Article from the Seminars on Science course:
The Link Between Dinosaurs and Birds: Evolution and Classification

Print Version
Therapod Fossil Hunt Dispatch
Mark Meets "Dave"

 
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The first feathered dinosaur fossil found in China—Sinosauropteryx. The feathers can be seen in the dark line running along the specimen's back.
The first feathered dinosaur fossil found in China—Sinosauropteryx. The feathers can be seen in the dark line running along the specimen's back. ©AMNH, Mick Ellison
 
Prospecting for fossils at one of the Liaoning quarries.
Prospecting for fossils at one of the Liaoning quarries. ©AMNH, Mick Ellison
   
The excellent environmental conditions at Liaoning preserved the color pattern, visible as light and dark bands, on this moth's wing.
The excellent environmental conditions at Liaoning preserved the color pattern, visible as light and dark bands, on this moth's wing. ©AMNH, Mick Ellison
   
Dr. Ji and Dr. Norell standing in a Liaoning quarry.
Dr. Ji and Dr. Norell standing in a Liaoning quarry. ©AMNH, Mick Ellison
   
Caudipteryx—a feathered dinosaur specimen that Dr. Norell and Dr. Ji collaborated on.
Caudipteryx—a feathered dinosaur specimen that Dr. Norell and Dr. Ji collaborated on. ©AMNH, Mick Ellison
   
This close-up of a Confuciusornis specimen shows feet that have been carved into the matrix. These carved feet make the specimen an obvious forgery.
This close-up of a Confuciusornis specimen shows feet that have been carved into the matrix. These carved feet make the specimen an obvious forgery. ©AMNH, Mick Ellison
   
Dave is one specimen split between two slabs.
Dave is one specimen split between two slabs. ©AMNH, Mick Ellison
   
This close-up of the rock layers from the Liaoning quarry shows the fine bedding that allows very flat slabs, like the two slabs that contain Dave, to be split off.
This close-up of the rock layers from the Liaoning quarry shows the fine bedding that allows very flat slabs, like the two slabs that contain Dave, to be split off. ©AMNH, Mick Ellison
   
Mick in the basement of the Geological Museum of China observing and photographing one of Dave's slabs.
Mick in the basement of the Geological Museum of China observing and photographing one of Dave's slabs. ©AMNH, Mark Norell
 
A jumble of Protarchaeopteryx fossil bones paired with a jumble of seemingly related fossil feathers.
A jumble of Protarchaeopteryx fossil bones paired with a jumble of seemingly related fossil feathers. ©AMNH, Mick Ellison
 
This hip socket, one character used to determine whether a specimen is a dinosaur, was destroyed when Dave was prepared.
This hip socket, one character used to determine whether a specimen is a dinosaur, was destroyed when Dave was prepared. Not only were many of the bones split in two, but part of the hip was lost and the empty space was filled with putty (center). ©AMNH, Mick Ellison
 
In this photograph of Dave's tail, a few of the rod-like, bony vertebral extensions can be seen as dark lines that flank the vertebrae.
In this photograph of Dave's tail, a few of the rod-like, bony vertebral extensions can be seen as dark lines that flank the vertebrae. ©AMNH, Mick Ellison
   
Dave's sickle claw, highlighted in this image, is more than twice as long as his other claws. The fish to the right of Dave's foot is on a different layer and therefore was not buried at the same time as Dave.
Dave's sickle claw, highlighted in this image, is more than twice as long as his other claws. The fish to the right of Dave's foot is on a different layer and therefore was not buried at the same time as Dave. ©AMNH, Mick Ellison
   
Dave's wrist bone, highlighted in the enlarged image, is crescent-shaped. His short first finger is visible at left.
Dave's wrist bone, highlighted in the enlarged image, is crescent-shaped. His short first finger is visible at left. ©AMNH, Mick Ellison
   
Dave's wishbone is highlighted in this image.
Dave's wishbone is highlighted in this image. ©AMNH, Mick Ellison
   
Single fibers on Dave's skull.
Single fibers on Dave's skull. ©AMNH, Mick Ellison
   
Sprays of fibers emanate from Dave's shoulders.
Sprays of fibers emanate from Dave's shoulders. ©AMNH, Mick Ellison
   
