Orbit size does not always equal eyeball size

Earlier we looked at the two-part orbit of Baphetes and Megalocephalus. I put forth a ‘shifting eyeball’ hypothesis, but I don’t buy into it, just to set things straight. I think the eyeball was in the dorsoposterior, more rounded portion. As we saw even earlier, basal tetrapods were evolving rostral loss of bone. So that sort of thing happened then.

Today we’ll talk about
an extreme case of tiny eyeball and enormous orbit.

Andrias davidianus (Blanchard 1871; 1.8m in length; extant) is a sister to Rana, the bullfrog and derived from a sister to Gerobatrachus. The jugal is absent. The orbit is much larger than the eyeball.

Figure 1. Skull of Andrias with skull bones identified. The jugal is absent. This extant amphibian has a tiny eyeball.

Figure 1. Skull of Andrias with skull bones identified. The jugal is absent. This extant amphibian has a tiny eyeball.

Images of the living
Andrias can be found here. You’ll be lucky if you do see the eyeball. It is very tiny. I probably overemphasized the size of the eyeball in figure 1.

References
Blanchard É 1871. Note sur une nouvelle Salamandre gigantesque (Sieboldia Davidiana Blanch.) de la Chine occidentale. Comptes Rendus Hebdomadaires des Séances de l’Académie des Sciences. Paris 73: 79.

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13 thoughts on “Orbit size does not always equal eyeball size

  1. You’re still saying “a sister” after I explained that that’s a contradiction in terms…

    …in a comment to a post you have now deleted. That was accidental, right?

    • Oops! The explanation is still there; it’s in a comment to an older post, not to the one you deleted. I misremembered.

  2. Oh wow. I just took an actual look at your painted photo.

    Congratulations! For the first time ever, you’ve discovered a lissamphibian with a postorbital, supratemporal or ectopterygoid. For the first time ever, you’ve discovered a lissamphibian that is not Eocaecilia and yet has separate postparietals and tabulars…

    No, of course not. The “postfrontal” is the sphenethmoid, an endochondral braincase bone. The “suture” between the parietals and the “postparietals” is just a crest, and so is the “suture” between the “supratemporal” and the squamosal. The “suture” between the “ectopterygoid” and the pterygoid seems to be completely made up. The “supratemporal” is part of the opisthotic; I can’t see what the “tabular” is.

    There is decades worth of research on the ontogeny of salamander skulls. Salamander skull anatomy is understood. You have no hope of making discoveries by looking at a photo of a particularly well known salamander.

      • And again, every new group you look at you misunderstand. How many occurances of this must happen before you admit DGS doesn’t work well if you aren’t familiar with a clade’s anatomy?

  3. No student dissecting their first frog knows what’s in there. Dave, I’ll grant you the ‘postfrontal’ is the sphenethmoid. The ectopterygoid is missing in this specimen. Filled in with glue in palatal view (not shown), but the way it looks from Utegenia as a base, the ectopterygoid fuses to the pterygoid. That means its still there, just fused. Likewise the post parietals are still there, just fused. The supratemporal and tabular are vestiges. Still, but vestiges with the originals present in Doleserpeton. We’re going to have to decide what that postorbital dish is. Doleserpeton has one in a similar spot. I checked some ontogeny papers. They provided no help.

    Maybe some of these bone identity issues are what plague your cladogram scores. I have noticed throughout paleontology that workers often consider a bone absent when it is fused to a larger bone. And when a bone reaches the vestige stage, it is often ignored and scored absent.

    Thank you for the heads up, David. Corrections have been made to images and scores. Could not have done it without you.

    Mickey, you need to reevaluate your POV. You’re missing all the good stuff.

    • The ectopterygoid is missing in this specimen.

      The ectopterygoid is absent in every single known salamander and every single known frog – throughout ontogeny, where known.

      That means its still there, just fused.

      No. That’s not what happens in any known salamander ontogeny.

      Likewise the post parietals are still there, just fused.

      That’s a possibility. Several, though apparently not all, salamanders have a pair of ossification centers that soon fuses to the parietals. However, bones that have nontrivial shapes very often have several ossification centers. The parasphenoid routinely has three, one for the cultriform process and a pair for the basal plate, and yet there is no known vertebrate – dead or alive – that has three or even just two separate bones instead of a unitary parasphenoid. The frontal of Apateon has three ossification centers…

      The supratemporal and tabular are vestiges.

      No, they’re plainly not there – not in any known salamander or frog for that matter.

      We’re going to have to decide what that postorbital dish is.

      This isn’t a matter of convention. It’s a matter of observation in salamander ontogeny.

