

I suggest that in the earlier days there were ill-developed, low-typed, wallowing birds, also some highly developed reptiles. Perverted sexual instinct exists now, why not then, and as a result of this, why has not the archaeopteryx been an anomalous false hybrid that has been incapable, like other mongrels, of reproducing its kind?

When I first read this, I had to wonder if the essay was meant as some kind of joke or satirical jab at the science of evolution. How could anyone seriously believe that Archaeopteryx was the product of a union between birds and reptiles? Yet Freeman’s essay is serious from start to finish, and I was able to find at least one other essay by him about his off-kilter creationist beliefs.

Frustratingly for Freeman—but fortunately for our understanding of the natural world—the idea that Archaeopteryx was the monstrous offspring of reptile and bird never took off. The animal truly was the first feathered dinosaur ever found, and, even though it took over a century to arrive at this view, the multiple Archaeopteryx specimens discovered so far remain important to ongoing research about the evolution of birds.

Anatomical drawing of Godzilla, courtesy of Flickr user modern_fred

Publish or Perish: At SV-POW!, Mike Taylor presents a tutorial on “How to become a palaeontologist.” His central message: write papers. “I know a whole bunch of people who should be published palaeontologists, but aren’t. Some of them know far, far more about extinct animals than I do, and I am frankly bewildered that they have somehow never made it into print: I assume they are letting themselves be defeated by some kind of psychological barrier.”

Say “Micropachycephalosaurus” Five Times, Fast: Everything Dinosaur makes the case for species pronunciation guides.

Pink Floyd and Paleontology: Yes, there is a connection.

Team Spirit: Dinochick provides us with this video of a drunken Bears fan climbing on top of the Brachiosaurus outside Chicago’s Field Museum: “You know you would like to do this. Maybe not in public, but how many of you have seen a sculpture or even a cast you think would be fun to scale?” (Not that the Field Museum lacks team spirit: back in April, the staff dressed the giant sauropod in a specially-made Blackhawks hockey jersey.)

Forewarned is Forearmed: Tetrapod Zoology publishes this extensive guide to the anatomy of Godzilla

A Mammoth Discovery: Bob’s Dinosaur Blog reports on a treasure trove of fossils discovered in Snowmass Village, Colorado: “a mere two weeks after a bulldozer operator accidentally unearthed a Woolly Mammoth skeleton while digging a reservoir, the Denver Museum of Nature & Science embarked on a full-throttle, week-long dig to recover as many bones from the site as possible before the onset of winter. So far, the results have been spectacular: workers have recovered the bones of five, count ‘em, five Mastodons, two Woolly Mammoths, three prehistoric bison, one Megalonyx (the Giant Ground Sloth that was first discovered by Thomas Jefferson), and even an Ice Age deer.”

Survivalists: A mass extinction event threatens the denizens of Walcott’s Quarry! Can two plucky trilobites survive?

A Dinosaur Symphony: Palaeoblog commemorates the 70th anniversary of Walt Disney’s epic film, Fantasia: “Igor Stravinsky’s ‘Rite of Spring’ provided the score for the evolution of the Earth including a wonderful sequence on the extinction of the dinosaurs at the end of the Cretaceous. Many school teachers actually showed this sequence in science class—that’s where I first saw it!”

Nazi Dinosaurs: The blog Lady, That’s My Skull calls our attention to a 1943 edition of “Clue Comics,” which recounts the adventures of the Boy King, “an exile from the Nazi-threatened land of Swisslakia who….fought spies and saboteurs that threatened America’s security, using his wits, royal fortune and a skyscraper-sized Golem that only he could command.” But Hitler has a trick up his sleeve and orders his minions to build a robot T-Rex. Does this mean the end for Boy King?!?

The entire gripping tale has been posted over at Flickr.[Disclaimer: Events presented in this comic book have not been vetted for historical accuracy.]

The wishbones of a turkey (left) and the dinosaurs Tyrannosaurus (top), Bambiraptor (middle), and Suchomimus (bottom). (Images not to scale.) The turkey wishbone is from Wikipedia, and the rest are from Nesbitt et al., 2009.

Tomorrow families all over the United States will be taking part in the ritualized, yearly tradition of dinosaur dissection. Granted, “Thanksgiving” is a much better name than “Annual Dinosaur Dissection Day“, but the fact of the matter is that the turkey on the table has a lot in common with its prehistoric, dinosaurian predecessors.

You don’t have to be a trained anatomist to see the correspondence between a dinosaur skeleton and a turkey skeleton. Take the wishbone, for example. This Y-shaped bone is situated in front of the turkey’s shoulders and was formed by the fusion of two separate bones called the clavicles. The terminology here will become important later. “Clavicle” is the term used when these shoulder bones are separated, whereas the words “wishbone” and “furcula” refer to the fusion of the clavicles into a single Y, V, or U-shaped bone.

For a long time it was thought that dinosaurs lacked clavicles. No one had ever found them, and the apparent absence of these bones caused some naturalists to discount dinosaurs as bird ancestors. Among them was the Danish artist Gerhard Heilmann, and he laid out his reasoning in his 1926 book The Origin of Birds.

