Gorgonopsid with Compound Odontoma

Researchers at the University of Washington have discovered evidence of a benign tumour in the fossilised lower jaw of a Late Permian predator, a gorgonopsid.  Thin sections of bone examined under the microscope reveal that this distant relative of modern mammals was suffering from a compound odontoma.  Scientists are studying the fossils of “mammal-like reptiles”, in a bid to learn more about how common diseases in mammals first evolved.

Fragment of Jaw

The fragment of jawbone was found by Professor Christian Sidor (University of Washington and curator of vertebrate palaeontology at the Burke Museum of Natural History and Culture), whilst on a field trip to the Late Permian beds of Tanzania.  The fossil was identified as belonging to a member of the Gorgonopsidae, a diverse group of Permian therapsids that evolved around 260 million years ago and ranged widely across the super-continent of Pangaea.

Although early gorgonopsids were small, some no bigger than a terrier, later gorgonopsids evolved into apex predators.  As members of the Therapsidae, they belong on the same branch as the vertebrate family tree as the mammals, although there is still much debate as to how closely related gorgonopsids are to extant mammals.

A Typical Late Permian Gorgonopsid – Inostranvecia alexandri

Scary monster from the Permian.

Picture credit: Everything Dinosaur

Models and replicas of gorgonopsids are quite rare, but collectors and fans of prehistoric animals can pick one up from Everything Dinosaur.  Safari Ltd added a model of the gorgonopsid Inostrancevia to their Wild Safari Prehistoric Life range in 2011, to view this product range: Wild Safari Prehistoric World Models.

A Compound Odontoma

In a letter published in the Journal of the American Medical Association Oncology, the research team report on the evidence that an animal that lived in Africa some 255 million years ago, had a small, benign tumour within its lower jaw.

The tumour has been identified as a compound odontoma, essentially, an abnormal growth in the jaw in which clusters of tooth-like structures complete with enamel, dentine and cementum form.  They are quite common in mammals and can affect our own species.  Although benign, most people have them removed as their growth and encroachment into other tissues and bone can cause considerable pain.

Senior author Professor Sidor stated:

“We think this is by far the oldest known instance of a compound odontoma.  It would indicate that this is an ancient type of tumour.”

Other odontomas have been found in the fossilised remains of mammals before, but as far as Everything Dinosaur team members are aware, all these fossils are associated with Quaternary deposits and thus, the fossils come from mammals that lived much more recently.

A Lateral View of the Skull of a Typical Gorgonopsid

Lateral view of a gorgonopsid skull.

Picture credit: Professor Sidor/University of Washington

Tracing the Origins of Pathology within the Mammalia

Finding evidence in an ancient jawbone suggests that the causes of odontoma in the Mammalia are nested deep within the ancestral roots of this Class of vertebrates.  The fragment of lower jaw was found in isolation, this single fossil was not found in association with other material, so its scientific value was minimal.  As such, it was selected to undergo thin slicing and subsequent microscopic analysis and CT scanning, a process that would destroy it.  Although the outside of the fossil showed no signs of pathology (disease or injury), when thin sections were viewed under high magnification evidence of the compound odontoma was revealed.

A Typical Fragment of Fossil Jaw Similar to the Specimen Used in the Study

A partial dentary of a gorgonopsid.

Picture credit: Professor Sidor/University of Washington

The Gorgonopsidae are synapsids, tetrapods that possess a single pair of openings low down in the skull behind the eyes.  Modern mammals are synapsids, and studying the pathology of extinct synapsids such as the “mammal-like reptiles”* can provide scientists with information on how diseases and other problems such as tumours first came about.

Lead author, University of Washington biology graduate student, Megan Whitney explained:

“Most synapsids are extinct, and we, that is, mammals, are their only living descendants.  To understand when and how our mammalian features evolved, we have to study fossils of synapsids like the gorgonopsians.”

Gorgonopsids have several mammalian characteristics.  Many species walked with an upright gait and like us, they have heterogeneous teeth (differentiated teeth with differing morphology designed for specialised purposes).  The jawbone of a gorgonopsid was studied to see if these ancient creatures had other mammalian characteristics too.

Megan added:

“Most reptiles alive today fuse their teeth directly to the jawbone, but mammals do not.  We use tough, but flexible, string-like tissues to hold teeth in their sockets and I wanted to know if the same was true for gorgonopsians.”

