Top: Juvenile (left) and adult (right) skulls of Massospondylus. Bottom: CT scans reveal the inner ear (displayed in pink), which contains the organ responsible for balance and orientation. This makes it an important structure to study how animals moved.

 

A novel study provides the most in-depth look ever at the growth of the inner ear of dinosaurs. The research, led by Dr James Neenan of the University of the Witwatersrand (Wits) and the University of Oxford, is published in the journal Palaeontology today. This research could contribute to understanding how baby dinosaurs walked.

 

The inner ear is an important organ present in all vertebrates, including humans, and plays an essential role in the maintenance of balance and head stabilisation. Animals with different postures and locomotion have inner ear shapes suited for their movement types. Because the inner ear is encased in bone, the researchers utilised cutting-edge CT scanning techniques to visualise its anatomy over a range of skulls of the early dinosaur Massospondylus – from babies to adults.

 

The results showed that the inner ear grew substantially during Massospondylus’ lifespan, nearly doubling in size.

 

“This was surprising to us,” said Wits PhD student Kimberley Chapelle, a co-author on the paper, “because in today’s birds and mammals we think the inner ear stops growing early in development. Clearly dinosaurs are different to most animals today in how their ears grew.”

 

Despite this growth, the shape of Massospondylus’ inner ear changed very little as it got older. The shape of the inner ear is related to locomotion, and the findings of this research contradict a long-held idea that Massospondylus walked on all fours as a juvenile and on two legs as an adult.

 

“We expected to see a clear distinction in the shape of the inner ear between juveniles and adults” said lead author Dr Neenan, “so we were surprised when we found that almost no shape changes occur. This means Massospondylus babies probably walked on two legs as soon as they left the nest.”

 

The team now think that the same approach can be used to study movement in other dinosaur and non-dinosaur groups with the aim of better understanding how they moved throughout their growth from nestlings into full-grown adults.

 

Massospondylus was a common plant-eating dinosaur that lived 200 million years ago in southern Africa. Hundreds of specimens of the species are known, from tiny embryos still within eggs discovered by Jam Kitching to 5m long adults. Recent work by scientists at the University of the Witwatersrand was able to digitally dissect the anatomy of the Massospondylus skull, and that study promoted this investigation.

 

“My PhD student Kimberley recently used CT scanning to investigate the anatomy of Massospondylus,” said Prof Jonah Choiniere, the supervisor of this research, “and during that work my postdoc James became fascinated with the anatomy of its inner ear. This project stemmed from that fascination.”

 

The Evolutionary Studies Institute at WITS University and the University of Oxford have been collaborating for the last five years on research projects involving dinosaurs, including the recent discovery of the giant sauropodomorph Ledumahadi mafube. Ongoing palaeontological discoveries and ground-breaking research in South Africa is proudly supported by the DST-NRF Centre of Excellence in Palaeosciences and the Palaeontological Scientific Trust (PAST). This research also received support from the European Synchrotron Radiation Facility, National Research Foundation African Origins Platform, Leverhulme Trust and the University of the Witwatersrand.

 

 

Left inner ears from a baby (left) and a large adult (right) Massospondylus. While the ear nearly doubles in size, the shape does not change very much. This means that Massospondylus may have walked on two legs all its life, and was not four-legged as a baby as previously thought

 

Issued by: Kimberleigh Tommy

Science Communications Officer

Palaeosciences Building

University of the Witwatersrand

Contacts: +27 11 717 6048

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For media interviews contact:

Dr James Neenan            

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+44 7495 398311

+44 1865 272995

 

Prof Jonah Choiniere

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+27 799063169

 

 

Dr James Neenan, the lead author of the study.