Original title: Sino-US team found the smallest dinosaur in the hundred million years of amber! Hummingbird size, big eyes, hundreds of teeth

At 00:00 on March 12th, Beijing time, the top academic journal Nature published a study jointly conducted by Chinese and American scientists "Hummingbird-sized dinosaur from the Cretaceous period of Myanmar ) ": They found one of the smallest dinosaurs (broad dinosaurs including birds) in the Cretaceous amber in Myanmar. The research team established a new genus and new species-Oculus dentavis khaungraae. The genus name has two of the most distinctive characteristics, namely, large eyes and dense teeth.

This research was conducted by Associate Professor Xing Lida of China University of Geosciences (Beijing), Jingmai K. O'Connor, a foreign researcher at the Institute of Paleovertebrate and Paleoanthropology, Chinese Academy of Sciences, and Lars Schmitz ) Ph.D., Researcher Li Gang, Institute of High Energy Physics, Chinese Academy of Sciences, and Professor Luis M. Chiappe, Dean of the Dinosaur Research Institute of the Natural History Museum in Los Angeles, USA (Ryan C. McKellar), Dr. Yi Qiru, Beijing Comprehensive Research Center of the Chinese Academy of Sciences, and other scholars. Zou Jingmei is the corresponding author.

The research team established a new genus and species, the Oculusentavis khaungraae. The wide-eyed eye-toothed bird is considered the smallest bird to date and the smallest dinosaur. It probably lived in northern Myanmar 99 million years ago, and was unfortunately covered by the resin flowing down the coniferous trees. It formed amber during a long geological age and is preserved to this day. The piece of amber that wraps it weighs less than 3 grams.

The research team believes that the size and shape of the eye-toothed bird shows us a new type of body structure and the ecology it represents. The discovery highlights the potential of amber deposits to reveal the smallest vertebrates. This discovery is of great significance for understanding the evolution of dinosaurs and ancient birds, especially the morphological evolution of miniaturized animals.

However, the authors mentioned that there is still some uncertainty in the classification of the eye-tooth bird specimen because it has only the head. They will continue to search in Maine, hoping to find more complete individuals in the future and uncover all the secrets of the eye-toothed bird.

Burmese amber about 100 million years ago: collected in the Amber Pavilion Museum in Tengchong

The amber fossils discovered were produced in the Hugang Valley in Kachin State in northern Myanmar, where amber has been produced continuously for at least the past 2000 years.

It is worth noting that bone fossils in sediments such as clay, silt and sand often crush and destroy the remains of smaller animals, and can also flatten and corrode soft parts such as skin, scales and feathers. In contrast, amber has the advantage of providing unparalleled preservation of paleontology, and small animals preserved in Burmese amber preserve their soft parts.

Over the past few years, a large number of invertebrates and small vertebrates have been found in Myanmar's amber, including lizards and birds. The paper mentioned that the amber inclusions of birds in the Hugang Valley in Myanmar are relatively rich, which is of great help in understanding the evolution of birds. The skeletal inclusions in this piece of amber in this study provide an unprecedented perspective on the soft tissue and skeletal anatomy of tiny animals.

Specimens preserved in Burmese amber are quickly becoming a special way to study small vertebrates of the dinosaur age. Geologists determined that the volcanic ash zircon isotope of the mining area was geologically considered to have formed amber in the Hugang Valley about 100 million years ago (about 99 million years). The earliest period of the late period) is considered to be the best window for humans to get a glimpse of the "real" Cretaceous world.

Birds are considered to be the descendants of dinosaurs and one of the most biodiverse vertebrates, with approximately 10,500 species. In the long evolution history of nearly 150 million years, it has experienced two radiative evolutions of the Cretaceous and Cenozoic. The Cretaceous is an important stage of bird evolution and one of the key stages of bird evolution from dinosaurs.

The piece of amber in this study is in the Hupoge Amber Museum in Tengchong, Yunnan, China. The full specimen HPG-15-3 contains a complete skull in amber, which measures 31.5mm × 19.5mm × 8.5mm and weighs 2.84 g.

According to the research team, the specimen belongs to the Tengchong Amber Pavilion Museum in Yunnan and the Yangon Branch in Myanmar. It was collected by the curator Mr. Chen Guang and his family Ms. Kuanya from the northern Myanmar mining area in 2016.

New genus and species

The specimen for this study was a complete animal skull wrapped in amber. The research team mentioned that the first challenge of conducting the research was how to obtain the complete high-resolution 3D information of the skull surrounded by layers of amber, fur, and impurities.

