The Significance of the Pterosaur Allkaruen

A few days ago, Everything Dinosaur featured an article on this blog about a newly described Early Jurassic pterosaur named Allkaruen koi.  We were subsequently emailed by one young dinosaur fan asking us to explain the significance of this fossil discovery.  Why was the pterosaur Allkaruen important?

Time to Get Excited About Pterosaurs – Learning Lots about Flying Reptiles

White bar shows scale.

Picture credit: Scientific Reports/Xiaolin Wang et al

The photograph above shows the fossilised remains of Ikrandraco avatar, a new species of pterosaur described in 2014.

To read our recent article on the discovery of a new pterosaur (A. koi) from Patagonia (Argentina): New Long-Tailed Pterosaur from Patagonia.

Pterosaur Fossils are Exceedingly Rare

Fossils of flying reptiles are exceedingly rare, of the 130 or so genera described to date, most are known from only a few fragmentary fossils, mere scraps of bone and teeth.  The light, delicate, pneumatic bones of pterosaurs rarely survive the ravages of time and the fossilisation process.  Most corpses, don’t even get buried, the chances are the carcase would have been scavenged long before it settled on a lake bed or the bottom of a shallow sea.

Therefore, the naming of a new flying reptile species is, in itself, a significant event.  For Allkaruen koi, even more so, as the rocks in southern Argentina where the fossilised bones were found indicate that this flying reptile lived around 180 million years ago.

For models and replicas of pterosaurs and other prehistoric creatures: CollectA Deluxe Scale Prehistoric Animal Models.

A Beautiful Braincase

The new pterosaur genus has been erected after careful study of the skeletal elements including an almost perfect, three-dimensionally preserved braincase.  Most pterosaur fossils are crushed, distorted or compacted but not in this case, one of just a handful of very well-preserved flying reptile braincases known in the fossil record.  The braincase of Allkaruen shows a unique combination of characteristics of both the Rhamphorhynchoids (non-monofenestratan breviquartossans) and the Pterodactyloidea – let’s explain what this means.

The Pterosauria – the Order of reptiles that includes all these flying reptiles can be split into to distinct and very different groups.

1. Formerly referred to as the Rhamphorhynchoids (as the very well known Rhamphorhynchidae family is included in this group), but now known to include a number of other pterosaur families that evolved in the Triassic and the Jurassic, characterised by long-tails and a lengthy fifth digit.
2. The Pterodactyloidea essentially the vast majority of known pterosaurs, a Jurassic/Cretaceous radiation of flying reptiles with thin bone walls, relatively long metacarpals and much shorter tails.

The Pterosaur Allkaruen

So, in short, the researchers have a braincase from an Early Jurassic pterosaur that shows features of both groups, the basal group and the later, short-tailed, long toed, thin bone walled Pterodactyloidea.  By studying the braincase of Allkaruen the palaeontologists can learn more about how the Pterodactyloidea evolved.  They can see how the brains of flying reptiles changed over time.

A Phylogenetic Assessment of Allkaruen Compared to Rhamphorhynchus and the Later Pterosaur Anhanguera

Where within the Pterosauria Order does Allkaruen fit in?

Picture credit: PeerJ

The researchers compared the changing shape and structure of pterosaur brains, comparing Allkaruen with the brain anatomy of Rhamphorhynchus (representing the basal group), with the brain anatomy of a later Cretaceous pterosaur Anhanguera, a representative of the short-tailed Pterodactyloidea.  Allkaruen could be described as a sort of “halfway house” between these two groups, a snapshot in pterosaur evolution permitting scientists to gain “insights into the origin of the Pterodactyloid neurocranium and improve our understanding of the tempo and mode of pterosaur evolution.”

The scientists mapped the various elements of the brain by comparing the braincases of these three pterosaurs, from this information they could plot the evolution of the inner ear, essentially the balance organ, vital if you are going to spend a long time in the air.

A Larger Brain Volume

The brain volume of Allkaruen is much bigger than that of Rhamphorhynchus and from this it can be inferred that Allkaruen was a more advanced animal capable of better co-ordinated flight and faster reactions than the Rhamphorhynchidae.  The cerebellum (show in yellow in the three brain diagrams included in the picture above), is much larger in Allkaruen than it is in Rhamphorhynchus.  The cerebellum in vertebrates is found towards the back of the brain it coordinates and regulates muscular activity.  A bigger cerebellum is another indicator that Allkaruen was a better flyer than the more basal pterosaurs.  This and other evidence is helping palaeontologists to understand more about how the pterosaurs evolved.

That’s why this fossil discovery is so important.

