In 2006, fossil prospectors came across the bones of not one massive dinosaur, but two, locked in a fight to the death. Peter Larson tells the story of the discovery – and why it is the most exciting find yet
In spring 2006, dinosaur cowboy Clayton Phipps, Chad O'Connor and Mark Eatman were prospecting for fossils in the Hell Creek Formation near Clayton's ranch in Central Montana. Clayton, an avid fossil collector, had already made some important discoveries over the years, such as the only complete Stygimoloch skull known to science. However, nothing prepared the two for what they were about to find.
The Hell Creek Formation is a 400ft thick layer of sediment, a slice of time that encompasses the last half-a-million years leading up to, and including, the mass extinction of the dinosaurs about 66.5 million years ago. The Hell Creek Formation is restricted to North America and is found in the states of South Dakota, North Dakota and Montana. It represents the best picture of life in the Latest Cretaceous.
This part of North America was as far north as it is today. However, it more closely resembled the current state of Florida, including the flat, low lying plains, its proximity to the sea (there was an inland seaway that stretched from the Gulf of Mexico to the Arctic Ocean), palm trees, crocodilians and lots of turtles. Occupying this territory was a host of dinosaurs including Triceratops, and, of course, a wide variety of the meat eating theropods such as Tyrannosaurus.
Prospecting alone, Mark first spotted fragments of bone along an embankment. He recognised what looked like a ceratopsian pelvis sticking out of the sand. After meeting up with Clayton and Chad, he took them to the site. The pelvis looked interesting and Chad and Clayton decided to excavate.
When Clayton and his team returned later that summer, they had a surprise. As they removed the sandstone from the bones, they discovered that the "back bone was connected to the hip bone, the hip bone was connected to the tail bone" and on and on. They were uncovering an articulated dinosaur.
Articulated skeletons are almost unknown in the Hell Creek Formation. Once the team had delineated the completely articulated skeleton of the ceratopsian (horned) dinosaur, Clayton brought in an earthmover to work around the specimen in preparation for plaster jacketing and removal. While digging around the tail, Clayton noticed a black bone falling out of his bucket full of sand. That bone turned out to be the claw from a meat eater. Clayton went to the spot the earthmover had just excavated and found a bone in the ground. He couldn't believe what he saw. More bones. They had discovered a second dinosaur.
After screening for parts from the sand removed by the earthmover, Clayton and Chad finished uncovering the second dinosaur and called in for reinforcements to help safely remove the dinosaurs from their tomb. The rest of the team was astonished at what had been unearthed.
What lay before the crew was the remains of two complete and articulated dinosaurs – the most complete specimens ever discovered in the Hell Creek Formation. Added to that, it was clear that the dinosaurs died together. They were touching. The foot of the ceratopsian was lying on top of the tail of the theropod. Between the foot of the ceratopsian and the head of the theropod lay a pile of theropod teeth.
Clayton and crew knew that they had something very special. So they decided to collect the specimens in as large blocks as was physically possible in order to retain as much contextual information of the site as possible. The specimen was divided into blocks, each block was covered in plaster and burlap, and the blocks were supported with timbers. Then the blocks were loaded onto a flatbed truck and transported to Fort Peck, Montana.
Once back in the lab, the plaster jackets were opened from the top and the long process of preparation began. Today we see the results of careful collecting and preparation of these truly exquisite skeletons which I would rate as one of the most important dinosaur discoveries of all time.
The horned dinosaur is the most complete Chasmosaurine skeleton found to date. It either represents a new genus and species, a new species of Triceratops, or the most complete and oldest individual of Triceratops horridus ever found. There are certain characters of the skull (very short brow horn, extra horny growth in front of the eye, etc.) and ischium that will need to be explored before it is relegated to Triceratops. If, in fact, it is eventually decided that it is a very old and pathologic Triceratops horridus, it still will bring to an end a very heated and current scientific debate: Is Torosaurus simply a very old Triceratops? The answer would be: No. And, of course this would be the most complete Triceratops skeleton ever found (the most complete to date is 75 per cent).