The faint but significant herringbone pattern of true feathers can be seen in the sprays of fibers that emanate from Dave's arms.
The faint but significant herringbone pattern of true feathers can be seen in the sprays of fibers that emanate from Dave's arms. ©AMNH, Mick Ellison
   
Since Dave is a dromaeosaur, his branch in this theropod cladogram is closest to Velociraptor, another dromaeosaur.
Since Dave is a dromaeosaur, his branch in this theropod cladogram is closest to Velociraptor, another dromaeosaur. Keep in mind that the proximity of Dave's branch to the bird clade in this diagram does not suggest a closer evolutionary relation to birds than Velociraptor has -- the cladogram would have exactly the same meaning if Dave and Velociraptor were switched. ©AMNH
 
Mick's illustration of what Dave might have looked like if alive.
Mick's illustration of what Dave might have looked like if alive. ©AMNH, Mick Ellison
   
A CAT scan image of a Velociraptor skull. Scientists interested in the 3-D shape of a bone can view a reconstruction like this without handling the specimen.
A CAT scan image of a Velociraptor skull. Scientists interested in the 3-D shape of a bone can view a reconstruction like this without handling the specimen, but the main purpose of CAT scanning is to reveal the internal structures of specimens without damaging them. ©AMNH, Mark Norell

It All Started With Feathers
October 1996
New York City, NY

Throughout the world, 560 million tons of corn are produced each year. Almost seven percent of the crop, over 39 million tons, never makes it to the market. This creates a significant financial burden on farmers. In the U.S. and Canada alone, corn damage and control costs are in excess of one billion dollars each year.

In 1996, at the annual conference of the Society of Vertebrate Paleontology, Dr. Mark Norell was shown a three by five inch photograph taken by one of his close colleagues from the Royal Tyrell Museum in Canada. The picture was of an exquisitely preserved, non-avian dinosaur fossil that had been recently found in China. This bird-like dinosaur specimen, Sinosauropteryx, appeared to have particularly well-preserved impressions of feathers.

Mark was stunned—for decades paleontologists had hoped that a non-avian theropod with feathers would be found. His excitement around the newly found specimen was twofold. First, the fossil is of a non-avian theropod dinosaur considered less closely related to birds, which suggests that feathers were much more widespread among dinosaurs, and less unique to definitive birds, than originally thought. Second, with such well-preserved feathers, paleontologists can finally study the feather microstructure to further clarify the relationship between dinosaurs and birds.

Mark hoped he could arrange a collaboration with the Chinese to examine more feathered specimens to further his own research focused on filling the gaps in the fossil record of dinosaur evolution. More specifically, he wanted to find evidence to develop the link between theropod dinosaurs and birds.

 

A Path Shrouded in Mystery
1960's to the mid 1990's
Liaoning Province, China

Since Mark saw the picture of the first feathered Chinese dinosaur fossil in 1996, eleven more fossils have been found. All of them have come from a handful of quarries in Liaoning Province, about 250 miles from Beijing. Since the 1960s, farmers who live in the area have turned to working in the local quarries as their source of income. They spend their days digging into the rock face and pulling out slabs of rock. Because the rock is layered, just a small tug will break off a layer of rock a few millimeters thick and a few inches wide. The farmers then carefully examine the outside of the rock slab for fossils and, if they find nothing, split the slab into two pieces with a hammer to see if anything precious might be inside.

From the 1960's to the mid 1990's, the farmers typically found 130-million-year-old fossilized dragonflies, wasps, and moths in the quarries. The preservation was excellent and even the patterns on the insects' wings were visible. The farmers also found fossil fish, turtles, frogs, and several different kinds of plants.

The photo of Sinosauropteryx Mark saw was actually found in 1995 when a local farmer pulled out a fossil that no one had seen before—it looked like a dinosaur, but appeared to be covered with feathers. It was soon discovered that a large layer of the quarry was actually filled with these feathered dinosaurs. With intense demand for these rare fossils from paleontologists and museums, the farmers quickly went to work extracting as many as they could. Even today it is primarily local farmers who collect the fossils. Some paleontologists hired by the Geological Museum of China and the Institute of Vertebrate Paleontology and Paleoanthropology prospect for fossils, but the farmers do the job more efficiently.

