You can predict how rabbits run by looking at their skulls (using this one weird trick!)

March 17, 2015

Kraatz et al 2015 Figure 1 - rabbit skull freak gallery

Meet some of my new friends: (A) Brachylagus idahoensis, (B) Lepus capensis, (C) Poelagus marjorita, (D) Pronolagus crassicaudatus, (E) Lepus americanus, (F) Oryctolagus cuniculus, (G) Nesolagus timminsi, (H) Bunolagus monticularis, and (I) Romerolagus diazi. Kraatz et al. (2015: fig. 1).

I have a new paper out today in PeerJ: “Ecological correlates to cranial morphology in leporids (Mammalia, Lagomorpha)”, with coauthors Brian Kraatz, Emma Sherratt, and Nick Bumacod. Get it free here.

I know, I know, I have fallen from grace. First Aquilops, now rabbits. And, and…skulls! I know what you’re thinking: that maybe I’m not just experimenting with the non-vertebrae of non-sauropods anymore – maybe I have an actual problem. But I don’t. I can quit anytime! You’ll see.

Actually rabbits are the freakiest of all mammals and their skulls are wicked cool. They have double incisors, with the second set right behind the first, hence the name Duplicidentata for rabbits and their close relatives. They have weird fenestrations in their maxillae (pretty much all taxa) and parietal and occipital bones (some more than others) – I’ll come back to that in a bit. And, as we discuss in our new paper, you can tell something about how a rabbit runs by looking at its skull. I thought it would be fun to relate how we figured that out, and why.

A long time ago in a graduate seminar far, far away…

1950: DuBrul, Laskin, and Moss

I met Brian Kraatz at Berkeley, where he and I were part of the cohort of students that came into the Integrative Biology Department in the fall of 2001 (faithful readers may remember Brian from his work tracking oliphaunts from, gosh, three years ago already). We took a lot of classes together, including a seminar by Marvalee Wake on evolutionary morphology. I’m pretty sure that seminar was the first time I’d actually read DuBrul and Laskin (1961), “Preadaptive potentialities of the mammalian skull: an experiment in growth and form”, or as I think of it, “How to turn a rat skull into a pika skull for fun and profit.”

Pikas (Ochotonidae) are the sister group to rabbits (Leporidae) and together these groups make up crown Lagomorpha. If you’re not familiar with pikas, Brian describes them as starting with bunny rabbits and then making them even cuter and cuddlier. Seriously, go do an image search for ‘pika’ and try not to die of cute overload.

Pikas are interesting because in many ways their skulls are intermediate between those of rodents, especially rats, and rabbits. This is maybe not surprising since rodents are the sister group to lagomorphs and are united with them in the clade Glires. E. Lloyd DuBrul was all over this rat-pika-rabbit thing back in the mid-twentieth century. Here’s an illustration from DuBrul (1950: plate 2; labels added by me):

Rattus Ochotona and Lepus skulls compared - DuBrul 1960 plate 2

So DuBrul knew from pikas and in particular he had the idea that you could maybe just tweak a rat skull – say, by knocking out the basicranial sutures in a baby rat to limit the growth of the skull base – and produce a gently domed skull like that of a pika. That’s what DuBrul and Laskin (1961) is all about. They did that experiment and here are their results (DuBrul and Laskin (1961: plate 3). Normal rat skull on the right, and dotted in the bottom diagram; experimental “pika-morph” rat skull on the left, and solidly outlined below.

Experimental skull doming in rats - DuBrul and Laskin 1961 plate 3

What’s going on here morphogenetically is that the facial skeleton is getting tilted down and away from the back end of the skull. DuBrul was hip to that, too – here’s a relevant image from his 1950 paper (plate 4; labels added by me):

Skull tilting in Rattus Ochotona and Lepus - DuBrul 1960 plate 4

The common reference point against which these skulls are registered is the cranial base (the floor of the braincase just forward of the foramen magnum). Again, the pika is a pretty good intermediate between the rat and a ‘normal’ rabbit, and the dang-near-dog-sized Flemish Giant rabbit takes the lagomorph face-tilting thing to its extreme. (‘Flemish Giant rabbit’ is another entertaining image search that I will leave you as homework.)

