The Sternberg Mummy

Among all their most remarkable and spectacular finds, one in particular holds special relevance for us here. By 1908, the Sternberg dynasty had graduated from being mere hired hands for Cope and had earned independent status. They were able to work autonomously and provide their finds to a range of very interested institutions. That summer Sternberg led his unique family team on a "great hunt" for "the largest skull of any known vertebrate, the great three-horned dinosaur Triceratops." Here was a quarry worthy of this outstanding team, since barely more than a handful of good skulls existed in American museums at the time. Nonetheless, their discovery would exceed their highest expectations.

Great discoveries are often written up in the popular press with the phrase that the discoverer has "stumbled across" this or that. In paleontology this may literally be true, but it belies the great amount of systematic effort that typically leads up to the "stumble." The harder you work, the luckier you get. In this 1908 summer season, the Sternberg team searched diligently through the endless rock formations littering the Wyoming landscape of Converse County for signs of what they sought. Yet they found nothing but tantalizing weathered shapes that provoked the imagination to see in them recognizable forms where only random erosion had been at work. "Day after day hoping against hope we struggled bravely on," Sternberg wrote of the campaign. "Every night the boys gave answer to my anxious inquiry, What have you found? Nothing." Having spent several weeks each field season tramping the grounds of the West, I too have experienced the long hot days of finding nothing more than dehydration, frustration, and occasional scraps of bone. But I would not wish it to be an easy task, because hard-found fossils seem all that more precious.

The determination to stay until they earned some kind of recompense led to food stocks running dangerously low. In 1908, a convenience store was not a mere hour or two away; the nearest supply of provisions lay 65 miles distant across roadless wilderness. As the men grew hungry, Sternberg Sr. finally gave in and made the trek toward their base, but he could not forbear from searching unexplored outcrops along the way. Finally, en route, Sternberg made his hoped-for find: a Triceratops skull two meters long. Removing this skull from the ground occupied Sternberg so intensely that before he returned, the two boys remaining back in the field camp had run down to no food left but boiled potatoes. However, the two younger Sternbergs had a surprise for their father, which they revealed to him in the quarry where they had uncovered it in his absence. It was a duck-billed dinosaur similar to Trachodon (Edmontosaurus), and not only was it the most complete fossil skeleton they had ever encountered, but it was covered in places with skin impressions. It was the first dinosaur to be given the badge of "mummy."

Even in the sandstone, less photographic in preservation than rock with extremely fine grain like the Solnhofen limestone, the specific details of the hadrosaur's scales could be observed where the skin impressions were preserved. Polygonal plates — tubercles—the scale-like structures of the dinosaur's skin, interlocked in patterns around the animal's chest area. Its skin had a pebbled look, for the tubercles made repeated mosaic patterns. Similar to the architecture presented in the skin of a crocodile, or that of a bird's foot, the hadrosaur's skin showed tubercles of smaller sizes where the skin needed to be more flexible—in the areas around the joints, for example—and larger tubercles in less flexible areas such as the flank and back. Tendons could be seen along the neural spines (the tops of which you feel if you run your fingers along the back of your spine) of the vertebral column. The mummy fossil presented the clearest and most complete evidence of dinosaurian external anatomy that had ever been discovered. The animal lay in an unusual pose, on its back with the front limbs stretched upward rather than on its side, as is most common with dinosaurs of this type.

I made my first visit to the American Museum of Natural History to see this remarkable fossil, among the wealth of its displayed dinosaur remains. Cased in a box of glass, the fossil can be viewed from every angle. The contorted remains look somewhat out of place in the dinosaur gallery, given the amount of skin impressions adhering to the emaciated body of the mummy. On closer inspection the detail of the skin that has been almost "shrink-wrapped" over large portions of the body is beautiful. It is hard to believe that the skin impression was preserved in the first place.

Sternberg noted with interest the preservation of many dozens of ossified tendons crisscrossing both sides of the hadro-saur's neural spines, running diagonally in parallel rows, each the thickness of a pencil. Sternberg imagined that they must be for protection from attack by predators seeking to injure the spinal column. Today, from additional specimens, we know that the network of ossified tendons extended beyond the pelvis well down the tail. The primary interpretation is therefore that this network of ossified tendons worked to stiffen the spinal column both forward and aft of the pelvis for efficient suspension of the animal's weight over its hip, reducing unnecessary muscular strain by rendering the primary support beam for the animal's body rigid. This structure would present a typical posture with the backbone held roughly parallel to the ground, rather than closer to vertical like our own spinal column. The animal's silhouette would, in other words, probably have been closer to that of a secretary bird than a kangaroo. However, the temptation to compare extinct species with that of modern relations can lead to speculative interpretations of biology, physiology, and mechanical abilities. Alas, nothing alive today looks like a dinosaur. Dinosaurs looked and walked like dinosaurs.

The presence of these ossified tendons was a feature of the unusual degree of preservation in the specimen. Regardless of the interpretation of their primary function, their effect of stiffening the backbone is clear, and this greatly affects the parameters of how such an animal would have moved. Contrary to the old tail-dragging bipedal posture given to duck-billed dinosaurs in the decades after 1900, a hadrosaur with such a network of ossified tendons would have been physically incapable of adopting such a pose. Its vertebral column would have to be fractured to describe the arc seen in illustrations created for certain museum displays. This conclusion was not apparent in the Sternberg specimen only because its tail had not been preserved. The importance of soft-tissue preservation for correcting and clarifying our understanding of extinct species' biology cannot be overestimated.

