Non-Mineralized Tissues in Fossil T rex

Reports of the National Center for Science Education
Title: 
Non-Mineralized Tissues in Fossil T rex
Author(s): 
Joe Skulan, University of Wisconsin, Madison
Volume: 
25
Issue: 
5–6
Year: 
2005
Date: 
May-August
Page(s): 
35–39
This version might differ slightly from the print publication.
In the March 25, 2005, issue of Science, paleontologist Mary Schweitzer and her co-authors reported the discovery of intact blood vessels and other soft tissues in demineralized bone from a 65- million-year–old specimen of Tyrannosaurus rex housed at the Museum of the Rockies (MOR). Scientists’ reaction to this discovery has been cautious; Schweitzer and others have not provided the biochemical data necessary to decide whether or not the “flexible vascular tissue that demonstrated great elasticity and resilience” is, in fact, T rex soft tissue. But while scientists have been appropriately skeptical of Schweitzer’s claim, many young-earth creationists improperly have seized on it as evidence that the T rex fossil from which Schweitzer extracted the putative soft tissue, and fossils generally, are not more than a few thousand years old.

The absolute ages of all fossils ultimately hinge on radiometric dating techniques, the validity and accuracy of which are beyond reasonable doubt. These techniques are derived from the pre-eminent scientific enterprise of the 20th century: nuclear physics. If we did not know enough about radioactive materials to date things, then we would not be able to build atomic bombs. I would eagerly admit that the earth was young if it meant that A-bombs were not real, but that Faustian bargain has been made and we must live with it. Multiple analyses using several independent radiometric techniques show that the rocks in which the MOR T rex was found are about 65 million years old. The age of this fossil is a settled fact. The question that I want to ask here is why creationists see the preservation of soft tissue as evidence that the MOR T rex is relatively modern. The answer lies not in the muddled thinking of creationists, but in the careless and ambiguous way that paleontologists themselves discuss “fossils” and explain how fossils form.

Fossils and Fossilization

While “fossil” originally referred to anything that originated in and was dug out of the earth, including gems and metals, the term in English has been used mainly in its modern sense since the early 19th century. But what is this modern sense? This turns out to be a difficult question to answer. Ignoring a handful of etymological fundamentalists, for the past few centuries “fossil” has had two distinct meanings: the remains or traces of ancient life (the time-based definition), and an object of biological origin that has undergone the process of “fossilization” (the process-based definition). The creationist challenge to the age of the MOR T rex is an equivocation based on this dual definition:

1. A fossil (time-defined) is old.

2. The MOR T rex is not a fossil (process-defined) because the presence of soft tissue demonstrates that it is not fossilized.

Therefore, the MOR T rex is not old.

The argument is invalid because each of the premises defines “fossil” in a different way. Few arguments used by creationists are as easily refuted as this, because most errors in creationists’ reasoning are not simple logical fallacies, and arise instead from misinterpretations of empirical evidence and hence requiring detailed refutation. But the equivocal use of “fossil” is not a creationist invention; it is a bad habit that they learned from paleontologists themselves.

It is curious that a term so central to their science should be used so carelessly, but paleontologists rarely differentiate the two definitions of “fossil,” and often use them interchangeably, even in situations that demand precision, such as in reference books. For example, Herve Bocherens (1997: 111) writes:
The chemical composition of fossilized vertebrate tissues is the result of the uptake, exchange, and loss of chemical elements, in two different sets of circumstances. First, during the life of the animal. ... Second, during the diagenetic evolution of the mineralized tissues (i.e., fossilization) this original organization of the chemical elements is altered ... [emphasis added]
Statements such as these are so common in paleontological literature — especially as throw-away remarks in prefaces and introductions — that they tend to roll smoothly off the brain without critical evaluation. But this passage is quite ambigious. Fossilization, here defined as the “diagenetic evolution of the mineralized tissues,” is a process. Unmineralized tissues apparently cannot undergo fossilization. But can unmineralized tissues be fossilized? “Fossilized” also implies a process-dependent definition of “fossil,” because, under the time-dependent definition, becoming a fossil simply is a matter of getting old, something that hardly qualifies as a process; calling a bone “fossilized” simply because it is old would be as meaningless as calling an old chair “antique-ized.” So if unmineralized tissues can be fossilized, then there must be some way of becoming fossilized other than through fossilization, and T rex soft tissue could be described as “unfossilization-ized fossilized tissue.” But if unmineralized tissues cannot be fossilized, this would imply that unmineralized tissues cannot be fossils. What, then, are “fossil” leaves, soft-body animal “fossils”, and petrified wood?

