Revising the Mamenchisauridae – Analong chuanjieensis

2020 has proved to be an important year for that enigmatic family of sauropods the Mamenchisauridae, which are predominantly associated with the Early Jurassic of China, although, as with most things relating to vertebrate palaeontology, there are exceptions to the consensus.  For example, the Late Jurassic Tanzanian genus Wamweracaudia is regarded by many scientists as a mamenchisaurid, based on the shape and structure of its tail bones (caudal vertebrae).

Revising the Mamenchisauridae

That’s the point with the mamenchisaurids.  They are one of the most extensively researched of all the Sauropodomorpha, thanks almost entirely to the numerous fossil bones found near Zigong in the Chinese Province of Sichuan.  However, even the most well-researched group of dinosaurs are subject to revision.

This is the case with a specimen of Chuanjiesaurus (C. anaensis) which is pronounced Chu-an-je-sore-us, a twenty-five metre long giant known from the Middle Jurassic Chuanjie Formation of Yunnan Province located in south-western China.

Chuanjiesaurus was named and described in 2000, from fossils found near to the town of Chuanjie in Lufeng County (Yunnan Province).  Intriguingly, a recent assessment of the disarticulated sauropod fossil remains found just a few metres away in the same quarry have demonstrated that these fossils are not the remains of a second Chuanjiesaurus as previously thought.

A Life Reconstruction of the Newly Described Mamenchisaurid Analong chuanjieensis

Picture credit: Everything Dinosaur

A New Scientific Paper

In a scientific paper published in the International Journal of Paleobiology, Ren at al erected a new mamenchisaurid taxon based on a revision of specimen number LFGT LCD 9701-1.  Analong chuanjieensis is based on several autapomorphies (unique characteristics).  This reassessment has important implications for the Mamenchisauridae as a whole.  Analysis of the bones of the newly described Analong with other related mamenchisaurids indicate that Analong chuanjieensis is the earliest branching of the Mamenchisauridae family, whereas the contemporary Chuanjiesaurus represents a later branching of these types of dinosaurs.

In Recognition of the Increasing Public Awareness of the Mamenchisauridae CollectA are Introducing a Scale Replica of Mamenchisaurus in 2021

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Thus, the establishment of a the new Analong taxon not only increases the number of long-necked dinosaurs known from the Middle Jurassic of China but also suggests that the ecosystem which was dominated by these herbivores was more complex and nuanced.  Furthermore, this reassessment of the fossil material suggests that the evolution of the Mamenchisauridae is more convoluted than previously realised.

For a related article on Chinese mamenchisaurs: Another Mamenchisaurid from Anhui Province – Anhuilong diboensis is described.

The scientific paper: “A revision of the referred specimen of Chuanjiesaurus anaensis Fang et al., 2000: a new early branching mamenchisaurid sauropod from the Middle Jurassic of China” by Xin-Xin Ren, Toru Sekiya, Tao Wang, Zhi-Wen Yang and Hai-Lu You published by An International Journal of Paleobiology (Historical Biology).

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Dinosaur Diversification Rates not in Decline at the End of the Cretaceous

A team of international researchers including scientists from the London Natural History Museum and the University of Bath have undertaken an extensive and sophisticated statistical analysis to try to establish whether the dinosaurs were in terminal decline prior to the end-Cretaceous mass extinction event that saw the demise of all non-avian forms.

Studying the Dinosaurs at the End of the Cretaceous

The detailed Bayesian analysis suggests had the extra-terrestrial object not hit planet Earth, then the dinosaurs might have continued to dominate terrestrial ecosystems.

If the Bolide (Extra-terrestrial Object) had not Hit – Would the Non-avian Dinosaurs Still be Around Today?

Picture credit: Chase Stone

How quickly the non-avian dinosaurs died out and what sort of health dinosaur populations were in around 66 million years ago has proved to be one of the most contentious issues in vertebrate palaeontology.  Some scientists argue that there were fewer genera of dinosaurs present in the Maastrichtian faunal stage of North America than in the preceding Campanian.  They propose that this is evidence to suggest that the non-avian members of the Dinosauria were in decline long before their final extinction.  Other scientists present data to support the idea that new species were still evolving and that the “terrible lizards” were showing no signs of being under population stress.

Were the Dinosaurs in Decline Prior to the K-Pg Extinction Event?

Picture credit: James Havens

The Extinction of the Dinosaurs

Extensive disagreements remain over whether the extinction of the dinosaurs was a sudden catastrophic event, essentially instantaneous when measured in deep, geological time or whether their ultimate die-off was the culmination of long-term evolutionary trends.

Writing in the open-access, on-line journal “Royal Society Open Science”, the researchers which include Professor Paul Barrett (London Natural History Museum) and PhD student Joe Bonsor (University of Bath), used sophisticated Bayesian statistical analysis to model three competing theories against a variety of taxonomies and phylogenies representing the Dinosauria.

In essence, the study set out to test the match between three competing hypotheses with regards to the dinosaur species-richness during the Late Cretaceous:

1). No evidence of a global downturn in dinosaur speciation rates prior to the end of the Mesozoic.

2). There was a decline in dinosaur species-richness over a timescale of hundreds of thousands or several million years prior to the bolide impact due to the effect of climate change, rising sea levels and the Deccan flood basalt volcanism (plus other factors).

3). That the Dinosauria were in global decline with falling speciation rates from around 100 million years ago.

Twelve Phylogenies Analysed

Bayesian statistical analysis was used to assess the fit of twelve dinosaur phylogenies from various authors.  The researchers did not find strong support for the downturn model in their analyses, which suggests that dinosaur speciation rates were not in terminal decline prior to the K-Pg boundary and that the Dinosauria was still capable of generating new taxa and evolving into new species to exploit resources and environmental opportunities.

Dinosaurs Dominated Terrestrial Ecosystems

Picture credit: Zhao Chuang

Urging Caution

The researchers  did urge caution when it came to interpreting the results of the models stating that they may be too simplified and therefore not able to reflect the complexities of the underlying data.  To help confirm the state of dinosaur populations prior to the K-Pg extinction event the research team concluded that the collection of more dinosaur occurrence data would be needed to test these ideas and to validate any proposed hypothesis.

The scientific paper: “Dinosaur diversification rates were not in decline prior to the K-Pg boundary” by Joseph A. Bonsor, Paul M. Barret, Thomas J. Raven and Natalie Cooper published by Royal Society Open Science.

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