Wade Miller and his colleagues made a major contribution to the field of paleontology when they discovered a fossilized dinosaur egg containing the oldest known embryo of any kind, about 150 million years old.
More than twelve thousand unarticulated, or separated, bones of dinosaurs, representing more than seventy individual dinosaurs, or at least twelve genera, have been found at the Cleveland-Lloyd Dinosaur Quarry
In September, 1987, two geologists from Brigham Young University, Wade Miller and Kenneth L. Stadtman, along with colleagues Karl Hirsch from Boulder, Colorado, and James H. Madsen, Jr., from Salt Lake City, Utah, found in the Cleveland-Lloyd Dinosaur Quarry a fossilized egg from the 100-million-year gap in the fossil record in geologic time between the Lower Jurassic period and the upper Lower Cretaceous. The egg from the Upper Jurassic period contains an embryo that is approximately 150 million years old—the oldest known embryo found of any kind of living creature to date. The egg was discovered with thousands of other dinosaur bones instead of in the traditional nest.
In the 1970’s, paleontologists John Horner
Wade Miller.
Another interesting speculation that has arisen from the idea of nests is that dinosaurs were warm-blooded, not cold-blooded like modern reptiles. There were several indications—such as the size of the bones—that the remains were those of babies, but there were indications also that the young were quite mature: the worn-down quality of their teeth (nearly three-quarters gone) and the hardness of the tendons found on the spine, which are normally soft in hatchlings. The babies were ill equipped to venture from the nest among adult dinosaurs to compete for food; therefore, one or both parents must have brought the food. Modern reptiles, which are cold-blooded, take a long time to grow; if the dinosaurs were cold-blooded, the growth process would have kept them in the nest for as long as a year, and such a lengthy stay in the nest has never been witnessed in modern cold-blooded reptiles. In comparison, warm-blooded creatures, such as birds, grow very quickly and in the nest. In any case, the dinosaur babies were growing in the nest and at a fast pace.
The fact that the egg Miller and his colleagues found at the Utah site containing the embryo was not found in a nest, in addition to two other unusual factors, is a possible indication that the egg was retained in the oviduct, or tube, through which the egg passes from the ovary in the birth process, a phenomenon termed oviductal retention. The egg was found broken into two parts that were connected by a hingelike area. The halves were both filled with a fine sediment similar to the shale that enclosed the egg. Computer-aided study of the egg revealed that it had fractured on the hingelike structure. The distortion that occurred in other places on the shell and its inverted curvature are both indications that, at some point during the breakage and deformation, the shell was at least semipliable. The only time a normally rigid eggshell is pliable is during the few minutes directly after the beginning of the shelling, the term used for the birth process of reptiles, or the oviposition. Furthermore, the shell can be pliable only in the oviduct. If the two halves of the egg were put together, it would be roughly 110 by 55 millimeters (4.3 by 2.2 inches). The structure of the shell is composed of calcite and calcium carbonate. The primary, or original, shell is preserved perfectly and coated by another layer, the pathological layer, caused by unusual circumstances.
The second unusual factor in the case of the embryo is the multilayering of the shell because of pathological, or disease-related, circumstances at the time of burial. The pathological condition of an eggshell, which is found in modern and fossil reptiles and mammals alike, can be caused by stress, disease, or other environmental conditions. The mother must be alive when the eggshell develops extra layers as a result of retainment in the oviduct; however, the length of time it takes to form the extra pathological layer of the shell is unknown. The embryo may live for a short time and even continue to develop, but the exchange of vital gases is hindered by the misalignment or maldevelopment of pores in the second layer in relation to the first, the end result of which is death by suffocation for the embryo. The hypothesis is that the mother was disturbed before she could lay her egg in the nest. The excellent condition in which the egg was found is perhaps a result of its being held together in the oviduct after fracturing until it was preserved by sediments.
The structure of the eggshell itself is that of rigid interlocking units and columns. The secondary, pathological eggshell is half the size of the primary eggshell. Its structure is similar to the primary shell but not fully developed in critical areas, such as the continuation of pores from the primary eggshell to the secondary eggshell, causing poor or restricted facility for gas exchange. The egg cannot be identified either by the known species and genera of dinosaurs or by the other dinosaurs found in the dig. The distinction that makes this eggshell different from any other among the Cleveland-Lloyd fauna is its eggshell structure, which contains a new type of pore canal, and its embryonic remains, which have not been identified. In addition to finding the oldest known embryo, the team of four paleontologists may have found a new dinosaur.