The topic of Bocherens’s article is not fossils per se, and the problems I point out here have no real bearing on the bulk of his excellent and informative article. Nevertheless Bocherens’s confused discussion of “fossilized” and “fossilization” is typical of the careless way that many paleontologists use “fossil,” especially when discussing “unusual” fossils such as ancient soft tissue.

For example, in reference to the purported T rex soft tissue in an interview with a BBC reporter (BBC 2005), Schweitzer said:
This is fossilised bone in the sense that it’s from an extinct animal but it doesn’t have a lot of the characteristics of what people would call a fossil.
As with Bocheren, this statement sounds reasonable until you think about it. “Characteristics of what people would call a fossil” presumably refers to decay of soft tissue, petrifaction or some other process. But what does “fossilized bone in the sense that it’s from an extinct animal” mean? Here Schweitzer clearly intended to use “fossil” in the time-defined way, but instead of simply using the word “fossil”, she adds the chronological qualifier “from an extinct animal” to “fossilized” — a term that connotes process. This leads to exactly the same confusion that we encountered in Bocheren. And again, as with Bocheren, I do not mean this as a critique of Schweitzer’s science. I cite these passages in order to demonstrate that we think so little about how we use “fossil” and related terms that even careful and accomplished scientists use them in careless and ambiguous ways.

What We Don’t Know

What accounts for this confusing hybrid terminology? The answer is the widespread assumption that the two definitions of “fossil” are logically dependent on each other; either because organic remains must be fossilized in order to become old enough to be a fossil, or because as things become old they inevitably become fossilized. These assumptions belong to the vast netherworld of scientific pseudoknowledge; bits of received wisdom that crowd encyclopedias and textbook introductions; answers to questions so basic and obvious that they are overlooked as things that must have been thoroughly discussed and decided generations ago. In the conflict over Schweitzer and her colleagues’ discovery, pseudoknowledge confronts pseudoscience.

The standard textbook account of “fossilization” might be termed the “Tin Man” story: soft tissues decay, the resulting cavities are filled with minerals precipitated from groundwater, and the original biominerals transform into or are replaced by other substances. This process results in a replica of the original object in which the original substance has been heavily altered and largely or entirely replaced by other materials.

The Tin Man story of fossilization is something of a fossil itself, having been around in essentially its present form since at least the end of the 18th century. The third edition of the Encyclopedia Britannica, published in 1795, describes “Petrafaction” as follows:
A petrified substance, strictly speaking, is nothing more than the skeleton, or perhaps image, of a body which has once had life, either animal or vegetable, combined with some mineral. Thus petrified wood is not in that state wood alone. One part of the compound or mass of wood having been destroyed by local causes, has been compensated by earthy and sandy substances, diluted and extremely minute, which the waters surrounding them had deposited while they themselves evaporated. These earthy substances, being then moulded in the skeleton, will be more or less indurated, and will appear to have its figure, its structure, its size, in a word, the same general characteristics, the same specific attributes, and the same individual differences. Farther, in petrified wood, no vestige of ligneous matter appears to exist.
More modern variants simply embellish this story with chemical language, substituting atoms, molecules, or minerals for “diluted and extremely minute” substances, for example. Pulling a book off my shelf at random, I encounter this:
After an animal dies, if it is to become a fossil, it must be buried before the elements destroy the carcass, completely…. After burial, minerals carried by percolating groundwater are deposited in vugs within the bone structure, or they may actually replace bone salts, literally turning the bone to stone. (Jacobs 1993: 47)
Both passages give readers the sense that scientists have a pretty good understanding of what happens to fossils in the ground. In reality we have no such understanding. Indeed, it is only in the past 15 years that paleontological geochemists begun to address, in a serious and organized way, basic questions about why some things endure long enough to become fossils. To date, these efforts have revealed important details about the chemical behavior of some fossils in some settings, but we are a long way from the kind of systematic knowledge implied by the cited passages.