In Heilmann’s day it was thought that dinosaurs had evolved from a group of early, crocodile-like creatures called pseudosuchians. These creatures had clavicles, but since no one had ever found a dinosaur with clavicles it was thought that dinosaurs had lost these bones during their evolution. This loss meant that – despite the bird-like anatomy of the coelurosaurs -  dinosaurs could not have been ancestral to birds. It would be impossible to lose a trait and then have it spontaneously reappear, and so Heilmann and other paleontologists proposed that birds had a much earlier ancestry among pseudosuchians like Ornithosuchus (the “bird crocodile”).

But dinosaurs really did have clavicles. The trouble was that these bones were either lost during preservation or overlooked. Among the first dinosaurs to be discovered with an intact wishbone was Oviraptor from the Cretaceous rock of Mongolia. When Henry Fairfield Osborn described its skeleton in 1924 he clearly marked a Y-shaped bone as the “interclavicle” – a bone present in some animals between the clavicles – but the bone really represented the entire “missing” wishbone. A wishbone was also found among the bones of the predatory dinosaur Segisaurus in 1936, but the discovery of these bones did not change the consensus that birds had evolved directly from crocodile-like ancestors.

It would not be until the late 20th century that small coelurosaurian dinosaurs would be rightly recognized as being ancestral to the first birds. As scientists discover more about dinosaurs, they continue to find that many “bird” traits – such as feathers and systems of air sacs inside the body – were widespread among dinosaurs, and the wishbone is just one small example of this evolutionary connection. Clavicles, both separate and fused, have been found in all major groups of dinosaurs, but true wishbones were only present among the theropod dinosaurs.

As reviewed in recent studies led by Christine Lipkin and Sterling Nesbitt, respectively, many theropod dinosaurs had wishbones. Even the mighty Tyrannosaurus rex had one, and enough Tyrannosaurus wishbones have been found to even detect variation among their shapes. Indeed, the wishbone was an extremely widespread and ancient trait among theropod dinosaurs, perhaps going back more than 215 million years. The wishbone was not a recent evolutionary innovation of modern birds, but a piece of ancient skeletal architecture which links your Thanksgiving feast with some of the most fantastic creatures to have ever evolved.

From all of us at Dinosaur Tracking, have a warm and happy Thanksgiving!

References:

CARRANO, M., HUTCHINSON, J., & SAMPSON, S. (2005). NEW INFORMATION ON SEGISAURUS HALLI, A SMALL THEROPOD DINOSAUR FROM THE EARLY JURASSIC OF ARIZONA Journal of Vertebrate Paleontology, 25 (4), 835-849 DOI: 10.1671/0272-4634(2005)025[0835:NIOSHA]2.0.CO;2

LIPKIN, C., SERENO, P., & HORNER, J. (2007). THE FURCULA IN SUCHOMIMUS TENERENSIS AND TYRANNOSAURUS REX (DINOSAURIA: THEROPODA: TETANURAE) Journal of Paleontology, 81 (6), 1523-1527 DOI: 10.1666/06-024.1

Nesbitt, S., Turner, A., Spaulding, M., Conrad, J., & Norell, M. (2009). The theropod furcula Journal of Morphology, 270 (7), 856-879 DOI: 10.1002/jmor.10724

H.F. Osborn (1924). THREE NEW THEROPODA, PROTOCERATOPS ZONE,
CENTRAL MONGOLIA American Museum Novitates

Skeletal reconstructions (top) and life restorations (bottom) of the dinosaurs Iguanacolossus (left) and Hippodraco (right). Images are not to scale. Art by Lukas Panzarin and from McDonald et al., 2010.

The parade of new dinosaur species continues this week with the description of two new iguanodont dinosaurs from Utah: Hippodraco and Iguanacolossus.

Iguanodont dinosaurs were among the first to be discovered by scientists. The genus Iguanodon itself was described by the English naturalist Gideon Mantell in 1825, although the way he initially envisioned it—as a gargantuan iguana—greatly differs from the dinosaur with a thumb-spike that we are familiar with today. Since the time of that first discovery, additional genera and species have been found. The latest two discoveries were found within the 124-million-year -old Cedar Mountain Formation of eastern Utah.

As described by Andrew McDonald, James Kirkland and their co-authors in PLoS One, the Cedar Mountain Formation contains a relatively rich collection of iguanodont dinosaurs. The dinosaurs Eolambia caroljonesa, Planicoxa venenica and Cedrorestes crichtoni have all been found in these rocks, and the two new dinosaurs from two separate sites add to this diversity. The larger of the two animals, Iguanacolossus, would have been about 30 feet long and is described as a “somewhat ponderous beast with robust limbs.” Hippodraco, at a comparatively paltry 15 feet, was a much smaller animal, and the remains described in the paper may have even belonged to a juvenile. Although both new dinosaurs are known from only partial skeletons, the bones are distinctive enough in anatomy and in their geologic context to justify placing them in new species. (Paleontologists also found the fragmentary remains of other dinosaurs at each of the two sites, but not enough was preserved to positively identify what genera or species they might belong to.)

