February 3, 2010
When I was a child, one of my uncles gave me what he said was a real dinosaur bone. The little black object certainly looked like some sort of bone, and I kept it in my little collection of shark teeth and other fossils in my closest. After a while I almost completely forgot about it, but when I took a college course on dinosaurs I remembered the little thing. I took it to my professor to ask what kind of animal it might have come from.
It was not a fossil at all, my professor told me. The “dinosaur bone” was really a concretion, or a small lump of mineral that had formed around some bit of detritus. A broken part of the object made the identification easy. The exposed internal structure was compact, uniform, and smooth. It entirely lacked any sign of internal bone structure that a real dinosaur bone would exhibit.
Paleontologists respond to dozens of similar queries each year. Many people find concretions or vaguely bone-shaped rocks and bring them in to ask what kind of dinosaur the “bones” came from and if the museum would be interested in buying them. Needless to say, most of those people leave a bit disappointed that they have not uncovered the find of the century in their backyard, but these common experiences bring up a simple question: how can you tell fossil bone from stone?
There is no single hard-and-fast rule for distinguishing rock from bone, but there are a few principles that can definitely help you tell the difference. One of the simplest is that you need to know where to look for fossils. If you spot a “dinosaur egg” in the soil while mowing your lawn the chances are pretty good that is is just a rock. Real fossils will be found in particular rock formations which geological maps and even some state-specific booklets can help you identify. Before you grab your pick and shovel, though, you will have to familiarize yourself with the type of land those deposits are on and what the rules are about collecting fossils. If you just walk to a formation and pick out a fossil without filling out the right paperwork and being absolutely certain of where you are, you are probably breaking the law (not to mention the fact that trained paleontologists are much better qualified at properly documenting and excavating fossil sites).
But let’s assume that, regardless of how it was acquired, you have what you think is a piece of fossil bone. Out of its geologic context it is impossible to compare it to the surrounding rock (fossils are often different in color and smoother than rocks from the same deposit), but if there is a break on the specimen you may be able to check its internal structure. A rock or concretion, like the one I showed to my professor, will be solid, and the inside of the rock will look like the outside. Fossil bone, on the other hand, will probably preserve the internal bone structure. In a fossil bone you will be able to see the different canals and webbed structure of the bone, sure signs that the object was of biological origin. You can even try a tongue test. The porous nature of some fossil bones will cause it to slightly stick to your tongue if you lick it, though you might want to have a glass of water handy if you feel compelled to try this.
By following these guidelines it becomes easier to determine whether or not you have really found a fossil bone. It does not take a Ph.D. education; just some attention to detail and common sense.
January 28, 2010
At one point or another, almost every general book about dinosaurs I have ever seen has said the same thing: we cannot know what color dinosaurs were. Scientists have found the skin impressions of some specimens, but as far as we know these traces contain nothing that might tell us what color those dinosaurs were. As described in this week’s issue of the journal Nature, however, scientists have been developing a technique that may allow us to see the colors displayed by some dinosaurs, and it is thanks to their connection with birds.
Last year the journal Biology Letters published the results of a study that identified preserved microstructures related to color in the feather of a fossil bird. The scientists could not say for sure what colors the feather exhibited in life, but they were able to document minute differences in the feather that are seen in living birds, meaning that evidence of color was preserved in the fossil even if it could not be fully understood yet. Now a different team of scientists has published a new study that has accomplished a similar task, but this time for two feathered dinosaurs and one of their bird relatives.
What the scientists behind the Nature study were looking for were melanosomes. These are color-carrying structures found inside pigment cells and are partially responsible for the colors we see in many organisms. The paleontologists found them in abundance in the feathers of the dinosaurs Sinosauropteryx and Sinonithosaurus, as well is in the preserved plumage of Confuciusornis. The structures were not preserved bacteria or some other remnant. Instead they were the preserved vestiges of dinosaur cell structure.
Clearly these animals had color-carrying cells in their feathers, but what color were they? That is a more difficult question to answer. The fossils that were examined contained two types of melanosomes: eumelanosomes and phaeomelanosomes. From the study of living organisms we know that eumelanosomes are associated with dark colors (i.e. black) while phaeomelanosomes are associated with lighter colors (i.e. yellowish to red). They cannot tell us specifically what color the dinosaurs were, but they can help us confirm color patterns and be used create hypotheses. The tail of Sinosauropteryx, for example, contains bands of feathers stuffed with phaeomelanosomes, and so the authors of the new paper suggest that it might have had bands of rich, reddish tail feathers. This hypothesis will require more evidence to confirm, however, especially since scientists are still learning how melanosomes are involved in producing particular colors.
