TRACKING AN ANCIENT KILLER The case was cold– the bones in the mass grave were 70 million years old. But critical clues pointed to the killer’s identity By Raymond R. Rogers and David W. Krause LARGE MEAT-EATING DINOSAUR Majungatholus atopus (above) met an untimely end some 70 million years ago in what is now northwestern Madagascar (opposite page, top). Members of the authors’ team carefully excavated the remains, including a jaw with serrated teeth used to slice through flesh (right), and packed them in plaster for transport to the U.S. (opposite page, bottom), where the researchers studied the fossils in detail for clues to the cause of death. RAYMOND R. ROGERS COPYRIGHT 2007 SCIENTIFIC AMERICAN, INC. TRACKING AN ANCIENT KILLER The case was cold– the bones in the mass grave were 70 million years old. But critical clues pointed to the killer’s identity ne body rests on its left side, head and neck pulled back toward the O pelvis—a classic death pose. The arms and legs are still in their anatomically By Raymond R. Rogers correct positions, but closer inspection re- veals that bones of the hands and feet are and David W. K rause dislocated, although most parts are present and accounted for. The skull, too, is some- what disjointed, and here again the compo- nent pieces lie near one another. Curiously, the tip of the tail is missing altogether. Near- by rest more corpses in markedly different states of preservation and disarray. Some are still largely intact, others represented by only a skull, a shoulder blade, a single limb bone. Did the unfortunate creatures die here, or were they brought together after their demise? Did they all perish at the same instant, or did their deaths transpire over time? And what killed them? Our team of Malagasy and American paleontologists and geologists started ask- ing such questions as soon as we discovered the mass grave in the summer of 2005 in the ancient sediments of northwestern Mada- gascar, an island whose Venetian-red soils COPYRIGHT 2007 SCIENTIFIC AMERICAN, INC. inspired its nickname, the Great Red Is- and small, young and old, entombed to- dental picks and fine brushes to expose land. We turned up some intriguing in- gether in spectacular bonebeds. And so the bones themselves. We took great formation as we searched for the an- as we worked to uncover what killed the care not to damage the fragile bone sur- swers, but how we went about the task animals in MAD05-42, we also could faces. Once we fully exposed the skele- is perhaps as interesting as what we not help but wonder why we find so tal remains, we mapped and photo- found. many bonebeds here and why they are so graphed them exactly where we found Before doing anything, we named the beautifully preserved. them to record any significant spatial re- site, designating it MAD05-42 to indi- lationships. We next soaked the delicate cate the year it was found and its se- Opening a Very Cold Case bones with consolidating glues and quence in the discovery of fossil localities we were millions of years too carefully jacketed them in protective in this area. The second task was identi- late to use most of the tools of modern- coats of burlap and plaster. After the fying the dead, and based on our discov- day coroners. To tease out the clues hid- plaster set, we catalogued the bones and eries elsewhere in the region, we quickly den in the bones and rock, we had to packed them for the long journey to our discerned that most of the remains were turn to geologic dating techniques and laboratories in the U.S., where later we dinosaurs of various species. to the field of inquiry known as taphon- painstakingly removed any remaining This dinosaur burial ground is not omy, which explores the fate of organic sediment and studied the bones in de- unique for northwestern Madagascar. It remains as they cross from the living tail, looking in particular for any marks matches a pattern we have seen repeat- world to the dead. on the surfaces that might reveal the edly over a decade of geologic investiga- After naming the site, we disinterred killer’s identity. tion in the semiarid grasslands near the the bones from the rocks in which they At the site we determined that the remote village of Berivotra. There we were embedded. We started with shov- dead were preserved in a distinctive have uncovered layer on layer of mass els and rock hammers to remove the body of sedimentary rock known as the death, with the remains of animals big overlying sediment, then moved on to Maevarano Formation, situated a few tens of meters below rocks laid down at GEOLOGIC EVIDENCE the Cretaceous/Tertiary boundary—the time, 65 million years ago, that all dino- The history of the Madagascar landmass provides clues about what killed so many saurs (apart from birds) and many other animals there 70 million years ago. At the beginning of the Mesozoic