The discovery that Miller and his colleagues made in the fossil beds of the Cleveland-Lloyd Dinosaur Quarry added to modern knowledge in the field of paleontology. The oldest known complete embryo, preserved perfectly for 150 million years, gave researchers a chance to learn more about the process of egg formation and dinosaur embryo development. In addition, the fact that the dinosaur could not be classed in any of the genera found at the same site is an indication that the egg might be of a previously unknown type of dinosaur. Adding to this possibility is the discovery of another specimen, in the Morrison Formation of Colorado in the Jurassic egg site, that has similar structure in the eggshell as well as the pore type. The researchers have mentioned the need to establish a structural morphotype for the eggs found from the Jurassic period.
The state of the embryo from Utah, which is most likely the result of oviductal retention, contributed to the study of egg retention and pathological eggshell formation. Because no systematic study of such phenomena had been undertaken, these areas of process are still being questioned; however, because oviductal retention still occurs in the mammals and reptiles of the modern era, there is good information available on possible causes of the abnormality. Sometimes, retention causes the movement of the egg backward into the area of its formation, a process called reverse peristalsis. When reverse peristalsis does not occur, the egg develops a second membrane in the oviduct. The Jurassic egg found in Utah is clearly the result of the development of a second membrane and calcareous layer, or one containing calcium carbonate.
The Jurassic eggshell is typical of modern pathological eggshells, and so adds to the body of study available on the shelling process in some dinosaurs and, hence, the indirect study of the oviduct. The discovery of dinosaur eggs in their entirety, eggshells that are pathological, and remains of embryos are all extremely rare, especially from the time before the Cretaceous. The discovery in Utah had a great impact on the world of paleontology, especially in view of the possibility that the fossilized embryo might be that of a previously unknown dinosaur.
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Alexander, R. McNeill. Dynamics of Dinosaurs and Other Extinct Giants. New York: Columbus Press, 1989. Excellent resource for all readers interested in dinosaurs, including scientists and nonscientists, students and professors. Gives detailed information about various kinds of dinosaurs in a readable style with a minimum of scientific language. Includes illustrations, graphs, and chapter bibliographies. -
Bakker, Robert T. The Dinosaur Heresies: New Theories Unlocking the Mystery of the Dinosaurs and Their Extinction. New York: William Morrow, 1986. Written with no scientific jargon by an adjunct curator at the University Museum, University of Colorado, a skilled artist and scientist; illustrated with the author’s own reconstructions of dinosaurs alive and in action. Excellent reference source for both student and layperson. -
Hirsch, Karl F., Kenneth L. Stadtman, Wade E. Miller, and James H. Madsen, Jr. “Upper Jurassic Dinosaur Egg from Utah.” Science 242 (March, 1989): 1711-1713. One of the best sources available for precise information regarding the egg and the state in which it was found. Intended for readers with background in paleontology. -
Horner, John R., and James Gorman. Digging Dinosaurs: The Search That Unraveled the Mystery of Baby Dinosaurs. New York: Workman, 1988. Excellent resource discusses the mystery of baby dinosaurs. Written by one of the men who first discovered dinosaur nests, the key to the past that unlocked many secrets of the ancient creatures and opened new doors of insight into other possibilities. -
Martin, Anthony J. Introduction to the Study of Dinosaurs. 2d ed. Malden, Mass.: Blackwell Science, 2006. Comprehensive college-level textbook aimed at both science students and non-science majors includes discussion of the history of dinosaur studies. Features end-of-chapter references, glossary, and index. -
Norell, Mark, Lowell Dingus, and Eugene Gaffney. Discovering Dinosaurs: Evolution, Extinction, and the Lessons of Prehistory. Expanded ed. Berkeley: University of California Press, 2000. Focuses on what the fossil record reveals about dinosaurs’ evolution and extinction. Includes maps and illustrations. -
Paul, Gregory S. Predatory Dinosaurs of the World: A Complete Illustrated Guide. New York: Simon & Schuster, 1988. Informative volume combines original research in the field with detailed illustrations to express new ideas about predaceous dinosaurs. Presents skeletal restorations of every predator dinosaur species for which a restoration can be done. Written for the nonscientific reader. Includes extensive bibliography.
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