Turns out there’s another way you can get rat skulls with different geometries: you can cut off their legs and make them walk on two feet. In an experiment that you might have trouble getting past an Institutional Animal Care and Use Committee today, Moss (1961) lopped off the forefeet or hindfeet in two experimental batches of rats, to see what effect this would have on their skulls. I’ll let Moss speak for himself on this one (Moss, 1961: pp. 301-303, emphasis in the original):

Circumnatal amputation of the forelimbs has successfully produced what are in essence “bipedal rats,” i.e., rats whose habitual mode of kinetic and static posture is permanently altered. […] The animals never became bipedal in the exact sense; that is, they never walked erect on two limbs at all times. […] Nevertheless, bipedal posture and motion were more frequently observed than in controls. […]

Animals whose hind limbs were removed represented another picture. They most certainly did not walk about on their intact forelimbs. Neither did they seem able to use their hind limb stumps as satisfactory substitutes. Their gait was not uniform and seemed to consist in a series of short pushes or hops. The most noticeable thing about them was, among other things, apparent accentuation of their cervical vertebral curvature. The sum of these changes was an upward rotation of the skull.

He wasn’t kidding: when the two groups of bipedal rats grew up, their facial skeletons were tilted relative to the control group, but in different directions (Moss, 1961: fig 3; ‘fore’ and ‘hind’ refer to which limbs the animals had left to locomote with):

Skull deformation in bipedal rats - Moss 1961 fig 3

Brian and I read Moss back at Berkeley, too. In fact, we were minor Moss junkies. If you’re interested in how living forms come into being, you owe it to yourself to read Moss (1968), “A theoretical analysis of the functional matrix”.

The upshot of all of this is that although neither Brian nor I had done anything with our deep (and, okay, deeply weird) knowledge of how to experimentally jack up rat skulls by the time we graduated from Berkeley, we were also primed to be thinking about how skulls attain their shapes – especially the skulls of rodents and rabbits.

2009: American Museum of Natural History

I went to the AMNH in February, 2009, to visit Brian, who was on a postdoc there at the time, and to spend one day looking at sauropods with Mike, who was over from England for a conference. What Brian and I planned to work on was the fenestration of rabbit skulls, because I’m always interested in the strategic loss of bone from skeletal structures. We spent probably half a day talking about that, and I filled a whole page in my notebook with related noodlings:

AMNH rabbit skull sketch 1

But as the sketch on the right shows, it didn’t take us long to figure out that there was something even more interesting to do with rabbit skulls. Brian had a whole shedload of rabbit skulls from different taxa sitting on his desk, and we noticed pretty quickly that one of the primary ways they varied was in the tilt of the facial skeleton relative to the back of the skull. Here’s the very next page of my notes from that trip:

The skull up top belongs to Caprolagus, the Hispid hare, which I tend to think of as the “bulldozer hare”. Seriously, it looks like a tank. It doesn’t bound or even hop, it scrambles. Here, stare into the abyss:

Caprolagus from ARKive

That rabbit will cut you, man. And just look at how flat its skull is. Even in life Caprolagus looks more rodent-y than rabbit-y. Or, more precisely, more Ochotona-y.

At the the other extreme are taxa like Bunolagus and Pronolagus, which really push the “I’m going to cute you to death by dint of my incredible bunnosity” thing:

Bunolagus from ARKive

As Brian and I started going through skulls of as many extant rabbits as we could, we noticed that the flatter-skulled taxa, with less pronounced facial tilt, tended to be the stolid, foursquare scramblers like Caprolagus, whereas the speed demons tended to have more strongly tilted skulls. It also seemed like the latter group were achieving that pronounced facial tilt by changing the geometry of the occipital region of the skull. Look back up at the red quadrilaterals I drew on the Caprolagus and Bunolagus skulls in my notebook – those mark the basioccipital ventrally and the dorsal exposure of the supraoccipital. Perhaps unsurprisingly, supraoccipital length is not the whole story; it turns out that some face-tilters get that way by having longer or more strongly arched parietals, BUT it remains true that if you find a rabbit skull with a long dorsal exposure of the supraoccipital, it will also have pronounced facial tilt.