The multiple thin slices of jaw, each slice no thicker than a piece of note paper, were polished so that their internal structure could be revealed.  When viewed under the microscope these slices revealed evidence of the compound odontoma embedded in the bone adjacent to the root of a canine tooth.  At higher magnification, the components of the tumour could be made out, tiny teeth, each with distinct layers of dentine, enamel and cementum.

A Highly-Magnified Image of the Compound Odontoma

Thin section of gorgonopsid lower jaw showing a cluster of tooth-like structures – a compound odontoma.

Picture credit: Professor Sidor/University of Washington

The picture above shows the “U” shaped structure of the canine tooth root with a cluster of tooth-like structures erupting around it and penetrating the adjacent bone.

Professor Sidor concluded by stating that this odontoma was possibly the first case found in a non-mammal, to have been reported.  Such an ancient tumour suggests that this mammalian condition existed tens of millions of years before the first true mammals evolved.

The professor summarised the research by stating:

“This discovery demonstrates how the fossil record can tell us a lot about our present-day lives, even the diseases or pathologies that are part of our mammalian heritage and you could never tell that this creature had it from the outside.”

“mammal-like reptiles”* a term falling out of favour with modern cladistics, groups like the pelycosaurs and the Gorgonopsidae are referred to as “stem mammals” or sometimes “proto mammals”.

For a video review of the Wild Safari Prehistoric Life Inostrancevia model: Inostrancevia Model Video Review.

Two New Ceratopsian Clades – Nasutoceratopsini and the Centrosaurini

Over the last few years, the number of horned dinosaurs described from fossils found in North America has risen at a rapid rate.  Today, we discuss two new clades the Nasutoceratopsini and the Centrosaurini.

New additions to the Ceratopsidae include Machairoceratops and Spiclypeus (2016), Wendiceratops along with Regaliceratops (2015), Pentaceratops aquilonius and Mercuriceratops (2014) Judiceratops, Nasutoceratops and Bravoceratops (2013), Medusaceratops, Utahceratops, Kosmoceratops and Mojoceratops (2010) and Albertaceratops (2007).  We did say that the number of identified North American genera had gone up rapidly!

All these new horned dinosaurs has led to an inevitable revision of the Ceratopsidae family tree.  Writing in the academic journal “The Canadian Journal of Earth Sciences”, researchers have erected two new clades, otherwise referred to as “tribes” – namely the Nasutoceratopsini and the Centrosaurini.

A New Tribe Helping to Sort Out Horned Dinosaurs – Nasutoceratopsini

A new type of horned dinosaur based on the fragmentary skull CMN-8804.

Picture credit: Canadian Museum of Natural History/Andrey Atuchin

International Rules of Taxonomic Classification

There are international rules laid out to help ensure that scientists are consistent in their use of appropriate terminology when it comes to classifying organisms.  Admittedly, we at Everything Dinosaur don’t always follow those rules on this blog, but when it comes to classification, the ending given to a word helps to define the rank within taxonomy of that word.  Here’s an example

Order: Ornithischia (bird-hipped dinosaurs)

Clade: Marginocephalia (bony shelf at the back of the skull)

Family: Ceratopsidae (note – all zoological families end in the letters “idae”)

Sub-Family or Clade: Centrosaurinae (a sub-family is written with the suffix “inae” to help denote the status in taxonomy)

Clade or Tribe: Nasutoceratopsini (a division of the family, above the rank of genus but below sub-family or family.  It is a rank always denoted by the ending letters “ini”)

Genus: Nasutoceratops (a taxonomic rank just above species that groups together very closely related species)

Species: Nasutoceratops titusi (the lowest of the major taxonomic classifications, denoting an individual species with the species name usually written in italics or underlined if the name is hand-written)

Nasutoceratopsini and the Centrosaurini

The scientists, which include lead author Dr Michael Ryan (Cleveland Museum of Natural History), have erected these two tribes, or clades within the sub-family Centrosaurinae based on an assessment of anatomical characteristics following extensive comparative analysis of the fossilised bones of these large, herbivorous dinosaurs.

A fragmentary skull which includes parts of the snout and beak of a ceratopsian, collected nearly eighty years ago in southern Alberta, has led to the establishment of the Nasutoceratopsini.  The fossil skull (pictured below), was collected by the famous palaeontologist Charles Sternberg from southern Alberta in 1937.  Although it is too fragmentary to allow the identification of autapomorphies (unique characteristics) that would allow a new species to be named, it has helped the research team to identify the Nasutoceratopsini based on several features such as the large, broad neck frill and the shape of the beak.

