Pterosaurs were likely floaters: evidence from manus only tracks

Yesterday we reviewed Hone and Henderson (2013) who conducted computational experiments with four misbegotten digital pterosaur models and reported that pterosaurs were unlikely floaters that would have struggled to keep their noses above the surface and so risked drowning, despite their air-filled skeletons.

Unfortunately
the Hone and Henderson results don’t agree with the facts as told by manus-only tracks, that can only be made by floating pterosaurs. As Hone has done in previous papers, these are all conveniently omitted. Case in point: the Summerville tracks (Lockley et al. 1996, Fig. 1).

Summerville tracks matched to potential trackmaker, Jidapterus, a basal azhdarchid.

Figure 1. Summerville tracks matched to potential trackmaker, Jidapterus, a basal azhdarchid pterosaur using a poling technique to produce manus-only tracks while floating.

Summerville (Late Jurassic) manus only tracks (Fig 1), likely made by a sister to Jidapterus, a protoazhdarchid with rather big fingers.

Is this the only explanation?
Oh, sure some have said that pterosaurs pressed their hands more deeply into the matrix and footprints were thereafter erased by geological processes. But doesn’t this strike you as trying to make excuses, on the order of Elgin, Hone and Frey’s infamous “membrane shrinkage“?

Figure 2. Manus only tracks of pterosaurs, Late Jurassic to Late Cretaceous.

Figure 2. A catalog of manus only tracks of pterosaurs, Late Jurassic to Late Cretaceous. Note the odd and large Las Hoyas track is now considered to be made by a theropod, which makes perfect sense.

The large Las Hoyas track
is impossible to fit to a pterosaur manus. No pterosaur has a longer and more robust manual digit 2 than 3. Some have these two digits subequal in length, but to scale these up to the track size creates a truly gigantic pterosaur. Vullo et al. 2009 got it right when they decided it belonged to a theropod dinosaur foot.

Figure 4. Tapejara compared to Albian tracks from South America. They are a close match in size and shape.

Figure 4. Tapejara compared to Albian tracks from  west-central Argentina (Calvo and Lockley 2001). They are a close match in size and shape. Pedal digits 2-4 are subequal and digit 1 is slightly shorter. Scale bars for tracks and pterosaur match. Footprints indicate no splay in the digits. Note the comparative sizes of the manus and pes.

The “first Gondwana pterosaur tracks” (Calvo and Lockley 2001) can all be matched to Tapejara-like (Fig. 4, 5) trackmakers. The Candeleros Member of the Rio Limay Formation (Albian–Cenomanian) at Lake Ezequiel Ramos Mexía, Neuquén Province, Argentina is contemporary with Tapejara bones on the east coast of Brazil. The palaeoenvironmental setting of the track beds was a lake shoreline, where dinosaur tracks also occur.

Figure 5. Tapejara poling while floating, producing manus-only tracks, all to scale.

Figure 5. Tapejara poling while floating, producing manus-only Albian tracks from west-central Argentina, all to scale .

Above, manus only tracks (Calvo and Lockley 2001) matched to Tapejara.

Figure 5. Price (Utah, Maastrichtian) tracks. These match up pretty well to Cycnorhamphus, except for size. Luckily we know of giant cycnorhamphids like Moganopterus, shown as a skull here to scale.

Figure 5. Price (Utah, Maastrichtian) tracks. These match up pretty well to Cycnorhamphus, except for size. Luckily we know of giant cycnorhamphids like Moganopterus, shown as a skull here to scale. Unfortunately, Moganopterus is from the Early Cretaceous of China.

Moganopterus, a cycnorhamphid, is a good model for the trackmaker of the Maastrichtian Price (Utah) racks, merely with a shorter digit 2 than Cycnorhamphus (Fig. 5). Unfortunately Moganopterus is from the Early Cretaceous of China.

If you’re interested
in finding a better match for any of these tracks, you are welcome to try. I had a catalog of pterosaur manus and pedes at reptileevolution.com and a matrix of pterosaur traits that made my search go rather quickly.