To add to that, there is soft tissue preservation on the specimen. Several patches of skin have been found on the pelvis and body. There is even skin preserved on the skull, proving that the frill of ceratopsians was covered in skin, not keratin, as has been proposed by some researchers. Because the patches of skin have been found on the "up" side of the specimen, the chances of more, and better preserved, skin on the underside is almost a sure bet.
The theropod skeleton is the most complete theropod ever recovered from the Hell Creek Formation. It is identified as Nanotyrannus lancensis. Nanotyrannus, described in 1985, came under fire from a group of scientists who claimed that the known specimens do not comprise a genus, but simply represent juvenile Tyrannosaurus rex. Clayton Phipps and his crew's discovery puts an end to that debate.
This skull shows the disparity in the number of teeth: Nanotyrannus lancensis has 15-16 maxillary tooth positions and 17 dentary tooth positions, Tyrannosaurus rex has 11-12 maxillary and 13-14 dentary. Nanotyrannus has an incisoform first maxillary tooth and Tyrannosaurus does not. All told there are more than a score of skull characteristics that separate the two.
With the addition of this skeleton, a number of new postcranial characters can be demonstrated. The hand on this specimen is not just proportionally larger than the largest T. rex hand, it is actually larger (every bone) than the hand of 'Sue', the largest T. rex discovered so far. To give you an idea how astounding this is, Sue's skull measures approximately 60 inches in length, This Nanotyrannus skull is only 21 inches long.
The wishbone (furcula) on this specimen is shaped like a U, T. rex wishbones are shaped like a V. The articulation for the arm (humerus) on the shoulder girdle (scapula-coracoid) faces outward. On T. rex this joint faces downward. The rear limb proportions, even given changes related to growth, do not match those expected for a juvenile T. rex. In short, this specimen validates the legitimacy of Nanotyrannus lancensis.
The discovery of two articulated and touching dinosaur skeletons in one excavation is remarkable in itself. However, there is more to the story. There is evidence that these dinosaurs not only died together, they probably caused each other's death. At least two teeth from Nanotyrannus have been discovered within the carcass of the Ceratopsian. One tooth is positioned in the lower back, between the lateral and dorsal spines of one of the posterior dorsal vertebrae. Because this tooth was implanted deeply in what would have been muscle tissue, it certainly appears that this was a tooth lost during a death struggle. The second tooth was found during the separation of the skull and neck block from the main body block. This tooth is at the base of the neck and appears to have been implanted deeply within the muscle tissue. It seems likely that both teeth were lost by the Nanotyrannus as a result of an attack upon the Ceratopsian.
Looking closely at the skull and chest region of the Nanotyrannus skeleton, it seems clear that this individual suffered some major trauma near the time of its death. Bones in the region of the chest (scapula-coracoids and furcula) are shattered, as if kicked in. In addition, the skull, which is preserved in situ, ventral side up, has been pushed in from the right side, crushing and folding it in the middle. Both maxillae are missing a number of teeth and broken roots project from some of the alveoli. Coincidentally, a group of broken Nanotyrannus teeth were found between the skull of the Nanotyrannus and the foot of the Ceratopsian.
The two specimens were buried so closely together that they were actually touching. It seems correct to assume that these dinosaurs died together after a fatal confrontation.
The preservation of the Montana Duelling Dinosaurs is, in every way, superb. The bones are nearly black in colour, unusual, but not unheard of for the Hell Creek Formation. Because the specimens are preserved in fine-grained, loosely consolidated sandstone, they are virtually uncrushed despite the weight of sediment originally deposited above them. I have collected fossils from the Hell Creek Formation for more than 35 years. Because I study T. rex and other dinosaurs from the Hell Creek Formation, I have visited every museum that has collections from this area. I have never seen a specimen from the Hell Creek, or any other Formation, for that matter, that compares with the Duelling Dinosaurs. This specimen is unique. There is nothing else with which one can compare them.
Peter Larson is a leading authority on Palaeontology and President of the Black Hills Institute in South Dakota.