more than dinosaurs

Two “Holy Grails” of Dinosaur Science Found

Fri, 25 Sep 2009 14:17:47 -0400

Raptorex and Anchiornis Fill Long-Puzzling Gaps in the Fossil Record

Some dinosaur fossils are so spectacular that they have become household names. Tyrannosaurus is one. It is clearly the most famous of dinosaurs and stokes the imagination of kids all over the world. Other dinosaur fossils are famous because they represent a critical point in the evolution of vertebrates. Fossils of Archaeopteryx are possibly the most important ever discovered because they clearly show a creature during a time of transition from one form of vertebrate to another—from reptiles to birds in this case.
But every fossil poses additional questions. Specifically, what came before and what came after? Over the years I have often asked my paleontologist friends what gaps in the fossil record they would like to see filled? What possible fossils, yet to be discovered, would rank among the most important in terms of extending our knowledge of dinosaur evolution? In other words, what is the Holy Grail of dinosaur science, yet to be discovered?
Two answers always rise to the top of the wish list. For all that we know about Tyrannosaurus, we know very little about its early evolution. Most tyrannosaurs, whether found in North America or Asia, have relatively the same body plan and existed in roughly the same time at the end of the Cretaceous Period. From what creatures did these gigantic theropods evolve? Finding a significantly earlier fossil that clearly shows the hallmarks of the tyrannosaur line would fill an important gap in our knowledge of these creatures.
The other Holy Grail most frequently mentioned is related to Archaeopteryx, the first bird, from the Late Jurassic Period. Until now, there has been very little fossil evidence of bird-like theropods such as troodontids and dromaeosaurids that lived prior to Archaeopteryx. Not much is known about dinosaurian adaptations leading to the first bird. Finding clear fossil evidence of feathered dinosaurs that existed prior to Archaeopteryx would begin to fill in the gaps about the evolution of birds.
In September, 2009, two discoveries have been announced that put these two Holy Grails in the hands of anxious researchers.
Raptorex—a human-size tyrannosaur from the Early Cretaceous of northeastern China includes all of the notable features found in later tyrannosaurids, from the short, two-clawed arms to long, muscular legs, oversized jaw, and a brain cavity showing evidence of enlarged olfactory bulbs for an enhanced sense of smell. The fossil was described by Paul Sereno of the University of Chicago. Read the Smithsonian article: http://blogs.smithsonianmag.com/dinosaur/2009/09/17/raptorex-a-new-tiny-tyrant/
Anchiornis—Chinese scientists have found the nearly complete specimen of a small, feathered dinosaur that predates Archaeopteryx by 5 to 10 million years. Discovered in northeastern China, the dinosaur was perhaps a foot long. It had four wings and feathered feet and shows that feathers were widely adapted by theropod dinosaurs prior to Archaeopteryx. However, the long legs of Anchiornis suggest a cursorial or running creature rather than a climbing one, a detail that bucks other recent findings that suggest a trees-down rather than a ground-up origin of birds. As the authors carefully point out, “…the extensive feathering of this specimen, particularly the attachment of long pennaceous [flight] feathers to the pes [foot], sheds new light on the early evolution of feathers and demonstrates the complex distribution of skeletal and integumentary [skin covering] features close to the dinosaur–bird transition.” The fossil was described by a Chinese team led by Hu Dongyu of the Paleontological Institute, Shenyang Normal University, China. Read the Nature article: http://www.nature.com/nature/journal/v461/n7264/pdf/nature08322.pdf