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Allkaruen koi – Braincase and All

A team of international scientists including Leicester University’s David Unwin and Oliver Rauhut (conservator at the Bavarian Collection for Palaeontology and Geology), have announced the discovery of a new species of long-tailed pterosaur from Patagonia (Argentina).

A Long-tailed Pterosaur

Writing in the academic journal “PeerJ”, the researchers were able to infer new information about how pterosaurs adapted to an aerial lifestyle thanks to the three-dimensional preservation of the cranial material.  From this skull material, the team were able to gain fresh insights into the braincase and the structure of the inner ear.  The new species of pterosaur will help palaeontologists to better understand differences between the primitive, primarily long-tailed “rhamphorhynchoids”, also known as non-pterodactyloids and the more derived and later, short-tailed pterodactyloids.

An Illustration of the New Pterosaur (Allkaruen koi)

An illustration of the newly described Jurassic pterosaur from Argentina called Allkaruen.

Picture credit: Gabriel Lio

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The Evolution and Radiation of the Pterosauria

The fossilised remains of this new pterosaur come from the Cañadón Asfalto Formation, exposed in the northern/central Chubut Province of southern Argentina.  The fossil material came from a single bedding plane formed from freshwater limestone deposits, indicating that there was a large, inland body of water present.  The fossils were scattered although elements such as the mandible preserved a degree of articulation.  The rocks of the Cañadón Asfalto Formation had been thought to be about 162 million  years of age (Callovian to Oxfordian faunal stages – latest Middle to earliest Late Jurassic), however recent radiometric and biostratigraphical analysis suggests that these rocks might be much older.

Research published in 2013 (Cúneo et al), indicates an age range for this formation of between 183 and 165 million years (Toarcian to Bathonian faunal stages).

The genus name comes from the local Tehuelche dialect word “all” for “brain” and “karuen” which means “ancient”, in recognition of the superb three-dimensional preservation state of the fossil  skull.  The species name means “lake” in the Tehuelche language, reflecting the fact that the fossils were found in lacustrine deposits,

Fossils and Line Drawings of the Allkaruen koi Material

Fossils of the braincase, line drawings of the braincase along with drawings of the mandible and vertebrae.

Picture credit: PeerJ

Two Main Types of Pterosaur

Pterosaurs have remarkable skeletal adaptations for life in the air and they were the first vertebrates to achieve powered flight.  Two major body plans have traditionally been recognised, rhamphorhynchoids (non-pterodactyloids) and the pterodactyloids.  These two types of flying reptile differ considerably in their general anatomy and also they exhibit very different head postures and neuroanatomy (nervous systems and the study of the brain).  Computerised tomography was employed to scan the uncrushed braincase that enabled the scientists to infer more information regarding the shape of the brain and the inner ear.

This study has provided new information on the origins of the highly derived neuroanatomy of pterodactyloids, as, until this new fossil discovery, only a few three-dimensionally preserved braincases of flying reptiles were known and these demonstrated a large morphological gap between the specimens.

The braincase of Allkaruen has helped fill in a portion of that gap to give scientists a better understanding of how the flying abilities of these reptiles evolved.

Dr Diego Pol (CONICET, Museo Paleontológico Egidio Feruglio, Trelew, Chubut, Argentina) and corresponding author for the published paper stated: 

“Allkaruen shows an intermediate state in the brain evolution of pterosaurs and their adaptations to the aerial environment.  As a result, this research makes an important contribution to the understanding of the evolution of all of pterosaurs.”

A Phylogenetic Analysis

A phylogenetic analysis was undertaken and Allkaruen is nested between monofenestratan breviquartossans (Rhamphorhynchidae) and derived pterodactyloids.  Given the age of the fossil and its phylogenetic affinities to Rhamphorhynchus and the pterosaur known as Darwinopterus it has been suggested that this flying reptile had a long tail with a diamond-shaped rudder on the end of it.  Analysis of the cranium indicates that Allkaruen had two parallel crests on the top of its skull and it appeared to have teeth restricted to the middle and anterior (front) part of its jaws.  Although the exact diet of this pterosaur is not known, given the context of the fossil material and the shape of the teeth, Allkaruen most likely fed on fish.

To read an article on the transitional fossil Darwinopterus: Darwinopterus – A Transitional Pterosaur.

Dr Oliver Rauhut has had a busy couple of weeks, he was also one of the principal authors of the scientific paper on the Early Jurassic meglosaurid Wiehenvenator.  To read about the “Monster of Minden”: Wiehenovenator – The “Monster of Minden”.

Everything Dinosaur is based in the UK.  We produce helpful and informative blog posts including articles about fossil finds.

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