Guest “amateur paleontology” by David Middleton

NEWS 11 MARCH 2020
This miniature skull belonged to a 2-gram dinosaur
The 100-million-year-old animal might have been the smallest dinosaur.

Giuliana Viglione

A miniature creature exquisitely preserved in amber for almost 100 million years is probably the smallest dinosaur ever discovered.

The animal’s bird-like skull, described in Nature on 11 March¹, is less than 2 centimetres long — suggesting that the creature was the size of the bee hummingbird (Mellisuga helenae), the smallest living bird. Its discovery could help scientists understand how such creatures evolved to be so small.

“It reveals to us a whole new lineage of birds,” says Jingmai O’Connor, a palaeontologist at the Chinese Academy of Sciences Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, who co-led the study.

[…]

Further research on the fossil — for example, looking for biomolecules in its preserved soft tissue — will require advances in research techniques that don’t damage the specimen, O’Connor says.

[…]

Nature

A dino-bird in amber…

Beats two mosquitoes in an amber mine…

NEWS AND VIEWS 11 MARCH 2020
Tiny bird fossil might be the world’s smallest dinosaur
A tiny skull trapped in 99-million-year-old amber suggests that some of the earliest birds evolved to become miniature. The fossil illustrates how ancient amber can act as a window into the distant past.

Roger B. J. Benson

Dinosaurs were big, whereas birds — which evolved from dinosaurs — are small. This variation is of great importance, because body size affects lifespan, food requirements, sensory capabilities and many other fundamental aspects of biology. The smallest dinosaurs¹ weighed hundreds of grams, but the smallest living bird, the bee hummingbird (Mellisuga helenae)², weighs only 2 grams. How did this difference come about, and why? In a paper in Nature, Xing et al.³ describe the tiny, fossilized, bird-like skull of a previously unknown species, which they name Oculudentavis khaungraae. The discovery suggests that miniature body sizes in birds evolved earlier than previously recognized, and might provide insights into the evolutionary process of miniaturization.

Fossilization of bones in sediments such as clay, silt and sand can crush and destroy the remains of small animals, and can flatten and decay soft parts such as skin, scales and feathers. By contrast, preservation of small animals in Burmese amber (which formed from the resin flows of coniferous trees about 99 million years ago) helps to protect their soft parts. A wide range of invertebrates⁴ and small vertebrates, including lizards⁵ and birds⁶, have been found in Burmese amber. Specimens preserved in this material are rapidly emerging as an exceptional way to study tiny vertebrates from the age of dinosaurs^5,6.

It is in Burmese amber that the single known fossil skull of Oculudentavis has been preserved (see Fig. 1a of the paper³). Oculudentavis means eye tooth bird, a name that Xing et al. chose because of two unusual features of the skull, each of which provides evidence about the likely lifestyle of this 99-million-year-old species.

[…]

The evolutionary relationships between Oculudentavis and other dinosaurs and birds are difficult to determine, but are central to clarifying the evolutionary implications of this discovery. Xing and colleagues’ analysis suggests two possibilities. Oculudentavis could belong to the most common group of birds of the Cretaceous period (about 145 million to 66 million years ago), the enantiornithines. Alternatively, it could be much more closely related to dinsosaurs, lying almost midway on the evolutionary tree between the Cretaceous birds and Archaeopteryx, the iconic winged dinosaur from the Jurassic.

[…]

Nature

The paper is pay-walled. Here’s the abstract:

Article
Published: 11 March 2020
Hummingbird-sized dinosaur from the Cretaceous period of Myanmar
Lida Xing, Jingmai K. O’Connor, Lars Schmitz, Luis M. Chiappe, Ryan C. McKellar, Qiru Yi & Gang Li
Nature volume 579, pages 245–249(2020)

Abstract

Skeletal inclusions in approximately 99-million-year-old amber from northern Myanmar provide unprecedented insights into the soft tissue and skeletal anatomy of minute fauna, which are not typically preserved in other depositional environments^1,2,3. Among a diversity of vertebrates, seven specimens that preserve the skeletal remains of enantiornithine birds have previously been described^1,4,5,6,7,8, all of which (including at least one seemingly mature specimen) are smaller than specimens recovered from lithic materials. Here we describe an exceptionally well-preserved and diminutive bird-like skull that documents a new species, which we name Oculudentavis khaungraae gen. et sp. nov. The find appears to represent the smallest known dinosaur of the Mesozoic era, rivalling the bee hummingbird (Mellisuga helenae)—the smallest living bird—in size. The O. khaungraae specimen preserves features that hint at miniaturization constraints, including a unique pattern of cranial fusion and an autapomorphic ocular morphology⁹ that resembles the eyes of lizards. 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 arc¹⁰. The size and morphology of this species suggest a previously unknown bauplan, and a previously undetected ecology. This discovery highlights the potential of amber deposits to reveal the lowest limits of vertebrate body size.

Nature

Cool schist! Unless… someone gets the bright idea to genetically engineer dinosaurs from “biomolecules in its preserved soft tissue”… 😉

Reference

Xing, L., O’Connor, J.K., Schmitz, L. et al. Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature 579, 245–249 (2020). https://doi.org/10.1038/s41586-020-2068-4

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