August 9, 2011
In almost every general dinosaur book I can remember from my childhood, there was at least one page dealing with the making of fossils. The story was always straightforward—almost like a recipe. Take one dead dinosaur, add a copious amount of sediment, throw in millions of years and, voilà, you’ve got a beautiful fossilized skeleton. Easier to follow than a Julia Child recipe, so long as you’ve got the time.
A few books added additional details. Scavengers might nibble at the carcass before burial, for example, though the scavengers almost always took the form of small, bird-like dinosaurs. I can’t remember any book mentioning the hordes of scavenging insects that helped break down dinosaur bodies. Maybe that’s because the role arthropods play in the breakdown of a dinosaur body has only been relatively recently appreciated. Over the past few years, paleontologists have reported a growing number of cases of interactions between dead dinosaurs and insects. Just last month one team of paleontologists reported fossil cocoons preserved inside a broken dinosaur egg—a possible indicator that parasitoid wasps used the rotting egg to give the next generation a head start—and an in-press Palaeogeography, Palaeoclimatology, Palaeoecology paper suggests that the dead dinosaurs of Cretaceous Mongolia often played host to insects.
The new paper, by Mototaka Saneyoshi, Mahito Watabe, Shigeru Suzuka and Khishigjav Tsogtbaatar, focuses on the damaged bones of Protoceratops, Velociraptor, Bagaceratops and an unidentified ankylosaur found in the Djadokhta and Barun Goyot Formations of Mongolia. All of these dinosaurs lived during the Late Cretaceous during a span of time between about 80 million and 70 million years ago. At this time the area was a sandy desert, and these conditions likely contributed to the rapid burial and preservation of the dinosaurs. When a dinosaur died, its body dessicated relatively quickly in the arid habitat and blowing sands soon covered up the carcass. Then the scavengers set in.
Saneyoshi and colleagues report on pits, notches, channels and borings from several dinosaur specimens. These are not the first such traces to be found on dinosaur skeletons from Mongolia; in the huge New Perspectives on Horned Dinosaurs volume published last year, paleontologists James Kirkland and Kenneth Bader described a well-preserved Protoceratops skeleton that had clearly been damaged by insects. In addition to chambers that may have harbored developing insect pupae, many of the surfaces along the dinosaur’s joints had been eaten away.
The damage to the skeleton described by Kirkland and Bader occurred after burial—if the insects had started chewing on the carcass before that, the skeleton would have fallen apart. This is how things may have gone down: The insects searched out the buried dinosaur carcass, dug down into the sand to reach it and then began their dirty work underground. Scarab or darkling beetles appeared to be the most likely candidates based on the behavior of modern scavengers. (Experiments were carried out by Bader with flesh-eating dermestid beetles to see if they would dig below the surface to feed on a carcass. “[M]ost of the beetles,” he reported, “either died in the cage or escaped in search of an alternative food source.” No word on whether the beetle exploratory mission was successful.) The additional specimens described by Saneyoshi and co-authors show similar types of damage, particularly around the joints, and these findings reinforce the notion that dead dinosaurs were an important staple of some flesh-eating insects of the day.
So why did the bone-chewing insects like dinosaur joints so much? That is difficult to say. As the authors of the in-press paper point out, very little is known about how desert insects utilize vertebrate carcasses. Studies of modern-day necrophagous insects will be needed to better understand what happened in Cretaceous Mongolia. In the past, though, some researchers have suggested that insects like termites have been attracted to fresh bones and cartilage as a handy source of nitrogen in dry environments in which the element may be relatively hard to come by. The positive evidence for this hypothesis is relatively thin at the moment, though, and further investigations will be needed to test the idea.
Mammals, according to Saneyoshi and co-authors, may have tucked into one dinosaur carcass, too. Even though the quick burial of the dinosaurs led the scientists to state “damage caused by vertebrate scavengers and transportation processes can be excluded in the case of present study” early in the paper, in a later section they mention a relatively large, 1.2-inch hole in one of the Protoceratops skeletons which they hypothesize was left by a mammal. The hole is near the shoulder blade, between the ribs and vertebrae, and is cited as being too large to have been made by an insect. Perhaps a multicuberculate—a variety of small mammal that became extinct many millions of years ago—dug out such a hole. Or perhaps not.