      Doleserpeton has one in a similar spot.

      I know. That doesn’t mean Andrias does.

      I checked some ontogeny papers. They provided no help.

      Google Scholar is your friend, and so are references sections.

      Maybe some of these bone identity issues are what plague your cladogram scores.

      You know, it’s really stunning how it never occurs to you that the problem might lie on your side: that you don’t quite understand what you’re talking about, that you have more to learn. No, it’s always everyone else. *headshake*

      I have noticed throughout paleontology that workers often consider a bone absent when it is fused to a larger bone.

      In the absence of ontogenetic data, fusion can hardly ever be distinguished from loss. In the presence of ontogenetic data, it has often turned out in extant animals that hypotheses of fusion were flat-out wrong: shape and position of a bone can never guarantee that it’s a fusion product.

      And when a bone reaches the vestige stage, it is often ignored and scored absent.

      I’m afraid that’s an alternative fact. Sure, I’ve seen character states called “reduced or absent”, but at least that’s explicit.

      Could not have done it without you.

      You’re kidding, right?

      Of course you could’ve done it without me. Just learn some basic anatomy and ontogeny, and you’ll never need me again. :-| After all, that’s what I’ve done myself.

      Mickey, you need to reevaluate your POV. You’re missing all the good stuff.

      It’s obvious that you are the one who needs to reevaluate his POV, and that “all the good stuff” only exists inside your skull.

      • In particular, you could have figured out the sphenethmoid by taking the skull in your hands and turning it around. You should try that sometime. Photos are two-dimensional, they’re incapable of telling the whole story.

  4. re: the sphenethmoid
    Actually, I considered the possibility and clearly made the wrong choice, both in terms of position and phylogeny. But that has been corrected. I make many wrong choices and I often use less than ideal data — always corrected when improved valid data arrives. You are correct, photos and published drawings by PhDs are indeed incapable of telling the whole story. In like manner Hubble telescope photos are incapable of telling the whole story. But we push forward with what we have.

    I hope you’re not against another person learning about paleontology, which is what I’m doing here. I do make mistakes, which is something every student does. And a few professors make mistakes too.

    re: vestigial and absent bones
    At some point between Doleserpeton and extant frogs and salamanders those temporal bones shrank away. That they appear, or don’t appear, as vestiges on the giant salamander is something worth studying and searching for among transitional taxa. Even if those vestiges only leave tell tale ridges or grooves as the only clue to their former existence, that’s worth noting.

    While I have your attention, David, I have several times tried to thank you for sending me PDFs and my replies have bounced back, undeliverable. Not sure what needs to be done here.

    • At some point between Doleserpeton and extant frogs and salamanders those temporal bones shrank away.

      We don’t quite know if they became smaller and smaller (beyond the small sizes they already have in Doleserpeton) until they were gone, or if one day they just failed to form altogether in an embryo, the parietals grew unchecked, the skull roof remained closed, and the embryo survived… The postparietals of Eocaecilia are actually pretty large, and the ?tabulars are larger than those of Doleserpeton.

      That they appear, or don’t appear, as vestiges on the giant salamander is something worth studying and searching for among transitional taxa.

      Yeah, but not in the giant salamander itself, because that one’s already understood. :-)

      tell tale ridges or grooves

      No, ridges and grooves can have all kinds of causes other than fusion. On their own, they’re not a sufficient argument.

      my replies have bounced back, undeliverable

      Sorry, my inbox happened to be full for about 24 hours.

      Say, if not from the papers, where do you get your information from? Just Wikipedia and re-re-redrawings you find on Google Images? Because that’s a scary thought. (It would explain a whole bunch of things, however.)

      • I get my data from a spectrum of sources. Rarely, but sometimes, original papers have errors, like the extra strip of bone in Yi qi, or the sixth toe in Tulerpeton. Or the labeling of the flat palate bones in pterosaurs as palatines and not the medial maxillary shelves they were later found out to be. It’s not a crime to say, “um, there might be a problem here.”

    • David, if all you were doing here was “learning about paleontology,” nobody would have the slightest issue with you. You do not portray yourself as “learning about paleontology,” you proclaim your observations to be new discoveries and your trees to be new paradigms, while everybody else who has worked in the field “has blinders on.” Ditch the unwarranted arrogance and *listen*, and maybe you really will learn about paleontology!

      • The blinders typically refer to taxon exclusion. For instance, not testing Cosesaurus and kin with pterosaurs and archosaurs, to refute or confirm Peters 2000. Or not testing Elginia with Meiolania. It’s not arrogance. It’s an invitation to include more taxa in analyses.

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