References
Calvo JO and Lockley MG 2001. The first pterosaur tracks from Gondwana. Cretaceous Research 22:585-590.
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Hone DWE, Henderson DM 2013. The posture of floating pterosaurs: Ecological implications for inhabiting marine and freshwater habitats, Palaeogeography, Palaeoclimatology, Palaeoecology (2013 accepted manuscript), doi: 10.1016/j.palaeo.2013.11.022
Lockley MG, Logue TJ, Moratalla JJ, Hunt AP, Schultz RJ and Robinson JW 1995.  The fossil trackway Pteraichnus is pterosaurian, not crocodilian: implications for the global distribution of pterosaur tracks. Ichnos, 4: 7–20.
Lockley MG, Hunt AP and Lucas SG 1996. Vertebrate track assemblages from the Jurassic Summerville Formation and correlative deposits. – In: Morales M. (Ed.), The Continental Jurassic. Museum of Northern Arizona Bulletin, 60: 249–254.
Lockley MG and Wright JL 2003. Pterosaur swim tracks and other ichnological evidence of behavior and ecology. – In: Buffetaut E and Mazin JM (Eds), Evolution and Paleobiology of Pterosaurs; Geological Society, London, Special Publications 217:297-313.
Lockley M, Harris JD and Mitchell L 2008. A global overview of pterosaur ichnology: tracksite distribution in space and time. Zitteliana B28: 185-198.pdf
Mickelson DL, Lockley MG, Bishop J, Kirkland J 2004. A New Pterosaur Tracksite from the Jurassic Summerville Formation, Near Ferron, Utah. Ichnos, 11:125–142, 2004
Parker L and Balsley J 1989. Coal mines as localities for studying trace fossils. In: Gillette DD and Lockley MG (Eds), Dinosaur Tracks and Traces; Cambridge (Cambridge University Press), 353–359.
Pascual Arribas C and Sanz Perez E 2000. Huellas de pterosaurios en el groupo Oncala (Soria España). Pteraichnus palaciei-saenzi, nov. ichnosp.  Estudios Geologicos, 56: 73–100.
Vullo R, Buscalioni A D, Marugán-Lobón J and Moratalla JJ 2009. First pterosaur remains from the Early Cretaceous Lagerstätte of Las Hoyas, Spain: palaeoecological significance. Geological Magazine, 146: 931-936.

16 thoughts on “Pterosaurs were likely floaters: evidence from manus only tracks

  1. You have two errors in here. The first is, “But doesn’t this strike you as trying to make excuses, on the order of Elgin, Hone and Frey’s infamous “membrane shrinkage“?”
    No, because ichnology is comlex and we can actually figure out whether a trace fossil represents an actual imprint or an undertrack (a compression of the sediment beneath the substrate surface). The same holds true for “swimming” sauropod tracks – look for a paper soon.
    The second is this: even if manus-only tracks represent pterosaurs moving across a body of water that still doesn’t disprove Hone and Henderson. If you can support your weight in water on locomotor limbs (in this case the forelimbs) it doesn’t matter how you are able to float. Humans float naturally in a prone/supine position but a quick glance at a pool shows most humans in the shallows walking with their feet on the bottom. Floating position doesn’t matter there. The same is the case here, even if the interpretation of the tracks is correct.

  2. Okay for sauropods, if that’s indeed the case, not okay for pterosaurs, which are several magnitudes of mass and size smaller. Following your hypothesis, it should be easy to determine if giraffe forelimbs impressed more deeply than hind limbs based on the weight of the shoulders and neck. Let me know your thoughts on the image found here of giraffe tracks:
    http://calleystravels.blogspot.com/2009_05_01_archive.html

    So, is poling on forelimbs with hind limbs elevated not “floating”? Are humans replicating this not floating in some fashion?

    In any case, no one is arguing that pterosaurs could not float. Hone and Henderson argue that it was dangerous for pterosaurs to float due to the position of their nostril near or under the surface based on a stiff neck, etc. So pterosaurs must have avoided floating, according to them. This goes against manus only tracks evidence and other ungual scratch evidence IMHO.

    See previous posts on this blog regarding terrestrial locomotion in pterosaurs, perhaps here:
    https://pterosaurheresies.wordpress.com/2012/05/28/doin-the-pterosaur-walk/
    and here:
    https://pterosaurheresies.wordpress.com/2012/03/25/giant-bipedal-pterosaur-tracks-from-korea/

    • The mass issue is real but in reality you are just dealing with scale. The same effects should be (and are) observable from smaller organisms, just on a correspondingly smaller scale. Again, there’s a paper coming out that comments on this. I’ll withhold comments until it has been published.
      Giraffe tracks: small picture makes it hard to tell much about them.
      Poling along on forelimbs isn’t really floating since it isn’t taking advantage of buoyancy: the pterosaurs (or humans) are still being biomechanically supported instead of floating (supported only by buoyancy).

      • re: buoyancy and biomechanics support, so, you believe that if the floating pterosaur lifted its forelimbs from the seafloor the pterosaur would sink? Think this through. All agree pterosaurs could float, it’s just their configuration in the water (nose high vs. nose low) that is the issue here.

        please google “giraffe tracks” to find better pix.

        re: missing hind limb tracks. Note there’s not a trace of hind limb impressions in certain tracks and there’s no erosion of the top half of the manus tracks. Please don’t agree to the selective erosion theory.

