A dinosaur is any of a group of creatures now known mainly from the fossil record.
Naming and description
Sir Richard Owen, a British anatomist, coined the term "dinosauria" in 1841 to apply to a number of fossils that had been found and scientifically described by that time.
Defining a dinosaur is not easy, but a key point is that they were reptiles which stood on legs under their body, as opposed to other reptiles such as crocodiles which stand on legs out the sides of their bodies.
Dinosaurs were originally believed to have been cold-blooded, like other reptiles, with which they have been grouped, but there is some evidence that at least some were warm-blooded. This evidence includes a fossilised four-chambered heart, such hearts being associated with warm-blooded animals.
Dinosaurs in history
As the term "dinosaur" was only coined in 1841, there are no historical records of creatures called "dinosaurs". However, there are historical descriptions and images of creatures which match the descriptions of dinosaurs. In many cases, these creatures were called "dragons".
The Bible is one such historical source, with references to "dragons", as well as a description of a creature called (transliterated from the Hebrew) "behemoth", which description matches the largest dinosaurs, such as Apatosaurus. Some scholars hold that dinosaurs "were, no doubt, the dragons" referenced several times in the Bible.
Other references to dinosaur-like creatures include cave paintings, a carving on a Cambodian temple, an etching in a British cathedral, and numerous written descriptions.
The dragon is also one of the creatures on the Chinese calendar, without any indication that the creature is different to the other creatures on the calendar in being mythical.
Those who do not hold the Biblical perspective believe that dinosaurs suddenly became extinct 65 million years ago, and have advanced numerous explanations for their sudden extinction.
Dinosaurs and the Great Flood
There is a series of dinosaur fossils at the Dinosaur National Monument stuck in a wall of lithified mud, and the Monument's secular scientists say that these dinosaurs died together in a very large flash flood.
Since no dinosaurs are thought to be alive today, the main source of information is the fossils they have left behind. Paleontologists have identified over 500 distinct genera and more than 1,000 different species of non-avian dinosaurs. Most commonly the fossils consist of bones that have been permineralized, that is, their inner cavities have been filled with deposited minerals. Sometimes this process results in the preservation of morphology down to the cellular level, that is, the shape not only of organs but even of individual cells can be recognized and studied in the mineralized fossils. In some geologic formations, this process takes place only partially or not at all, so that the inorganic components of the bone, largely the mineral carbonated hydroxyapatite, is found largely in its original state.
In contrast to the mineral portions of bones, the organic components usually decay rapidly. DNA is particularly unstable and is thought to decay within at most a few thousand years at 20° C, a temperature considered typical for the climate at the time the dinosaurs were alive. The successful extraction of ancient DNA from dinosaur fossils has been reported on two separate occasions, but neither of these reports could be confirmed and are now generally discounted.
Contrary to widespread expectations, the extraction of organic material from multiple specimens of dinosaur bones has been reported from 1997 on by paleontologist Mary Higby Schweitzer and her team. These findings include
- flexible tissues, apparently bone matrix and blood vessels,
- microscopic structures reminiscent of cells, specifically red blood cells and osteocytes, and
- a variety of compounds with similarities to certain proteins.
Protein (osteocalcin) in dinosaur fossils had already been reported as early as 1992 by another team.
These findings, while persistent, have also been challenged and remain controversial due to the challenge they present to the evolutionary timescale and/or to the current understanding of how biomolecules decay. Schweitzer cites several studies proposing models to account for the preservation of non-biomineralized tissues, organic matter and kerogens in the fossil record, as well as the possibility that original molecules or fragments of molecules may be preserved in fossil remains. She comments that it is particularly difficult to definitively characterize the microstructures that appear to be cells, and "a geological explanation for the presence of these intravascular microstructures has not been eliminated." She considers and "tentatively eliminate[s]" several explanations, but "the possibility that the vessels represent altered remnants of the original lipid components of cell membranes ... has not been eliminated as the primary constituency of preserved vessels in fossil bone." The strength of the evidence that the fibrous matrix is composed of collagen is similarly uncertain. "The data for older specimens are ambiguous and do not uniformly support remnant collagen as a source for this material". She considers the case for osteocytes to be on a firmer basis: "We have been unable to postulate alternative hypotheses consistent with all the data regarding the source of these microstructures, and pending further analyses, consider these cell-like structures to be remains of original cells." Proceeding on the assumption that the materials in the fossils really are derived from original tissues and cells, Schweitzer (and others) proposes a hypothesis to explain what to an evolutionist is an extraordinary degree of preservation. The idea is that the original molecules may be transformed into related but more durable molecules through polymerization and/or cross-linking of organic components, protein polycondensations and/or clusters, and lipid peroxidation of membranes. An essential second step in Schweitzer's model is the mineralization of tissue and cell surfaces through phosphatization in a process similar to bone formation. The calculated decay rates for proteins may not apply because "it may be that these materials are remnants of original proteinaceous material, highly altered by beta oxidation of original proteins to form long-chain hydrocarbon polymers".