The new understanding we do have of fossils unfortunately has been used to revamp and reinforce the Tin Man story, rather than to challenge it. For example, in the introduction to their textbook on dinosaurs, Fastovsky and Weishampel (2005: 8–10) write:
Bone is made out of calcium (sodium) hydroxyapatite, a mineral that is not stable at temperatures and pressures at or near the surface of the earth. This means that bones can change with time, which in turn means that most no longer have original bone matter present after fossilization. This is especially likely if the bone is bathed in the variety of fluids that is associated with burial in the earth. ... If, however, no fluids are present throughout the history of the burial … the bone could remain unaltered, which is to say that original bone mineralogy remains. This situation is not that common, and is progressively rarer in the case of older and older fossils.
This explanation of what happens to buried bones is vastly better than most. It makes the important but seldom articulated point that bone will not necessarily decay just because it is unstable, and leaves open the possibility that unaltered bone and soft tissues can survive. The authors make no implausible claims, and it is possible that a century from now we will know that everything they wrote was entirely correct.

But we are not living a century from now, and in the meantime much of what Fastovsky and Weishampel present as fact is really educated conjecture. We do not know that most fossil bone no longer contains its original bone material; we do not know that for bone to survive unaltered it must be isolated from fluids throughout its history; most importantly we do not know that the preservational state of bone is directly related to its age. As in the previously quoted passages, Fastovsky and Weishampel present their story of how things become fossils as if it were based on well-understood facts. And their story still largely is the Tin Man story: except under extraordinary conditions, fossils undergo the same replacement process that was expounded in the Encyclopaedia Britannica over 200 years ago.

It is this habit of presenting conjecture and tentative knowledge as settled fact that makes paleontologists vulnerable to creationist attacks based on “extraordinarily” well-preserved fossils. In reference to the MOR T rex, the ICR claims:
Would evolutionary theory have predicted such an amazing discovery? Absolutely not, soft tissue would have degraded completely many millions of years ago no matter how fortuitous the preservation process. Will evolutionary theory now state — due to this clear physical evidence — that it is possible dinosaurs roamed the earth until relatively recent times? No, for evolutionary theory will not allow dinosaurs to exist beyond a certain philosophical/evolutionary period. (Sherwin 2005)
The discovery of intact T rex soft tissue indeed would challenge prevailing scientific thinking, if not, as the author claims, “evolutionary theory”. This discovery can be reconciled with the Tin Man story only by invoking extraordinary causes. These invocations come across as makeshift attempts to prop up an exhausted hypothesis — which in fact they are. From the same BBC article previously cited:
Dr Schweitzer is not making any grand claims that these soft traces are the degraded remnants of the original material — only that they give that appearance.

She and other scientists will want to establish if some hitherto unexplained fine-scale process has been at work in MOR 1125, which was pulled from the famous dinosaur rocks of eastern Montana known as the Hell Creek Formation. (BBC 2005; emphasis added)
Rich Deem, writing at the creationist site godandscience.org, explains:
[Schweitzer] indicated that the bones have a distinct odor, characteristic of “embalming fluids.” Therefore, it is possible that the bones landed in some chemical stew that preserved the soft tissue inside from decomposition….The new study reveals that the cortical bone within T rex [femora] 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. (Deem nd; emphasis added)
Creationists know a weak spot when they see one, and dodgy phrases like “some hitherto unexplained fine-scale process” and “some chemical stew” advertise a weak spot like a giant gorilla balloon over a used car lot. The fact that the weakness is in our understanding of fossils, not of evolution or the age of the earth, is a subtle distinction that creationists do not make and their audience does not grasp.

Often the best defense is a frank admission of ignorance. “How do you explain the presence of soft tissue in a 65 million year old fossil?” Based on what we really know about fossils (and assuming the soft tissues are real and not just globs of glue) the best answer to this journalistic question is “I have no idea. But since we don’t know very much about why things become fossils in the first place, that’s not surprising. What we do know is that this particular fossil is 65 million years old.” Neat narratives like the Tin Man story are betrayals of the honest ignorance that is the heart and engine of science.

Things Fall Apart

Everyday experience teaches us that dead organisms and their traces do not last long when they are exposed to the ordinary wear and tear of the earth’s surface: scavengers of all sizes, the effects of sunlight, mechanical and chemical weathering, and so on. From this experience it is easy to apprehend the notion that things spontaneously fall apart unless some process intervenes to preserve them. To the extent that “fossilization” means anything, it means preservation from destruction.

