Reposted from Yale News

As the Yale Peabody Museum prepares to reopen after a major renovation, a team of skilled specialists is helping its smaller fossil exhibits come to life. A pair of prehistoric predators stand together in the preparators’ lab in the basement of the Yale Peabody Museum. Poposaurus, a 200-million-year-old bipedal carnivore, bares its pointy teeth. To its right, Deinonychus, a nimble raptor that roamed present-day Montana 108 million years ago, seems poised to sink its sickle-shaped talons into hapless prey. Both skeletons will reside in the Peabody’s Burke Hall of Dinosaurs alongside refurbished and reposed Brontosaurus and Stegosaurus specimens, among other fossilized wonders, when the museum reopens this spring after a transformative, building-wide renovation.

Deinonychus, whose discovery in the late 1960s by Yale paleontologist John Ostrom helped dispel the notion that dinosaurs were plodding brutes, prowled Burke Hall for decades before the renovation. Poposaurus, a more recent discovery, will make its debut in the revamped space where Rudolph Zallinger’s famed mural, “The Age of Dinosaurs,” still stretches across the south wall. For the Peabody’s preparators, whose work often combines scholarly discipline with artistic techniques to reanimate these and other prehistoric creatures for public view, readying Deinonychus for public display required just a few touch ups. But creating the new Poposaurus skeleton demonstrated the full range of the preparators’ skills. The team’s expertise in excavating and preserving fossils, their mastery of long-extinct animals’ anatomy, and a creative touch bring the predatory reptile specimen to life.   But it’s just one example of the work the preparators — Marilyn Fox, Cathy Lash, and Christina Lutz — have done, with the help of a group of dedicated volunteers, to ready the Peabody’s fossil specimens for the museum’s historic reopening. In 2003, Yale paleontologists discovered the Poposaurus skeleton in Utah’s late Triassic Chinle Formation. The excavated bones include the hind legs and feet, the left forelimb, and much of the spine and tail, making it by far the most complete specimen of its kind. To allow for the original fossil material to remain accessible for ongoing research, the Peabody preparators reproduced the skeleton, making molds and casts of the fossilized bones, and carefully crafted reconstructions of the missing pieces based on existing fossils from the ancient predator. The reconstructed specimen — about 14 feet long from the tip of the snout to the tip of the tail — demonstrates the importance of the preparators to the museum’s scientific and educational missions, said Vanessa Rhue, the Peabody’s collections manager for vertebrate paleontology.

The team collected the specimen in Utah, made the field jackets to protect the fossils, removed the bones from the rock matrix that encased them, molded and casted each existing bone, and sculpted the absent components based on meticulous research, she said. No Poposaurus skulls are known to exist, so Lash sculpted one based on the skulls of related animals. “His head and neck had weathered out in the gulley before we got there,” said Fox, the museum’s chief preparator for vertebrate fossils. “Cathy did a lot of research to figure out the most accurate shape for the reconstruction.” Lutz painted the cast portions of the mounted specimen that represent the actual fossils so that they resemble the genuine bones — mottled and cracked — while the remaining components are a flat brown, which will allow visitors to discern the elements based on fossilized bones from those that are not. (A fragment from the end of the snout was the only portion of the skull the paleontologists discovered.) “When you look at this specimen, it’s very difficult to distinguish, even with a trained eye, that it’s not an actual fossil,” Rhue said. “That’s no easy feat. It’s a phenomenal job and every step of it was a product of Yale expertise.” Burke Hall’s exhibits will trace the evolution of life on Earth from the earliest ocean life, through the Permian-Triassic extinction event 251 million years ago — when volcanic eruptions poisoned the air and oceans, killing off most plants and animals — to the meteor strike 66 million years ago that wiped out all non-avian dinosaurs. Visitors will learn how animals adapted to life in water and on land, and how scientists believe birds developed the ability to fly. “Roughly speaking, visitors will be traveling through time as they walk through the gallery,” said Chris Norris, the museum’s director of public programs.

The next gallery takes visitors across the extinction boundary to explore the interplay between plants, animals, and the environment, including the effects of a changing climate over the past 66 million years. The final gallery introduces human evolution to the story, examining how modern humans have changed the environment, and how the environment has changed them. Exhibits throughout the three galleries have benefitted from the preparators’ time and attention, said Kailen Rogers, the museum’s associate director of exhibitions. “The preparators are incredibly knowledgeable,” Rogers said. “We’ve had wide-ranging conversations about what is best for the specimens and how they should be displayed. It’s been rewarding to work with them and recognize how they care for and understand these materials.” A skeleton of Hesperornis, a 5-foot-long flightless bird with tiny wings and a beak lined with sharp teeth, offers a sense of the preparators’ role in creating the displays. Discovered in 1876 during a Yale expedition to Kansas (which was led by famed paleontologist Othniel Charles “O.C.” Marsh), the extraordinary fossil provides insight into the evolutionary link between modern birds and dinosaurs. A mainstay at the Peabody since it was mounted more than a century ago, the skeleton has acquired a new and more scientifically accurate skull during the museum’s closure.