The path the fossils take once removed from the quarry to get into the hands of scientists is shrouded in some mystery. Every farmer seems to have his own system of extracting fossils from the rock, putting them back together, and transporting them. The fossils pass through many hands along the way before they reach a paleontological institution.

 

International Collaboration
1998
New York City, NY and Beijing, China

In 1998, Mark began to work with Dr. Ji Qiang, a respected Chinese paleontologist and former director of the Geological Museum of China. Dr. Ji (in Chinese, a person's first name comes after their last name) had worked with other international paleontological institutions and was known to be a strong proponent of fossil sharing among international teams of paleontologists. Such collaborations enable colleagues to discuss specimens, complete analyses, and promote collective publication. This would be the first time, however, that Dr. Ji would work with scientists at the American Museum of Natural History.

Over the next few years, as their professional relationship developed, Mark saw more and more impressive specimens. He flew to China periodically to see these new specimens and spend time with Dr. Ji identifying, describing, and eventually publishing studies on them. Their publications, which include articles on Confuciusornis, Caudipteryx, and Protoarchaeopteryx in well-respected journals like Nature and the American Museum of Natural History's Bulletin, have led to great advances in our understanding of the origin of birds.

But if Mark thought that these early fossils he studied with Dr. Ji were incredible, which he did, he had a surprise waiting for him.

 

The Short Email
May 2000
New York City, NY

In May of 2000, Mark received a short email from Dr. Ji that alluded to another big find: "Small dino with great preservation. Come ASAP." Within a few weeks, one member of the AMNH/Chinese collaboration team, Mick Ellison, made his way to China. Mick is a photographer and illustrator at the Museum who has worked closely with Mark for over ten years, documenting hundreds of specimens. Mark would follow him a few days later.

But even with the promise of an important specimen, Mark never assumes a big find until he sees it for himself. There has been a recent rise in the number of fossil forgeries, as well as mistaken identifications and descriptions of specimens. A famous example of a misidentification is when National Geographic published an article about a "new" specimen a few years ago, called Archaeoraptor. This specimen seemed to bolster the link between non-avian theropod dinosaurs and birds because it appeared to have a head and body like a bird and the tail of a more primitive non-avian theropod. After careful observations and analyses of the specimen, however, scientists finally concluded that the fossil was a composite of two separate specimens.

 

A Coat of Feathers
June 5-8, 2000
Beijing, China

After a 28-hour-long flight from New York to Beijing, Mick finally touched down in China. He wearily made it to his hotel room and fell asleep, only to be awoken four hours later by someone pounding on his hotel room door and frantically ringing the doorbell. It was a very excited Dr. Ji. Mick quickly headed over to the Geological Museum of China with him. Upon arrival, they immediately descended into the basement of the Museum where the vertebrate paleontology collections are held.

In the almost complete darkness, with dull green florescent lights flickering above, a few museum technicians brought out two rock slabs and rested them against the wall. Mick recalls that he looked at the specimen and, "My jaw just dropped. It's the most beautiful fossil I'd ever seen. While it is usually difficult to see the feathers on other fossils, there was nothing difficult to see with this fossil. You can clearly see the animal's whole body covering … the feathers are just erupting from its body."

A few days later, when Mark arrived, he was similarly stunned. "It was the most complete and best articulated specimen I had ever seen … the preservation was amazing." This specimen was clearly the best one yet discovered to exhibit such a clear, feathered body covering. As paleontologists often do, Mark and Mick nicknamed the specimen, in this case "Dave," after an old Cheech and Chong routine until they determined what species he was.

As Mark and Mick scanned the specimen from feathered head to tail, they noticed Dave was on two mirror slabs of rock, each a few millimeters thick, and each slab was a glued composite of about 30 smaller pieces of rock. This was because the person who pulled the slab of rock from the quarry did not pull out the entire specimen all at once. He first pulled out a piece of rock that had Dave's foot or arm or other part of his skeleton. It is also likely that the person who found Dave did not initially see Dave's skeleton. He would have scanned the outside of the rock, found nothing of interest, and then split it with a hammer to see if anything interesting was inside. The slab would have broken along its naturally weak point. Since bone is more brittle than rock, the slab would have broken along the bone. The farmer or prospector would have then noticed Dave's skeleton, marked the rock with a marker or lipstick (which explains the black and red marks on the matrix) for future reference, placed the rock aside, and then hunted in the quarry for the rest of the skeleton. In addition, sediments that collected on top of Dave over millions of years crushed him with their weight, making him look flatter than a pancake.

