Wednesday, July 25, 2012

Wrong for the Right Reasons

Outdated restoration of a Protoceratops andrewsi nesting
ground. Painting by Charles R. Knight, 1922.

Flipping through an old dinosaur book from the 1970s or early 1980s can be pretty fun. Nostalgia aside, it's great to see how far the science of paleontology has progressed in just a few decades, and also have a few laughs at the (from our modern perspective) outrageously outdated ideas and reconstructions we find. (David Orr's blog Love in the Time of Chasmosaurs has a great, long-running series covering "vintage dinosaur art" that lovingly pokes fun at some of the mistakes made by past palaeontographers.) Old dinosaur TV shows can be just as good. Last week, Mrs. M recorded a bunch of dinosaur shows for me which were airing on the Science Channel. I hadn't seen any of them before, and didn't realize until I hit play that I was in for a blast from the past. The shows were obviously old-school, narrated by Jeff Goldblum (I assumed these had come out around the time of The Lost World: Jurassic Park until one episode started discussing finds from later in the 1990s like Beipiaosaurus). One episode featured a segment on Roy Chapman Andrew's famous discovery of dinosaur eggs in the Gobi Desert, and the infamous misinterpretation of the eggs as belonging to Protoceratops rather than Oviraptor. This is just the kind of paleontological gaffe we paleo fans get schadenfreude out of today. After discussing the refuted hypothesis that an Oviraptor found on a nest of these eggs was first thought to be eating them rather than guarding them as later finds suggested, Mrs. M asked the obvious question: Why, given that this thing was found on top of the eggs, did they assume the eggs belonged to a different dinosaur?

We often look back with hindsight and, somewhat smugly, judge outdated hypotheses as inferior to those of today. We do this because, presumably, our modern notions about how prehistoric animals looked, moved, and behaved are closer to reality. However, 'The Truth' is a tricky concept when it comes to science, and its easy to forget that more than a quest for 'Truth', science is actually a long process of ever-refining hypotheses.

Inaccurate(?) reconstruction of Spinosaurus aegyptiacus as a partially quadrupedal allosauroid-like animal. Painting by Giovanni Caselli, from the book The Evolution of Ecology of the Dinosaurs by L.B. Halstead. Originally posted by Marc Vincent here.
For better or worse, many scientists, even (especially) those who work to popularize science for the lay public, talk about currently-supported hypotheses as if they are The Truth. Ask pretty much any paleontologist to describe, say, a Spinosaurus, and he will likely say it's a bipedal carnivorous and/or piscivorous theropod dinosaur with a tall ridge along its back and a long, crocodile-like snout full of conical teeth. However, Spinosaurus is only known from very fragmentary remains, mainly a few sets of jaws and some vertebrae. So how do we know all this is true? Well we don't, really. That description is a conservative, reasonable hypothesis based on several lines of evidence including comparative anatomy, taphonomy (the arrangement of the fossils in the ground which lead us to reasonably suppose that the jaws go with the verts, rather than coming from different animals), etc. Is it possible that the jaws of Spinosaurus come from a crocodilian with baryonychid-like teeth, while the verts come from an allosauroid? Is it even possible Spinosaurus was actually a quadruped as envisioned by some older reconstructions? Sure. But those hypotheses go above and beyond the current evidence. There is no reason to think those things are true, in favor of the simpler hypothesis that Spinosaurus was a typical theropod with a few weird features. Right now, that's our working version of the truth, and it's the best we've got. If further evidence comes along to prove us completely wrong, great! That kind of dramatic overturning of an accepted hypothesis can lead to some of the most exciting moments in science. But at the moment, it is incumbent on any reasonable person to assume the simplest explanation is the most likely.