ANYWAY, by my last night in New York, Brian and I decided that the best way to attack this would be to go down to the basement and stay up most of the night drinking beer and measuring rabbit skulls. We then tried to correlate the various measurements and angles with information on the locomotor and burrowing habits of each species. That was a big job, and after a couple of years with little forward progress (to be fair, Brian was moving across the country and taking his first tenure-track job in this interval, and I was helping birth a sauropod) we brought in Brian’s graduate student, Nick Bumacod, to do most of it. Later on the three of us were forced to acknowledge that we knew enough statistics to get ourselves into trouble but not enough to get back out. Brian had taken a geometric morphometrics course for which Emma Sherratt was a TA, and he started bugging her for help with the stats. Emma has been involved in writing new software packages for R, and we realized that the paper would be a lot stronger if we just brought her on as an author and gave her free rein with the data. Along the way Brian and Nick were giving presentations on the project everywhere from the local Western Area Vert Paleo meeting to the World Lagomorph Conference in Vienna. I got my name on four abstracts along the way, which I think is record abstract-to-paper ratio for me (especially considering that 90% of my effort on the paper was invested in a single evening in 2009 over a couple of six-packs).

But enough navel-gazing, what did we find?

2015: Rabbit skulls reveal their mode of locomotion

Our results, which you can read for free, support the hunch that Brian and I had back in 2009: slow-moving rabbits that locomote by scrambling or scampering instead of hopping tend to have less facial tilt, and faster-moving saltatorial (hopping) and cursorial (leaping and bounding) rabbits have more facial tilt. Interestingly, facial tilt does not distinguish the saltators from the cursors. So the break here is between scrambling and any kind of hopping or leaping, but not between hoppers and leapers.

Kraatz et al 2015 fig 5a

Kraatz et al. (2015: fig. 5a)

Why would that be so? We don’t know for sure yet, but our top hypothesis is that if you’re moving fast, it pays to see the ground in front of you more clearly, and getting your nose down out of the way probably helps with that. This is pretty similar to the hypothesis that tyrannosaurs have pinched nasals for better binocular vision (Stevens, 2006). Rabbits are prey animals and probably can’t afford to point their eyes forward, and they may need wide nasal airways as air intakes while they’re sprinting. Tilting the nose down may be the next best thing.

Guinea pig and mara skulls - DuBrul 1960 plate 6

Some circumstantial support for this comes from the Caviidae, the family of South American rodents that includes guinea pigs, cavies, maras, and capybaras. Here’s another plate from DuBrul (1950: plate 6) contrasting the flatter skull of the guinea pig (Cavia porcellus, top) with the decidedly arched skull of the mara or Patagonian hare (Dolichotis magellanica, bottom). Compare the mara skull to the sectioned rabbit skull in the other DuBrul plate, above – there aren’t a lot of obvious characters to separate the two (beyond the lack of double incisors in the mara).

Mara photo from Wikipedia

Mara photo from Wikipedia

Despite being commonly referred to as ‘hares’ and looking a lot like short-eared rabbits, maras are rodents that evolved their rabbit-like form independently. The acquisition of pronounced facial tilt in two separate lineages of small fast-moving herbivorous mammals is further evidence for the influence of locomotor mode on skull form. Irritatingly, I think we neglected to mention the guinea pig : mara :: pika : rabbit correspondence in the paper. Oh well, it wasn’t our novel observation, and we did cite DuBrul (1950).

Kraatz et al 2015 Figure 4 - skull measurements

Relevant to the next paragraph: DILU is ‘diastema length upper’ and BLD is ‘bulla diameter’. Kraatz et al. (2015: fig. 4).

We found lots of other interesting things, too. The PCA plots we produced from our data separate the living rabbits in unexpected ways. The length of the diastema (the toothless portion of the upper jaw) and the diameter of the auditory bulla seem to be particularly important. Diastema length isn’t too hard to figure out – most of the face-tilters have long diastemas, and the flat-heads tend to have short ones. We have no idea what bulla diameter means yet. I mean, obviously something to do with hearing, but we don’t have any ecological variables in our analysis to address that because we didn’t see it coming. So there’s a chunk of new science waiting to be done there.

Speaking of new science, or at least a relatively new thing in science, we published the full peer-review history alongside the paper, just as Mike and I did back in 2013 and as Mike did with his stand-alone paper last December. More than 80% of PeerJ authors elect to publish the peer review histories for their papers. I can’t wait until it’s 100%. PeerJ reviews are citeable – each one gets a DOI and instructions on how to cite it – and I’m tired of having my effort as a peer reviewer used once and then thrown away forever.