Specimen Number CMN-8804 Helping to Define the Nasutoceratopsini 

Highly fragmentary Ceratopsian skull collected by Charles Sternberg in 1937.

Picture credit: Canadian Natural History Museum/The Canadian Journal of Earth Sciences

The new Nasutoceratopsini grouping includes Avaceratops from Montana as well as the recently described Nasutoceratops from Utah), along with an as yet undescribed skull specimen from Malta, Montana (specimen number GPDM-63).  Unlike, their ostentatious contemporaries within the Centrosaurinae, the Nasutoceratopsini had prominent frills that lacked well-developed ornamentation.  In a press release, the scientists state that the Nasutoceratopsini were not dinosaur show-offs, choosing instead to blend into their environments.

A Close View of the Head of the Dinosaur (Specimen CMN-8804)

The broad frill lacking excessive ornamentation of a Nasutoceratopsini.

Picture credit: Canadian Museum of Natural History/Andrey Atuchin

Lacking Shield Ornamentation

Although all nasutoceratopsins lack shield ornamentation, they had two long brow horns above their eyes.

Dr Ryan explained:

“Nasutoceratopsins took a different evolutionary path from their centrosaurine cousins, which typically have highly ornamented skulls.  We believe that the skull ornamentation was important for attracting mates.  If nasutoceratopsins lacked bony ornamentation, it’s possible that they may have used distinctive coloration patterns, social behaviours or vocalisations, like modern birds do in their courtship behaviours.  But we’ll never know for sure since those latter features don’t fossilise.”

The second new tribe described by the scientists, Centrosaurini, formally acknowledges its members (such as Centrosaurus) as being a natural grouping of horned dinosaurs with highly ornamented frills and short brow horns.

The Nasutoceratopsini and the Centrosaurini dinosaurs are represented in the Beasts of the Mesozoic modle range.

To view the Beasts of the Mesozoic figures: Beasts of the Mesozoic Figures and Models.

The Phylogeny of the Centrosaurinae

A Reassessment of the Centrosaurinae (Phylogeny)

Looking at the phylogeny of the Centrosaurinae.

Picture credit: The Canadian Journal of Earth Sciences with additional annotation from Everything Dinosaur

In the consensus tree diagram above, the phylogenetic relationship between members of the tribe Nasutoceratopsini are shown within the sub-family Centrosaurinae.  The new clades Nasutoceratopsini and Centrosaurini are underlined in red.

The fact that the two tribes are found together over a great distance in rocks of the same age indicates that they would have overlapped in the same regions at the same time.  Nasutoceratopsins and centrosaurins co-existed.  The research team examined the strata in the Belly River Group (southern Alberta) and compared it to the roughly same-aged rocks that comprise the Judith River Formation of north-central Montana.  They then mapped the Ceraptosidae fossils so that they could estimate which types of ceratopsids were contemporaneous.

Which Types of Horned Dinosaur Lived When?

Nasutoceratopsini and Centrosaurini species were contemporaries in Laramidia.

Picture credit: The Canadian Journal of Earth Sciences with additional annotation from Everything Dinosaur

In the sequential strata diagrams above different members of clades that comprise the Ceratopsidae have been identified.

Key

B C = Basal ceratopsid

C = Centrosaurini

N = Nasutoceratopsini

P =Pachyrhinosaurini

Co-author of the paper, Dr Jordan Mallon (Canadian Museum of Nature), compared the ceratopsids of North America in the Campanian stage of the Late Cretaceous to extant populations of African rhinos, Dr Mallon stated:

“It’s probably similar to how two species of rhinoceros can broadly overlap in their geographic ranges, but do not actually compete with each other for resources.  Black rhinos will feed on woody browse, while white rhinos are primarily grass grazers.  Thus, the two species tend to utilise different parts of the same environments.  The assumption that centrosaurins and nasutoceratopsins may have had different feeding strategies is supported by the fact that the two tribes had different types of jaws, with the lower jaws of nasutoceratopsins being shorter and deeper.”

The scientific paper: “A Basal Ceratopsid (Centrosaurinae: Nasutoceratopsini) from the Oldman Formation (Campanian) of Alberta, Canada” published in The Canadian Journal of Earth Sciences.

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