Derek Turner writes . . .
I’m married to an archaeologist, and my spouse and her archaeology friends have lots of stories about conversations that go like this:
“So, what do you do?”
“I’m an archaeologist.”
“That’s exciting! What dinosaurs have you discovered?”
This sort of exchange is messed up on two different levels. First, and most obviously, there’s the confusion about archaeology vs. paleontology. Not that readers of this blog need to be told, but archaeologists study humans, not dinosaurs! But even once you correct the exasperating archaeo/paleo confusion, there’s a deeper problem here, and one that’s less often noticed. Many people also have the mistaken impression that paleontology = dinosaur science. In the exchange above, the questioner assumes that archaeologists must be looking for dinosaur bones. But that assumption isn’t even true of paleontology!
Science education fail. Twice over.
An ammonoid fossil on display at the Naturhistorisches Museum in Vienna. Photo by the author.
The Drosophila of Paleontology
When I first started to do some work in philosophy of paleontology, as a grad student in the late 1990s, I was primarily interested in thinking about dinosaur science. Who wouldn’t be? Of course, I knew that paleontology is the study of prehistoric life more generally, but in my own work, I kept coming back to examples from dinosaur science. My very first effort was a paper on functional morphology: How do scientists figure out what strange fossilized structures were for?[1] I started looking, in particular, at the history of scientists’ attempts to discern the function(s) of the cranial crests of the duckbilled dinosaurs—the hatchet-shaped crest of Lambeosaurus, the Greek helmet crest of Corythosaurus, and the incomparable cranium of Parasaurolophus (below). What's the headgear all about?
Parasaurolophus walkeri. Image courtesy of Wikimedia commons.
Increasingly, though, as I’ve learned more and more about paleontology I’ve come to wonder if dinosaurs might be overrated in one important respect. Dinosaurs are intrinsically fascinating. They have a larger cultural significance, and they also have a starring role to play in science education. Dinosaur paleontology is like the scientific version of a gateway drug. Not only that, but the fact that so many people are generally familiar with dinosaurs makes them a great way to begin to engage readers with issues in philosophy of science (for example, in many of our essays on this blog). But although the love of dinosaurs is what drew me into the philosophy of paleontology in the first place, if I were a paleontologist, I’m not sure if I would devote all my energy to studying them.
You may have noticed that every contributor to the Extinct blog has a caricature with a prehistoric totem animal. My own animal—the critter with the tentacles and the coiled shell—is an ammonoid.[2] The German paleontologist Adolf Seilacher once wrote that “ammonoids are for paleontologists what Drosophila is in genetics.”[3] Drosophila, the ordinary fruit fly, was the easy-to-work-with model organism that facilitated the rise of modern genetics. The implication is that ammonoids are more central to paleontological research than dinosaurs are. Why would Seilacher say this?
An early 20th century rendition of prehistoric ammonoids. Image courtesy of Wikimedia commons.
The Underrated Richness of the Ammonoid Fossil Record
The answer has to do with quality of data. The fossil record for ammonoids is better than the dinosaur record. Consider just one genus, Acrochordiceras, that lived during the Triassic period, some 247 – 242 million years ago. (You can see some nice pics of Acrochordiceras here.) The Paleobiology Database lists 167 specimens assigned to this genus alone. Compare that to Parasaurolophus, which has only 17 occurrences in the database, and most of those are seriously incomplete, with just a small handful that include both the distinctive skull and significant portions of the post-cranial skeleton. That's an order of magnitude difference. There are over 82,000 ammonoids in the Paleobiology Database, as compared with 20,000 dinosaurs, and most of those dinosaur specimens are fragmentary.
One further indication of ammonoid abundance is the fact that you can buy small fossils very cheaply at many rock shops. Someone once gave me this one as a Secret Santa present.
I took this picture of a snakestone at the Naturhistorisches Museum in Vienna. In medieval Europe, people thought that ammonites were petrified snakes--perhaps the remains of snakes that St. Patrick drove out of Ireland. In some cases, people would carve heads on them--an early example of fossil preparation?
The soft parts of ammonoids rarely fossilize, but the abundance of fossil shells gives us a high resolution look at the evolution of a group of organisms that flourished for something like 300 million years, before they finally went extinct (with the dinosaurs) at the end of the Cretaceous. The abundance is due partly to the fact that there were a lot of ammonoids swimming around in ancient seas, and partly to the fact that their shells fossilized readily. Scientists have studied the group quite intensively, and have documented some fascinating evolutionary patterns and trends. To give just one of many, many possible examples, it’s been shown that during the Triassic, the family Acrochordiceratidae (to which Acrochordiceras belongs) exhibited size increase but without any significant increase in shell ornamentation.[4] So you get size increase with no increase in structural complexity. This is not to say that we have no clue at all about patterns and trends in dinosaur evolution. It’s just that the ammonoid record is finer grained and more complete, by comparison, giving us a window even on evolutionary change within families.