If you’ve been reading this whole post with gritted teeth, wondering why we were using linear measurements instead of geometric morphometrics, chillax. Brian and Emma are on that. They’ve been CT scanning the skulls of as many extant rabbits as possible and plotting landmarks for 3D morphometrics – if you were at SVP last fall, you may have seen their talk (Kraatz and Sherratt, 2014). So stay tuned for what will soon be a new ongoing series, Rabbit Skulls: The Next Generation. (Update: pilot episode here.)

I probably won’t be on that voyage. I’ve had fun getting acquainted with a completely different part of the tree of life, but there are an awful lot of shards of excellence – busted-up sauropod vertebrae, that is – crying out for my attention, and I need to stop neglecting them. I’m done with rabbit skulls, I promise. I’m going clean. (Wish me luck!)

References

  • DuBrul, E. L. (1950). Posture, locomotion and the skull in Lagomorpha. American Journal of Anatomy, 87(2), 277-313.
  • DuBrul, E. L., & Laskin, D. M. (1961). Preadaptive potentialities of the mammalian skull: an experiment in growth and form. American Journal of Anatomy, 109(2), 117-132.
  • Kraatz, B., and Sherratt, E. (2014). Evolution, ecology, and modularity of the lagomorph skull. Journal of Vertebrate Paleontology, 35(3, Supplement), 162A.
  • Kraatz, B.P., Sherratt, E., Bumacod, N., and Wedel, M.J. 2015. Ecological correlates to cranial morphology in leporids (Mammalia, Lagomorpha). PeerJ3:e844.  https://dx.doi.org/10.7717/peerj.844
  • Moss, M. L. (1961). Rotation of the otic capsule in bipedal rats. American Journal of Physical Anthropology, 19(3), 301-307.
  • Moss, M. L. (1968). A theoretical analysis of the functional matrix. Acta Biotheoretica, 18(1), 195-202.
  • Stevens, K. A. (2006). Binocular vision in theropod dinosaurs. Journal of Vertebrate Paleontology, 26(2), 321-330.
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26 Responses to “You can predict how rabbits run by looking at their skulls (using this one weird trick!)”

  1. Newt Says:

    Well that is just completely fascinating. I will never look at a bunny skull the same way again. Now I’m very interested to know if there are any skull morphology correlates for semi-aquatic rabbits (some Sylvilagus) or rodents.

  2. Matt Wedel Says:

    Brian Kraatz may weigh in here, but the quick take is “probably not” for rabbits. There are only a couple of taxa that are facultatively semi-aquatic, and they don’t spend that much time in the water. But it’s a possible avenue for future research. Heck, since we published our raw data (in the Appendix to the paper) anyone who is curious could run that analysis right now.

  3. Brian K Says:

    Yes, there are facultatively aquatic species, with the most well-known being the Marsh rabbit. We didn’t look at this specifically, and I’d wonder if there were enough semi-aquatic species to actually test this. My gut says this behavior wouldn’t influence cranial shape, particularly if our visual field hypothesis holds water. There are also a couple species that hang out in bushes, and could cautiously considered to be facultatively arboreal. They’re crazy animals. On a related note, here’s the story of President Jimmy Carter being attacked by an aquatic rabbit.

    http://en.wikipedia.org/wiki/Jimmy_Carter_rabbit_incident

  4. DK Fennell Says:

    What mechanism would account for the result discovered by Moss? It’s a pure developmental response to having legs wacked off. It’s oddly Lamarckian.

  5. Matt Wedel Says:

    Moss was interested in the fact that the otic capsule (the box of bone around the middle and inner ears) does not fuse to the rest of the skull until fairly late. Most animals keep their horizontal semicircular canals in some semblance of a relationship with the horizontal plane (BIG error bars, though – see Taylor et al. 2009). Moss was curious to find out whether, if he could get the rats to hold their heads differently, the otic capsule would rotate into a new orientation before it fused – or, more accurately, whether the rest of the skull would rotate around the more static otic capsule.

    But I guess that still doesn’t really answer your question about mechanism, in that it doesn’t address the actual force that warps the skull bones. Maybe just nearly-constant tension from posture-maintaining muscles when the head is held at a weird angle? If someone who actually knows what they’re talking about wants to jump in at this point and rescue me, feel free!

    You’re right, it does sneak up on the Lamarckian idea of biological form being molded by its circumstances within the lifespan of a single individual, although without the hereditary transmission. Still very curious.