So is it really fair to laugh at those silly old scientists in the 1930s who thought Oviraptor was an egg thief that preyed on Protoceratops nests just because it was found near eggs? Just like us and our Spinosaurus, that was actually a reasonable explanation at the time. The eggs were attributed to Protoceratops primarily because there were lots of both. Protoceratops was the most common dinosaur found in the area, so it made sense to attribute the numerous eggs to that genus. The fact that the Oviraptor, known only from the one skeleton, was found associated with one nest seemed likely to be a fluke, which could reasonably be written off as a chance association due to other factors like predation. The scientists who labelled Oviraptor an egg thief were drawing the most logical conclusion they could given the current evidence. The fact that later evidence proved this conclusion wrong doesn't make them foolish--that's how all science is supposed to work. Assuming right off the bat that the Oviraptor was the parent brooding its own eggs would have been an extraordinary claim lacking extraordinary supporting evidence (e.g. embryos or a clearly preserved  brooding posture) and therefore could not be considered justifiable until the discoveries of really extraordinary specimens in the 1990s.

We can take this view all the way back to the earliest reconstructions of dinosaurs. It's well known that those silly Victorians reconstructed theropods and ornithopods as plodding, four-legged, lizard-like beasts. It's easy to overlook the fact that this was actually an entirely reasonable interpretation given the evidence at the time. Bipedal reptiles were unheard of, and anatomical evidence in the early days of dinosaur paleontology led many researchers to conclude that these animals were indeed lizard-like or crocodile-like, if not actual giant squamates. Anyone who suggested to William Buckland that the bones of Megalosaurus may in fact have come from a bipedal animal would rightly have been ignored. They would have been right, of course, but it would have been a position based on a lucky guess rather than good science. Given the scrappy material Victorian scientists had to work with and almost complete lack of closely related forms outside lizards and crocodiles, concluding that Megalosaurus was a basically lizard- or croc-like quadruped with some odd mammal- or bird-like features was the most reasonable thing to do.

Citipati osmolskae embryo in egg.
Photo by Jordi Paya, licensed.
In sciences like paleontology, when somebody says "we know x", this is simply convenient shorthand for "x is the most parsimonious hypothesis given the current evidence." It's usually not necessary to state those caveats unless you're trying to be particularly careful with your wording, because those caveats are the basic underlying principles of science itself. The scientific method doesn't really allow us to ever arrive at 'The Truth', but rather, like Zeno's parodox, we incrementally get closer and closer to truth without ever hoping to reach it. No matter how solid the evidence, those caveats can and must always exist. As reasonable, logical people, we can only accept what we currently know as true, but always with the understanding that more evidence could potentially change that truth. In that light, "truth" in science is always provisional. Even now, we can't say with 100% certainty that the original Oviraptor specimen was brooding those eggs rather than eating them. While we can now recognize the eggs as oviraptorid rather than ornithischian in anatomy, it's always remotely possible that the theropod was raiding the nest of a different species or even another Oviraptor. But given the weight of the current evidence, these assertions are now the unsupportable ones.

So, the next time somebody claims Spinosaurus was a lumbering quadruped mistakenly given the head of a crocodile, you should feel justified in ridiculing the idea as pure fantasy, but don't be too disappointed if it later turns out to have been an incredibly lucky guess.


  1. "While we can now recognize the eggs as oviraptorid rather than ornithischian in anatomy, it's always remotely possible that the theropod was raiding the nest of a different species or even another Oviraptor."

    While brooding is the most likely possibility, I can't help but wonder why no one else ever mentions the possibility of cannibalism. AFAIK, you're the 1st, so thanks for that.


  2. I agree in general, but...

    There are more complete Spinosaurus specimens known (though privately owned), which don't indicate anything too surprising about its anatomy.

    Did it really make sense to attribute the eggs to Protoceratops just because they were both abundant? While attributing them to Oviraptor in the 20s may have been just as problematic, surely the most scientifically defensable choice Osborn et al. could have made was to not assign the eggs to a genus.

    Regarding early reconstructions of Megalosaurus, that's surely due to their crappy methods back in the 1800s. If they had used synapomorphies and cladistic analysis, even the Megalosaurus paralectotypes would probably have emerged sister to Aves due to the inturned femoral head, long pubis and ischium, appressed metatarsals, more than four sacrals, elongate pre/postacetabular processes, open acetabulum, etc.. And if that was the case, then bipedality would be ambiguous.

