Bolet et al. 2020 bring us specimen #2 of ‘Oculudentavis’.
“Here we describe a more complete, specimen [GRS-Ref-286278, Fig. 1] that demonstrates Oculudentavis is actually a bizarre lizard of uncertain position. The new interpretation and phylogenetic placement highlights a rare case of convergent evolution rarely seen among reptiles.”
Convergence is rampant within the clade Reptilia.
Whenever they say ‘bizarre’ you know they did not have pertinent taxa on their inclusion list.
When they say ‘uncertain position’ they mean it jumps around on their cladograms depending on the whether characters were ordered, unordered, etc. (see below).
We looked at Oculudentavis #1 several times earlier here, here, here, and elsewhere. and nested it with Cosesaurus, a taxon that has been ignored since March 2020 when it was listed on the Nature comments page.
Bolet et al. correctly nest ‘Oculudentavis‘ #2
close to the basal tritosaur, Huehuecuetzpalli in their figure 3 (reproduced here in Fig. 2). It represents only one of several of their recoveries, as noted below.
due to taxon exclusion and some bad scoring, Oculudentavis #1 does not nest with Oc2 close to Huehuecuetzpalli, but continues to nests with Cosesaurus in the large reptile tree (LRT, 1223+ taxa; subset Fig. 3). Only Oc2 nests with Huehuecuetzpalli (Fig. 3). In order to move Oc2 close to Oculudentavis 21 additional steps are required. So, Oc2 requires a new generic name.
From the abstract:
“Here we describe a more complete, specimen that demonstrates Oculudentavis is actually a bizarre lizard of uncertain position.”
Unfortunately, Oc2 is not Oculudentavis. The two specimens only vaguely resemble one another. The differences (see below and compare Figs. 1 and 4) turn out to be important.
Its not ‘bizarre’ when correctly nested. Bolet et al. are unaware of the third clade of lepidosaurs, the Tritosauria. The paper describing this clade was rejected several years ago by well-meaning paleo-referees. It could have been useful here.
Sometimes the authors misspell Oculudentavis ‘Oculodentavis’. How many of the 10 co-authors were in charge of proofreading?
The authors note the skull proportions are not as tall and attribute that to distortion. Nothing else is distorted in the rest of the skeleton, including the slenderest of bones. That’s the beauty and wonder of amber preservation.
Notable differences between Oculudentavis and Oc2.
- The maxilla of Oc2 is deeper without an antorbital fenestra.
- The palate of Oc2 is much more open and wider with larger choanae.
- The basiocciput of Oc2 is inflated.
- Oc2 has supratemporals missing in Oculudentavis.
- The postorbital extends to the posterior parietal in Oc2.
- The quadratojugal is a tiny splinter attached only to the jugal in Oc2.
- Oc2 has a vomernasal opening missing from Oculudentavis.
- Tiny vomer teeth are present in Oc2.
- The vomers contact the maxilla and premaxillae broadly in Oc2. By contrast, the slender medial vomers are squeezed between and above a long posterior extension of the premaxilla in Oculudentavis.
- In Oc2 the ectopterygoid continues the posterior rim of the pterygoid transverse process.
From the text:
“In its bird-like skull shape (vaulted cranium, tapering rostrum), the skull of Oculudentavis is strikingly different from any known lizard and represents a startling instance of convergent evolution.”
I will remind readers
the first several times Cosesaurus (Fig. 5) was described (Ellenberger and de Villalta 1974, Ellenberger P 1978, 1993) it was considered to be a pre-bird. When faced with the possibility that Cosesaurus was a pre-pterosaur (Peters 2000a, b, 2007, 2009), Elllengerger shrugged off the hypothesis. He was too invested. He never considered the possibility, despite years of work with comparative anatomy, just as other workers do today. Cosesaurus also has a vaulted cranium, a tapering rostrum and a rostral crest, by convergence or reversal.
From the Discussion
“Using the squamate data set, the phylogenetic placement of Oculudentavis within Squamata is markedly different depending on how the data is treated.”
“If the characters are treated as ordered, the two specimens form a sister-clade to the limb-reduced, vestigial eyed, fossorial Dibamidae, near the base of Squamata.”
“If characters are treated as unordered, then Oculudentavis is recovered within the crown-squamate clade Toxicofera (snakes, iguanians, anguimorphs, on the stem of mosasaurians and snakes.”
This usually means taxon exclusion. No such problems exist in the LRT, which minimizes taxon exclusion by its large taxon list. Legless Dibamus nests as a highly derived amphisbaenid squamate in the LRT.
“The convergence between Oculudentavis and birds is clearly depicted in the phylomorphospace plot of the amniote data set.”
Unfortunately, no fenestrasaurs (= Cosesaurus and kin including pterosaurs, the most bird-like of all lepidosaurs), are included in the Bolet et al. study.
Even if ALL they had to work with
were just Oculudentavis and the new specimen, the differences, especially in the palate, are striking and should have raised the hypothesis that the two taxa were not congeneric.
Keeping fenestrasaurs out of the taxon inclusion list
can be attributed to 20 years of suppression and omission. This is what happens when that happens. Mistakes are made.
Bolet A et al. (9 co-authors) 2020. The tiny Cretaceous stem-bird Oculudentavis revealed as a bizarre lizard. Biorxiv the preprint server for biology. https://www.biorxiv.org/content/10.1101/2020.08.09.243048v1
Ellenberger P and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
Ellenberger P 1978. L’Origine des Oiseaux. Historique et méthodes nouvelles. Les problémes des Archaeornithes. La venue au jour de Cosesaurus aviceps (Muschelkalk supérieur) in Aspects Modernes des Recherches sur l’Evolution. In Bons, J. (ed.) Compt Ren. Coll. Montpellier 12-16 Sept. 1977. Vol. 1. Montpellier, Mém. Trav. Ecole Prat. Hautes Etudes, De l’Institut de Montpellier 4: 89-117.
Ellenberger P 1993. Cosesaurus aviceps . Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.
Li Z, Wang W, Hu H, Wang M, Y H and Lu J 2020. Is Oculudentavis a bird or even archosaur? bioRxiv (preprint) doi: https://doi.org/10.1101/2020.03.16.993949
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330
Xing L, O’Connor JK,; Schmitz L, Chiappe LM, McKellar RC, Yi Q and Li G 2020. Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature. 579 (7798): 245–249.