    • Forgot to add: those manus-only tracks are inconsistent with what we have preserved in the fossil record for swim traces from various tetrapods.

    • “you believe that if the floating pterosaur lifted its forelimbs from the seafloor the pterosaur would sink?”
      No, what I said was polling was not floating and that biomechanically supported organisms in water don’t have to correspond to a neutral buoyancy position if they are otherwise supported. There is nothing in this not-yet-published paper by Hone and Henderson that appears to contradict this statement, nor in your reconstructions. The reason I am bringing this up is that you are saying (to paraphrase), “polling pterosaurs provide evidence that pterosaurs could float well, contra Hone and Henderson.”
      To be clear here I am saying this; polling pterosaurs have no bearing on whether pterosaurs were adept floaters because they do not have to be supported by their own buoyancy. The two are not linked.

      “re: missing hind limb tracks. Note there’s not a trace of hind limb impressions in certain tracks and there’s no erosion of the top half of the manus tracks. Please don’t agree to the selective erosion theory.”
      WftP.

      “as you already know, there’s nothing quite like a pterosaur. What you see is what they did.”
      They don’t defy physics. There are certain propulsive marks that are tell-tales as to if an animal is actually floating and just scraping the substrate for forward propulsion. Pterosaurs aren’t exempt from this unless they were magical non-Newtonian beings (we agree that they are not). Every action has an equal and opposite reaction. If the pterosaur is truly buoyant and not supporting its weight on its forelimbs (polling) then the act of propelling the animal forward will leave drag marks opposite the direction of travel. This is basic physics and has been supported by swim tracks both modern and prehistoric. If a pterosaur was floating and using its forelimbs to move forward against the bottom it will leave those marks. Period.

      • Not period. There is another solution to your problem. Pterosaurs used their forelimbs (on land) not for propulsion but for support when quadrupedal. We know this because you just can’t get their hands behind their shoulders to exert a forward force vector. So, taking this to shallow waters, shallow enough to reach the bottom, imagine them using this same motion while poling for propulsion. If you were poling with ski poles would you leave drag marks? I presume you’ve seen my quadrupedal Pterodactylus walking animation. Now the hind limbs are a different matter. They leave drag marks because they’re floating just enough to not leave more than a scrape.

    • “We know this because you just can’t get their hands behind their shoulders to exert a forward force vector.”


      Animal moves forward with manus never behind the shoulder. Not sure where you’re getting the idea that the manus has to move posterior to the shoulder to generate a forward movement.

      “If you were poling with ski poles would you leave drag marks?”
      Skiing is not subaqueous so it is not comparable. I’d look into gondolliers or swamp boats for a better analogous track maker.

      • Rob, rob, rob, this movement is caterpillaring. Note the back doesn’t move until the front stops. Do this: crawl on the floor, keep your hands and elbows in front of your shoulder, then tell me about the force vector – how much your hand contribute to forward motion. They are supports in that instance. Note that your torso doesn’t move until the hind limbs push forward our your pelvis starts to tilt.

  3. On the question of why manus prints would leave deeper impressions than pes prints (pes prints being lost due to subsequent erosion), my three dimensional pterosaur skeleton models suggests that most of the weight is borne by the pectoral girdle, even if you factor in viscera. If the seemingly manus only prints were made by a pterosaur walking in a soft substrate, the manus would be expected to push deeper into the substrate than the pes.

  4. You do your best, from what I can see, to match reality (manus only tracks) with a possible reality (pterosaur types whose known hands could make the prints), instead of making a theory then trying to make cases for why the aforementioned realities cannot exist. I applaud your efforts, and agree–so far!–with your thesis.

    One caveat though; while I do agree with your assessment of Mr. Hone’s paper, it IS up for before publishing reviews, to help correct errors. Even if Hone and Henderson won’t listen to you, taking the high ground and pointing out mistakes is better for your case than saying their work is substandard. IMO, that is.

  5. I very happy that you have presented both sides of this argument: one side saying that pterosaurs couldn’t float, and another saying that they could. This is what good scholarship is supposed to be like, and I wish that more academics would follow your example. It was very interesting and enjoyable to read both of your blog posts regarding this subject. I look forward to reading your next entry.

  6. Agreed. That’s why I mentioned their prior work is often less than perfect, then pointed out the errors in the present work. The status of the paper indicates spelling, capitalization and other such non-technial errors are still up for changes. The referees and editors have already approved the gist of their subject matter.

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