  6. ncmncm Says:

    It can’t be called Lamarckian at all without hereditary transmission, no matter how much fun the word is to say. But if plastic cranial (and other) morphology drive choices of diet, lifestyle, and favored predator, those might be taught to offspring, the which might then force matching morphological changes in offspring. To the degree that these changes affect mate recognition and predatorial preference, it could drive accelerated genetic drift and in situ speciation.

    I don’t know if predator favor is a thing in animal behavior study. But there are lots of behaviors that, while they expose you less to one predator, increase your exposure to another. Adaptations to avoid that other are likely to be different than for the first, and not necessarily back toward the mean.

    Of course you don’t need developmental morphological changes to speciate this way, but everything participates, innit?

  7. Matt Wedel Says:

    It can’t be called Lamarckian at all without hereditary transmission, no matter how much fun the word is to say.

    I’m sorry, but that’s just flatly incorrect. Lamarck promoted a number of original hypotheses, any of which can fairly be described as ‘Lamarckian’, whether they have anything to do with heredity or not. One example would be his theory of continental motion, which proposed that continents eroded at their eastern borders and the eroded material was carried across the ocean to be deposited at their western borders, so the continents would gradually march around the globe from east to west.

    Turning to Lamarck’s evoluionary ideas, he hypothesized two forces that worked to mold the morphology of organisms during their lives: a complexifying force, based on ‘subtle fluids’ (including heat and electricity!) literally carving new channels through the body’s tissues, and an adaptive force that molded organisms to their circumstances. If those changes were passed on to an organism’s offspring, that would be Lamarckian evolution. Every evolutionary theory that was floated in the 1700s and 1800s included some kind of hereditary transmission, and pretty much all of them – even Darwin’s – accepted the inheritance of acquired characteristics. But the complexifying force and the adaptive force are unique to Lamarck. So the hereditary transmission is actually the least Lamarckian aspect of Lamarckian evolution.

    In the present case, we’re talking about anatomical modification of a single physical body to better fit (or reflect) its circumstances, which is a weird thing to talk about because it doesn’t get discussed much. Usually when people talk about adaptation within an organism they mean physiological adaptation, like producing more red blood cells when you go live at high altitude for a while. And usually when we talk about morphological adaptation we mean in the evolutionary sense, over several generations. Someone must be working on morphological adaptation of individual organisms, though, probably under the heading of phenotypic plasticity. I know that some of Keith Stewart Thomson’s work addresses individual adaptation. If anyone can point me at good papers in this area, I’d be grateful. (To be clear, I’m not saying that morphological adaptation within an individual would be heritable.)

    But in any case, DK Fennell didn’t say that Moss’s results were fully Lamarckian or constituted Lamarckian evolution – just that they were ‘oddly Lamarckian’. And that is a perfectly fair description. As for the mechanism, I need to go reread Moss and see what he said about it. Stay tuned.

  8. DK Fennell Says:

    The reason I ask about the mechanism behind the “warping” of the cranial architecture is that, possibly, selective pressures might have acted on that mechanism and not the resulting domed top or lower nose. For instance, if your suggestion is right (that pressure exerted by certain muscles during development accounts for the result), then perhaps it was changes in these muscles that were selected for–for instance thicker muscles might have been able to better cushion the skull from the shocks which jumping and bounding must cause. Those thicker muscles might then contribute to even greater pressure on those very bones during development. (This all is of course rank speculation, especially since I do not understand the mechanism for the skull development in the artificially hobbled rodents.)

  9. Matt Wedel Says:

    I checked Moss (1961), and he didn’t know. Here’s what he had to say on the matter (p. 305; emphasis added):

    Seemingly the operated animals are unable to completely compensate for the alteration in habitual head position through changes in the angulation of the cervical vertebrae. Since we do not understand the ultimate mechanisms involved, the best we can say at present is that the rat otic capsule is capable of rotation relative to the adjacent cranial structures in whatever direction necessary to permit the otolith organs to regain a more nearly normal orientation in space and so eliminate the constant afferent neural inflow.

    This is a pretty darned interesting problem. There has to be some normal range of variation in the facial tilt in rats and rabbits and everything else. Moss discusses this – baby rats have more strongly tilted skulls that flatten out over ontogeny. So Moss described the tilting of the facial skeleton in the experimental rats as an increase or decrease in this normally-occurring process.