Over three feet long from head to tail, Dave is slightly larger than a common barnyard chicken and is preserved in profile with his long arms folded inward and feet slightly apart and pointed outward. For an experienced paleontologist, a quick glance at him is all that is needed to notice the small tufts of feathers on his head, forelimbs and legs, and the plumes on his tail.

 

An Initial Hypothesis
June 8, 2000 9:00am
Basement of the Geological Museum of China, Beijing, China

Mark was pretty confident upon initial study that Dave was a dromaeosaur. Years of field and lab experience with dinosaur fossils allowed him to look at a few key characters on the specimen, such as its tail, toe, wrist, and wishbone, and make this conclusion. He also saw, even without a microscope, that Dave's body covering was particularly well preserved. But Mark wasn't able to confirm that Dave was a dromaeosaur until a more complete analysis was done.

Mark was excited. The initially observed characters identified this specimen as a dinosaur, but the specimen was also covered with feathers. Some scientists have argued that other feathered dinosaur specimens were birds (and not dinosaurs), and even suggested that the specimens did not have real feathers. If Dave was authentic, and Mark's more formal analysis agreed with his preliminary scan of the specimen, Mark believed the evidence of a link between dinosaurs and birds might be irrefutable.

Eager to get started on the more formal analysis, Mark first had to answer the most basic question -- is the specimen authentic?

 

Is it Authentic? The Analysis Begins
June 8, 2000 (A few minutes later…)
Basement of the Geological Museum of China, Beijing, China

Without further ado, Mark and Mick began their work. For fourteen hours a day, for a whole week, they toiled in the basement of the Geological Museum of China. While Mark identified characters on one slab, Mick photographed the other slab to document the specimen. They were on an emotional rollercoaster, one minute amazed with such a remarkable specimen, and the next minute disappointed that it was split in two.

In order to determine the specimen's authenticity, Mark needed to look at it closely. Did anything look wrong? Were the two slabs mirror images? Did all of the specimen's characters match up? After a close examination, without even using a microscope, Mark determined that Dave was an authentic dinosaur specimen because everything matched up.

Mark then looked more closely at Dave's feathers to determine their authenticity. He put Dave under a standard dissecting microscope and looked for stains of feathers. As feathers fossilize, they stain the rock, without looking carved or painted. Nothing unusual turned up, which was a good sign. Then Mark did one last check -- he thought he might be able to see the feathers' micro fibers. When Mark saw the subtle structures of the feathers, which are impossible to recreate, he knew he had an authentic and priceless feathered specimen on his hands.

Then the real fun began -- the systematic study of the characteristics that would tell Mark what species Dave belongs to. Mark had a hunch that it might be a new taxon (a new group of organisms), but had to run through an extensive checklist before he would know for sure.

 

The Examination and Description Marathon
June 8, 2000 12:00 Noon
Basement of the Geological Museum of China, Beijing, China

In the basement of the Geological Museum of China, the two slabs were placed on makeshift tables. Mark began with one slab, a dissecting microscope poised over the specimen and a standard ruler close by. His laptop was beside him to record the data.
Using the cladistic method for classification, Mark picked up a six-page document that lists the 205 characters that describe advanced theropods to guide him through the examination and description of Dave. He began with the first one:

"Vaned feathers on forelimb symmetric (0) or asymmetric (1). The barbs (branches) on opposite sides of the rachis (central feather shaft) differ in length; in extant birds, the barbs on the leading edge of flight feathers are shorter than those on the trailing edge."

Mark had to determine whether there were vaned feathers on Dave's forelimbs, and if so, whether the feathers were symmetric or asymmetric (similar to flight feathers on modern birds). As Mark peered through the microscope, he noticed that Dave's feathers were symmetric, and typed a "0" into the computer. Thus began an examination and description marathon. He had to examine each character on the specimen and record the appropriate number, or a "?" if the character was unclear on the specimen.

