Another biologist disputes the nature of the tiny “bird/dino” fossil

On March 12, I wrote about the new Nature paper describing the fossil of Oculudentavis khaungraa, identified as a tiny (2-gram) dinosaur/bird found in Burmese amber. But the very next day I had to hedge the results after reading Darren Naish’s Tetrapod Zoology post, not only on humanitarian grounds (the amber used in the study may be “blood amber”, used to fund the military), but, most important for the science, because other paleontologists started doubting that this fossil was indeed that of a theropod. As Darren notes,

“. . .  a number of experts whose opinions I respect have expressed doubts about the claimed theropod status of the fossil discussed below and have argued that it is more likely a non-dinosaurian reptile, perhaps a drepanosaur or lepidosaur (and maybe even a lizard).”

The article below, translated from the Italian by Google (click on screenshot), was called by my attention by reader Gerdian de Jong who wrote this to me:, “The respected paleontologist Andrea Cau writes in his blog Theropoda.blogspot why Oculudentavis is not a bird or theropod and that wider analysis points to stem-Gekkota.”

First, though, here are two reconstructions of O. khaungraa by Darren, who kindly gave me permission to reproduce them here (© Darren Naish/Tetrapod Zoology). The captions are his.

Speculative life reconstruction of Oculudentavis, its feathering and other details inspired by Jeholornis and other archaic members of Avialae. I’ve depicted it on the forest floor but am not necessarily saying that this is where it spent all of its time. Image: Darren Naish.

A to-scale reconstruction by Darren. Note that the ruler is in centimeters, not inches (2.54 cm/inch, so the 10-cm ruler is only about four inches long.

A very rough, semi-schematic skeletal reconstruction of Oculudentavis which I produced in order to gain a rough idea of possible size. As you can see, it would have been tiny. The overall form of the skeleton is based on that of jeholornithiform birds; read on. Image: Darren Naish.

I’ll call attention to other articles/critiques about this specimen as they come to my attention. At any rate, right now it’s unwise to regard this as a theropod dinosaur that was also avian.

Click on the screenshot to read in Italian or get a translation. I’ll provide a summary of the translation (indented) below.

After reading the study, and observing in detail the navigable 3D model of the skull, produced by the authors, I believe that the interpretation proposed by Xing et al. (2020) is very problematic. Oculudentavis in fact has numerous anomalous characteristics for a bird and even for a dinosaur. And this makes me doubt that it is classifiable within Dinosauria (and Avialae).

Absence of anti-orbital fenestra.

Quadrate [bones] with large lateral concavity.

The maxillary and posterior teeth of the maxillary extend extensively below the orbit.

Dentition with pleurodon or acrodont implant.

Very large post-temporal fenestra.

Spoon-shaped sclerotic plaques.

Coronoid process that describes a posterodorsal concavity of the jaw.

Very small size.

Oculudentavis is much smaller than any other Mesozoic avian discovered so far. Its dimensions are comparable to those of the skulls of many small squamata found in Burmese amber.

In conclusion, there are too many “lizard” characters in Oculudentavis not to raise the suspicion that this fossil is not a bird at all, let alone a dinosaur, but another type of diapsid, perhaps a scaled lepidosaur, if not possibly a specimen very immature than some other Mesozoic group (for example, a coristodero). 

If I had to bet money between the hypothesis that it is a very small bird with unusual “lizard” convergences and the hypothesis that it is a very immature skull of a non-dinosaurian reptile, I will point the second.

To read more about why the traits in bold are more indicative of a lepidosaur than a dinosaur, read the original article.

But what are lepidosaurs? They are a monophyletic group of reptiles that contains the extant snakes, lizards, tuataras and worm lizards (“legless” lizards). “Monophyletic” means that the group contains all descendants, living or extinct, from a common ancestor. Lepidosaurs do not include dinosaurs. Here’s a family tree from Quora, which shows that dinos aren’t within the Lepidoauria, as the latter group is over on the right.

 

Now the fact that this fossil may not have been a theropod dinosaur but a lepidosaur, like a lizard, doesn’t make the original results uninteresting. In fact, to me it makes them more interesting. First, it shows that there could have been convergent (independent) evolution to birdlike forms in both dinosaurs and lepidosaurs (perhaps from a lizard-like ancestor). That would be stunning.

