Another week, and another new dinosaur.  This time, it is a tyrannosaur, and it has been named Asiatyrannus xui.  The fossils consist of a nearly complete skull and postcranial material. The postcranial material comprises leg bones and caudal vertebrae. A cross-sectional analysis of the right fibula has permitted the researchers to estimate the age of this tyrannosaur. It was at least thirteen years old when it met its demise.

Asiatyrannus co-existed with the much larger, Qianzhousaurus sinensis. Qianzhousaurus had a long, narrow snout.  When it was formally described in 2014 it was nicknamed “Pinocchio rex”.  The different skull morphologies and their different body sizes suggest that Asiatyrannus xui and Qianzhousaurus sinensis likely had different feeding strategies and occupied different ecological niches.  Asiatyrannus is the first deep-snouted tyrannosaurid to have been described from the Late Cretaceous of south-eastern China.

A skeletal reconstruction of the newly described (2024) deep-snouted Asian tyrannosaur (Asiatyrannus xui). Known fossil material in (A) shown in yellow. Photographs of the fossils (B-H). Picture credit: Zheng et al.

Picture credit: Zheng et al

Asiatyrannus xui

The fossil material was unearthed in September 2017 at a construction site in Shahe Town, Nankang District, Ganzhou City (Jiangxi Province).  The fossils were taken to the Zhejiang Museum of Natural History, Hangzhou, China for cleaning and preparation.  The genus name translates as “Asian tyrant king”, whilst the species name honours Dr Xing Xu (Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences).  Dr Xing Xu has made a huge contribution to the study of Chinese dinosaurs including research into and the naming of other tyrannosaurs (Dilong, Guanlong and Yutyrannus).

The discovery of Asiatyrannus highlights the diversification of deep-snouted tyrannosaurids towards the end of the Cretaceous.  It demonstrates that during the Late Cretaceous (Maastrichtian), different types of tyrannosaurs co-existed in south-eastern China.  Numerous dinosaurs are known from the strata in this area (Nanxiong Formation).  Ornithischians and sauropods have been described, but the majority of dinosaurs discovered are theropods, overwhelmingly oviraptorosaurs.

To read a blog post from 2016 about another oviraptorosaur from the Nanxiong Formation: Tongtianlong – A New Oviraptorosaur.

For an article describing a new oviraptorosaur (Corythoraptor) named in 2017: Another New Oviraptorosaur from Jiangxi Province.

Isolated teeth and other fragmentary elements suggest that there could have been other tyrannosaurid taxa present in this area at the very end of the Cretaceous.

Photograph (A) and line drawing (B) of the skull of Asiatyrannus xui (ZMNH M30360) in right lateral view. Picture credit: Zheng et al.

Picture credit: Zheng et al

Tyrannosaurid Growth Spurts

The open-access study published in “Scientific Reports”, includes details of bone histology.  This analysis revealed that this dinosaur died when it was a least thirteen years of age.  This is significant as the research team conclude that whilst this individual was not fully-grown, it had already passed through its most rapid growth phase.  Early tyrannosauroids such as Guanlong and Moros reached their adult size at around six to seven years of age.  In contrast, large-bodied tyrannosaurs from the Late Cretaceous (Campanian/Maastrichtian) such as Daspletosaurus, Tyrannosaurus rex and Albertosaurus had rapid growth spurts in their teenage years.  These theropods did not reach their full adult size until at least twenty years old.

Qianzhousaurus and Asiatyrannus xui

The skull of Asiatyrannus measures 47.5 cm in length.  Based on this, and the limb sizes, the research team estimate that Asiatyrannus had a body length of around 3.5 to 4 metres.  Qianzhousaurus (Q. sinensis) was over twice as big.  It had an estimated body length of around 9 metres.

