Atopodentatus Will Blow Your Mind

The fossil record is replete with wonders. Humungous fungus, dazzling dinosaurs, intricate ammonites, and perplexing protomammals just scratch the surface of such a wide array of fantastic organisms that sometimes it’s easy to become acclimated to the enigmatic and weird. Yet, even then, there are fossils so strange that they make me jolt upright in my seat and think “Wait, what the hell is that?” The latest prehistoric creature to leave me gobsmacked is Atopodentatus unicus.

The skeleton of Atopodentatus with a close-up of the skull. From Cheng et al., 2014.
The skeleton of Atopodentatus with a close-up of the skull. From Cheng et al., 2014.

The roughly 245 million year old marine reptile is beautifully preserved. Uncovered in southwest China and described by Wuhan Institute of Geology and Mineral Resources paleontologist Long Chen and colleagues, the reptile’s nearly complete, nine-foot-long skeleton is laid out as charcoal-colored bones against gray rock. And while not as wholly adapted to an aquatic lifestyle like the eel-like ichthyosaurs found in the same deposits, the stout limbs, hips, and geological context of Atopodentatus hint that this reptile divided its time between land and sea. Then there’s the skull.

Preserved in profile, the cranium of Atopodentatus looks like a bony version of a Scotch tape dispenser.  In front of a rounded orbit, the creature’s snout is a downturned hook that creates an arc of tiny, needle-like teeth that are fused to the sides of the jaw rather than sitting in sockets. Stranger still, most of the teeth in the upper jaw faced each other in a split running between the two halves of the upper jaw. Head-on, Atopodentatus had a zipper smile of little teeth.

As Cheng and colleagues say in the title of their paper, this is a “highly specialized feeding adaptation.” But for what? Chomping down on fish seems unlikely. The reptile’s tiny teeth would have been too delicate for struggling prey, the researchers note, and muscle attachment sites on the bones suggest that Atopodentatus wasn’t capable of biting hard.

Atopodentatus as envisioned by artist Julius Csotonyi.
Atopodentatus as envisioned by artist Julius Csotonyi.

Filter feeding seems a better option for the unusual Atopodentatus apparatus. In a fashion similar to living gray whales, Cheng and coauthors hypothesize, the Triassic reptile may have swum to the muddy bottom of the shallows and turned its head sideways to scoop sediment into piles. Then, scratching or grasping with that hooked upper jaw, Atopodentatus could have strained worms, small crustaceans, and other morsels through its toothy sieve. Nightmarish as Atopodentatus looked, only tiny invertebrates had much reason to fear.

Testing such a scenario is the tricky part. Gut contents and maybe even traces Atopodentatus left behind as the reptile dredged the seabottom could help paleontologists investigate how the “peculiar-toothed” reptile ate. For now, how the ancient swimmer employed such an unprecedented dental apparatus is still open to investigation. I’m grateful that such petrified puzzles exist. For as much as paleontologists have discerned about life’s past, there are likely even odder discoveries yet to be made. Ain’t evolution grand?

Top image by Julius Csotonyi. And for another take on Atopodentatus as an embodiment of a Lovecraftian horror, see this post at The Bite Stuff.

References:

Cheng, L., Chen, X., Shang, Q., Wu, X. 2014. A new marine reptile from the Triassic of China, with a highly specialized feeding adaption. Naturwissenschaften. doi: 10.1007/s00114-014-1148-4

20 thoughts on “Atopodentatus Will Blow Your Mind

  1. Evolution grand? No, it’s not a human to be admired or a god to be worshiped. Evolution just happens, there’s nothing grand about it. In this case, we don’t even see it happening. It’s like something a creationist would imagine as a challenge to evolution: “If a fossil turned up with a totally unique feature, something surprising because we hadn’t seen hardly any incipient stages, and it didn’t have any obvious, simple use, wouldn’t that be more consistent with an independent creation?” I must say I immediately saw a parallel with the seaweed-eating iguanas of the Galapagos and wonder if the teeth could be used for scraping, snipping, or combing underwater rocks or plants, or maybe even something like sea anemones.

  2. David — sorry, but it IS grand to imagine critters like this in the flesh, and to understand how diverse life was in the past. Even in familiar living forms we get a very constricted understanding — a couple of years ago, I visited San Diego Natural History Museum, and was amazed to see the diversity of marine mammals — walrus relatives and sirenia especially. On the one hand, they clearly expanded the possibilities for coastal marine vertebrates, on the other, you could see gradations filling in anatomic gaps of living species.