The large hole in the Protoceratops skeleton is difficult to interpret—it is not a clear bite mark, and the fact that the space is between bones makes it difficult to determine how the damage was created. Saneyoshi and co-authors mainly point to the size of the gap as being indicative of a mammal, but there don’t appear to be any tell-tale mammal toothmarks like those reported on Cretaceous dinosaur bones by Nicholas Longrich and Michael J. Ryan last year. (The paper by Longrich and Ryan is not cited in the in-press manuscript by Saneyoshi and collaborators.) There’s also the problem of timing. If Kirkland and Bader are correct about the timing of insect scavenging in these kinds of environments—namely that these types of insect traces were made after the dinosaurs were buried—then it is significantly less likely that a mammal created the damage in question. Tooth scores or gouges on a bone—a limb bone, a rib, a shoulder blade, or something similar—would help make the mammal connection, but as it presently stands, I think the large hole on the Protoceratops skeleton cannot be confidently attributed to a little, gnawing multituberculate.
We are only just beginning to understand how insects made the most of dinosaur bodies. There are plenty of damaged fossils out there which need description, and there is much we don’t yet understand about how modern insects utilize vertebrate carcasses. We need to know more about the prehistoric past as well as processes still in action today. There are still many mysteries for fossil forensic investigators to solve.
Kirkland, J.I. and Bader, K., 2010. Insect trace fossils associated with Protoceratops carcasses in the Djadokhta Formation (Upper Cretaceous), Mongolia. In: Ryan, M.J., Chinnery − Allgeier, B.J., Eberth, D.A. (Eds.), New Perspectives On Horned Dinosaurs. Indiana University Press, Bloomington, pp. 509-519.
Saneyoshi, M., Watabe, M., Suzuki, S., & Tsogtbaatar, K. (2011). Trace fossils on dinosaur bones from Upper Cretaceous eolian deposits in Mongolia: Taphonomic interpretation of paleoecosystems in ancient desert environments Palaeogeography, Palaeoclimatology, Palaeoecology DOI: 10.1016/j.palaeo.2011.07.024
September 3, 2010
When Charles H. Sternberg and his sons excavated one of the first hadrosaur mummies ever found, in the summer of 1908, it was a major discovery. For nearly a century naturalists and paleontologists could only imagine what a dinosaur’s skin was like, but the Edmontosaurus the Sternbergs collected gave scientists an unprecedented look at the hadrosaur soft tissue anatomy. In the century since that discovery, though, so many hadrosaur skin impressions have been found that they don’t make the news anymore—only the most spectacular finds, such as the Brachylophosaurus “Leonardo,” get much attention.
Despite the number of hadrosaur skin impressions that have been found, there is still much to learn about the skin of different hadrosaurs and how the impressions came to be preserved. In the latest edition of PalArch’s Journal of Vertebrate Paleontology, for example, high school student Lucia Herrero and paleontologist Andy Farke have described the partial skin impressions associated with a disarticulated hadrosaur skeleton from southern Utah’s 76- to 74-million-year-old Kaiparowits Formation. The specimen was too broken up to determine what genus and species of hadrosaur it had been, but among the scattered bones were patches of skin imprints left in the rock.
On its surface, the association of skin impressions with a busted-up skeleton might appear to be a contradiction. The depositional environment was delicate enough for traces of soft tissue anatomy to be preserved, yet the dinosaur’s bones were moved out of place or destroyed. As hypothesized by Herrero and Farke, what this may indicate is that—in the right circumstances—dinosaur skin was durable enough to survive becoming detached from the rest of the carcass and enter the fossil record. Rather than being just an oddball case, the specimens described by Herrero and Farke represent a kind of preservation that may simply have been overlooked at other disarticulated hadrosaur sites, and the Kaiparowits Formation appears to be rich enough in both hadrosaurs and skin impressions to further investigate the way in which traces of dinosaur skin entered the fossil record.
Lucia Herrero & Andrew A. Farke (2010). HADROSAURID DINOSAUR SKIN IMPRESSIONS FROM THE UPPER CRETACEOUS KAIPAROWITS FORMATION OF SOUTHERN UTAH, USA PalArch’s Journal of Vertebrate Palaeontology, 7 (2), 1-7
August 2, 2010
As stated in many popular-audience books and documentaries, the fossilization of a skeleton involves the gradual transformation of bone into stone, often by way of mineral-rich groundwater percolating through bones over a long period of time. Yet things are not that simple. Thanks to recent discoveries, we know that remnants of soft tissues and even original chemical components of bone can remain preserved for many millions of years, and even though the creation of fossilized bones is often portrayed as a geologic process, a new study published in the journal PALAIOS suggests that the activity of bacteria may play an important role in how fossils form.