These two carnivores very probably co-existed.  The long-snouted Qianzhousaurus was likely to have been the apex predator, with the smaller Asiatyrannus having the role of a secondary predator in the ecosystem.  Their different body sizes, and different shaped skulls suggest that these two dinosaurs may have had different hunting behaviours and perhaps, preyed on different animals.  They may not have directly competed, each tyrannosaur becoming adapted to a different ecological niche.  This could be an example of niche partitioning within coeval tyrannosaurids.

A size comparison between the probable, coeval tyrannosaurids Qianzhousaurus and Asiatyrannus. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The image above shows an approximate size comparison between the newly described Asiatyrannus xui and the probably coeval Qianzhousaurus sinensis.

Note: the models used to show the comparison are the PNSO Lythronax and Qianzhousaurus figures.

To view the PNSO range of prehistoric animal models: PNSO Dinosaur Models.

Implications for Mid-sized Theropod Carnivores

The paper’s authors comment that the discovery of Asiatyrannus might have implications for the way in which Mesozoic ecosystems are perceived.  Medium-sized carnivorous dinosaurs are relatively rare in the fossil record.  For example, in the Late Cretaceous carnivore guilds are monopolised by tyrannosaurids.  Adult, medium-sized predators are exceptionally rare.  Scientists have postulated that the “missing mid-sized” niches in the theropod guilds of Late Cretaceous Laramidia and Asia could be a consequence of these types of carnivores being outcompeted by juveniles and sub-adults of much larger taxa.

To read an article about a scientific paper that postulates the juveniles of apex predators out-competed mid-sized theropod carnivores: Why Are There So Few Medium-sized Carnivorous Dinosaurs?

The polar tyrannosaur Nanuqsaurus (N. hoglundi) was thought to be a mid-sized Late Cretaceous carnivore.  However, new fossil material from the Prince Creek Formation of Alaska suggests that it was comparable in size to the likes of Gorgosaurus and Daspletosaurus.  In the light of the continuing speculation as to the taxonomic validity of Nanotyrannus, the paper’s authors propose that Asiatyrannus xui currently represents the only definitive small to medium-sized member of the tyrannosaur family.

Everything Dinosaur acknowledges the assistance of the scientific paper in the compilation of this article. The paper is licensed under a Creative Commons Attribution 4.0 International License: The Creative Commons License.

The scientific paper: “The first deep-snouted tyrannosaur from Upper Cretaceous Ganzhou City of southeastern China” by Wenjie Zheng, Xingsheng Jin, Junfang Xie and Tianming Du published in Scientific Reports.

Research into a living fossil has provided scientists with a fresh perspective on animal evolution.  A new brachiopod study, involving the careful analysis of over a thousand genera, indicates these ancient creatures were diversifying and evolving but this did not result in many new species.  The research published in the journal “Nature Ecology & Evolution”, challenges some of the core principles of evolution.

Let’s hear it for the humble brachiopod!

What is a Brachiopod?

Brachiopods (Brachiopoda) are shelled animals that originated during the Cambrian.  Many resemble Roman oil lamps, hence their common name “lamp-shells”.  Their shells consist of two parts (valves), with one part larger than the other.  They are entirely marine and benthic.  These filter feeders have shells around two to five centimetres in diameter, although some genera grew much larger.  Although superficially similar to molluscs such as clams, mussels and oysters, they are not closely related.

Triassic brachiopod fossils (left), recent brachiopod shells (right). Picture credit: Zhen Guo.

Picture credit: Zhen Guo

In many species of brachiopod, the animal is attached to the sea floor by a fleshy stalk (pedicle).  The presence of a pedicle is indicated by the hole located on the larger of the valves (see picture above).  They were abundant in the Palaeozoic and Mesozoic and are often the most common fossil found in Palaeozoic marine deposits.  These ancient creatures are still around today but most species are confined to deep water.  Some 12,000 fossil species have been named.  In contrast, it has been estimated that there are less than 500 extant species.