The Debate Over Bird Origins
Archaeopteryx may be the earliest known bird but it tells us little about the evolution of bird flight. Until the discovery of Anchiornis, there has been very little fossil evidence of bird-like theropods such as troodontids and dromaeosaurids that lived prior to Archaeopteryx and not much is known about dinosaurian adaptations leading to the first bird. Two main hypotheses have been offered for the beginnings of bird flight. One hypothesis assumes that bird flight began as a trees-down phenomenon, probably with creatures that could glide from a tree to the ground before they evolved powered flight. The other hypothesis assumes a ground-up origin, where small running dinosaurs gradually adapted their leaping and maneuvering into flapping flight.
The “trees down” hypothesis is attractive because it assumes that gliding was possible in some coelurosaurs before they developed powered flight. One can easily imagine a feathered dinosaur (early bird) gliding down from a tree branch. It simply makes sense. As those coelurosaurs became more skilled at gliding, turning their bodies and feathered forelimbs to steer themselves and control their fall, they evolved the anatomical adaptations that resulted in powered flight over many generations. A requirement of the trees-down hypothesis is that it requires that some small dinosaurs were already climbing trees. Before the discovery of Anchiornis, evidence for theropods that lived prior to Archaeopteryx and may have had claws well-adapted for climbing trees has been slim, but includes two recent specimens from Inner Mongolia that may be from sediments of Middle Jurassic age. One of these, Pedopenna (possibly Middle Jurassic, Mongolia) might be the first record of a non-avian feathered dinosaur that lived before the time of Archaeopteryx. The other is a tiny non-avian arboreal dinosaur named Epidendrosaurus, which places some theropod dinosaurs in trees before the evolution of bird flight.
There is growing evidence for the “trees-down” hypothesis of bird evolution. In addition to the recent discovery of the arboreal theropod Epidendrosaurus, the anatomy of the Early Cretaceous dromaeosaur Microraptor strongly suggests arboreal habits and locomotion by gliding. It may have had a tree-based lifestyle similar to flying squirrels today. These kinds of specimens strongly suggest that birds evolved from the "trees down,” arboreal, gliding, non-avian theropods.

Trees-Down or Ground Up—The Debate over Anchiornis
Where does Anchiornis fit into the picture of bird origins? While this newly described theropod provides spectacular evidence for a small feathered dinosaur that existed prior to Archaeopteryx, but did it live on the ground or climb through trees?
The authors of the paper on Anchiornis suggest that the long legs of Anchiornis made it a ground-dwelling creature but carefully couch their words so as not to exclude Anchiornis from the general trees-down or ground-up debate. Indeed, other paleontologists who are beginning to chime in on the debate have found ways to interpret this small dinosaur both ways. One side of the argument is that the feathered feet would have made it difficult for Anchiornis to walk or run on the ground, therefore making it a tree dweller.
One thing is sure, the discovery of four-winged theropods from the time before and after Archaeopteryx show that this condition was an important aspect in the transition of small dinosaurs to birds. While Archaeopteryx is generally considered to dead-end genus in the evolution of birds, the abundance of specimens of other non-avian, feathered dinosaurs from Asia are beginning to fill many gaps in the evolutionary story of birds. It also suggests that the debate over a trees-down or ground-up origin of birds is possibly more complex than we can now imagine. Ultimately, such a debate is meaningless. Why try to subsume a remarkable specimen such as Anchiornis into one argument or the other, an approach that surely only blinds the proponent to other possibilities being revealed with each new piece of the dinosaur-bird puzzle?
Like most startling fossil specimens, these will not only tell us more about the evolution of dinosaurs and birds but raise even more questions about what came before and after.

illustrations credits:
Raptorex, AP Photo/Science, Todd Marshall
Anchiornis, Zhao Chuang and Xing Lida, Nature

