Longisquama is too Weird for this World


Longisquama insignis Sharov, 1970, based upon the holotype, with rib-bearing dorsal vertebrae and jaw tips included. This image is released to the general public to with whatever they should please.

I might be a little safe with this reconstruction, but it represents a further attempt to clean up and add to the number of controversial archosauromorphs for which few skeletals exist, or whose existence is owed to controversial reconstructors or miseducators seeking personal fame over accuracy.

Longisquama insignis is a little odd for many reasons, and which have led to some debate over its affinities or the nature of the integumentary structures associated with the holotype skeleton and which are known from isolated blocks. Here, however, I will merely note that the reconstruction above differs in some substantive details from my previous attempt, shown below:

An outdated reconstruction of Longisquama insignis Sharov, 1970, with the limbs held in an erect, potentially terrestrial posture. (I no longer agree with this interpretation.)

Even at the time I placed this image on this blog, I’d decided that evidence didn’t favor an erect, archosaur-style posture. My reasons at the time were based on some details of the shoulder and hand, but these are not entirely consistent only with erect postures or digitigrade limbs.

For one, the shoulder suggests a lateral orientation for the humerus, the forearm presents a bowed ulna consistent with flexed elbows, and while the metacarpals are long, the carpals are small and irregular, and I am reminds of the feet of frogs and other tetrapods in which the metapodial elements contribute to digit length. Meaning, the limbs would be possibly splayed and plantigrade. Be aware this is speculation, and details of the original specimen are sparse as the preservation is terrible aside from the impressions, with the granularity of the slab extremely rough, meaning some elements are less differentiated than grains in the matrix.

Another departure involves the presence or absence of an antorbital fenestra; I’ve here opted for the latter, rather than the former. This is merely an option: the material is broken and a large apse on the side of the skull can suggest either, but does not indicate, a conclusion Buchwitz and Voight (2012) arrived at and which I can now agree with. However, depending on the phylogenetic affinities of the taxon, such a fenestra might still be inferred, albeit poorly.

Longisquama insignis with model showing the unusual dermal appendages. This image is released to the general public to with whatever they should please.

Perhaps one oddity that needs resolving is the strap-like, elongated scapula, a feature seen in other non-avian tetrapods but which predominately finds itself amongst the birds. Chameleons, amongst other lizards, and the peculiar Drepanosauridae also feature such scapulae, which are held vertically and may limit excursion of the humerus in certain directions due to orientation of muscles. This shouldn’t be an issue for Longisquama, as the scapula is in an avian-like position, but it leads us to ask why, as this feature is peculiar to a quadruped without extensive head-supporting muscles (many sauropod, hadrosaur and ceratopsid dinosaurs also have strap-like scapulae and large, outsized heads or very long necks, or both).

References

Sharov, A. G. 1970. A peculiar reptile from the lower Triassic of Fergana. Paleontologicheskii Zhurnal 1(1): 127-130. [in Russian]
Buchwitz, M. & Voigt, S. 2012. The dorsal appendages of the Triassic reptile Longisquama insignis: reconsideration of a controversial integument type. Paläontologische Zeitschrift 86(3): 313-331.

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8 Responses to Longisquama is too Weird for this World

  1. Dominic says:

    “controversial reconstructors or miseducators seeking personal fame over accuracy”

    Now who *could* you be referring to here?!?!

  2. Jaime was kind enough to send me this post unsolicited. I wish Jaime could examine the fossil first hand, as I have. I also wish Jaime would start his own phylogenetic analysis. That way he could properly nest all the enigmas we all find so fascinating.

    There is no fame in this, unless you call infamy fame. Discovery is personally satisfying. The response by others is completely out of my hands. Stoicism helps.

    Many workers (Sharov, Martin, Senter, Peters) have attempted a reconstruction of the skull. All are different, but all traced an antorbital fenestra. Senter traced one, but denied its existence. To opt out, as you put it, Jaime, sets you apart from the consensus.