Since Dave was split down the middle, the matrix did not cover the internal structure of Dave's bones, and so Mark didn't need to prepare the specimen in order to look at its characters. He did use a ruler, at times, to measure the proportions of specific characters. His patience paid off when his analysis of Dave's characters was finally complete.

 

A Feathered What?
June 8-12, 2000
Basement of the Geological Museum of China, Beijing, China

Mark's methodical examination and description over four days confirmed that Dave is a non-avian theropod dinosaur. In the cladistic method of classification, organisms that share characteristics are grouped together. These groupings can then show the evolutionary history of the organism by illustrating its relatedness to other organisms, identifying a common ancestry for their closest relatives, while describing the characteristics unique to their group. More specifically, Mark was confident that five of the characteristics he observed conclusively identified the specimen as a dromaeosaur:

  • rigid tail
  • enlarged sickle-like claw on the second toe
  • crescent-shaped wrist bone
  • proportions of the fingers
  • wishbone

Rigid Tail
Dave's tail is comprised of vertebrae with small stiff bony rods on the side that extend from each vertebra across sometimes six, seven, eight, or nine adjacent tail vertebrae. This is typical for dromaeosaurs but not usually found in other non-avian theropods. In other dinosaurs, small stiff rods only connect one tail vertebra to the next.

Sickle-like Toe Claw
The second toe on Dave's foot is easily identified because it is two to three times larger than the other claws on dromaeosaurs. This pronounced second toe is also typical of dromaeosaurs in comparison with other non-avian theropods. In addition, the claw has a small piece of bone that makes it more mobile than the other claws. Dave's entire claw is not visible—only the tip shows because the claw lies underneath most of the other toes.

Crescent-shaped Wrist Bone and Length of Fingers
Dave has a crescent-shaped bone in the wrist, called a semi-lunate carpal. In addition, Dave's first finger is by far the shortest of his three fingers. These features are not unique to dromaeosaurs; they are present in other dinosaurs like oviraptorids and troodontids, and more importantly for Mark's research, in modern birds.

Wishbone
Finally, Dave has a wishbone, a character that is present in both non-avian theropods, including dromaeosaurs, and birds.

Once Mark entered values for all 205 characters, he ran a statistical software program which compares the characters found in Dave against a representative sample of advanced theropods already described and in his database. The software produced a few possible cladograms to explain where Dave might fall in relation to these other theropods. The resulting cladograms clearly show that Dave is a non-avian theropod and falls into the group Dromaeosauridae, consistent with Mark's initial prediction. Because some of Dave's characters are destroyed, there is some incomplete information. This prevents the software from producing, with confidence, only one cladogram.

Mark then shifted his focus to document Dave's body covering to demonstrate that Dave is truly a feathered dromaeosaur.

 

Feathers, Feathers, Feathers
June 13-16, 2000
Basement of the Geological Museum of China, Beijing, China

Mark observed that Dave's feathers cover his entire skeleton and are beautifully differentiated into three types: single fibers, long "sprays" of fibers, and fibers oriented around a central axis in a herringbone pattern. Each type is located on different parts of his skeleton.

Single Fibers
Single fibers run along the midline of Dave's skull and down his neck. These feathers are loosely organized and unbranched. At first glance, they might look more like a crest or Mohawk, but remember you can only see Dave in cross-section. The feathers are also preserved between several layers of sediments, which led Mark to conclude that the feathers would have covered Dave's entire head and neck.

Sprays of Fibers
On Dave's shoulders and torso, long, thin sprays of fibers are organized around a central axis. These feathers are particularly dense around the shoulders. In addition, there are shorter sprays on the tail that resemble plumaceous feathers (like the large, fluffy, and curved ostrich feathers).

Herringbone Sprays of Fibers
Of all of Dave's feathers, the ones on his arms most strongly resemble modern bird feathers. These structures are complex, bunched, and tightly organized. In particular, they have a tight herringbone pattern around a central feather shaft (rachis) very similar to modern bird feather structure. These structures also originate from a single point and form a radiating spray.

As Mark concluded, "This animal must have been really fluffy. If you would have seen it living, it would have looked like a Persian cat with the amount of fuzz and fluff on it." But he also cautions that some of the feathers on Dave might not be feathers as we think of feathers on modern birds. The fossil record can only tell us so much about the material composition of the feathers. Dave's position on a cladogram places him near the point at which birds split from non-avian theropods, so his feathers are most likely not exactly the same as modern feathers.