Organic remains must not be destroyed if they are to endure, yet there is a subtle but important error in jumping from this tautology to the view that preservation is an active process. Preservation is nothing more than the evasion of the process of decay. Decay, not preservation, is the active process; and decay can be avoided in many — perhaps in infinitely many — ways. If nothing happens to stop it, a dead organism will become a fossil. This applies to all parts of the organism, soft tissues as well as hard.

Imagine that, before you leave your house in the morning, you put a rock on your kitchen table. When you return home that evening, you expect the rock to be there. It would never occur to you to think of a cause for its still being there, because things that do not happen do not have causes. If nothing happened to change it, the rock still would be there after a week, or a year or a hundred years. Not finding the rock where you left it is what would demand an explanation, regardless of how long you left the rock untended.

This reasoning would also apply if you built a house of cards on your kitchen table. A house of cards is intrinsically less stable than a rock, so upon your return you would not be surprised to find that it had collapsed. In fact, you might be surprised to find it still standing, especially if you had been gone for a long time or you owned cats. But even so, if the house of cards did survive, you would not invoke a special process to explain this. You might say “I didn’t expect that — it must be stronger than I thought,” but I doubt that you would ask yourself what stabilizing force, or process, intervened to spare your creation. Merely extending the time that you left the house of cards standing would not change this. If you checked back in a billion years from now you would be amazed to find your continent in the same place you left it, not to mention your kitchen and its tabletop sculpture. But if you did find the house of cards intact, it still would not demand a cause. Again, things that do not happen do not have causes.

The same is true of fossils. We may be surprised to find fragile structures and materials, that in ordinary experience are impermanent, preserved after millions of years; but preservation does not have a cause. Preservation simply means that nothing has happened. This is not to deny that the continued existence of fossils has explanations, and it is true that certain conditions strongly favor the preservation of fossils; but these explanations and conditions are not the cause of the fossil’s survival, any more than not taking a pain killer is the cause of pain. The fossil owes its survival to its own intrinsic stability.

The Stability of Unstable Things

No part of any organic remain is absolutely stable. For example Fastovsky and Weishampel are correct when they note that apatite in bone is unstable at surface temperature and pressure. Indeed bone apatite is unstable at any pressure and temperature and will tend to recrystalize into other, more stable, minerals. But, as Fastovsky and Weishampel point out, this does not mean that bone mineral actually will make this change. The mere fact that something is unstable does not mean that it will decay, just as the fact that a house of cards is unstable does not mean that it will fall down. Decay happens only if the bone is in an environment that permits it.

But even if we know that a material is unstable and is in an environment that permits it to decay, we still know nothing about how quickly that decay will happen. It can be easy to determine the thermodynamic stability of materials, but it is notoriously difficult to predict the rate at which an unstable material actually will decay into something else, or even if it will decay at all. All forms of carbon other than carbon dioxide are thermodynamically unstable in the earth’s oxygen rich atmosphere, yet we live in a world full of carbon-based paper, plastic, tables, clothes, and carpets; and have adopted one of the most thermodynamically unstable forms of carbon, the diamond, as a symbol of permanence. Many familiar minerals, including pyrite, feldspar, and quartz, are unstable on or near the earth’s surface. Yet we do not marvel at the discovery of intact grains of quartz in half-billion year old sandstone.

Human versus Chemical Time

The crux of the creationist argument that the MOR T rex could not be more than a few thousand years old is the commonsense idea that the older the fossil, the more altered it will be. This also is part of the Tin Man story. But the relationship between age and alteration is not as straightforward as common sense would suggest, because the humans experience time differently than molecules and atoms.

The various processes that cause decay tend to work on very short time scales. As humans, we would regard a chemical compound that completely degrades after one minute as extremely unstable, but from a molecule’s point of view a minute is a very long time. A molecule that has survived for a minute has beat the odds; it has survived trillions of bond-straining vibrations and contortions, and assaults from an army of chemical agents that destroy most molecules almost the instant they form.

Radioactivity provides us with a well-studied example of how decay processes work. Atomic nuclei contain protons and neutrons. In theory protons and neutrons could be combined in an infinite number of ways. For example, we could combine one proton with 100 neutrons and make a nucleus of hydrogen-101. But this nucleus would be so unstable that it would break apart the instant that it formed. Almost all conceivable combinations of protons and neutrons are so unstable that for all practical purposes they cannot exist.