era (250 million creatures suffered extinction on a glob- years ago), Madagascar rested in the heart of Gondwana. Tectonic activity rearranged al scale [see “Repeated Blows,” by Lu- the earth’s lithospheric plates, and by the early Cretaceous ann Becker; Scientific American, (130 million years ago), Madagascar was positioned about March 2002, and “The Day the World 400 kilometers away from the African mainland; it then Burned,” by David A. Kring and Daniel rejoined the African plate and began moving northward. When the deaths under investigation D. Durda; Scientific American, De- occurred (map below), northern Madagascar lay cember 2003]. The deathbed lay 44.5 EQUATOR near 30 degrees south latitude, where climatic meters beneath the mass extinction ho- conditions alternated between prolonged droughts rizon and 14.5 meters beneath the local and intense rainy periods. top of the Maevarano Formation. Mea- suring the radioactive decay of minerals 2007 from volcanic rocks in the layers below NORTHERN Europe MADAGASCAR the formation yielded ages of approxi- Latitude: 16° S mately 88 million years. Marine sedi- North Atlantic ments above and interbedded with the Ocean Asia Tropic of Cancer formation, laid down by seas that ebbed Pacific and flowed along the western shores of Ocean the island, contained seashells and tiny EQUATOR skeletons of single-celled microorgan- Africa South Indian isms dated from other sites to near the America Ocean Tropic of Capricorn India end, but not the very end, of the Creta- 30° S ceous period. All the temporal evidence thus indicates that the deaths occurred 66 Million Years Ago approximately 70 million years ago. NORTHERN Australia MADAGASCAR Whatever killed the dinosaurs in quarry Latitude: 30° S MAD05-42 was unrelated to the great Antarctica global extinction that took place several million years later. LUCY READING-IKKANDA 44 SCIENTIFIC AMERICAN FEBRUARY 2007 COPYRIGHT 2007 SCIENTIFIC AMERICAN, INC. More Mass Death One of the first sites discovered, MAD93-18, reveals the recurrent nature of mass mortality in ancient Madagascar more dramatically than any other site. MAD93-18 has three discrete deathbeds stacked one on top of the other. Excavations there produced nearly complete skeletons of the large sauropod Rapetosaurus (bottom left and bottom right) as well as the skeletal remains of many other animals new to science, including a primitive bird, Rahonavis ostromi (right), which had small, fragile bones. 1 CM ) bottom right io B Centre Val ); RAYMOND R. ROGERS ( Taphonomy advanced our inquiry as For example, some carcasses were large- Scene of the Crime well. Taphonomic study examines bone ly intact and others were dismembered the geologic history of the modification (were the bones burned, and scattered widely, which would not Madagascar landmass also provided im- bottom left ( broken or bitten?), carcass disturbance have happened instantaneously. In ad- portant clues about what killed these di- (dismemberment and selective removal dition, some bones were in exquisite nosaurs. At the onset of the Mesozoic of body parts by scavengers or preda- condition, whereas others showed evi- era (250 million years ago), Madagascar ); DESIRE RANDRIANARISTA tors), and burial history (how the bodies dence of advanced weathering and sur- rested in the heart of Gondwana (the top ( were buried and what happened to them face degradation. When the animals in southern half of the supercontinent Pan- after burial). The study of fossilization an ancient bonebed have died at differ- gaea), sandwiched between Africa and processes—essentially, what turns bone ent times, we describe the site as “time- India, with Antarctica near its southern into stone—also falls within the realm averaged” and use taphonomic clues to tip. Tectonic activity soon rearranged of this science. assess the amount of time between the lithospheric plates on a massive scale, Stony Brook University When we considered the dead in first death and the last. Although we and by the late Jurassic (160 million quarry MAD05-42 from a taphonomic cannot determine exactly how much years ago), Madagascar had rifted away perspective, we could tell that they per- time transpired in the formation of this from Africa and was moving southward, ished over a prolonged period, perhaps particular deathbed, we do know that with India in tow. By the late Cretaceous weeks or months, because their corpses death did not come at the same instant (88 million years ago), Madagascar had CATHERINE(International FORSTER Training Center forrevealed the Study of Biodiversity) variable postmortem histories. for the animals entombed here. resutured to the African plate, albeit www.sciam.com SCIENTIFIC AMERICAN 45 COPYRIGHT 2007 SCIENTIFIC AMERICAN, INC. ANCIENT SOILS and rocks present convincing evidence of a semiarid climate during the late Cretaceous.