Most studies that have considered the role of bacteria in fossilization have focused on how bacteria breaks down bone—in order for a skeleton to be preserved in the fossil record, conditions for fossilization must be in place before the microscopic organisms entirely destroy the material. As argued by scientists Joseph Daniel and Karen Chin, however, some preliminary experiments using cubes of bone have suggested that bacteria may also foster bone preservation in some circumstances, and they designed a new experiment to test the idea. The setup, simply put, involved placing cubes of cow bone in river sand for three months while water saturated with calcium carbonate was percolated through them. Four trials were run, but in two of them sterilizing agents were added to the setup in order to remove the presence of bacteria. By doing this, the scientists could observe whether bacteria played a significant role in the preservation or degradation of the bone cubes.
At the end of the experiment, Daniel and Chin noticed significant differences between the bones used in the “natural” and bacteria-reduced trials. The cow bone from the natural trials showed a significant amount of mineral deposition within the bone, that is, the beginnings of fossil preservation. The bone from the trials in which antibacterial agents were introduced, however, apparently did not change at all—it was virtually indistinguishable from fresh, untreated bone cubes.
Even though the role of groundwater and other factors remains important to the formation of fossil bone, the results of the experiment suggest that the activity of bacteria play an important role in introducing minerals into bone during early stages of preservation. In fact, if bacteria precipitate minerals while consuming organic material inside a carcass, they may effectively create mineral barriers within bones, thereby cordoning off soft materials that can become preserved for long periods of time in the right conditions. What this means is that, shortly after the death of an organism, minerals precipitated by bacterial activity may be more important to preserving parts of bone than minerals precipitated through inorganic means—there are important biological aspects of the fossil preservation that are just now beginning to be understood.
JOSEPH C. DANIEL and KAREN CHIN (2010). THE ROLE OF BACTERIALLY MEDIATED PRECIPITATION IN THE PERMINERALIZATION
OF BONE PALAIOS, 25, 507-516 : 10.2110/palo.2009.p09-120r
June 25, 2010
Mammals have long been characterized as the underdogs of the Mesozoic world. They diversified in habitats ecologically dominated by dinosaurs, but, even though most were small, they did not simply cower in their burrows until the non-avian dinosaurs were wiped out 65 million years ago. In fact, Mesozoic mammals were more varied in anatomy and habits than is often appreciated, and, as has just been reported in Palaeontology, some small mammals gnawed the bones of the giant archosaurs.
As described by paleontologists Nicholas Longrich and Michael Ryan, a number of fossil bones from the Cretaceous rock of Alberta, Canada were damaged by bites which could only have been made by mammals. A dinosaur rib fragment, a piece of dinosaur limb bone, a partial lower jaw from the marsupial mammal Eodelphis and a femur from a reptile called a champosaur bear bite marks made by an animal with closely-spaced, paired teeth. This bite pattern matches the tooth placement of an extinct variety of mammal called multituberculates—these mammals had long incisor teeth at the front of their jaw separated from the other teeth by a gap, thus explaining why the only toothmarks on the bones were made by incisors. While other mammals could potentially have been the culprit, the anatomy of the multituberculates make them the best fit.
The multicuberculate-made toothmarks are, at present, the oldest known fossil traces of mammal toothmarks. More than that, the authors suggest that some multituberculates used their incisors to gnaw on hard, resistant food items, meaning that they were perhaps more versatile in their diets than had previously been presumed. From the traces on the bones it appears that these small mammals scavenged dead dinosaurs and other creatures for food (leaving behind the relatively shallow tooth marks on some of the specimens) and sometimes bit into the bone itself, perhaps to obtain minerals like calcium (as seen by the deeper bite marks). Now that these traces have been recognized, perhaps other paleontologists will see similar marks in bones they collect, potentially helping us better understand the lives of the mammals that lived alongside the dinosaurs.
LONGRICH, N., & RYAN, M. (2010). Mammalian tooth marks on the bones of dinosaurs and other Late Cretaceous vertebrates Palaeontology DOI: 10.1111/j.1475-4983.2010.00957.x