The Edmontosaurus mummy AMNH 5060, nicknamed the AMNH mummy, is an exceptionally well-preserved fossil of a dinosaur in the collection of the American Museum of Natural History (AMNH). Discovered in 1908 in the United States near Lusk, Wyoming, it was the first dinosaur specimen to be found encased in skin impressions. It is ascribed to the species Edmontosaurus annectens (originally known as Trachodon annectens), a hadrosaurid ("duck-billed dinosaur"). The mummy was found and excavated by fossil hunter Charles Hazelius Sternberg and his three sons in the Lance Formation. Although Sternberg was working under contract to the Natural History Museum, London, Henry Fairfield Osborn of the AMNH managed to secure the mummy. Osborn described the fossil in detail in 1912, coining the name dinosaur mummy for it—several dinosaur mummies of similar preservation have been discovered since then. This specimen has considerably influenced the scientific conception of hadrosaurids. Skin impressions found in between the fingers were initially interpreted as webbing, bolstering the now-rejected perception of hadrosaurids as aquatic animals. Today, the mummy is considered one of the most important fossils of the AMNH.
The mummy was discovered lying on its back, its neck twisted backwards and its forelimbs outstretched. The skeleton is complete save the tail, hind feet, and the hind portion of the pelvis. All bones are preserved unflattened and still connected to each other. Almost two-thirds of the skin is preserved. Delicate for the size of the animal, the skin includes two different types of non-overlapping scales that were between in diameter. A flexible frill of skin is preserved in the neck area. In contrast with other similar dinosaur mummies, the skin of AMNH 5060 was tightly attached to the bones and partially drawn into the body interior, indicating that the carcass dried out before burial. The specimen would thus constitute the fossil of a natural mummy. After dehydration, the mummy likely would have been rapidly buried by a meandering river and rapidly filled with sediment. After burial, a thin clay layer would have formed on the skin, preserving the external shape of the latter.
Discovery
The mummy was discovered and excavated in August 1908 by Charles Sternberg and his three sons George, Charles Jr. and Levi. An independent fossil collector, Sternberg earned a living by selling his finds to museums in North America and Europe. The sons worked as assistants for their father, and later became renowned paleontologists. Early in 1908, Sternberg planned an expedition to the Lance Creek area in eastern Wyoming, where the family had not worked before. In search of acquirers of potential fossil finds, he wrote to the Natural History Museum, London, that he knew where in Wyoming to find a skull of the horned dinosaur Triceratops, knowing that the museum was lacking a good specimen; the museum agreed to buy any good fossil finds if such were made. The Sternbergs left their family residence in Kansas in early spring, and arrived in the Lance Creek area in July. Sternberg's plan foresaw the exploration of an uninhabited area of approximately north to the North Platte River and south to the Cheyenne River in Converse County (today Niobrara County). The predominant badlands of this area expose sedimentary rocks of the Maastrichtian stage of the Upper Cretaceous, which today are known as the Lance Formation. The area had already been intensively explored by paleontological expeditions; before the start of his expedition, Sternberg learned that the American Museum of Natural History had been unsuccessfully working in the area for years.
Although the party was enthusiastic (Sternberg's sons had never discovered dinosaur fossils before), the first weeks of search were unsuccessful. Sternberg wrote in his 1909 book The Life of a Fossil Hunter:
At the end of August, Sternberg finally discovered a fossil horn weathering out of the rock; subsequent excavation revealed a long Triceratops skull. Soon after, George, the oldest son, found bones sticking out of the rock while prospecting new territory near Boggy Creek with Levi, the youngest son. Levi discovered more bones nearby, apparently belonging to the same skeleton. By then, the group had traveled from their base camp, and food was running short. Sternberg instructed George and Levi to carefully remove the sandstone above the skeleton, and Sternberg himself set off for Lusk with Charles Jr. to purchase new supplies and to initiate the shipping of the Triceratops skull to the Natural History Museum, London. The third day after their father's departure, George and Levi recognized that they had found an apparently complete skeleton lying on its back. When removing a large piece of sandstone from the chest region of the specimen, George discovered, to his surprise, a perfectly preserved skin impression. In 1930, George remembered:
When Sternberg finally returned at the fifth day, George and Levi had run out of food, and had only eaten potatoes for the previous two days. Nevertheless, they had exposed the skeleton; the dig measured in width, in length and in depth.
When paleontologist Henry Fairfield Osborn, manager of the American Museum of Natural History, learned about the new find, he immediately sent staff member and paleontologist Albert Thomson, to attempt to secure it for the museum. Osborn knew about the agreement between Sternberg and the Natural History Museum, London, which gave the latter rights to acquire any of the finds; he appealed to Sternberg's patriotism and promised permanent exhibition of the fossil. When Thomson arrived, he was unable to evaluate the fossil as it had already been wrapped in burlap and shellac for transport, yet the asking price of $2,000 () was high. On the same day as Thomson, William Holland, director of the Carnegie Museum of Natural History, arrived at Lusk. Osborn, now worried about losing his opportunity, quickly acquired the specimen for an unknown sum.
