The First Stegosaur Dacentrurus armatus

Situated amongst specimens of marine reptiles in the Mary Anning gallery at the London Natural History Museum is a remarkable fossil specimen.  Behind its glass case the viewer can make out a block of bones containing various vertebrae, a massive right femur (thigh bone), ribs and a near complete pelvis.  At approximately two metres across this is an impressive fossil specimen.  It is the holotype material for Dacentrurus armatus (NHMUK OR46013), the first large collection of dinosaur bones associated with a member of the Stegosauridae to be scientifically described and studied.

The Main Bone Block (D. armatus) at the Natural History Museum (London)

Picture credit: Everything Dinosaur

The Everything Dinosaur website: Everything Dinosaur.

The Fossils of Dacentrurus

The fossils come from a clay quarry close to the town of Swindon in the county of Wiltshire.  Richard Owen (later Sir Richard Owen), who was to play a pivotal role in the foundation of the institute that we now know as the London Natural History Museum, studied the fossils and erected the name Omosaurus armatus in 1875.  The genus name, Omosaurus had already been used to describe a North American phytosaur (O. perplexus) in 1856.  Therefore, the original genus name for this armoured dinosaur was invalidated.  In 1902 the eminent American zoologist, Frederick Augustus Lucas erected Dacentrurus.

CollectA have produced a Dacentrurus figure. This model is in their Deluxe model range.

To view the CollectA Deluxe range: CollectA Deluxe Prehistoric Life.

With the recently published paper describing a new specimen of Miragaia longicollum, a “Rosetta Stone” moment in vertebrate palaeontology permitting scientists to better understand the Dacentrurinae subfamily of the Stegosauridae, it is fitting that whilst in London an Everything Dinosaur team member took the opportunity to take a photograph of the main Dacentrurus block.  The beautiful fossils are notoriously difficult to photograph, but still, they continue to play a role in helping to decipher Late Jurassic stegosaurs.

On Display in the Wrong Gallery?

One mystery still remains, why is this important dinosaur fossil on display in the marine reptiles gallery?  Perhaps, one day, these hugely significant fossils we will placed in the dinosaur gallery, where visitors could be given the opportunity to learn more about the world’s first extensively studied armoured dinosaur specimen.

To read our recent article on the M. longicollum paper: Turning a Stegosaur Fossil into the Rosetta Stone.

Animal-like Embryos Evolved Before the First Animals Appear in the Fossil Record

Catching up with our reading, examining university press releases and having a little time to review some scientific literature enabled team members at Everything Dinosaur to get to grips with this research.  A new paper has been published in the journal “Current Biology” that sheds light on how the Animalia evolved.  Researchers led by scientists from the University of Bristol and Nanjing Institute of Geology and Palaeontology (Nanjing, China), have discovered that animal-like embryos evolved long before the first animals appear in the fossil record.

The study centred around a multicellular organism found in 609-million-year-old-rocks in Guizhou Province.  The organism is called Caveasphaera and it blurs the definition as to what is and what is not an animal.  However, analysis of tiny embryonic fossils suggests that as Caveasphaera developed it went from a single-cell stage to a multi-cellular stage and that it developed distinct, specialist cells and tissues.

Remarkable Fossils Reveal Ancient Organism May Have Set the Blueprint for Animal Body Plans

Picture credit: Philip Donoghue and Zongjun Yin

Fossil Record Reveals Animals Evolved from Single-celled Ancestors

Animals evolved from single-celled ancestors, subsequently, the Animalia diversified into thirty or forty body plans.  How and when animal ancestors made this evolutionary transition from a microbial state into complex multicellular creatures has been discussed and debated for many years.  The researchers, using sophisticated X-ray computer tomography, analysed tiny fossils from southern China and identified that a key step in this major step in the story of life on our planet occurred long before complex animals appear in the fossil record, in the fossilised embryos that resemble multicellular stages in the life cycle of single-celled relatives of animals.

X-ray Microscopy – Fossils on the Cellular Level

Analysis of the Ediacaran fossils preserved in the strata, revealed that the tiny 0.5 mm in diameter Caveasphaera material had been preserved all the way down to their component cells.

Co-author of the study paper, Kelly Vargas (Bristol University), commented:

“X-Ray tomographic microscopy works like a medical CT scanner, but allows us to see features that are less than a thousandth of a millimetre in size.  We were able to sort the fossils into growth stages, reconstructing the embryology of Caveasphaera.”

Fellow co-author Zongjun Yin, (Nanjing Institute of Geology and Palaeontology), added:

“Our results show that Caveasphaera sorted its cells during embryo development, in just the same way as living animals, including humans, but we have no evidence that these embryos developed into more complex organisms.”

Scanning Electron Microscope Image of Caveasphaera Showing Cell Division

Picture credit: Philip Donoghue and Zongjun Yin

A Life Cycle that Mirrors the Development of Animals

The researchers concluded that Caveasphaera had a life cycle very close to the life cycle of animals which alternate between single-celled and multicellular stages, however, Caveasphaera goes one step further, reorganising those cells during embryology.  This is the earliest fossil evidence found to date that shows such development and the setting up of more complex distinct tissue layers and organs.

Whether the enigmatic, Caveasphaera is a member of the Animalia remains open to debate.  It resembles the embryos of some starfish and corals but no adult forms are known as they may not have been easily fossilised.

Professor Philip Donoghue from the University of Bristol’s School of Earth Sciences, stated:

“Caveasphaera shows features that look both like microbial relatives of animals and early embryo stages of primitive animals.  We’re still searching for more fossils that may help us to decide. Either way,  fossils of Caveasphaera tell us that animal-like embryonic development evolved long before the oldest definitive animals appear in the fossil record.”

Sequential Development of Caveasphaera Mirrors the Development Seen in the Animalia

Picture credit: Philip Donoghue and Zongjun Yin

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

The scientific paper: “The early Ediacaran Caveasphaera foreshadows the evolutionary origin of animal-like embryology” by Z. Yin, K. Vargas, J. Cunningham, S. Bengtson, M. Zhu, F. Marone and P. Donoghue published in Current Biology.

The Everything Dinosaur website: Everything Dinosaur.