During the skeleton’s original mounting, the replaced skull was sculpted from plaster and wasn’t closely based on actual fossils. But a few years ago, Michael Hanson, at the time a Yale graduate student in geology and geophysics (and who is now a research fellow at the Smithsonian Institution), used a CT scanner to image fragments of Hesperornis skulls in the museum’s collection. He assembled the scans into a more accurate digital version of the skull, which was then 3D printed at the Yale Center for Engineering Innovation & Design (CEID). “It’s much more detailed, delicate, and accurate than the original reconstructed skull. Every bone is represented,” said Fox, who conserved the specimen and worked with Hanson and the CEID on the skull. “The folks at the CEID did a great job printing it.” The restored Hesperornis will be displayed alongside fossilized remains of other animals that inhabited the Western Interior Seaway, a vast inland sea that split the North American continent in two, including the paddle of a Plesiosaur — a marine reptile with a long neck and small head — and the flattened skull of a Pteranodon, a flying reptile that inhabited cliffsides along the seaway and preyed on the fish that inhabited it. New galleries charting life on Earth after the cataclysmic meteor impact at the end of the Cretaceous Period offer more examples of the preparators’ ingenuity. Plans for the display originally included the fossilized front portion of a skull that belonged to a small, female Arsinoitherium — an extinct rhino-like herbivore with a pair of horns protruding above its snout that inhabited North Africa 30 million years ago. (The specimen was unearthed by Yale paleontologists in the Oligocene Jebel el Qatrani Formation in the Fayum region of Egypt in 1966.) But Rogers, the associate director of exhibitions, thought the incomplete specimen would be difficult for non-paleontologists to understand. “To me, I could look at the fossilized portion of the skull and still have no idea what the animal looked like,” she said. “I suggested we make it easier for visitors to understand what they’re seeing.” To that end, preparator Lutz sculpted the skull’s back section based on existing casts of complete skeletons and the skulls of similar animals. She attached the reconstructed portion with magnets so that it can be easily removed, allowing researchers to access the fossilized portions. Making the reconstructions reversible also allows for the fossil mounts to be revised as more is learned about how the animals looked and behaved, Rhue said. “The foundational conservation the preparators have done on this material allows for individual parts of the skull to be modified if needed at a later date and you can also remove individual portions of the specimen off exhibit for research as well,” she said. “Providing scholars access is very important for the Peabody as a research institution because not a lot is yet known about Arsinoitherium and many of the other extinct animals on display.”  

Not far from the reconstructed skull is a hulking skeleton of Megacerops, which inhabited present-day South Dakota 35 million years ago. A behemoth with two blunt horns protruding from its snout, it appears ready to step from its exhibit platform and stride through the gallery. A previous inhabitant of the museum’s mammal hall, the skeleton was completely covered in old paint and adhesives, which stained its bones dark brown. Armed with toothbrushes and ethanol, Fox, Lutz, and volunteers scrubbed the entire skeleton — which is about the length of a pickup truck and composed of hundreds of genuine and reconstructed bones, restoring the fossil’s bright eggshell color. Back in the lab, a state-of-the art facility built during the renovation to accommodate the preparator’s needs, volunteer Joe Peters works to free a fossil — a plate that belonged to an armored reptile called an aetosaur from the Triassic Period — from its matrix, the rock surrounding the specimen. Peters, a retired industrial chemist and engineer who lives in North Haven, Connecticut, uses a small, stainless-steel spatula to carefully scrape away red-colored dirt and rock. “It’s nice to have something to do that is mentally stimulating,” said Peters, who has volunteered at the museum for several years, working as a docent and teaching geology classes in addition to lending the preparators a hand. “This is interesting work.” “It can also be frustrating because fossils are delicate and tend to fall apart,” Fox said. Peters shrugs. “I try not to panic when that happens,” he said. A skull larger than a Thanksgiving turkey rests on a table behind Peters’ workstation. It belonged to a duck-billed dinosaur known as Lambeosaurus, which was collected by paleontologist Charles Sternberg in 1919 from the Oldman Formation in Alberta, Canada. The skull was covered with an unknown adhesive that the preparators cleaned off. Lutz is painting the skull’s reconstructed sections before it returns to the Great Hall. “It’s almost done,” Fox said.

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