At the American Museum, preparation of the skin impressions was completed by preparator Otto Falkenbach. Subsequently, the mummy was scientifically described by Osborn himself and the famous paleontologist Barnum Brown in three articles published in 1911 and 1912, and afterwards was put on display. In the exhibition, the mummy, protected by a glass showcase, is shown lying on its back as it was discovered; the museum decided not to restore missing parts. Today, the mummy is regarded as one of the museum's most important fossils. It is cataloged under the specimen number AMNH 5060.
Significance and classification
AMNH 5060 is considered one of the best preserved dinosaur fossils ever discovered. The scientific value of the mummy lies in its exceptionally high degree of preservation, the articulation of the bones in their original anatomical position, and the extensive skin impressions enveloping the specimen. In 1911, Osborn concluded:
As dinosaur skin impressions were previously known only from a few fragments, the mummy became a paleontological sensation. As noted by Osborn in 1912, the Trachodon skeleton AMNH 5730, found in 1884 by Jacob Wortman, originally also contained extensive skin impressions, but most had been destroyed during excavation, leaving only three fragments from the tail region. As explained by Osborn, the very thin layer containing the skin impressions in the stone is difficult to detect, and many such impressions might have been lost in previous years as they were not expected nor recognized by excavators.
In his 1911 description, Osborn coined the term dinosaur mummy for the specimen. This term was later used to refer to similar hadrosaurid ("duck-billed dinosaurs") specimens with extensive skin impressions, all of which have been discovered in North America. The second such mummy, now in the Senckenberg museum in Frankfurt am Main, Germany, was discovered by the Sternbergs in 1910, just two years after the discovery of AMNH 5060. Although the skeleton of the Senckenberg mummy is more complete, it is less well preserved than AMNH 5060 in some other aspects. Another mummy specimen was discovered by Barnum Brown 1912 in Alberta, Canada, and subsequently described as the new genus Corythosaurus. Yet another mummy was discovered by Sternberg, which he sent to the Natural History Museum, London, during World War I. The transport ship, the , was sunk by a German raider ship in 1916, resulting in the loss of this mummy as well as many other fossils discovered by Sternberg. Additional mummies have been excavated since the turn of the millennium, such as a Brachylophosaurus mummy nicknamed "Leonardo" and an Edmontosaurus mummy nicknamed "Dakota". In 2025, Paul Sereno and colleagues described two additional Edmontosaurus mummies that had been discovered in 1998 and 2002, respectively, in the same area in which the Sternbergs found their first two mummies.
Gregory S. Paul, in 1987, stated that the life appearance of Edmontosaurus and Corythosaurus can be more accurately restored than that of any other dinosaur thanks to the well-preserved mummy specimens. Yet, evidence provided by AMNH 5060 was not regularly taken into account by paleoartists, possibly because it was described before World War I, during which activity in dinosaur research abated, only to be revitalized in the mid-1960s.
AMNH 5060 belongs within the Hadrosauridae, a family of ornithischian ("bird-hipped") dinosaurs. The mummy was initially identified as Trachodon annectens. At the time, the genus Trachodon encompassed nearly all known hadrosaurid specimens. In a 1942 monograph on North American hadrosaurs, Richard Swann Lull and Nelda E. Wright moved the species together with the mummy into the new genus Anatosaurus, as Anatosaurus annectens. In 1990, Michael K. Brett-Surman and Ralph Chapman decided that the species instead belongs within the genus Edmontosaurus, which was followed by subsequent reviews. The majority of dinosaur skin impressions are referable to the Hadrosauridae. In North American specimens from the Maastrichtian age, skin impressions are 31 times more abundant in association with hadrosaurid specimens than with any other group. The reasons for this distribution are unclear. Of all known hadrosaurid skin impressions, 25% belong to Edmontosaurus.
Description and interpretation
Most of the skeleton is preserved, the bones still attached to each other in their original anatomical position. The tail, hind feet, and hind portion of the pelvis had eroded away before the mummy was discovered. Fossils often become flattened during fossilization, but AMNH 5060 is preserved three-dimensionally, without significant deformation. The specimen was found lying on its back, with head and neck twisted upwards, backwards, and to the right side of the body. Both knees are drawn forwards, while the forelimbs are outstretched. Although the tail curves upwards and forwards over the body in many dinosaur skeletons, it was probably straight in the mummy as movement would have been restricted by . Almost two-thirds of the total skin area is preserved, often with excellent preservation. The skin impressions are pressed tightly onto the bones, and are partially drawn into the body in between the bones. When discovered, skin impressions probably encased the whole skeleton, but were partially destroyed while freeing it from the surrounding rocks. Skin impressions are preserved on the forelimbs, neck and throat, and the chest, as well as on the right side of the trunk. As well as the skin impressions, Sternberg noted the preservation of muscle impressions. In 2007, paleontologist Kenneth Carpenter suggested that even impressions of inner organs are possibly preserved; this cannot be evaluated without detailed computer tomography and x-ray analyses.
Skin