    (Side note: that makes me wonder if baby pikas have more strongly tilted skulls than adults. Maybe in terms of skull morphology, rabbits are paedomorphic pikas.)

    BTW, I was probably misleading when I wrote about “the actual force that warps the skull bones”. I had forgotten the results of DuBrul and Laskin (1961), which showed that you can get very different skull shapes just by differential growth at the sutural boundaries between the skull bones. So there’s no need to invoke muscular force. If growth at the frontal-parietal suture is accelerated or extended – or if growth at the basisphenoid-basioccipital suture is slowed or cut short – the skull will be more domed (more facial tilt), and vice versa.

    I still don’t know how that’s regulated within the ontogeny of a single individual. I can see how faster growth at the frontal-parietal suture could be favored by selection for* increased facial tilt in a population over time. I’m still not sure how a postural change in a baby rat can elicit the same effect within that individual’s lifetime.

    * Strange and possibly pointless language thing: since natural selection is accomplished by the decreased viability or fecundity of the least optimal phenotypes, it makes sense to me to talk about selection against this or that, but not selection for anything. What is “selected for” is whatever’s left standing (and procreating) after the filtering effect of selection. It’s like describing the survivors of some catastrophe as having been selected to live. They weren’t selected to live, they just failed to be killed. It’s analogous to how we (sometimes, pedantically) say that good hypotheses are not confirmed, they’re just not falsified yet. Am I the only one with this hangup?

  10. DK Fennell Says:

    On the language thing, you are of course right on how natural selection operates. But “selection” as a term is simply a metaphor. Nature doesn’t select one individual for destruction and one for reproductive glory. A white moth in a suddenly besooted industrial town can theoretically survive, and a black one might land right in front of a bird and be history notwithstanding its now more advantageous coloration.

    The metaphor chosen by Darwin was to animal breeders, who actually select for a desirable trait (not against undesirable ones). And Darwin seems to imply that nature acts the same way (i.e., selecting for a desirable trait) in the following passage (1st ed.: John Murray, 1859, p. 102):

    “In man’s methodical selection, a breeder selects for some definite object, and free intercrossing will wholly stop his work. But when many men, without intending to alter the breed, have a nearly common standard of perfection, and all try to get and breed from the best animals, much improvement and modification surely but slowly follow from this unconscious process of selection, notwithstanding a large amount of crossing with inferior animals. Thus it will be in nature; for within a confined area, with some place in its polity not so perfectly occupied as might be, natural selection will always tend to preserve all the individuals varying in the right direction, though in different degrees, so as better to fill up the unoccupied place.”

    And of course sexual selection has volition to it; a specific trait (colorful tail feathers) is selected for. It seems awkward to say that in a certain bird sexual selective pressures operated against birds with non-blue tail feathers. Wouldn’t the word for that be “rejection” not “selection”? Perhaps if Darwin had thought through his analogy more clearly he would have seen that breeders reject certain individuals for breeding and thus he would have called the means by which species originate Natural Rejection.

  11. Matt Wedel Says:

    Good point about Darwin and his analogy with artificial selection, which does involve deliberate selection for a positive trait. I sort of leapfrogged over Darwin in my earlier comment, to get to the way I started thinking about selection while I was at Berkeley. It’s precisely because there’s no intelligence or active participant choosing who lives and procreates in natural selection that it strike me as odd to say that there is “selection for” anything. The most that can be said for those that survive and pass on their genes is that they failed to be selected against by the myriad forces that doom most individuals to personal and genetic extinction. Or at least, that’s how I conceive of it. I’d be interested to hear compelling arguments in other directions.

    Sexual selection is interesting for sure, because there we often are talking about positive selection for a trait by an active participant. Particularly persuasive are those experiments where the desirable trait is enhanced beyond the natural range of variation, like tacking on unnaturally long tails to certain birds and fish, and the positive response by the choosy mates is even stronger. So I have no problem saying that a trait is sexually selected for, because that seems like a fair description of what is actually going on.

    There is also a strong probability that I’m just circling around one of the inevitable eddies that form whenever we have to describe a complex natural reality with the imperfect tool of language.

  12. DK Fennell Says:

    When it comes to abstractions, as long as I am sure everyone is one the same page, I generally go with the flow. And being on the same page depends on context.