The new research is a step closer to understanding what colors some dinosaurs were, and it is another piece of evidence confirming that the structures preserved around dinosaurs like Sinosauropteryx and Sinornithosaurus really are feathers. The melanosomes are contained entirely inside the feathers, just like in living birds, and there no longer can be any reasonable doubt that these animals were feathered dinosaurs. Even better, this line of inquiry has only just begun, and perhaps in a few years we will be able to tell with greater certainty whether dinosaurs were as colorful as their living relatives.
Zhang, F., Kearns, S., Orr, P., Benton, M., Zhou, Z., Johnson, D., Xu, X., & Wang, X. (2010). Fossilized melanosomes and the colour of Cretaceous dinosaurs and birds Nature DOI: 10.1038/nature08740
January 5, 2010
We don’t usually give much thought to who discovered a fossil. Museums rarely include much more information than species name and the state or country where the remains were found.
The exception, in several museums in England at least, is fossils found by Mary Anning in the early 19th century. And two new books, one biography and one novel, bring her story to life.
Mary was born in 1799 in Lyme Regis, on the southern coast of England. Her father was a cabinetmaker who preferred to hunt for fossils, but neither occupation brought the family much money. When he died in 1810, he left behind a pregnant wife, two children and a large debt. Mary and her brother took to fossil hunting for survival.
Her brother found what he thought was a crocodile head in 1811 and charged Mary with removing it from the rock and searching for the rest of the skeleton. (Mary often gets credit for the discovery, though that is not technically correct.) She eventually dug out the skull and 60 vertebrae, selling them to a private collector for the handsome sum of £23. But it was no common crocodile. It was an Ichthyosaurus, a “fish-lizard,” and the first of many amazing finds.
Mary’s brother would become an upholsterer, leaving fossil hunting to his sister. She would become one of the most prolific fossil hunters of the time, discovering more ichthyosaurs along with long-necked plesiosaurs, a pterodactyl and hundreds, perhaps thousands, of other fossils.
Though she had little formal education, Mary taught herself geology, paleontology, anatomy and scientific illustration. She corresponded with, provided fossils for and sometimes hunted with well-known scientists of the time, such as William Buckland and Richard Owen (who would coin the word “dinosaur” in 1842). Her finds were key to the reconstruction of Earth’s past and the development of the theory of evolution (as well as the development of several scientists’ careers).
But Mary never published a scientific paper of her own—men wrote up her finds. Even if she had written one, it was unlikely that it would have been published because she was female. Mary was never wealthy. Until a friend convinced the British Association for the Advancement of Science to provide her with an annuity of £25 per year, she was always one accident away from total destitution. And though the Geological Society marked her 1847 death from breast cancer a year later in a president’s address (a rare honor), the organization didn’t admit its first female member until 1904. Even today many of her finds will never be associated with her name, the records lost long ago.
Mary is now emerging from history. The Natural History Museum in London, for instance, has made her and her finds the main attraction of their Fossil Marine Reptiles gallery. The Lyme Regis Museum stands on the site of her birth. She is the subject of several children’s books. And the Geological Society has placed one of her ichthyosaur skulls and a portrait of her and her dog in their front reception hall.
A new biography, The Fossil Hunter by journalist Shelley Emling, tells Mary’s story in detail for the first time. The book is detailed and well researched, drawing on Mary’s own diaries when possible. And the story is captivating enough to forgive Emling for the slightly annoying habit of reconstructing her subject’s hypothetical thoughts and feelings.
Mary truly comes alive, though, in a novel published today: Remarkable Creatures, by Tracy Chevalier, author of Girl With a Pearl Earring. Chevalier imagines Mary’s life into her twenties, told through both her own point of view and that of a friend, the older Elizabeth Philpot. There are conceivable explanations for mysteries of Mary’s life, such as why she never married and how one collector comes to sell all of his fossils and give the proceeds to Mary and her family. Chevalier knows how to tell a good tale, and her story of Mary is definitely that.
November 12, 2009
The sauropod dinosaurs were the largest animals to have ever walked on the earth. They were so incredibly huge, in fact, that they had to move about on four legs—but since the earliest dinosaurs were bipedal, paleontologists have long known that the ancestors of giants like Brachiosaurus and Apatosaurus actually trotted about on two legs. A dinosaur just described in the Proceedings of the Royal Society B sat close to this major transition in sauropod evolution.