Nevertheless, it is irrefutable, according to Mark, that the sprays of fibers on the back of Dave's arms are feathers; they have a branched herringbone pattern very similar to modern bird feathers. Although characters can evolve twice in the evolutionary history of a group, paleontologists have only found feathers in non-avian theropods and birds, and Mark argues that the complexity of such a structure as feathers probably did not evolve twice.

The combination of Mark's two conclusions from his analysis—Dave is a dromaeosaur and Dave has a complete, differentiated, and complex body covering—provides the best evidence yet that the origin of feathers is unrelated to the origin of flight in birds. These conclusions are also corroborated with evidence that Dave's feathers are not flight feathers and that his arms are not wings; even if they were, they could not have supported his weight for flight.

 

If Not for Flight, Then What?
A few weeks later.to the present
New York City, NY

In his attempt to clarify the phylogenetic tree of theropod dinosaurs, however, Mark has inevitably cast doubt on the common belief that feathers evolved for the sole purpose of flight.

Dave is the best specimen yet to show that feathers existed long before modern birds and flight. But if feathers predated flight, then Mark points out, "we need to come up with another explanation to account for both the presence of feathers in modern birds, as well as their origin in evolutionary time."

This is another scientist's task for another time, but here Mark proposes two hypotheses based upon some evidence from non-avian theropod physiology and modern bird social interaction. First, a highly active, small predator like Dave would have needed a metabolism that allowed him to engage in a high level of activity over a prolonged period of time in order to chase down prey. A metabolism where the metabolic rate is regulated internally by the animal rather than by the outside environment allows this type of activity, but only if little heat is lost to the environment. Dave's body covering of feathers would have been extremely beneficial for insulation purposes to allow him to retain heat and energy. Thus, Mark hypothesizes that feathers originated not for flight, but as an insulation mechanism.

Mark's second hypothesis is that feathers were useful for courtship and other social interactions. Modern male birds often have colored feathers in order to attract a potential mate, and research concludes that many female birds seem to choose a partner based upon certain physical characteristics that indicate a particularly healthy male, such as a bright feather color or elaborate feather display. Thus, feathers could have evolved for reproduction purposes.

Even though Mark has suggested two plausible hypotheses to explain why feathers predated flight, his research does not focus on which, if not both of these, is more likely. Mark's interest and primary research is in filling the gaps in the fossil record of dinosaur evolution.

 

Dave Takes a Trip to the States
A few weeks later. to the present
Beijing, China and New York City, NY

As Mark conducted his thorough analysis of Dave, he noticed a few differences between Dave's wrist and the wrist of another seemingly closely related Chinese specimen, Sinornithosaurus.

To examine Dave in greater detail, Mark wanted to get Dave back to the States to complete his analysis and to have the specimen CAT scanned. The fossil, however, was the property of the Geological Museum of China and the Chinese government. Mark spent the last two weeks of his stay in China working with Dr. Ji to get approval for the specimen to be loaned to the United States. Mark never thought he would succeed, but just a few weeks later, after he had already returned to the AMNH, Dr. Ji had Dave packed by art movers and shipped to New York in a large crate.

Back at the American Museum of Natural History, Mark began the process of communicating his and Dr. Ji's findings which were published in the April 26, 2001 issue of the journal Nature. Their discovery hit the headlines of major national and international newspapers with much fanfare.

In August 2001, Dave was shipped to Texas to be CAT scanned. This technique takes three-to-ten-millimeter X-rays of a specimen in two dimensions and from different angles. These photographed "slices" of the specimen can be digitally recombined to construct a three-dimensional model of the specimen. With Dave, one of his slabs (both the fossil and the surrounding matrix) was inserted into the CAT scan.

Mark is now involved in the analysis of the CAT scan data, which can be done easily if there is enough difference in the densities of the fossil bone and the matrix. Mark can digitally remove the matrix from these photographs so he can view the subtleties of Dave's wrist bone, which is currently hidden in the matrix. When his research on Dave is complete, the specimen will return to the Geological Museum of China and Mark will undoubtedly look forward to the next email from Dr. Ji. So stay tuned until the next feathered adventure!


©2003 American Museum of Natural History