Kaye has presented the most detailed challenge to the interpretation of Schweitzer's findings as original dinosaur organic molecules. His hypothesis is that bacteria penetrated the bones, producing a biofilm on the inside of the hollows left by blood vessels and osteocytes. In this model, the morphology of the dinosaur tissue was preserved in microscopic detail as mineral casts over geologic time and was only recently recast as flexible biological material by the action of bacteria. He also presents evidence that the material identified as collagen is more likely biofilm. He cites work demonstrating bacterial contamination even in well-preserved dinosaur bones, and the recent discovery of collagen-like proteins in bacteria and viruses. The structures bearing a resemblance to red blood cells are, in his view, an oxidized form of formerly pyritic framboids, micromorphological features seen world wide in black smokers, algal mats, and many sediments. However, Kaye has failed to explain all of Schweitzer's observations, including proteins having similarity to chicken proteins, and Schweitzer and others have rejected the biofilm explanation.
Like Kaye, Buckley also emphasizes the point that "microscopic preservation does not equate with molecular preservation".
It was later discovered that iron can act as a preservative so it was suggested that the fossilization environment and iron helped preserve the tissue. However, the laboratory tests were using conditions quite unlike the conditions in which the bones were preserved, ruling this out as a viable explanation.
That explanations such as Kaye's were not generally accepted was illustrated in an article announcing the iron preservation hypothesis. It made no mention of other explanations, declaring with reference to the iron preservation that "The controversial discovery … finally has a physical explanation".
- ↑ Wieland, Carl. Fascinating Four-Chambered Fossil Find. Retrieved 4-1-2009.
- ↑ Steele, DeWitt et al. Science of the Physical Creation, in Christian Perspective, 2nd ed. Pensacola, FL: A Beka Book, 1996.
- ↑ Covey, Jon. Evolutions's Embarrassment: The Fossil Record. Retrieved 1 April 2009.
- ↑ Wang, S.C., and Dodson, P., "Estimating the Diversity of Dinosaurs", Proceedings of the National Academy of Sciences USA 103:37 (2006), pp.13601–13605
- ↑ Will the real dinosaurs stand up?, BBC, September 17, 2008
- ↑ 6.0 6.1 Nielsen-Marsh, Biomolecules in fossil remains: Multidisciplinary approach to endurance, The Biochemist, June 2002.
- ↑ 7.0 7.1 7.2 Buckley, et al., Comment on "Protein Sequences from Mastodon and Tyrannosaurus rex Revealed by Mass Spectrometry", Science 4 January 2008: Vol. 319 no. 5859 p. 33.
- ↑ Wang, H., Yan, Z. and Jin, D., Reanalysis of published DNA sequence amplified from Cretaceous dinosaur egg fossil, Molecular Biology and Evolution 14:5, 1 May 1997, pp. 589–591.
- ↑ Schweitzer et al., Heme compounds in dinosaur trabecular bone, Proc. Natl. Acad. Sci. USA, Vol. 94, pp. 6291–6296, June 1997.
- ↑ Schweitzer, et al., Soft-Tissue Vessels and Cellular Preservation in Tyrannosaurus rex, Science, 307:1952-1955, March 25, 2005. (link requires free subscription)
- ↑ Schweitzer, et al., Analyses of Soft Tissue from Tyrannosaurus rex Suggest the Presence of Protein, Science, 316:277-285, April 13 2007.
- ↑ Schweitzer, et al., Soft tissue and cellular preservation in vertebrate skeletal elements from the Cretaceous to the present, Proc. R. Soc. B 22 January 2007 vol. 274 no. 1607 183-197.
- ↑ 13.0 13.1 13.2 Schweitzer, et al., Biomolecular Characterization and Protein Sequences of the Campanian Hadrosaur B. canadensis, Science 1 May 2009: Vol. 324 no. 5927 pp. 626-631. (link requires free subscription)
- ↑ Muyzer et al., Preservation of the bone protein osteocalcin in dinosaurs, Geology 20, 871–874.
- ↑ Catchpoole, David, and Sarfati, Jonathan, Schweitzer’s Dangerous Discovery, 19 July 2006
- ↑ Kaye et al., Dinosaurian Soft Tissues Interpreted as Bacterial Biofilms. PLoS ONE 3(7): e2808. (2008)
- ↑ Zimmer, Carl, Slime versus dinosaur, The Loom, 1 August 2008.
- ↑ 18.0 18.1 Stephanie Pappas, Controversial T. Rex Soft Tissue Find Finally Explained, LiveScience, Tue. 26th November, 2013Tue. November 26th, 2013.
- ↑ Schweitzer, Mary H. et al. A role for iron and oxygen chemistry in preserving soft tissues, cells and molecules from deep time Proc. Royal Soc. B. Wed. 22nd January, 2014Wed. January 22nd, 2014, 281 (1775).
- ↑ Calvin Smith, [Dinosaur soft tissue Dinosaur soft tissue], Tue. 28th January, 2014Tue. January 28th, 2014.