Extreme Mammals

Sun, 14 Jun 2009 13:52:31 -0400

New Exhibit Opens at the American Museum of Natural History

by Thom Holmes

On May 16, the American Museum of Natural History (AMNH) in New York opened the doors to its latest, temporary exhibit Extreme Mammals The exhibit takes a look at mammalian evolutionary milestones and oddities spanning extinct creatures to living species that still swim, walk, run, fly, and glide among us. Prehistoria attended a blogger’s preview of the exhibit and we highly recommend it to any visitor passing through the city between now and January 3, 2010 when it closes.
In what was at first an unfortunate coincidence in timing, the opening of Extreme Mammals was overshadowed only two days later by the announcement of the discovery of Darwinius masillae (nicknamed Ida, pronounced “EEE-dah”), an event also staged by the AMNH. Darwinus is, of course, the fantastic fossil from Messel, Germany representing a transitional form of primate dating from 47 million years ago. Interest in Ida was no doubt fueled by a public relations campaign that dubbed the fossil as a “missing link” in human evolution. But the publicity blitz didn’t end there. The Darwinus announcement was accompanied by a History Channel documentary, The Link and also the simultaneous publication of a book, The Link: Uncovering Our Earliest Ancestor. The use of the term “missing link”—which does not appear even once in the scientific paper describing the fossil—must have annoyed the scientists involved because they spent most of the time in their press interviews backtracking and qualifying what was meant by that term. Anyone interested in the straight poop about the fossil should check out the scientific paper published for free on the PLoS ONE website: Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology.
In the end, however, the creators of Extreme Mammals benefited from the announcement of Darwinus by adding a complete cast of the specimen to its exhibit. A helpful description of the fossil and its importance can be found on the home page of the Extreme Mammals website.
Getting back to Extreme Mammals, the exhibit comprises an ingenious set of displays explaining evidence behind evolution but at a level of comprehension suited to kids and parents alike. The entrance to the exhibit is literally overshadowed by a life-size replica of Indricotherium (actually, a medium-sized female according to museum scientist Will Harcourt-Smith). Visitors walk between the legs of Indricotherium to enter the exhibit. Although not quite as large as the wire-frame outline of the specimen found in the museum’s hall of extinct mammals, it’s definitely a thrill to see this extraordinary life-size replica. Be aware that some kids may need a helping hand entering the exhibit because the beast is very real in appearance and may give them the jitters.

Once inside the exhibit there is a wealth of approachable and often interactive displays detailing the essence of mammaldom and its most unusual examples of evolutionary trends. Special attention is given to heads (e.g. the convergence of saber-teeth in North American cats and South American marsupials, body types, living in extreme climates, and mass extinctions that either harmed or helped the spread of mammals. The evolution of the whale, from a land-roving mammal and back to the sea, is a particular highlight of a section devoted to mammals in motion. The life-size model of Ambulocetus, a terrestrial ancestor of the whale, is much smaller than I expected.
AMNH paleontologist Will Harcourt-Smith and Ambulocetus (photo: Anne Benkovitz)
The exhibit is not without a live attraction. In this case it comes in the form of several sugar gliders, a small, gliding nocturnal mammal that is native to New Guinea. These individuals, by the way, were captive-bred in the United States and gently acclimated to life in the exhibit by using an artificially controlled pattern of day and night lighting.
The exhibit space is not huge by any means, but generous enough to occupy a family for an hour or two. I’ve included a floor plan for the exhibit from the AMNH to give you a preview of the layout and sequence of displays.
Here’s hoping that you can make the trip to see Extreme Mammals and the other wonders of the AMNH.

Notable Dinosaur Research of 2008

Sun, 5 Apr 2009 16:52:14 -0400

The First Annual Prehistoria Survey of Dinosaur Paleontologists

In our January edition of Prehistoria we noted that 2008 was another productive year for dinosaur research by compiling a list of 718 academic references to papers about dinosaurs, Mesozoic ecosystems, and related topics. This led us to wonder about the impact of these discoveries on continuing research and field work. Who is there better to answer this question than paleontologists themselves?
In January and February of this year, Prehistoria conducted its first annual poll of dinosaur scientists regarding notable dinosaur research and discoveries of 2008. Nearly 200 paleontologists from around the world were invited to participate. Each was asked to nominate up to three discoveries or research items that were published in peer-reviewed scientific journals during 2008. In each case, we asked respondents to explains why a particular discovery is important to the discipline of dinosaur paleontology. The results are fascinating and speak both to the spectacular nature of some field discoveries as well as the quieter, but equally significant results of laboratory research.
Please join us in reviewing some of the most notable discoveries in the field of dinosaurs for the year 2008. We hope to make this poll an annual event.

