Previous studies of dinosaur fossils have indicated that organic material may be found in the femur (long leg bone) of certain dinosaurs (primarily Tyrannosaurus rex). The studies were limited to superficial morphological examination and rudimentary immunological analysis of some of the Organic compounds made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.proteins. The results were, at best, equivocal. Certainly, some heme Organic compounds made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.proteins (the An organic compound made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.protein that makes up hemoglobin found in red blood cells) or their breakdown products were found in the bones. The current study1 examines a newly discovered T. rex skeleton for the presence of intact soft tissue within the creature's femur (long leg bone).
New morphological study
The new study, published in the respected journal Science, revealed the presence of morphological objects that seem to be blood vessels (picture) with endothelial nuclei visible (picture), red blood cells, and osteocytes (bone cells, picture). Scientists removed the inner cortical bone from the femur and soaked it for 7 days in a solution of dilute acid to remove the surrounding bone. The resulting tissue (picture) was flexible and retained at least some cellular and subcellular structures. These structures were compared to those of modern ostriches, which were processed in a similar manner (except that the tissue needed to be chemically stained to visualize the tissue. Remarkably, nucleated red blood cells could be visualized within the blood vessels of the specimen. Both reptile and bird red blood cells possess nuclei in circulation, whereas mammalian red blood cells lose their nuclei prior to entering circulation.
Normal bone structure
Most kinds of vertebrates possess similar bone structure to allow for the growth of their skeletons as they mature. Bones are not solid structures, since to be so would require them to be far too heavy to enable efficient movement. The outer compact bone is largely solid, with only a few holes to allow blood vessels to enter and exit the inner part of the bone. The spongy inner bone is composed of a network of thin bone interspersed with blood vessels and marrow (which produces red and white blood cells). In a living animal, the inner spongy bone is moist tissue.
Normally, when an animal dies, its remains are scavenged and/or destroyed through decomposition. However, under rare circumstances (e.g., burial under sediment at the bottom of a lake, stream, river, or sea during a flood, or under sand during storms, or under ash during volcanic eruptions) animals can be preserved through rapid burial. After a period of time, the biological molecules of the organism are replaced by minerals which precipitate out of the water. The surrounding sediments are also turned to stone, thus encasing the fossil in stone. The skeleton in question was found in sandstone, a common mineral that is formed through this kind of process. In addition, the geology indicated that the area in which the fossil was buried was part of an estuary. It seems reasonable to conclude that the animal had died and was washed down into the sea, which had made up much of the current central portion of the United States.
Why was the soft tissue preserved?
Normally, following death, the remains are destroyed through scavenging and decomposition. However, during fossilization, hard materials are replaced with minerals. Normally, bacteria enter into the center of bones through breaks or through the holes through which blood vessels and nerves pass. The soft tissue is usually destroyed within a short period of time. In this instance, the soft tissue seems to have been preserved through dehydration and sealed from the presence of water and further decomposition. Contrary to the claims of some young earth creationists, the tissue is obviously not fresh, since it exhibits coloring that is not characteristic of fresh tissue. Fresh blood vessels and connective tissue are nearly transparent (except the blood cells themselves), which is why the ostrich tissue had to be chemically stained to produce the pictures used in the article. Another difference between the ostrich tissue and T. rex material was the requirement to use collagenase to release blood vessels from ostrich bone matrix. This fact indicates that much of the collagen from the T. rex sample was already degraded. The primary author indicated that the bones have a distinct odor, characteristic of "embalming fluids."2 Therefore, it is possible that the bones landed in some chemical stew that preserved the soft tissue inside from decomposition. For example, peat bogs produce chemicals that have preserved human bodies for thousands of years. It is likely that some similar rare process has preserved the soft tissue inside some T. rex bones.
"Tissue" contains little protein
Despite the appearance of being intact soft tissue, an analysis of fossil showed that it contained little intact protein. Whereas greater than 90% of the protein in living bone is collagen, ~1% was found in the medullary bone of the T. rex fossil.3 Multiple purification steps (solid-phase extraction, strong cation exchange, and reversed-phase microchromatography) were required in order to increase the protein content enough to perform mass spectrometry of the sample.4
The new study reveals that the cortical bone within T. rex femurs may, under certain conditions, retain cellular and subcellular details. Under normal conditions, fossilization replaces living material with minerals. In this case, the soft tissue was protected from degradation, possibly through some chemical process, then desiccated to prevent further changes. Upon treatment with water and dilute acid, the tissue was rehydrated, returning to an appearance similar to how it originally looked. Since no molecular studies have yet been done with the specimen, it is uncertain if the specimen contains original organic material or if the material was replaced by some mineralization or other chemical process. When more information is available, this page will be updated.
- Erik Stokstad. 2005. Tyrannosaurus rex Soft Tissue Raises Tantalizing Prospects Science 307: 1852.
- Stokstad, E. 2005. Tyrannosaurus Blood Vessels Found Science Now.
- Schweitzer, M. H., J. L. Wittmeyer, J. R. Horner, J. K. Toporski. 2005. Soft-Tissue Vessels and Cellular Preservation in Tyrannosaurus rex. Science 307: 1952-1955.
- Schweitzer, M. H.. 2005. Personal correspondence.
- Schweitzer, M.H., Z. Suo, R. Avci, J.M. Asara, M.A. Allen, F. Teran Arce, and J.R. Horner. 2007. Analyses of soft tissue from Tyrannosaurus rex suggest the presence of protein. Science 316: 277-280.
- Asara, J.M., M.H. Schweitzer, M.P. Phillips, L.M. Freimark, and L.C. Cantley. 2007. Protein sequences from mastodon (Mammut americanum) and dinosaur (Tyrannosaurus rex) revealed by mass spectrometry. Science 316:280-284.
Last updated May 1, 2009