When compared with other iguanodonts, Iguanacolossus and Hippodraco fall in different parts of the group’s evolutionary tree. Whereas Hippodraco was most closely related to the 112-million-year-old Theiophytalia from Colorado, Iguanacolossus was placed near Dakotadon from South Dakota and Cedrorestes from Utah. Frustratingly, though, many of the North American iguanodonts are known only from partial remains which do not overlap with one another, and as excavations continue it is likely that some species will be lumped together and some unique specimens will be taken to represent new species.

Determining the true diversity of these iguanodonts and their relationships to one another will require more time and additional fossils, but at present it appears that  the Early Cretaceous iguanodonts in western North America were quite different from their cousins elsewhere. Compared with relatives that lived at the same time in other places, both Hippodraco and Iguanacolossus appear to be relatively archaic species, meaning that they were more similar to earlier varieties of iguanodonts than the more specialized species such as Iguanodon. Andrew McDonald has already begun sorting all of this out, but for now it is clear that the Early Cretaceous West was home to a unique and varied collection of iguanodonts which we are only just beginning to understand.

For more, see Andy Farke’s post on these dinosaurs.

References:

McDonald, A., Kirkland, J., DeBlieux, D., Madsen, S., Cavin, J., Milner, A., & Panzarin, L. (2010). New Basal Iguanodonts from the Cedar Mountain Formation of Utah and the Evolution of Thumb-Spiked Dinosaurs PLoS ONE, 5 (11) DOI: 10.1371/journal.pone.0014075

The remains of Koreaceratops - the tip of the tail is to the upper right and the partial legs are to the lower left. From Lee et al., 2010.

Hot on the heels of a team of researchers who described Zhuchengceratops from the Cretaceous of China, paleontologists Yuong-Nam Lee, Michael J. Ryan and Yoshitsugu Kobayashi have just announced the discovery of another ceratopsian dinosaur—Koreaceratops hwaseongensis—from the 103-million-year-old rock of South Korea. It is the first dinosaur of its kind to be found in the country, though it shows some peculiar similarities to other dinosaurs found elsewhere.

Represented by a nearly complete tail, portions of the hips and partial hindlimbs, Koreaceratops was discovered on the west coast of the Korean peninsula in 2008 near Jeongok harbor. Not very much of it was left to compare to other dinosaurs, particularly since no elements of the skull were found, but the handful of distinctive characteristics in the hindlimbs and tail identified it as a ceratopsian dinosaur closely related to Archaeoceratops and Cerasinops.

The most prominent feature of Koreaceratops is its deep tail. Like Protoceratops, Montanoceratops and similar horned dinosaurs, Koreaceratops had a series of exceptionally long neural spines sticking up from its tail vertebrae which get progressively longer towards the end of the tail before becoming shorter near the tip. This would have given Koreaceratops a tall, deep tail which would have looked superficially like a paddle. Over the past century, several paleontologists have argued that ceratopsians with this tail shape may have been amphibious.

The authors of the new study approach the possibility that Koreaceratops was semi-aquatic tentatively. The paper’s abstract states that the tall neural spines of Koreaceratops, Montanaceratops and other ceratopsians may have evolved multiple times as a possibly adaptation to swimming, but in the body of the paper they state that the evidence that these dinosaurs were regular swimmers is equivocal.

I am doubtful that the deep tails of these dinosaurs can be taken as a good indicator of their swimming ability. As the authors of the new study document in the paper, the tail shapes of each of these deep-tailed ceratopsians varies significantly. Koreaceratops had a tail with taller and taller neural spines approaching the tip—making the end portion of the tail the deepest—while in Protoceratops the deepest portion is closer to the hips, being in the middle of the tail or just a bit closer to the rest of the body. If all of these dinosaurs had tails that independently evolved to allow them to propel themselves through the water, it might be expected that they would all have tails with the same shape, namely with the deepest part of the tail being near the tip as this would give them the most thrust. Instead, the different deep tail types may have been involved in display or species recognition, in which case we would expect for there to be variation in tail shape from one dinosaur to another.

Admittedly it is relatively easy to come up with hypotheses about tail function. What is more difficult is finding a way to test ideas about long-extinct organisms. In this case anatomy alone may not provide an unambiguous answer, but there may be a way to determine whether or not Koreaceratops and its kin were semi-aquatic. Paleontologists have regularly used levels of oxygen isotopes preserved in the teeth and bones of prehistoric animals to determine whether or not certain animals spent a great deal of time in the water. Earlier this year a different group of paleontologists used this technique to provide support for the idea that the predatory spinosaurs were semi-aquatic animals, and the same line of evidence could be applied in this long-running debate about ceratopsians. No single study will shut the case entirely, but the more lines of evidence we can draw upon to approach the question of swimming ceratopsians, the better.

References:

Lee, Y., Ryan, M., & Kobayashi, Y. (2010). The first ceratopsian dinosaur from South Korea Naturwissenschaften DOI: 10.1007/s00114-010-0739-y