The Findings

Austroraptor cabazai—description of a large and bizarre South American Dromaeosaur
Lead author: Fernando Novas
Publication: Novas, F. E., D. Pol, J. I. Canale, J. D. Porfiri, and J. O. Calvo. 2008c. A bizarre Cretaceous theropod dinosaur from Patagonia and the evolution of Gondwanan dromaeosaurids. Proceedings of the Royal Society B: Biological Sciences. doi: 10.1098/rspb.2008.1554

With its large size, reduced arms, elongate snout, and carnivorous teeth lacking serrations, this dromaeosaur from South America came as a surprise to many and showed that raptors from the southern hemisphere were from a more distantly related clade than those in the north.
“This new animals helps establish that the dromaeosaurs from the southern hemisphere form a distinct clade, suggesting a split from more widely distributed dromaeosaurs in Jurassic. Also long skull, with small teeth, and short forelimbs represents a completely new morphology within the dromaeosauridae” (James Kirkland, Utah Geological Survey).
“This discovery pushed the size and diversity of dromaeosaurs into hitherto uncharted territory” (Andrew A. Farke, Raymond M. Alf Museum of Paleontology).

Evidence that dinosaurs probably didn't actually have functional cranial kinesis
Lead author: Casey Holliday
Holliday, C. M., and L. M. Witmer. 2008. Cranial kinesis in dinosaurs: intracranial joints, protractor muscles, and their significance for cranial evolution and function in diapsids. Journal of Vertebrate Paleontology 28:1073-1088. doi: 10.1671/0272-4634-28.4.1073

Cranial kinesis in vertebrates is found most commonly in birds and reptiles. Nearly all birds utilize some form of cranial kinesis which is defined as the ability to move the upper bill or some part of it in relation to the braincase. Cranial kinesis provides for the flexibility of bony elements in three dimensions, while the jaw muscles and ligaments remained intact.[1] There has been an assumption for many years that the skulls of some dinosaurs were capable of cranial kinesis. This research by Holliday and Witmer assessed this assumption by analyzing modern animals with cranial kinesis. As Andrew A. Farke remarked, “The finding that dinosaurs probably were not capable of kinesis in the sense of birds or reptiles requires a major rethinking of their cranial functional morphology.”

Some Species of Male Dinosaurs Brooded Eggs
Lead author: David J. Varricchio
Varricchio, D. J., J. R. Moore, G. M. Erickson, M. A. Norell, F. D. Jackson, and J. J. Borkowski. 2008b. Avian paternal care had dinosaur origin. Science 322:1826-1828. doi: 10.1126/science.1163245
In at least some dinosaurs, the males brooded the eggs. The research also suggests that basal maniraptorans practiced paternal parental care of their young.
“Suggests that the ratite pattern (male brooding) is inherited from primitive ancestors, and not just a derived condition among ratites” (Thomas R. Holtz, Jr., Dept. of Geology, Univ. of Maryland).

Epidexipteryx hui—aa new avialan dinosaur with caudal feathers
Lead author: Fucheng Zhang
Zhang, F., Z. Zhou, X. Xu, X. Wang, and C. Sullivan. 2008c. A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers. Nature 455:1105-1108. doi: 10.1038/nature07447
This nearly complete skeleton of a small theropod with elongate, caudal feathers provided additional evidence that basal avialans were not all flyers. The feathers on this dinosaur were mostly likely used for display or possibly as part of an anatomical scheme for insulation.