    For instance, quantum experiments show that this expression is wrong: “The angle of incidence [of light] is equal to the angle of reflection.” But in all things I am interested in the introduction of quantum theory is as useful as the introduction of Hitler into a discussion of public policy.

    But like everyone else I have limits and one is the use of “evolved” in this sense: “The Leptomyrex evolved in North American 38 mya.” This incorrect use of a term when “first appeared in the fossil record” or even “arose” is more appropriate makes the history of life look like random burping out of species, much like Genesis. (Even Prothero, if I recall correctly, uses this annoying expression.) This is not helpful in a country which struggles for basic scientific literacy.

    But the reason I keep coming back to this post is completely different; it’s the question: if we really can’t conceive of an explanation for a counterintuitive result, can we really trust the data? I’m not suggesting academic fraud. But the question that keeps bugging me is: aren’t there all sorts of red flags? Isn’t there obvious confirmation bias? Were there enough data sets to make the result significant/? (I assume there is much variety of rat skull architecture, having read the section in Darwin on variation). Even if there was significance, is the drawing of the result trustworthy?

    I don’t mean to be a troll here, but when the result of an unusual experiment seems to contradict longstanding ways of looking at things and that is combined with lack of any explanation for the outcome, isn’t the next step to question the data?

    I realize that current squeamishness about lopping off rodent parts prevents any replication (except in a high school science project) but short of talking to a local high school biology teacher, is there any way to test Moss’s results?

    Matt,. I’m not questioning any part of your paper (which I read with interest). I am only focused on the Moss experiment which seems too pat to be true absent some explanation.

  13. Coherent Ape Says:

    I apologize for posting completely off topic, but I’ve started a new blog that will include paleontology. There will be no sense to the update schedule. http://cosmicspacemonkey.blogspot.com

  14. Mike Taylor Says:

    That’s good news, Coherent Ape. Best wishes with it!

  15. Matt Wedel Says:

    Been meaning to get back to this. In response to the last on-topic comment, no, I don’t think Moss fudged his results (EDIT – that’s not what DK Fennell was writing about anyway. See the next comment down for clarification). I don’t question them (any more than I challenge any other scientific observation that hasn’t been repeated yet) for three reasons:

    1. Moss wrote in that paper about how that mechanism of producing bipedal rats had a long and successful history in laboratory experiments, and he was working in what at the time was a vigorous and fast-moving field of research. He probably expected that other researchers would confirm his results and build on them in the near future. Fudging his data would have been career suicide.

    2. There are plenty of other examples of morphology being altered by a change of posture within the lifespan of an individual – Slijper’s bipedal goat is one of the most famous. So this is not an unprecedented class of phenomena.

    3. Moss’s results might be inexplicable in terms of mechanism, but given the long history of study of things like this, I think it’s FAR more likely that I’m just ignorant of the mechanism. In general, when confronted with confusing data, it’s more profitable to assume that you have something to learn, than that someone else faked the data. Especially if that someone else is a respected researcher with a long career who would have every expectation of being caught.

    And even if no-one on the planet understands how this works yet, that is a horrible argument that the data are fudged. If we reached for that explanation every time we encounter something inexplicable, science would make no progress at all.

  16. Matt Wedel Says:

    Whoops, sorry, DK Fennell, I see that in your comment you weren’t arguing that the data were fudged, just that the results were wonky and that might raise some red flags about experimental errors. I’m not overly troubled by that – I still think it’s much more likely that the mechanism is known or at least reasonably inferred, and I’m just ignorant of it. I’ve only read about half a dozen papers in this area and none of them are more recent than 1970. I’ve learned enough for transformations like the one Moss found to be inspiring, as they were in the case of our rabbit paper, but I haven’t learned enough to comment intelligently on what morphogenetic factors give rise to those results. I keep hoping that someone who knows more than me will pop in and comment, or at least point us to some recent papers. Anyway, I’m sorry that I misrepresented your argument – I should actually reread comments before responding to them!

  17. Mike Taylor Says:

    “The most that can be said for those that survive and pass on their genes is that they failed to be selected against by the myriad forces that doom most individuals to personal and genetic extinction.”

    You’re this close to renaming Darwin’s mechanism “survival of the survivors”.

