Scientists from the Hokkaido University Museum in collaboration with colleagues from the Okayama University of Science have named a second hadrosaurid from the Late Cretaceous of Japan. Described from a partial skeleton, Yamatosaurus izanagii lived at the same time as the first duck-billed dinosaur named from Japan (Kamuysaurus japonicus), but these two dinosaurs probably did not co-exist, instead Kamuysaurus may have been restricted to more northern coastal environments whilst the newly described Yamatosaurus may have been confined to more southerly habitats.

Did the Hadrosauridae Originate in Asia or North America?

The researchers, who included Yoshitsugu Kobayashi, Ryuji Takasaki and Anthony R. Fiorillo (who wrote the scientific paper describing Kamuysaurus in 2019), plus Katsuhiro Kubota (Hokkaido University Museum), conducted a phylogenetic analysis suggesting that Yamatosaurus was a primitive member of the hadrosaur family. Intriguingly, the team also undertook a biogeographical analysis (plotting age of ornithopod fossil finds against geographical location). They conclude that basal hadrosaurids were widely distributed in both Asia and Appalachia (the landmass representing eastern North America). In addition, the scientists postulate that the discovery of Yamatosaurus supports the theory that the sub-families of more derived duck-billed dinosaurs the Lambeosaurinae and the Saurolophinae originated in Asia and that towards the end of the Cretaceous, basal hadrosaurids such as Plesiohadros djadokhtaensis (Mongolia), Tanius sinensis (C‌hina) and Yamatosaurus (Japan) continued to thrive in eastern Asia but were extinct elsewhere.

Discovered in Marine Sediments

Amateur fossil collector Mr. Shingo Kishimoto discovered the fossilised remains in 2004, whilst exploring exposures of the Kita-ama Formation on the island of Awaji (Hyogo Prefecture). The fossil material consists of a dentary (lower jawbone), along with the surangular, neck bones, bones from the tail, cervical ribs and a coracoid plus some isolated teeth. Although hadrosaur fossils have been found in several locations in Japan (all four main islands – Hokkaido, Honshu, Shikoku, and Kyushu), they are, with the exception of the Kamuysaurus material, highly fragmentary consisting of teeth, portions of the limbs and vertebrae, this is only the second time that a new genus of duck-billed dinosaur has been erected from Japanese fossils.

The stratum from which the Yamatosaurus material was collected consists of marine mudstones of approximately the same age (early Maastrichtian), as the sediments in which Kamuysaurus was found.

Unique Traits and Basal Characteristics

Study of the nearly complete right dentary helped the researchers to erect a new, basal hadrosaur genus. Unlike other hadrosaurs Yamatosaurus had just one functional tooth in several battery positions and no branched ridges on the chewing surfaces. This suggests that Yamatosaurus evolved to feed differently compared to other duck-billed dinosaurs. Furthermore, the coracoid (that with the scapula would have formed the shoulder joint), shows traits linked to the movement away from a bipedal gait to becoming quadrupedal. This bone shows transitional characteristics that in later, more derived hadrosaurs, were more fully developed permitting these animals to become facultative bipeds (adopting a quadrupedal gait but able to run on their hind legs if required to do so).

To read Everything Dinosaur’s article from 2019 about the formal description of the first hadrosaur named from Japan (Kamuysaurus japonicus): Japan’s Greatest Fossil Dinosaur Gets a Name.

The scientific paper: “A new basal hadrosaurid (Dinosauria: Ornithischia) from the latest Cretaceous Kita-ama Formation in Japan implies the origin of hadrosaurids” by Yoshitsugu Kobayashi, Ryuji Takasaki, Katsuhiro Kubota and Anthony R. Fiorillo published in Scientific Reports.

An opposable thumb gives us apes a huge advantage, just ask a dog to hold a spoon for you, however, opposable thumbs are not just limited to gorillas, chimps, orangutans and our own genus Homo. Other apes have them too, as do some marsupials and tree frogs. In reality, opposed thumbs are rare in the Kingdom Animalia, but an international team of scientists including researchers from the University of Birmingham, have just described a new species of flying reptile and it’s the earliest example known to science of a vertebrate with an opposed thumb.

Kunpengopterus antipollicatus

The new Jurassic pterosaur has been named Kunpengopterus antipollicatus, it was discovered in the Tiaojishan Formation of Liaoning, China.

It is a small-bodied darwinopteran pterosaur, with an estimated wingspan of 85 cm. Most importantly, the specimen was preserved with an opposed pollex (“thumb”) on both hands. The species name “antipollicatus” means “opposite thumbed” in ancient Greek, in light of the opposed thumb of the new species. This is the first discovery of a pterosaur with an opposed thumb. It also represents the earliest record of a true opposed thumb in the fossil record.

“Monkeydactyl”

Kunpengopterus lived in a forested environment approximately 160 million years ago. It was nicknamed “monkeydactyl” as a true opposed thumb (pollex) is extremely rare amongst extant reptiles, only chameleons possess opposed thumbs. They use their thumbs to help them climb, the researchers writing in the academic publication “Current Biology”, also suggest that Kunpengopterus evolved such dexterity to help it to climb.

In order to test the arboreal interpretation, the team analysed K. antipollicatus and other pterosaurs using a set of anatomical characters related to arboreal adaptation. The results support K. antipollicatus as an arboreal species, but not the other pterosaurs from the same ecosystem. This suggests niche-partitioning among these pterosaurs and provides the first quantitative evidence supporting the theory that at least some darwinopteran pterosaurs were arboreal.

Minimising Competition Amongst Pterosaurs

Lead author Xuanyu Zhou (China University of Geosciences) commented:

“Tiaojishan palaeoforest is home to many organisms, including three genera of darwinopteran pterosaurs. Our results show that K. antipollicatus has occupied a different niche from Darwinopterus and Wukongopterus, which has likely minimised competition among these pterosaurs.”

Micro-CT Imaging Assists in Discovery

Fion Waisum Ma, co-author of the study and PhD researcher (University of Birmingham) explained:

“The fingers of “Monkeydactyl” are tiny and partly embedded in the slab. Thanks to micro-CT scanning, we could see through the rocks, create digital models and tell how the opposed thumb articulates with the other finger bones. This is an interesting discovery. It provides the earliest evidence of a true opposed thumb, and it is from a pterosaur – which wasn’t known for having an opposed thumb”.

Everything Dinosaur acknowledges the assistance of a press release from the University of Birmingham in the compilation of this article.

The scientific paper: “A new darwinopteran pterosaur reveals arborealism and an opposed thumb” by Xuanyu Zhou, Rodrigo V. Pêgas, Waisum Ma, Xuefang Wei, Caizhi Shen and Shu’an Ji published in Current Biology.