More dinosaur growth patterns
Lead author: A.H. Lee
Lee, A. H., and S. Werning. 2008. Sexual maturity in growing dinosaurs does not fit reptilian growth models. Proceedings of the National Academy of Sciences 105:582-587. doi: 10.1073/pnas.0708903105
There is always room for more evidence and statistics related to dinosaur growth patterns. This important research caught the eye of many dinosaur scientists because it “filled in some gaps (primitive iguanodontians, allosaurs) on dinosaurian growth curves” (Holtz). The research also revealed that some dinosaurs bred before reaching full skeletal maturity, “an aspect of dinosaur growth and biology that makes sense of a lot of other observations, e.g. fast growth rates” (Adam Yates, University of Witwatersrand).

Sense of Smell in Theropods
Lead author: Darla K. Zelenitsky
Zelenitsky, D. K., F. Therrien, and Y. Kobayashi. 2008b. Olfactory acuity in theropods: palaeobiological and evolutionary implications. Proceedings of the Royal Society of London B. doi: 10.1098/rspb.2008.1075
How well did theropods smell? This study discovered differences in degree of development of olfaction among theropods. The findings have implications for the use of smell in predatory behavior and the relationship of olfaction to territory size. The findings help to quantify the differences in brainpower of different kinds of theropods with implications for their individual predation strategies.

Futalognkosaurus dukei, a Titanosaurian Sauropod from the Upper Cretaceous of Patagonia
Lead author: Jorge Calvo
Calvo, J. O., B. J. González-Riga, and J. D. Porfiri. 2008a. A new titanosaur sauropod from the Late Cretaceous of Neuquén, Patagonia, Argentina. Arquivos do Museu Nacional, Rio de Janeiro 65:485-504.
The discovery of a large titanosaur, the most complete yet recovered in this size range. The specimen provides revealing “anatomical information about this dinosaurian clade” that has not been so well preserved in other specimens (Fernando E. Novas, Museo Argentino de Ciencias Naturales, Buenos Aires, Argentina).
Illustration: Calvo

Looking Forward

Another important discovery that caught the eye of many dinosaur paleontologists was revealed in the popular Chinese media in December 2008. Although we still await the scientific publication of the discovery, it is well worth mentioning as part of this poll.

Chinese Centrosaurine Skul
Xu Xing, Institute of Vertebrate Paleontology and Paleoanthropology
Not published in a scientific journal yet, but reported in December. Click here for the news story.
The Chinese Institute of Vertebrate Paleontology and Paleoanthropology announced the discovery of "world's largest" dinosaur fossil field near Shandong. Among the finds is a reportedly 2m-long skull of a large ceratopsian, the first such discovery outside of North America. Adam Yates called this discovery “a rather dramatic and somewhat unexpected range extension for a clade that had always thought to be purely North American.”

The Shandong fossil site and an unidentified dinosaur specimen.

1. Sander W. S. Gussekloo, M. George Vosselman, and Ron G. Bout. “Three-Dimensional Kinematics of Skeletal Elements In Avian Prokinetic and Rhynchokinetic Skulls Determined by Roentgen Stereophotogrammetry.” The Journal of Experimental Biology 204, 1735–1744 (2001)

The Year in Dinosaurs--and Other Extinct Creatures

Wed, 7 Jan 2009 18:09:53 -0500

2008 was another banner year for paleontological research on dinosaurs, fossil hominins, and other extinct creatures. The purpose of this edition of the Prehistoria blog is to provide a comprehensive--but selective--bibliography of paleontological research published in scholarly journals in 2008. The listings are provided as two bibliographic collections. The first was compiled by paleontologist Jerry Harris of Dixie State College and includes 718 references to papers about dinosaurs, Mesozoic ecosystems, and related topics. The second was compiled by myself and includes 160 references in the field of biological anthropology, primate, and human evolution.

Having collected these materials in one location for quick access will hopefully be of service to other researchers and workers in the field. Enjoy and here’s wishing you a successful 2009!