  18. Mike Taylor Says:

    As a community, we have a real problem with Moss’s findings. On one hand, they are important, and seem to show us something new (at least, new to readers of this blog). On the other hand, they have not to our knowledge been replicated, and quite possibly never will be in this age of ethics committees. (Note, I am not saying I think this is a bad thing. When Matt first told me about this paper, back in 2004 he said “this was published in the American Journal of Physical Anthropology, although you might understandably be thinking of the New England Journal of Evil”.)

    I don’t know what to do with these two observations. Should we — must we? — ignore a potentially very important avenue of research because we don’t want to hurt rats? (And how does that sit alongside the fact that we recently caught and killed 13 mice that infested our house?)

    I don’t know.

  19. Zachary Miller Says:

    First of all, awesome.
    Second, World Lagomorph Conference? I just imagine a gigantic open room filled with free-ranging rabbits, hares, and pikas while people try to give talks about husbandry and state fair winners.
    Third, and this has always bugged me, are lagomorphs a sister group to rodents or are they deeply nested within rodents? Do they have major differences apart from that second set of incisors? Keep in mind I know next to nothing about rodents or lagomorphs.

  20. Matt Wedel Says:

    Lagomorphs are sister to rodents, not nested within them. I know the separation is based on more than just the double incisors, but I don’t know what other characters specifically. The split happened in the Eocene, if not farther back. The big mammalian phylogeny from the Mammalian Tree of Life project probably has the most up-to-date details (buried in the supplementary information, no doubt). I’ll ping Brian Kraatz and see if he has any recommendations for other papers to check out.

  21. Brian K Says:

    Hi Zach –

    Great questions. More properly, Glires is separated into two main clades. Duplicidentates (Lagomorpha and its stem) and simplicidentates (Rodentia and its stem). This was really first firmly established in a morphological data set in Meng and Wyss (2001) expanded on by Meng et al. (2003) and again by Asher et al. (2005)
    The short of it is that some really, really great fossils out of Asia from both stems (e.g. Rhombomylus, Tribosphenomys, and Gomphos) really helped clarify the Glires split. Check out Meng et al. (2003), but the jist of it is that the split is driven by various dental, tarsal, and masticatory features. Since then, all of the mega mammal analyses have shown a monophyletic Glires.


  22. […] on Facebook. So when I do need to know something about ankylosaurs (hey, stranger things have happened), I know where to turn – and who to cite. I, the user, have options. Give your users more […]


  23. […] when we put up too many posts in a row on open access or rabbits or…okay, mostly just OA and bunnies. If that’s you – or, heck even if it isn’t – your good day has come. Saddle […]

  24. John Scanlon Says:

    I know this post is months old, but I popped in to look at the rabbit skulls and notice that most of the ones illustrated are missing the lacrimal bones. This seems to be one of the consistent weirdnesses of rabbits, that the lacrimal has no sutures but just slots loosely into the space between the adjoining bones, held in place by a minimum amount of soft tissue (or just the intraocular pressure?).
    I noticed this because my kids dug up nearly all the bones of an ex-pet the other day and it cleaned up very nicely, but both lacrimals as well as most of the teeth fell out during the last rinse. (Managed to infer the correct orientation from videos on DigiMorph).


  25. […] thanks to the corrupting influence of my friend and colleague, Brian Kraatz. At the end of my last post on this sordid topic, I mentioned that Brian and Emma Sherratt were working on a version 2.0 based in 3D morphometrics. […]


  26. […] The coronoid process of the mandible, which is a muscle attachment site. A few fibers of the masseter and buccinator muscles can encroach onto the coronoid process, but mostly it is buried in the temporalis, one of the primary jaw-closing muscles. Put your fingers on the side of your head a little above and in front of your ear and bit down. That muscle you feel bulging outward is the temporalis. Back in the 1960s, Melvin Moss (1968) discovered that if he removed the temporalis muscles from newborn rats, the coronoid processes would fail to develop. Moss’s ambition was to discover the quanta of anatomy, which in his view were “functional matrices” – finite sets of soft tissues related by development and function, which might contain “skeletal units” that grew because of the morphogenetic demands of the functional matrices. His tagline was, “Functional matrices evolve, skeletal units respond”. Not all of Moss’s ideas have aged well in light of what we now know about the genetic underpinnings of skeletal development, but he wasn’t completely wrong, either, and functional matrix theory is still an interesting and frequently productive way to think about the interrelationships of bones and soft tissues. For more horrifying/enlightening Moss experiments on baby rats, see this post. […]


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