Monday, March 16, 2020

What is Oculudentavis if it's not a theropod?

In my last post, I argued the recently described Oculudentavis (Xing et al., 2020) is not a theropod.  So what is it?  To answer that question, I entered it into Simoes et al.'s (2018) sauropsid analysis which emphasizes basal lepidosauromorphs and comes out with basal gekkos and nested iguanians even using just morphological characters.  To test Jingmai's avialan hypothesis, I also added Archaeopteryx to the matrix.  The result is 384 MPTs of 2337 steps each.

Strict consensus of 384 MPTs of Simoes et al.'s (2018) analysis after adding Oculudentavis and Archaeopteryx.  Compare to Extended Data Figure 3 of Simoes et al..
As you can see, Oculudentavis resolves as a stem-squamate in a trichotomy with Huehuecuetzpalli and squamates, while Archaeopteryx is an archosauromorph sister to Erythrosuchus.  And this matrix didn't score for scleral ossicle shape, posttemporal fenestra size or maxillary tooth row length.  After scoring Oculudentavis, its teeth are clearly not acrodont, it seems to have a ventral parietal fossa and  lacks an ossified laterosphenoid.  The authors could have made it easier to evaluate by separating the cranial elements in the 3D pdf file.  As it is, a lot of palatal and braincase info is uncertain.  But Huehuecuetzpalli is Albian compared to Oculudentavis' Cenomanian, and has a skull length of 32 mm (19 mm in the juvenile) versus 14 mm in Oculudentavis.


Huehuecuetzpalli skull (top; after Reynoso, 1998), Oculudentavis skull and separate mandible (middle; after Xing et al., 2020), and Archaeopteryx skull (after Rauhut, 2014).

References- Reynoso, 1998. Huehuecuetzpalli mixtecus gen. et sp. nov: A basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodriguez, central Mexico.  Philosophical Transactions of the Royal Society B: Biological Sciences. 353, 477-500.
Rauhut, 2014. New observations on the skull of Archaeopteryx. Paläontologische Zeitschrift. 88(2), 211-221.

Simōes, Caldwell, Talanda, Bernardi, Palci, Vernygora, Bernardini, Mancini and Nydam, 2018. The origin of squamates revealed by a Middle Triassic lizard from the Italian Alps. Nature. 557(7707), 706-709.



Xing, O'Connor, Schmitz, Chiappe, McKellar, Yi and Li, 2020. Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature. 579, 245-249.

8 comments:

  1. Nice!

    (I'd say you should publish, but let's publish the other thing first. ...On the other hand, a brief reply to Nature, using a phylogenetic analysis that was after all published in Nature, should be able to get to submission quickly.)

    BTW, there aren't any queens in Proganochelys quenstedti.

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  2. Well, it supposedly is an island environment, maybe Oculudentavis is a relictual basal lizard that has survived there while relatives elsewhere disappeared.

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    1. Huehuecuetzpalli is Albian, so is comparable to Oculudentavis' Cenomanian age without any sort of special argumentation.

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  3. According to the preprint of the Chinese team, CT-scans revealed also a pineal foramen and both palatine and pterygoid teeth. And the published images confirmthe lateral conch of the quadrate.
    The lizard scenario is thus definitive.

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    1. Hi, Cau. I saw some people claim that the lepidosaur status is quite debatable. I see you say "the lizard scenario is thus definitive". I am no expert, but I've been reading about this specific issue, and I agree with you (and others). However, this disagreement - "quite debatable" x "definitive" - kind of bothers me. Well, time will provide the truth.

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    2. Well, a list of the features dismissing a lepidosaur status is welcome.
      Since I am more a Mesozoic bird paleontologist than a Mesozoic lizard paleontologist, based on the provided evidence, I can surely affirm the Oculudentavis is not a bird or an archosaur. So, we have to options: a lepidosaur (likely, squamate) or some late-surviving Triassic reptile clade. Pending explicit evidence to the "Triassic guy scenario", the lepidosaur one keeps being the best available.

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    3. Even a Late Triassic reptile clade is dubious given the specific lizard-like attributes like the pleudorodont teeth. As much as I wanted it to be a drepanosaur or a weird tuatara relative, a lizard status is most plausible.

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  4. Li, Wang, Hu, Wang, Yi & Lu 2020. Is Oculudentavis a bird or even archosaur? bioRxiv (preprint)
    https://www.biorxiv.org/content/10.1101/2020.03.16.993949v1.full.pdf

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