    Surprised you didn’t mention the combination of the interclavicles, clavicles and sternum, which Wild 1993 called a sternal complex for the MCSNB 8950 pterosaur specimen. The strap-like scapula you mentioned is matched to a strap-like immobile coracoid, as in pterosaurs. That trait is shared with birds, an analog with the immobile elongate clavicle of bats, in other words, all flapping tetrapods.

    Sharov traced a complete hind limb, but identified it as displaced plume.

    I know you hate hearing this, but both hands, both feet, an attenuated tail, deep pelves and prepubes were preserved in this crushed fossil. Smaller, precursor dorsal plumes are found in Middle Triassic Cosesaurus.

    Longisquama teaches us that pterosaurs and their ancestors were the birds-of-paradise of the Middle to Late Triassic, creating extradermal decorations and flapping to attract mates prior to flying. Longisquama went one way with large plumes and small flapping forelimbs. Pterosaurs went another way with smaller plumes and larger, flapping forelimbs. Details here: http://reptileevolution.com/longisquama.htm

    • As of the last time I believe we talked on this *particular* taxon, the “material” you observed was a plaster cast; but this is also true of me. As was discussed at that time, there is no way to improve the textural resolution of the original with a cast, any type, simply because a cast always loses quality and the material no matter how fine loses definition in the transfer from positive or negative to its reverse.

      This is most important when you use smudges on the slabs of multiple specimens or the presence of carbonized remains of the bacteria that invade the stone itself (not even around the fossil) — such as the well known nature of manganese dendrite crystals (which aren’t organic) in Solnhofen and Lujiatun fossils. It’s the same with Longisquama, and will always be the same. The rank dishonesty with which you present this technique of resolving digitally rendered pixels from photographs whose lighting source, angle, and distance you do not know and which was used in the earlier days and every time a new paper on some tetrapod or other comes out.

      A fossil that angles off the slab suddenly has all elements of its body cleanly tucked above an unnatural break on the slab? Ludicrous. Always has been, and always will be. You’ve been challenged to present your proofs of your techniques and results through peer review and provide the means for them to be reproducible and you have failed — blaming others for their inability to sense pareidolia.

      Hold off on your replies, though. More is coming.

    • B. says:

      You believe nautiloids are chordates instead of the invertebrates they literally are. Any argument you make is completely and utterly invalid.

  3. Andrea Cau says:

    “I wish Jaime could examine the fossil first hand, as I have.”
    Said the man who did not examine first hand dozens and dozens and dozens of fossils which then he in any case has reconstructed and published in his blog.

  4. Silvio Renesto says:

    I have never seen the specimen, thus mine are only speculations, however, if the reconstruction by Sharov, as redrawn by Unwin in Benton and Unwin (2001, Age of Dinosaurs in Russia), has any reliability, it seems to me that Longisquama had elongate digits with a preungual phalanges much longer than preceding ones, a feature usually found in arboreal lizards (and in drepanosauromorphs).
    Interestingly, the carpus and manus of Longisquama seems as long as the forelimb, a feature also found in some arboreal tetrapods and shared with the drepanosauromorph Vallesaurus which manus is quite similar to that of the reconstruction of Longisquama.
    Finally, the apparent furcula-like structure resemble the one we have found in Megalancosaurus (Castiello, Renesto and Bennett 2016, Historical Biology 28: 1090-1100), but proportionally much larger in Longisquama.
    I am not proposing that Longisquama is a drepanosauromorph, only suggesting that mamy features along with the elongate scapula fit very well in the frame of an arboreal adaptation. Given the dorsal displacement of the supposed “clavicles + interclavicle (furcula-like)” complex, the scapula may have been shifted from the original position possibly more vertical as in cameleons (and drepanosauromorphs).
    If the reconstruction is not reliable, please disregard all what I have written.
    Chers

    • And I am fully willing to alter the skeletal to agree with such an intepretation, as it would make some of the other features and issues with reconstruction easier and more consistent. Thank you for the comment, Silvio!

      • Andrea Cau says:

        Sharov (1970) explicitly mentioned the absence of cervical ribs in Longisquama diagnosis. Note this is also a drepanosaurid feature.

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