Bird dinosaur.jpg


Oculudentavis is an extinct saurian of uncertain taxonomic placement, originally classified as a bird. It was discovered in Myanmar.

The O. khaungraae specimen preserves features that hint at miniaturization constraints, including a unique pattern of cranial fusion and a morphology that resembles the eyes of lizards.

Xing et al 2020 reconstruction of Oculudentavis as a basal saurian lizard

Outdated Wang et al. 2020 (original publication naming the genus) classification as a bird

Description

Skeletal inclusions in approximately 99-million-year-old amber from northern Myanmar. The size and morphology of this species suggest a previously unknown role, and a previously undetected ecology. This discovery highlights the potential of amber deposits to reveal the lowest limits of vertebrate body size. [1]

The detailed description of the Fossil

The conically arranged scleral ossicles define a small pupil, indicative of diurnal activity. Miniaturization most commonly arises in isolated environments, and the diminutive size of Oculudentavis is therefore consistent with previous suggestions that this amber formed on an island within the Trans-Tethyan zone [2] 

Classification

Specializations caused by the small size of Oculudentavis lead to difficulties in making precise conclusions on its classification. A phylogenetic analysis in the original description supports a basal placement for Oculudentavis within Avialae, only slightly closer to modern birds than Archaeopteryx. This suggests that a ~50 million year ghost lineage exists between the Late Jurassic and the middle of the Cretaceous. A small amount of most parsimonious trees instead suggest that it is an enantiornithean, like other birds preserved in Burmese amber.[3]

Soon after the publication of the article, a number of paleontologists have voiced skepticism on whether Oculudentavis is even a dinosaur, due to a much higher number of similarities with squamates than with theropods. The general skull shape is considered the largest argument in favor of bird affinities, but some living lizards (Meroles, Anolis) and extinct reptiles (Avicranium, Teraterpeton) are known to have convergently evolved a bird-like skull shape. The usage of a bird-focused phylogenetic analysis (without considering lizards) also has been criticized. The editors of the Institute of Vertebrate Paleontology and Paleoanthropology's Fanpu publication have published an editorial arguing for an interpretation of Oculudentavis as a lizard rather than an avialan.[4]

References

  1. https://www.scientificamerican.com/article/smallest-known-dinosaur-found-in-amber/
  2. https://www.nature.com/articles/s41586-020-2068-4
  3. Xing, L.; O'Connor, J. K.; Schmitz, L.; Chiappe, L. M.; McKellar, R. C.; Yi, Q.; Li, G. (2020). "Hummingbird-sized dinosaur from the Cretaceous period of Myanmar". Nature. 579 (7798): 245–249. doi:10.1038/s41586-020-2068-4. PMID 32161388.
  4. Wang, W.; Zhiheng, L.; Hu, Y.; Wang, M.; Hongyu, Y.; Lu, J. (2020). "The "smallest dinosaur in history" in amber may be the largest mix-up in history" (in Chinese). Institute of Vertebrate Paleontology and Paleoanthropology. Retrieved 2020-03-16.
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