While closer study of the bones alone might well have revealed the "fractured tail" error eventually, the extraordinary soft-tissue preservation seen in the first dinosaur mummy offered a major boost to understanding the configuration of the animal. Sternberg predicted from his observations, in 1909, that the typical hadrosaur did not carry its arms high in the air while walking, but instead more likely used its hooflike hands for quadrupedal locomotion, employing the forelimbs as arms only when standing to reach out and bring branches into convenient grazing range. In this apprehension Sternberg was ahead of his time, as scientists frequently continued to depict bipedal hadro-saurs for some decades, following the restoration produced by Charles R. Knight from this very same specimen, as directed by leading paleontologist Henry Fairfield Osborn in 1912.

For Charles H. Sternberg, the dinosaur mummy was the treasure of treasures, surpassing anything he had ever seen in his forty years of fieldwork. "Shall I ever experience such joy," he wrote, "as when I stood in the quarry for the first time?" This find, in the happy company of his sons, was "the crowning achievement of my life work!" His must have been not unlike the feelings of Howard Carter upon opening the intact tomb of the Egyptian pharaoh Tutankhamun in 1922.

The posture of the fossil hadrosaur suggested to Sternberg that the animal had died in water, which he interpreted as its frequent habitat in life. The body, he presumed, had been turned on its back by decomposition gases in the abdomen, swelling the cavity and making it buoyant. Meanwhile the heavier skull and head had angled the upper part of the body downward in the water. When the trapped abdominal gases were finally released, the body sank, the heavier skull folding sharply back and to the right shoulder as the carcass impacted the sediments at the bottom headfirst. The knees were drawn against the body. The skin caved into the abdominal area, where apparently the internal organs of the body had largely deteriorated, leaving a hollow cavity. The arms remained in the outstretched configuration given to it by the initial floating stage of the dead body, the right arm still reaching upward.

An interesting feature of some hadrosaur fossils is that they are often closely associated with some species of garfish (Lepisosteus sp.). The fish are often found in the gut region of articulated skeletons, but they were not eaten by the hadrosaur —almost certainly the opposite. The fish were probably scavenging the carcasses of the hadrosaurs, swimming into the body cavity to feed upon the soft tissues. Some careless fish got stuck, died, and became a fossil within a fossil. However, the fish might have also died in the same floodwaters that swept up the hadrosaur's carcass, with the two ending up together in a watery grave.There is always more than one way to interpret such associations. As Mark Twain wryly commented, "There is something fascinating about science. One gets such wholesale returns of conjecture from out of a trifling investment of fact."

Henry Fairfield Osborn published a description of the mummy find in 1912, classifying it as a Trachodcn and noting a number of salient features, including the presence of a dorsal frill of skin projecting above the neck and backbone, a feature that could never have been discovered from skeletal evidence alone.

Osborn differed with Sternberg on the interpretation of the decaying process. Osborn proposed that the mummy must have lain exposed to the sun in order for its internal organs and flesh to have desiccated sufficiently for the skin to have been drawn so deeply into the abdomen and rib cage. He proposed that the skin had become leathery in this desiccation process, which had effectively "eviscerated" the carcass, at least as far as volume was concerned.Thus the skin survived the contraction process largely intact, wrinkling only where it no longer fit the changed geometry of the body it contained. Osborn's model for the taphonomic process theorized that after desiccation, perhaps on a sandbar, the carcass was caught in a flood that then conveyed it into the water and quickly buried it. Osborn's theory perhaps better accounts for the good condition of the skin, which one might suppose to have been more greatly deteriorated by long exposure to water than the extremely well-preserved topography evidenced in the fossil. Osborn further noted that he believed the skin to be preserved only in the form of impression casts, not actual survival of any original organic material. He presumed that the rapid burial of the stiffened and desiccated carcass promoted conditions allowing the formation of a superb mold of the body's surface details before the submersion began to decompose the soft tissues themselves.

As a clear trace fossil, the skin impressions are considered "fossilized skin," since a fossil is any physical trace attesting to the existence of past life. It is important to note that this term does not imply anything about the preservation of original bio-molecules, which may or may not be present. Technically speaking, dinosaur mummies are a combination of both trace (skin impressions) and body (bone) fossils.

Osborn's taphonomic model for the Sternberg mummy recalls the process by which the Pompeii bodies died. They are preserved artificially as plaster of Paris casts poured into hollows discovered in the volcanic ash sediments that covered the ancient Roman city during the catastrophic eruption of Mt. Vesuvius in A.D. 79. The hollows are left by the entirely absent skin and flesh of the victims, while their skeletons remain in all but a few of these hollows. We call such remains moldic fossils. The plaster poured into these natural molds produces an artificial cast reflecting the topography of the original soft tissue, clothing, hair, and only rarely preserving actual biomolecules of hard tissue—and the skeleton—while preserving none of the soft tissue. The extreme heat of volcanic ash and pyroclastic flows that destroyed the Roman city incinerated the bodies to dust, albeit after the writhing bodies had been cast rapidly in the volcanic material.

The Sternberg mummy quickly gained renown that it has retained ever since. Henry Fairfield Osborn managed to obtain this peerless find for the American Museum of Natural History (ANMH), paying Sternberg the sum of $2,000. Known originally as a Trachodon, the specimen is now classified by varying authorities as an Anatotitan (per the American Museum) or an Edmontosaurus.

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