Further, it shows that regardless of whether the species in amber was a theropod or a lepidosaur, there may have been a whole radiation of miniature, bird-like creatures from an entirely different group of reptiles. Whether that was true depends on finding more specimens. Since these are small and fragile, it’s unlikely that they’d be found in anything other than amber. We shall see.

In the meantime, I hope the mainstream press, which touted this specimen as a form of dinosaur, at least gives a clarification.  While the messy details of anatomy are unlikely to interest the public, at least they’ll know that science is an ongoing process, and what is regarded as “true” is provisional, only becoming less provisional when more data are gathered. Right now we have but a single specimen of this type.

 

14 Comments

  1. merilee
    Posted March 15, 2020 at 9:15 am | Permalink

    🐾🐾

  2. merilee
    Posted March 15, 2020 at 9:15 am | Permalink

    🐾🐾

  3. ThyroidPlanet
    Posted March 15, 2020 at 9:50 am | Permalink

    Interesting!

  4. A C Harper
    Posted March 15, 2020 at 9:55 am | Permalink

    Now this is the sort of article, exploring an aspect of evolution, that really interests me. Just sayin.

  5. Janet
    Posted March 15, 2020 at 10:17 am | Permalink

    Wish we had the DNA from these critters to compare!!

  6. Posted March 15, 2020 at 10:45 am | Permalink

    Why science is so wonderful, and believable …science should always check, doubt, until a wider consensus is eventually reached, and even then never totally certain.

  7. rickflick
    Posted March 15, 2020 at 10:46 am | Permalink

    I know it’s problematic, but I kinda hope there are more of these discovered (maybe after the war and after the amber mines have become national parks). A complete articulated specimen would probably answer our questions.

  8. loren russell
    Posted March 15, 2020 at 12:35 pm | Permalink

    Another group of Chinese workers also explode the idea that this is a bird, or any other kind of dinosaur: Wang, Wei; Zhiheng, Li; Hu, Yan; Wang, Min; Hongyu, Yi; Lu, Jing (13 March 2020). “[Back to the Park] The “smallest dinosaur in history” in amber may be the largest own goal in history”. Institute of Vertebrate Paleontology and Paleoanthropology (in Chinese).

    I can’t read the Chinese text, but the illustrations show the lizard-like traits. And “largest own goal” in the English title says a lot!

    IF a lepidosaur, there’s no reason to assume this is a hatchling of a larger species. Then as now, lepidosaurs [esp. lizards] dominate the tiny reptile niches.

  9. Posted March 15, 2020 at 1:10 pm | Permalink

    I think that widely advertising discoveries to the media before reaching an expert consensus does a disservice to science and the public.

    • ThyroidPlanet
      Posted March 15, 2020 at 1:26 pm | Permalink

      In my view this is simply problem solving. Spectators can watch the scientific problem solving unfold in the moment.

  10. Posted March 15, 2020 at 2:02 pm | Permalink

    I don’t totally disagree with your point but our host’s last paragraph in this post probably sums up how we, the public and media should ‘learn’ to handle science posts from here, there and everywhere… 🙂 the point here though, did the scientists (if thats what they are) that released their speculations to the media learn a leason.

  11. grasshopper
    Posted March 15, 2020 at 2:49 pm | Permalink

    And just when I was about to exclaim how this miraculously miniscule dinosaur showed the wonder and glory of God’s creation ….

    Bet it was still a herbivore, though.

  12. Posted March 15, 2020 at 7:32 pm | Permalink

    The “Reptile family tree” from Quora notably includes a branch shared by “Mammal-like reptiles” and mammals, and this branch is sister to the branch with birds and reptiles. That was an odd thing to see. I had always thought reptiles were a monophyletic group; how could thre also be reptiles in another branch of the tree? Wikipedia came to the rescue, as it so often does. I learned that the name “mammal-like reptiles” is actually defunct, and a better name for this group is the “non-mammalian synapsids”. “Reptiles” in the modern sense really are monophyletic.

  13. Posted March 16, 2020 at 3:15 am | Permalink

    Reblogged this on Rashid's Blog: An Educational Portal.


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