    Per the scraping — the Atopodentatus lineage no doubt started with a more-or-less marine iguana lifestyle, but the description shows that these teeth wouldn’t be up to abrasive substrates. And the upper jaw would be in great need of flossing if it tried.

  3. Wow. It’s odd isn’t it, that it has such a specialised aquatic feeding adaptation, but not so specialised aquatic locomotion?

  4. It seems to me that an “unconventional” snout like that would also point to an unconventional food source. Why else would the adaptation come about?

    Just off the top of my head I’m inclined to think of its prey perhaps hanging out on a vertical surface. Or maybe even on the ceiling of a cave.

  5. It is fantastic to be able to find “new” fossils all the time. I always wanted to be a paleontologist or a zookeeper, loving animals (fossilized or alive). The element of marvel and suspense after discovering something totally new to science will keep people working at solving the mysteries of nature. Keep up the good work.

  6. It looks to me like it could have ensnared small fish that would have been lacerated by the strange jaws, and that opportunistic feeders could then be swallowed whole pelican style by an as yet not evidenced flap of flesh.

    I think calling them filter feeders so early is a mistake.

  7. It should be said that some of its body adaptations are marine-adapted:

    Short legs and a long body; splayed hands and feet; and the very form of its teeth which would be (generally) ill-suited for many foodstuffs to be found on land. This is a big animal, and those teeth seem unsuitable for eating meat or vegetation as found on land, so we then look to marine lifestyles. There’s a lot to be said for the peculiarities of this animal, whether the split between the front its skull is real, and as to its purpose. But it seems certain that this animal was as welcome in the water as Pakicetus (a terrestrial animal that hunted in the water) and Amblyrhynchus (the marine iguana; which feeds almost exclusively underwater, but otherwise dwells on land). I am utterly amazed at how well Julius Cstonyi’s illustration captures the idea of the marine iguana with a grey/right/bowhead whale style jaw, as the two were likely the best comparisons possible for this freaky guy.

    The evidences of evolution do not cease to amaze me.

  8. Considering that such a simple, nearly undetectable process has accounted for all of the beauty, wonder, and mystery of life…..yeah, pretty damn grand.
    @David Bump

    1. Well, it’s grand to imagine that the leaps of reindeer could eventually account for them just staying up in the air, but we don’t have any proof that that happened, either.

  9. @David Bump

    Why is it necessary for you to be so aggressive about this? A process exists in no less a way than a person or a thing, there’s no reason it cannot be admired or called “grand”. Nobody is trying to suggest that evolution didn’t create Atopodentatus, in fact the opposite. It’s even MORE impressive that a directionless process is capable of producing such variety, and it is thus worthy of our awe.

    1. @ James Alver, Oh, sorry, I seem to have been too “aggressive” and yet too subtle at the same time. I’m actually suggesting that Atopodentatus was not created by evolution, at least not from something that didn’t have anything like its specially-designed mouth. Furthermore, if I DID believe that a directionless process produced such a unique design, I could not consider it a “grand” thing or something “worthy of our awe.” It may have been due to a rare conjunction or series of factors and events, but every one of them would have been just small examples of perfectly ordinary, normal processes of nature. It would be no more “grand” than burn marks on toast being comparable to an image of Elvis, no more awe-inspiring than a coin toss coming up 50 heads in a row somewhere during a trial of 1267650600228229401496703205376 tosses.

  10. That “tape dispenser” jaw could be used, while swimming a few feet below the surface, to snag bird’s feet and other small limbs dangling in the water without having to turn one’s head 90 degrees.

  11. I don’t really see why there’s resistance to this being a filter feeder. Given the “zipper slot” in an assumedly rigid snout, there wouldn’t really be any alternative function other than permitting the passage of water between the teeth. Secondly, a downturned rostrum in marine mammals (sea cows, and some extinct cetaceans) is correlated with benthic feeding.

    JasonWS – regarding a pelican-like function – although soft tissue evidence of such a pouch is absent, “lunge feeders” like pelicans and balaenopterid whales have a number of osteologic adaptations towards this sort of behavior wholly absent in this fossil, such as a long and broad-based rostrum, and a similarly long and longitudinally twisted mandible that can rotate about its longitudinal axis during jaw opening (among other features such as rostral kinesis).