There are about 4800 exceptions, nuclides that are stable enough to be studied. About 400 of these nuclides are so stable that they are called “stable nuclides”: they either do not decay, or decay so slowly that we have not observed it. The remaining 4400 nuclides are known to decay, with half-lives ranging from a few millionths of a second to over one trillion years.

Among these unstable nuclides, the median half-life is about two minutes. This means that if you randomly assembled nuclei and measured the half lives of those that were stable enough to hold together for a millionth of a second or so, the average half life would be about two minutes. From a human point of view, two minutes is a very short time. But in the first two minutes of its existence, nature has expended half of its destructive arsenal at any randomly constructed nucleus; such a nucleus will experience the same total intensity of destructive forces during its first two minutes that it will experience during the next trillion years. In terms of the likelihood of decay, two minutes is half way to a trillion years. About 97% of unstable nuclides have half-lives shorter than 75 years. So, from a nuclide’s point of view, a human lifespan and the age of the universe are about the same.

The same is true of the molecules and crystals that make up organic remains. When thinking of how a dead plant or animal decays, we tend to concentrate on processes that occur on time scales that are easy for humans to observe, and then extrapolate these into the future. But humans observe only the very early stages of decay, a period corresponding to the first few minutes in the life of a nuclide. Even so, we observe the same steep decline in the rate of decay that nuclides display. A raccoon that dies in your attic will decompose rapidly for a month or so, but thereafter will change little for many years. Unless someone moves it, the coyote skull on my shelf will still be there tomorrow, 20 years from now, and 1000 years from now.

From the point of view of a fossil, 1000 years probably is a lot closer to 100 million years than it is to a month. If the preservational state of a fossil correlates in any law-like way with its age, it most likely is with the nth root of its age, and not its age directly.

Conclusion

Anyone who believes that fossils must undergo radical transformations in substance that are proportional to their age will always be confounded by discoveries such as those reported by Schweitzer and others (2005). For over 100 years the scientific world regularly has been surprised by accounts of fossil bones that are so “extraordinarily well preserved” that microscopic details, such as the cavities left by bone cells, still can be seen. Yet such preservation is not only common, but in some categories of fossils it is the rule. Probably most fossil bone preserves microscopic detail, and exquisite preservation also is common in plant, mollusk, and many other kinds of fossils.

Exquisite preservation is surprising only because it clashes with poorly supported preconceptions about what fossils are and how they form, preconceptions that are reflected in loaded yet ambiguous terms like “fossilization.” We cannot properly describe any fossil as “extraordinary” unless we first know what “ordinary” is. This is something that paleontologists only are beginning to understand.

The creationists have found a real weakness in the way scientists discuss fossils and hardly should be blamed for using this weakness to their advantage. The creationist challenge provides us with a good opportunity to clarify our thinking, and with object lessons in the dangers of using poorly defined terms when clarity is needed, and substituting time-honored narrative for real knowledge.

References

[BBC] British Broadcasting Corporation. 2005 Mar 24. T rex fossil has “soft tissues”. Available on-line at ; last accessed May 1, 2006.

Bocherens H. 1997. Chemical composition of dinosaur fossils. In: Currie P, Padian K, editors. The Encyclopedia of Dinosaurs. San Diego: Academic Press. p 111–17.

Deem R. nd. Dinosaur soft tissue found in T rex bones. Available on-line at ; last accessed May 1, 2006.

Fastovsky DE, Weishampel DB. 2005. The Evolution and Extinction of Dinosaurs. 2nd ed. New York: Cambridge University Press.

Jacobs L. 1993. Quest for the African Dinosaurs: Ancient Roots of the Modern World. New York: Villard.

Schweitzer MH, Wittmeyer JL, Horner JR, Toporski JK. 2005. Soft-tissue vessels and cellular preservation in Tyrannosaurus rex. Science 307: 1952–5.

Sherwin F. 2005. The devastating issue of dinosaur tissue. Acts and Facts 34 (6): 5. Available on-line at ; last accessed May 1, 2006.

About the Author(s): 
Joe Skulan
Department of Geology and Geophysics
University of Wisconsin, Madison
1215 W Dayton St
Madison WI 53706
jlskulan@geology.wisc.edu