Li Gang's team used the Shanghai Light Source (SSRF) hard X-ray imaging line station and the high-modulation transfer function (MTF) high-efficiency hard X-ray detector developed in Beijing Synchrotron Radiation Facility (BSRF). Optimized hard X-ray phase contrast CT scanning scheme.

Use monochromatic high-energy X-ray and high-efficiency detectors to avoid radiation damage and achieve non-destructive imaging; use coherent X-ray phase contrast and high MTF of the detector to achieve high-sensitivity imaging; use high-resolution detectors , Off-axis CT scanning and virtual stitching to achieve large field of view and high resolution 3D imaging. After phase restoration, tomographic reconstruction, data fusion, and virtual segmentation of specific structures, the high-resolution and high-contrast 3D structure of the skull hidden inside the amber was finally obtained losslessly.

The skull in this amber is only about 14 mm long, has a sharp beak, dense teeth and huge eye sockets, and the length of the posterior beak is only 7.1 mm. This animal's bone features are somewhat "four dislikes", some like dinosaurs, and some like very advanced birds.

The research team did not find specific skull features to accurately classify the animal as a bird, a non-bird dinosaur, or another host dragon. Moreover, they cannot completely exclude this skull from belonging to another animal. "This is the strangest fossil I've been lucky enough to study," said Zou Jingmei.

However, in vertebrates, only birds have sharp beaks and huge eye sockets, so the research team assigned the animals to birds.

In view of the morphological characteristics of this specimen being different from all other birds, the research team established a new genus and new species, the Oculusentavis khaungraae. The genus Oculusdentavis is derived from the Latin Oculus (eye), dentes (teeth), and avis (bird), and points out the characteristics of the specimen, namely, large eyes and dense teeth. The species, Kuanya, pays tribute to Ms. Kuanya, a Burmese amber collector who first discovered and solicited the specimen.

The smallest dinosaur in history: carnivorous, day type

The smallest known living bird is the hummingbird. The smallest hummingbird is the Melisuga helenae. It weighs about 1.95 grams and is 5.5 cm long. It is the smallest bird in the world.

The research team mentioned that in terms of skull size, the eye-toothed bird named this time is shorter than the hummingbird, the smallest ancient bird ever discovered, and the smallest dinosaur in history.

They speculated that about 100 million years ago, the eye-toothed bird lived in the humid tropical environment of northern Myanmar, and was unfortunately wrapped in resin flowing down by conifers such as cypresses and araucaria, forming amber during the long geological age and preserve to date.

The most interesting aspect of the eye-toothed bird is its miniaturization. The research team mentioned that animals that have become so small must face many new problems, such as how to integrate all the sensory organs into their tiny heads and how to maintain their body temperature.

This miniaturization process usually occurs in an isolated environment, most typically islands. It happened that Myanmar was an isolated island arc in the middle of the Cretaceous.

The first of the eye-toothed bird is its "tooth", which is one of the reasons why the research team named it the eye-toothed bird. Generally, miniaturization is accompanied by features such as tooth loss and eye enlargement. However, despite the small size of the specimen, it has more teeth than all other ancient birds. The dentition is also longer than other birds and extends all the way under the eyes. There are 18–23 teeth on each side of the upper jaw, and 29–30 teeth on each side of the dental bone. All teeth add up to about 100 teeth.

The large number of teeth also suggests that, despite its small size, it is a carnivorous animal.

The second special feature of the eye-toothed bird is its "eye", which is about 4 mm in diameter. The eyes of birds and most reptiles (including dinosaurs, pterosaurs, and ichthyosaurs) have a scleral ring composed of scleral bones, which surrounds the eyeball and plays a supporting and protective role.

The sclera bones in birds are generally square and very simple, but the sclera bones of the eye-tooth birds are spoon-shaped. This form has only been found in some living lizards, which is one of the places where the research team is very confused.

In addition, the eye-tooth bird's eyes are also different from birds with developed scleral rings such as owls. The owl's eyes are forward, and the eye-tooth birds are facing to the sides. Eye-toothed bird's metatarsus is curved, eyes protruding from the side of the head. This visual system has never been found in live animals, making it difficult for authors to understand how its eyes work.

In addition, the opening of the eye bone (inner diameter of the eye circle) indicates that the activity mode of the eye-tooth bird is daytime.

The research team also analyzed the phylogenetic relationship and thought that the phylogenetic relationship between the eye-toothed bird and other birds was also very special. Analysed from the skull alone, this newly discovered tiny bird is very primitive, between the most primitive Archaeopteryx of the Late Jurassic in Germany and the long-tailed Jeholornis of the Early Cretaceous .

This may indicate that, like these two taxa, eye-toothed birds have a long tail similar to non-bird dinosaurs. (Surging news reporter He Liping)