  3. I essentially agree with what you've said about the eggs and the posture of Megalosaurus, Iguanodon, and Hylaeosaurus (one and a half out of three isn't too bad!), altho' I agree with Mickey about being more circumspect about assigning eggs to species described only from skeletal material.

    However, what about silliness such as sauropods up to their nostrils in water? Was this ever taken seriously by 20th century palaeontologists or was it some sort of children's book meme that was started by a writer of popular-science books or, perhaps, a "researcher" way out of their field? I ask because this hypothesis (and other similar flights of fantasy) seems fairly easily to falsify with the knowledge and methods that were available at the time.

  4. @ Mickey Good points. While I was mainly talking about making the most sound decision based on the tools and methods available at the time, I have to wonder if, given that the available sample size of non-avian panavians at the time was essentially 2, if even had Owen produced a decent cladogram Megalosaurus and Iguanodon would not have been pulled over to the pancroc side. Even if not, as you said bipedality would be ambiguous, and I'd argue given the extremely large body sizes relative to crocs and birds, quadrupedality would still have been the more conservative conclusion.

    I'm not sure how seriously the nose-deep sauropod thing was ever taken by real scientists (though I feel like this has probably been covered at TetZoo or SV-POW at some point). Certainly the pneumatic vertebrae of sauropods was noted very early on, at least.

    More problems with this scenario are mentioned here:
    It seems obvious that this kind of depiction should have been seen as unrealistic from the get-go, so I wouldn't include it in the list of outdated ideas that were defensible at the time.

  5. If we confine ourselves to the tools and methods available at the time, then we're really just saying we have no objective tools or methods. Buckland (1824) says Megalosaurus' vertebrae and limbs are like mammals, but that the teeth indicated it was oviparous (wha?!) and thus it was a member of Sauria, which contained lizards and crocodilians, but not snakes. So the method was choosing key characters and subjectively classifying, and this makes almost any result possible. Does it make much sense then to say their ideas were reasonable given their methods, when their methods had no way to judge between reasonable and unreasonable alternatives?

    As for Owen's hypothetical cladogram, remember he had Pterodactylus to work with too. Honestly, that would have probably emerged closest to birds until Compsognathus was described. Hey, 1858- the last time BAND was cladistically defensable. In any case, while Megalosaurus shares plenty of symplesiomorphies with crocs (thecodonty, saurischian pelvis, unfused bones, anteriorly concave dorsal centra), I can't think of many apparent synapomorphies it would share to the exclusion of birds. The fourth trochanter is one. Hmm. regarding size, since there is no biomechanical reason something with a femur 860 mm long can't be bipedal, Owen couldn't come up with it using good methods and would have had to rely on bad methods like personal incredulity. So again, their crappy methods led to crappy ideas.

  6. Thanks Matthew (not Matty anymore?). I had read Brian's smackdown of Ford's Fantasy along with a few others (Darren Naish's response in Laboratory News itself is particularly good - for those that haven't read it).

    I recall reading in a children's book many years ago that the sauropods' skeletons were lighter, higher up (or something - presumably referring to pneumatic vertebrae but not mentioned at all) but this was explained as being due to them having a water-line. At eight years-old, that made perfect sense.

  7. There's more to the association than just incidental closeness to what was eventually found to be possibly the animal's own nest. But the kicker was two things, one not noted by Osborn in his description, but visible in the photograph of the whole specimen. For a look-see, try this post of mine, in which I lay out what Osborn actually argued. Osborn was wrong about two factors, that the association was incidence of predation and that the ventral projections of the palate were used for egg-eating (because he didn't realize they were incomplete palatal bones with no evidence for penetrating objects). New data has shown that oviraptorids would likely have been generalist, durophagous still, and possibly herbivorous to a large degree. Despite this, what is generally also overlooked is that there are remains of an animal (and eggshell) in the breast area around the arm. Osborn, and most others, never mention this.

  8. Excellent post, and a great comment thread (thanks all!), but my unjustifiably colossal ego couldn't let one error pass - for it was I that posted the LITC entry on the Halstead book! Me, I tell you!