    Dave: in modern marine mammals, the majority of skeletal disparity is focused in the skull (and the rostrum, at that) as the postcranial skeleton – despite all sorts of crazy specialized behaviors and adaptations in/with the head- is generally quite conservative, and major locomotory constraints are placed upon the postcranial skeletons of marine tetrapods. In other words, as long as something can swim efficiently, it can feed (and modify its head) however it likes.

  12. It being a filter feeder is a perfectly reasonable hypothesis. Doesn’t mean that other hypotheses can’t be proposed as alternatives. The flamingo/whale analogy is a good one. I wonder if it could eat jellyfish, too?

  13. @David Bump
    I’m sorry, apparently something that doesn’t have a specific ‘creator’ cannot be grand, according to you?

    Thankfully the worldview is not simply defined by your lack of wonder at all things natural, so we (and others in this small discussion) must agree to disagree.

    I think the aurora borealis is a wonderful visual phenomenon, even if it ‘just happened’. I also think that the crystallisation formation of snowflakes is pretty, for something that ‘just happened’.

    Perhaps you could enlighten people with what you consider ‘grand’, instead of haughtily disparaging everything else you don’t.

    1. @ “David Grump” — it’s been awhile, but I think I had a specific sense of “grand” in mind, based on the expression concluding the article. Certainly, a creator-free history of life over billions of years would be grand in a sense of “impressively large or long, etc.” But as you go on to indicate, there seems to be here also a desire to infuse it with the sense of “wonderful” and other nuances that traditionally have been used with things associated with admiration of the behavior of an intelligent being or something considered supernatural, unexplainable — or something that displays amazing intellect, wise provision and consideration, goodness, etc. “Ain’t it grand?” often uses “grand” in the sense of “very good.” For example, there’s an old song, “Ain’t it grand to be a Christian?” In other cases it is used sarcastically, but that clearly wasn’t the case here. So It is this connotative sense which I regard, not with haughty disdain, but with surprise and a bit of shock at the logical dissonance, when applied to something totally void of intent, intellect, wisdom, provision, and has nothing to do with forces which are beyond our understanding.

      When I imagine myself as an evolutionist, I regard such expressions as clinging to “magical thinking,” a sort of weakness which seeks to imbue things with the borrowed, threadbare clothes of a worldview that needs to be left behind entirely if we are to see things clearly as they are. It is this alternative version of me who brings the haughtiness into my view of applying such expressions to the ordinary, everyday workings of nature. As a creationist, I have no lack of wonder at the marvels and mysteries of nature, and I would hope you would see there’s good reason to have such a view; if I thought everything could be explained as natural processes without any intellect or supernatural intervention involved, I would throw off such outdated modes of perception and encourage you to do likewise.

      “Pretty” is something else entirely, a subjective estimation of beauty — although one might wonder why we would have evolved to see beauty in a barren, snow-covered scene or the icy crystals associated with months of hard living. Perhaps we needed such an aesthetic to cheer us up, and now it’s a harmless reflex.

      You might find enlightening an exchange I had with a fellow who believes in evolution but not Darwinism or neo-Darwinism, precisely because he feels the materialistic, reductionist view of life leaves no room for, or lacks the power to explain, human wonder and other aspects of humanity and the humanities. Being a thoroughly atheistic evolutionist, he seeks a new view or a new science that will encompass such things… a quixotic quest at best, it seems to me. See especially the ZZizzm Experiment linked near the end: http://takeondarwin.com/index.php/conversations/169-exchange-1?catid=28%3Ashaun-and-david-bump

  14. The filter feeder was the first thing to come to mind. Very interesting whatever diet they lived on. Their tongues and how they used them would be fascinating to know about. Exciting! 🙂

  15. Let’s keep in mind the age of the fossil: 245 million years old. This was at the beginning of the Triassic, when tetrapods were just starting to invade the marine realm. As such, all kinds of invertebrates were swimming and crawling about, since fish and other invertebrates had been the only predators previously. With all kinds of food to be had, it’s no wonder specialized feeders evolved. Placodonts as well come to mind. Once the invertebrate community evolved more “infaunal” strategies, however, these early specialized feeders disappeared.

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