The relative completeness of the ammonoid fossil record also makes it more useful for addressing “high altitude” questions about evolution. Suppose you want to explore questions about extinction: how is extinction risk related to other variables, such as body size, geographic distribution, longevity of the taxon (i.e., does extinction risk increase with age?) morphological complexity, or morphological disparity within the taxon (roughly, how much variation there is in shell shape and size). The rich ammonoid fossil record contains a wealth of data that can be subjected to statistical analysis and brought to bear on these questions. The dinosaur record contains information, too, just not as much. Of course, for certain sorts of questions, a single specimen might be all you need. But if you want to draw inferences about evolution, it helps to have a larger sample size.
The Dinosaur Paradox: Rarity and Value
The abundance of ammonoid fossils, relative to dinosaurs, means that there is an important sense in which they have greater scientific value. The ammonoid fossil record is, quite simply, a better dataset (at least with respect to certain sorts of questions) and one that offers a less ambiguous and finer-grained picture of evolution. The record for other marine invertebrate groups is even better still. This is the perspective from which dinosaurs might seem overrated. The bigger and more representative the sample the better, and dinosaur scientists are almost always working with smaller sample sizes, relative to invertebrate paleontologists.
Notice how this straightforward point about evidence—that a bigger fossil sample is evidentially better (at least, relative to certain kinds of questions)—runs directly counter to powerful intuitions about value. Anybody who has ever collected anything, from postage stamps to baseball cards to antiques to fossils, knows that rarity increases value. The famous upside down Jenny stamps command such a high price (you might be able to get $1 million for one) because they are so rare: only 100 were printed in 1918. I’m not saying that paleontology is mere stamp collecting, a comparison that people have made in the past with the aim of disparaging paleontology. My point is nearly the opposite of that: Thinking scientifically about fossils might mean setting aside ordinary intuitions about rarity and value.
Fascinatingly, one environmental philosopher, Lily-Marlene Russow, once wrote a paper applying the idea that rarity enhances value to endangered species.[5] Part of what makes giant pandas so incredibly valuable aesthetically, she argued, is that there just aren’t very many of them. Our duty to protect them is a lot like our duty to conserve rare postage stamps, or Stradivarius violins.
One of the famous inverted Jenny stamps from 1918. Image courtesy of Wikimedia commons.
The intuitive idea that rare things have greater value can also affect our thinking about dinosaurs. A nearly complete skeleton of a big dinosaur is an extremely rare thing. When somebody finds one, or when a museum buys one, it’s a big deal, reported widely in the news. Part of the thrill and the romance of dinosaur science is that complete specimens are so unusual. The excitement of finding, or even just seeing, a rare skeleton is heightened by our intuition that rare things are especially valuable.
This, then, is the dinosaur paradox. (No, it’s not a paradox in the strict sense, but hopefully the term is not too inapt.) Rarity both enhances and diminishes value. It diminishes scientific or evidential value. But it enhances other kinds of value, market value certainly, and arguably also aesthetic value. This is at least part of the story about why dinosaurs are a bigger deal, culturally speaking, than ammonoids, and also why they are not the Drosophila of paleontology--in spite of their unique capacity for blowing minds. The dinosaur paradox arises from evidential considerations pulling in the opposite direction from aesthetic ones.
[1] D. Turner (2000), “The Functions of Fossils: Inference and Explanation in Functional Morphology,” Studies in History and Philosophy of Biology and Biomedical Sciences 31(1): 193-212.
[2] A word about terminology: The ammonoids (Ammonoidea) were a subclass of cephalopods. Ammonitida is a distinct order within that subclass. People often use the informal term “Ammonite” to refer to the larger group, the ammonoids. The term “ammonite” comes from Pliny the Elder, who thought that the coiled shapes of the fossils resemble the horns of the Egyptian god Ammon.
[3] A. Seilacher (1988) “Why are nautiloid and ammonite sutures so different?” Neues Jahrbuch für Geologie und Paläontologie 177: 41-69. The quotation is from p. 67.
[4] Monnet C., Bucher H., Guex, J., Wasmer M., (2012), “Large-scale evolutionary trends of Acrochordiceratidae Arthaber 1911 (Ammonoidea, Middle Triassic) and Cope’s Rule,” Palaeontology 55: 87-107. Also Monnet C., Brayard A., Brosse M. (2015), “Evolutionary trends of Triassic ammonoids,” in C. Klug et al., eds., Ammonoid Paleobiology: From Macroevolution to Paleogeography. Topics in Geobiology 44. Springer, pp. 25-50.
[5] Lily-Marlene Russow (1981), “Why do species matter?” Environmental Ethics 3(2): 101-112.