Recovered from Early Jurassic (about 183 – 200 million year old) rock in South Africa, Aardonyx celestae was an approximately 20-foot-long dinosaur that combined elements that are both strange and familiar. It had a small head, a long neck, a large body, and a long tail, but it still had relatively short forelimbs compared to its hind legs. While it could occasionally walk on four legs, its limbs indicate that it primarily walked around on two , and an evolutionary analysis that was part of the new study placed it relatively close to the earliest sauropod dinosaurs (thus fitting Aardonyx within the larger category of dinosaurs called sauropodomorphs).
Aardonyx was not actually ancestral to the larger, four-feet-on-the-floor sauropods—it lived during a time when such dinosaurs already existed—but it preserves some of the transitional features that we would expect to find in the actual ancestor. (Contrary to a headline published by the BBC, it is not a “missing link” and the entire concept of “missing links” is a hopelessly out-of-date idea that was discarded by scientists long ago. The phrase goes back to a time when life was viewed as proceeding from “lower” forms to “higher” ones in a straight line, and scientists have rightly rejected it in favor of a branching bush of evolutionary diversity.)
While not a direct ancestor of dinosaurs like Diplodocus, this new dinosaur will help us better understand how sauropod dinosaurs evolved. If you would like to know more about it check out the blog of the lead author of the new description, Adam Yates, where he summarizes the important details about Aardonyx. It is good to see working paleontologists take a more active role in communicating their discoveries to the public, and I hope that other dinosaur specialists will follow the example made by Yates and others.
May 21, 2009
This week news services were all a-twitter about a 47-million-year-old fossil primate from the famous Messel deposits of Germany. Named Darwinius masillae and described in the journal PLoS One, the lemur-like primate was heralded as being a transitional form between a group of extinct primates called adapids and anthropoid primates (monkeys and apes). As it turns out the fossil may not be all it has been cracked up to be, but it is still a spectacular find that represents one branch of the primate radiation that occurred after the mass extinction that killed off the dinosaurs at the end of the Cretaceous. Creatures like Tyrannosaurus perished, but primates survived.
Tracing the record of the earliest primates is a challenge. Since primates started off small and lived in forested habitats their fossils are extremely rare, and most fossils that are found are teeth. This can make comparisons between these creatures difficult, and the relationships among early primates or primate-like creatures are controversial. The fact that some molecular studies places the origin of primates even further back in the Cretaceous, about 85 million years ago, makes things even more complicated as no verifiable primate fossils have yet been found from that age. Despite these complexities, however, scientists do have a broad outline of early primate evolution.
One of the earliest primate-like creatures was Purgatorius, a tree-shrew-like mammal that lived right around the end of the Cretaceous 65 million years ago. Whether it was one of the first primates or only closely related to the first primates is still controversial, but it does seem to represent what the ancestors of primates were like during the time that dinosaurs were the dominant land-dwelling vertebrates.
After the mass extinction, mammalian evolution exploded. Mammals were no longer under the feet of dinosaurs, and among the groups that diversified were primate-like creatures called plesiadapiformes. Whether these creatures were true primates or just very primate-like is still being debated, but they underwent a boom and bust during the Paleocene (about 65 to 55 million years ago). In many ways these creatures were somewhat squirrel-like, with clawed hands and eyes on the sides of their heads, but at the very least they seem to be the closest extinct relatives to other primates.
The creatures that are regarded as “true” primates flourished during the Eocene (about 55 to 33 million years ago), and can largely be placed into two groups: the adapids and omomyids. The adapids were lemur-like primates, while the omomyids closely resembled living tarsiers, but both had forward-oriented eyes and adaptations to life in the trees. Both these groups are relevant to yesterday’s big announcement.
According to the new paper, Darwinius is an adapid, and many scientists presently regard this group as being more closely related to modern lemurs and lorises than to monkeys or apes. Many paleontologists who study extinct primates favor omomyids and ancient tarsiers as being closer to monkeys and apes, but the authors of the new paper don’t think so. In the paper itself they claim that Darwinius belongs to the same large group of primates, haplorrhines, as tarsiers, monkeys, and apes, thus placing adapids in a position to potentially become our ancestors. This conclusion has caused the scientists involved in the study and the popular media to herald it as a “missing link” that connects us to other primates.
Unfortunately, however, the scientists who wrote the paper did not conduct a detailed evolutionary analysis of the new fossil or its relationships to other primates. The fossil is spectacular, the first fossil primate to be find in such a state of exceptional preservation, but it has been oversold by the History Channel (who organized the media hype) and the scientists involved in the study. They simply did not do the work to support the conclusions they drew from the fossil, and the real relationship of Darwinius to other primates will have to wait for further studies.