Lots of brachiopod and coral fossils to find at Wren’s Nest.  The strata were deposited during the Silurian, a time when the Brachiopoda were abundant. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

New Brachiopod Study

This new brachiopod study is a collaboration between the University of Bristol, the China University of Geosciences and the Open University.  The team found that following the end-Permian mass extinction event, the Brachiopoda were evolving in new directions, but this did not lead to many new species.  In comparison, the Mollusca became increasingly dominant.  Today, the Mollusca is an amazingly diverse phylum with more than 50,000 species. The Brachiopoda currently contains just 394 known species.  The research team found that brachiopods were evolving new shell shapes and ecological behaviours following the end-Permian mass extinction, but their diversity did not grow.

Lead author Dr Zhen Guo (China University of Geosciences) explained:

“In the Palaeozoic, from 540 to 250 million years ago, brachiopods ruled the seabed.  Most of them are quite small–you could hold twenty of them in your hands; but others were big and thick-shelled and lived a long time. Their shells were anything from circular to widely stretched and they had either smooth shells or carried deep ridges and troughs.”

Professor Michael Benton (University of Bristol), a co-author of the new brachiopod study, commented:

“The brachiopods were hit very hard by the end-Permian mass extinction 252 million years ago.  The group could have disappeared completely, and indeed from that point, molluscs just became more and more successful. For a long time, it was thought that the brachiopods remained rare because the survivors were stuck in just a few modes of life.”

Studying Over 1,000 Brachiopod Genera

This new research involved the analysis of a vast brachiopod database.  More than 1,000 genera were studied.  This database was comprised of brachiopods that lived after the Permian.  For each genus, the analysts recorded dozens of measurements of the overall shape of the shells, their external sculpture, and internal anatomy. These features were analysed together to provide measurements of overall diversity of shapes for each major brachiopod group at each point in geological time. This measure of “diversity of shape”, is referred to in biology as “disparity”.  An understanding of shape innovations and changes over time could then be plotted.

These Mesozoic-Cenozoic brachiopods were adapting to different modes of life, but there were fewer species evolving than expected.

Reconstructions of some Mesozoic-Cenozoic brachiopods, showing adaptations to certain environments. Picture credit: Shunyi Shi.

Picture credit: Shunyi Shi

The co-author from the Open University, Dr Tom Stubbs added:

“In fact, the post-extinction brachiopods were innovating and trying new modes of life. One group, the terebratulids, were diversifying their body shapes and ecological functions from the end of the Permian to the present day, but their diversity did not increase.”

To read about an earlier, related brachiopod study conducted by University of Bristol researchers: Brachiopods and Bivalves (Mollusca) Faunal Turnover Study.

Unexpected Results

Fellow researcher Professor Zhong-Qiang Chen of the China University of Geosciences said:

“This was quite unexpected. Brachiopods were far from failures after the end-Permian extinction. They were evolving in new directions and exploring new modes of life, just as the molluscs were at the same time. But this did not turn into evolutionary success in terms of the numbers of species. Despite their bursts of evolution in form and function, they could not spread widely, and the exact reason remains unclear.”

Modern brachiopods represent the tip of the ecological iceberg for this once immensely abundant phylum.  Extant species do not provide scientists with an understanding of their extremely successful lineage, but we don’t know why these marine creatures did not become super-abundant again after the Permian.

Dr Zhen Guo explained the importance of this research.  This new brachiopod study suggests that disparity and diversity are effectively decoupled, at least as far as the Brachiopoda after the Permian are concerned.

Dr Zhen Guo concluded:

“It’s important to understand modern biodiversity in terms of the processes that lie behind it.”

Everything Dinosaur acknowledges the assistance of a media release from the University of Bristol in the compilation of this article.

The scientific paper: “Morphological innovation did not drive diversification in Mesozoic–Cenozoic brachiopods” by Zhen Guo, Michael J. Benton, Thomas L. Stubbs, and Zhong-Qiang Chen published in Nature Ecology & Evolution.

The Everything Dinosaur website: Prehistoric Animal Toys.