All about dinosaurs, fossils and prehistoric animals by Everything Dinosaur team members.
27 09, 2014

Evolution and Genetics (KS3 and KS4) – Trilobites

By | September 27th, 2014|Key Stage 3/4|Comments Off on Evolution and Genetics (KS3 and KS4) – Trilobites

A Case Study in Evolution – the Trilobites (Trilobita)

When Key Stage 3 students are being taught about genetics and evolution as part of the national curriculum for schools in England, it is important for teachers to set the work of Darwin, Wallace et al into context.  For example, natural selection within a species relies on variation existing within that species (a form of intra-specific competition).  Natural selection between two different species relies on variation between these species (an illustration of inter-specific competition).  This variation between species and from organisms within a single species means that some members of a particular species or some species as a whole will compete more successfully.

It is this competition that drives natural selection.

Environmental Changes

Changes in the environment may lead to some less well adapted individuals within a species to fail to reach maturity and breed.  Some entire species that are less well adapted to compete and reach maturity when compared to other species will fail to breed.  If they fail to breed, they cannot pass on their inherited characteristics to the next generation.  The inability to compete successfully may lead to population decline and ultimately extinction.

Why Did the Trilobites Become Extinct?

Trilobite fossils - the Selenopeltis slab.

Trilobites galore – the Selenopeltis slab, but why did these arthropods become extinct.

Picture credit: Everything Dinosaur

Extension Activity

Introduce the class to trilobites, collect pictures and images of different types of trilobite fossil and depictions of them as living marine organisms.  Explore their senses (calcite eyes) and adaptations to a marine environment.  Consider the reasons for their success as a group, develop theories on why these once diverse, successful creatures became extinct.  More capable learners might be able to apply extinction theories to climate change issues happening today.


Trilobites were an extremely abundant and speciose group of Palaeozoic arthropods that evolved into a least ten different Orders.  The first trilobites evolved in the Early Cambrian (540 million years ago approximately), the last of the trilobites became extinct at the end of the Permian geological period nearly 300 million years  later.  These sea-living arthropods had a distinct, threefold, longitudinal division of the body and hard, calcified exoskeletons.  To grow, the external exoskeleton had to be moulted.

A Model of a Trilobite (Redlichia rex)

CollectA Redlichia rex trilobite.

CollectA Redlichia rex trilobite model.

To view models of iconic prehistoric animals such as trilobites, belmenites, orthroceras and ammonites: Models of Iconic Prehistoric Animals.

The trilobites rapidly diversified and by the Early Ordovician period there were over sixty different families.  This number fell to around forty by the end of the Ordovician and despite spurts of adaptive radiation during the Silurian, Devonian and into the Carboniferous by the end of the Carboniferous period around 299 million years ago there were just four families left.  Two families of Trilobita survived until the late Permian before the Trilobita finally became extinct at the end of the Permian (mass extinction event).

What is the Family Classification?

In Linnaean Classification, there can be one or more closely related species in a genus.  These genera (plural) are then grouped together into closely related Families, then Orders, then Classes, Phyla, Kingdom and Domain.

For the Trilobita (H. spasskyi)

  • Domain = Eukaryotes
  • Kingdom = Animalia
  • Phylum = Arthropoda
  • Class = Trilobita
  • Order = Harpetida
  • Family = Harpetidae
  • Genus = Harpes
  • Species = Harpes spasskyi

Relate the study of trilobites to the importance of maintaining biological diversity and compare and contrast to current extinction issues seen today.

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27 09, 2014

New Armoured Dinosaur from New Mexico

By | September 27th, 2014|Dinosaur and Prehistoric Animal News Stories, Main Page|5 Comments

Ziapelta sanjuanensis From New Mexico but Closely Related to Canadian Ankylosaurs

For some strange reason, the ankylosaurs don’t seem to be held in quite the same awe as the horned dinosaurs by most members of the public.  We at Everything Dinosaur have our own theory about this.  The horned dinosaurs are much easier for the lay person to recognise.  There is the spectacular spiked frill of Styracosaurus, the peculiar nasal boss of Pachyrhinosaurus, a dinosaur genus which came to greater prominence with the “Walking with Dinosaurs in 3-D” movie.  Then there is of course, the most famous horned dinosaur of all – Triceratops (three horned face).

The Ankylosauridae

Members of the Ankylosauridae tend to have the same basic body plan.  They have broad rumps, bony clubs on the end of their tails and of course, all that body armour.  Model makers often find it difficult to distinguish different armoured dinosaurs.  For example, the Saichania replica made by Schleich, to the uninitiated, resembles Ankylosaurus.

The Saichania Model made by Schleich

Saichania means "beautiful"

Saichania means “beautiful”.

Picture credit: Everything Dinosaur

When it comes to films and television documentaries, the ankylosaurs are rarely given star billing.  So today, in our own small way, we are going to champion the Late Cretaceous armoured dinosaurs by discussing the newest member of their family – Ziapelta, from the San Juan Basin of north-western New Mexico.  The fossils of Ziapelta consist of elements of the skull and incomplete neck rings of spiky bone and fragments of the famous, scaly Ankylosauria body armour (osteoderms).