Access the online dinosaur reference list by clicking here. [download PDF version here]
Access the biological anthropology list by clicking here. [download PDF version here]

The Evolving Images of Sauropod Dinosaurs

Thu, 2 Oct 2008 23:52:33 -0400

The scientific study of sauropod dinosaurs has been replete with its own evolution in the depiction of these most giant of all land animals. Cetiosaurus was the first named sauropod in 1841, but when Sir Richard Owen first classified it, he had little to go by except five vertebrae, some scattered pieces of limb, and a chunk of rib. He thought it was a giant crocodile, so attempts at illustrating it as a dinosaur did not emerge until much later when better specimens were available.
The history of illustrating sauropods closely parallels the various debates surrounding their lifestyle. Were sauropods primarily aquatic? Could they lift their heads high and bend their necks with great flexibility? Did they have a robust terrestrial lifestyle, or were they sluggish, sauntering creatures?
The dinosaur bone rush in America during the 1870s uncovered the first remarkably complete specimens of sauropods and inspired the first attempts to create scientifically accurate illustrations of them. As mentioned, Cope was arguably the first paleontologist to reconstruct a dinosaur skeleton on paper, and he did so with great gusto. The skeletal restoration of Camarasaurus that he created in 1877 depicted a creature with a sturdy, upright posture and a robust vertebral column that paralleled the ground from head to tail.
This view was remarkably modern by today’s standards; but only a year later, in 1878, Cope’s view of sauropods had begun to change. On a brown paper bag, Cope sketched a scene of living sauropods that spent their time almost fully submerged in the water and fed on bottom-dwelling plants.

Almost 20 years later, in 1897, the first great dinosaur artist Charles Knight (1874–1953) transformed Cope’s sketch of submerged sauropods into a drawing that was reproduced in The Century, a popular magazine of the day.

In 1883, Othniel Marsh completed his influential drawing of a complete skeleton of Brontosaurus, now known as Apatosaurus. Like Cope, Marsh thought that sauropods were sluggish swamp dwellers, and his beautiful illustration featured a droopy neck and a dragging tail.
Around the turn of the Twentieth Century, the debate over sauropod lifestyles began to heat up. Artists and scientists alike began to wonder if these creatures were better suited for life on land or in the water. Working with paleontologist Henry Fairfield Osborn (1857-1935) of the American Museum of Natural History, Knight began to hedge his bets in his portrayals of Apatosaurus. Rather than depicting sauropods as either aquatic or terrestrial, Knight showed them as both in the same paintings, one individual firmly entrenched in the water and others standing about on dry land. His depiction of 1898 is shown here. Knight is, to this day, the most often imitated artist of dinosaurs, and his images that combined aquatic and terrestrial sauropods became the accepted approach to illustrating sauropods for 80 years.

Over time, images of sauropods have undergone some extremely strange transformations. In 1906, believing that sauropods may have had a sprawling posture, model makers Otto Falkenbach (1878-1952) and Charles Falkenbach (1878-1952) of the American Museum of Natural History created a scale model of a creeping brontosaur.

This image was questioned in 1908 by American paleontologist, Oliver P. Hay (1846-1930), and German, Gustav Tornier (1859-1938). Each man took potshots at the Falkenbach reconstruction. Both argued for an even more extreme sprawling posture that would have required the dinosaurs to drag their bellies.

Though this view was renounced by other paleontologists, the view of sauropods as lazy, partly-aquatic creatures remained in vogue for many years. This popular view of water-loving sauropods was reinforced by such world-famous paintings as the one by Rudolf Zallinger (1919-1995) that appeared on the cover of Life magazine in 1953.

The evolution of sauropod illustration began to come full circle in 1986, when paleontologist Robert Bakker (b. 1945) published his enthusiastic arguments for fully terrestrial, active sauropods. Bakker’s extreme sauropods inspired today’s generation of artists. In many ways, however, the current depiction of Apatosaurus as an active land-dweller owes much to Cope’s first spectacular illustration of 1877.

This blog is adapted from Time of the Giants by Thom Holmes (The Prehistoric Earth, volume 5, 2008, Chelsea House).