Discovered in 2011

The material was discovered in 2011 by Robert Sullivan, subsequently excavated by Dr Sullivan and colleagues and then stored at the New Mexico Museum of Natural History and Science.  Once extracted from its silt and sandstone matrix, the scientists had enough fossil evidence to assign these fossils to a new genera.  A thorough exploration of the surrounding area produced no further post-cranial material.  It seems the head and neck of this armoured dinosaur were separated from the rest of the body prior to burial.  How this came about, one can only speculate.

Ziapelta sanjuanensis

The fossils were collected from the De-na-zin Member of the Kirtland Formation which as been dated to around 74 to 72 million years ago.  At perhaps as much as six metres long, the herbivorous Ziapelta would have been a very formidable adversary for even the largest tyrannosaurid.

An Illustration of Ziapelta (Z. sanjuanensis)

New Armoured Dinosaur from New Mexico

New armoured dinosaur from New Mexico.

Picture credit: Sydney Mohr

To the lay person, the spiky-looking Ziapelta might just look like any other Ankylosauridae, so let’s explain why the skull and neck material have allowed scientists to erect a new genus of armoured dinosaur.  Firstly, elements of the skull have been found, the skull morphology (shape) and composition can be very helpful when looking to identify an animal new to science, dinosaurs included.  Co-author of the scientific paper, which is published in the on line academic journal PLOS One, Victoria Arbour commented:

“The horns on the back of the skull are thick and curve downwards and the snout has a mixture of flat and bumpy scales – an unusual feature for an ankylosaurid.”

Closely Related to Canadian Ankylosaurids

Dr Arbour (University of Alberta) is a renowned expert on all things ankylosaur, she was invited to examine the fossils along with PhD student Mike Burns (University of Alberta).  The scientists concluded that unlike the armoured dinosaur Nodocephalosaurus kirtlandensis, which is also known from the San Juan Basin and is believed to be related to Asian genera of the Ankylosauridae, Saichania for example, Ziapelta was more closely related to the ankylosaurids of Canada.

The Formidable Spiky Cervical Rings of Ziapelta

Bony and spiky neck armour of Ziapelta.

Bony and spiky neck armour of Ziapelta.

Picture credit: PLOS One

Dr Arbour stated:

“Bob Sullivan, who discovered the specimen, showed us pictures and we were really excited by both its familiarity and its distinctiveness.  We were pretty sure right away we were dealing with a new species that was closely related to the ankylosaurs we find in Alberta.”

Unusual Features

Ziapelta has another unusual feature that distinguishes it from other ankylosaurids, a feature that we at Everything Dinosaur find quite endearing considering the size and fearsome nature of these reptiles.  The layout of the scales that make up the top of the skull are often very distinctive.  In the case of Ziapelta, it has a large triangular-shaped scale on the tip of its snout, in contrast to many other ankylosaurids which have a six-sided scale on their snouts

Views of the Skull Fossil of Ziapelta (Z. sanjuanensis)

Views of the skull fossil material of Ziapelta.

Views of the skull fossil material of Ziapelta.

Picture credit: PLOS One

The photograph above shows various views of the holotype skull material, A – dorsal view (view from the top), B = ventral view (viewed from underneath), C = anterior view (view from the front), D = occipital view (viewed from the rear) and finally E – left lateral view (view of the left side of the skull).  In photograph A, we have highlighted in red the outline of that large triangular scale on the snout (referred to as mnca – median nasal caputegulum to use the formal scientific term).

Dr Arbour put it very succinctly stating:

“There’s also a distinctive large triangular scale on the snout, where many other ankylosaurids have a hexagonal scale.”

Specialising in Studying Ankylosaurs

The University of Alberta scientist has specialised in studying ankylosaurs, especially those specimens which are known from the Late Cretaceous of North America.  Back in 2013, Everything Dinosaur reported on Dr Arbour’s research into the Ankylosauridae which was helping to redefine this family of dinosaurs.

To read more about this research: When is a Euoplocephalus a Euoplocephalus?

Ankylosaurid fossils make up a small, but significant proportion of the Dinosauria fossil assemblage of southern Alberta, but to date, no ankylosaurid material has been found in the Horseshoe Canyon Formation (lower parts of this formation, the Strathmore and the Drumheller Members) of Alberta.  These rocks are roughly the same age as the strata in which the fossils of Ziapelta were found.  This New Mexico armoured dinosaur is helping palaeontologists to plug a gap in the record of ankylosaurid fossils known from North America.

Dr Arbour explained:

“The rocks in New Mexico fill in this gap in time, and that’s where Ziapelta occurs.  Could Ziapelta have also lived in Alberta, in the gap where we haven’t found any ankylosaur fossils yet?  It is possible, but in recent years there has also been increasing evidence that the dinosaurs from the southern part of North America – New Mexico, Texas and Utah, for example, are distinct from their northern neighbours in Alberta.”

There is a lot of evidence to support the idea of “dinosaur provinciality” in North America.  It seems that although the overall mix of dinosaurs was about the same in the regions, the actual genera that made up the dinosaur populations differed markedly.  How or why these distinct faunas came about remains something of a mystery.  The discovery of Ziapelta may help to add more pieces to the picture as palaeontologists strive to solve this puzzle.

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