Meet Allkaruen – the new Argentinian pterosaur

New pterosaurs, and especially new well preserved pterosaurs, are rarely found. As I’ve mentioned in the past, pterosaurs exhibit significant skeletal pneumaticity, meaning their bones are often filled with air. This is common in skulls of animals (like the sinuses in your own head), and is especially prevalent in pterosaurs. For this reason, pterosaur skulls are often crushed, making their brain cases hard to study. This is why the new pterosaur Allkaruen koi found in Argentina and described in PeerJ by Codorniú et al. is so important.

Brain cases are useful in understanding extinct animals, because they let us see the general structure of the brain, which can teach us about which regions were well defined. As different regions of the brain are responsible for different behaviours or senses, we can then make inferences about the capabilities of these animals when alive. If the portion of the brain related to smell is particularly well developed, the animal probably relied on smell significantly, which can indicate that it was a keen predator or scavenger. The same things can be said for areas relighted to eyesight, flight, etc. This is where the new pterosaur comes in.

Allkaruen comes from the Early/Middle Jurassic of Argentina, a time  in which pterosaur fossils are rare. It sits just outside of the Monofenestrata, the group including the transitional pterosaurs (wukongopterids) and more derived pterodactyloids. The specimen is very fragmentary, but it has an exceptionally 3D preserved braincase, allowing for Codorniú et al. to study the evolution of the pterosaur braincase through CT scanning, since primitive non-pterodactyloid braincases, and derived pterodactyloid cases have been studied before. Now we have a braincase from one of these animals in between.

screen-shot-2016-09-11-at-20-09-46
Braincase (A-C), mandible (D, E), and cervical vertebra (F, G) of Allkaruen. From Codorniu et al. (2016).

The braincase of Allkaruen shows some features in common with basal “rhamphorhynchoids” or non-pterodactyloids, while some are shared with derived pterodactyloids. Additionally, it has some unique features that appear to be transitional features between the two groups. The interesting part of this mosaic of features, is that it is a different pattern than in what is seen in other parts of the body in the evolution of basal non-pterodactyloids into wukongopterids and pterodactyloids. The discovery of the transitional Darwinopterus showed us that pterosaurs exhibited modular evolution with different parts of the skeleton evolving at different times. The first stage includes changes in the skull, neck and ribs, while the second stage shows changes to the wing and feet. The fact that the braincase shows a mosaic of features means that although pterosaurs seem to have evolve different regions of the body in phases, not all “modules” of the body follow this trend. The other significance of this find is the age. Pterodactyloids didn’t evolve until the Late Jurassic, but Allkaruen is from the Early-Middle Jurassic, meaning at least some features of the pterodactyloid brain and skull had already started to evolve at this point. Since pterosaur fossils from this time are so rare, we had no reason to expect them so early in pterosaur evolution.

Slowly but surely more pterosaur fossils are being found, teaching us more and more about pterosaur diversity and evolution. As more specimens are found, we are starting to better understand how pterosaurs evolved. Now all we need are some better Triassic fossils to figure out exactly where pterosaurs came from! For now, however, new specimens such as Allkaruen are great for us pterosaur workers to help understand their evolution.

Reference:

Codorniu, L., Carabajal, A.P., Pol, D., Unwin, D., and Rauhut, O.W.M. 2016. A Jurassic pterosaur from Patagonia and the origin of the pterodactyloid neurocranium. PeerJ 4: e2311.

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5 thoughts on “Meet Allkaruen – the new Argentinian pterosaur

  1. Allkaruen – a slightly different view?

    If I might go slightly ‘off-message’ on this one. Our original paper emphasised the ‘mosaic’ set of characters exhibited by the braincase/endocast of Allkaruen. However, take a look at the row of endocasts seen in left lateral view in our Figure 6, and ask yourself ‘how much does Allkaruen look like Rhamphorhynchus (to the left) or Anhanguera (to the right)? I would suggest that Allkaruen looks much more like Anhanguera, than Rhamphorhynchus, and would argue (departing slightly from my co-authors position) that, overall, the endocast of Allkaruen is essentially pterodactyloid (insofar as comparisons can be made between just three endocasts!). The endocast of Allkaruen exhibits a marked degree of flexure and many concomitant effects of this including changes in the shape, size and position of key structures such as the optic lobes. My interpretation of Allkaruen, then, is that in so far as we have it, evidence for skull anatomy points to a condition that is more or less pterodactyloid, with the retention of some non-derived features.

    An analogy here might be ‘Rhamphodactylus’ from the Solnhofen Limestones – see beautifully illustrated paper by Tischlinger & Frey, 2013, Archaeopteryx 31, 1-13 on the ‘Painten pro-pterodactyloid (which I treat here as a second specimen of ‘Rhamphodactylus’). ‘Rhamphodactylus’ has many pterodactyloid features, but does also retain some non-derived features (e.g. in the fifth toe and tail). Despite these, phylogenetic analysis clearly places it as a sister taxon to Pterodactyloidea, and more derived than basal monofenestratans such as Darwinopterus.

    Going back to Allkaruen, my feeling is that when fully elucidated the skull will be found to be essentially pterodactyloid and the idea of modularity, as currently conceived for the basal pterosaur – pterodactyloid transition will remain largely intact. That said, the combinations of plesiomorphic and apomorphic characters states exhibited by Allkaruen (and Rhamphodactylus) suggest that the process by which key structures such as the cranium, tail and fifth toe evolved to reach the condition seen in these taxa were not necessarily all that modular. Highly detailed, fine-scale anatomical studies and phylogenetic analyses will be needed to try to pin-point exactly what happened – for which we will certainly need more fossils. Happily, in the case of Allkaruen there is more, as yet undescribed material (although it is very difficult to prepare) so we can at least look forward to learning a lot more about this particular Middle Jurassic pterosaur in the future.

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    1. Thanks for the comment Dave! Definitely look forward to see what else is described for Allkaruen, and am interested in seeing what comes out of it. It would be interesting to see if it does follow your thoughts on the brain evolution.

      On ‘Rhamphodactylus’ – I don’t know a lot about it, but my understanding was that it was probably not a valid taxon based on the fact that what it was described from was extremely fragmentary and isolated. Anytime I’ve ever found any material in museums labelled as ‘Rhamphodactylus’, it was a single isolated element that looked pretty similar to any other isolated element from the Jurassic. I am looking forward to when the Painten pro-pterodactyloid is properly described though. It’s a beautiful specimen, and I’d love to see it written up!

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  2. Hi Liz,

    You might be confusing ‘Rhamphodactylus’ with ‘Rhamphocephalus’. ‘Rhamphodactylus’ was the name used by Rauhut (2012) for a disarticulated, but more or less complete skeleton of what seems to be a basal pterodactyloid from the Mörnsheim Formation of Mühlheim, Bavaria. A second specimen, described by Tischlinger and Frey (2013) from the Painten Formation of Painten, Bavaria, is probably the same taxon (see my earlier post), although that has yet to be formally demonstrated. ‘Rhamphocephalus’ is one of the problematic names that has been used for some of the many isolated and often incomplete pterosaur bones and teeth from the ‘Stonesfield Slate’ and coeval deposits of southern England. Mike O’Sullivan (Portsmouth) has been revising the taxonomy and systematics of these (and other British Jurassic) pterosaurs for his PhD – I’m looking forward to seeing the results of this study (for a summary see Mike’s abstract in the Portsmouth Flugsaurier volume) especially as there does seem to be at least one basal monofenestratan in the ‘Stonesfield Slate’ assemblage, a fragmentary rostrum (NHM’s PV R464), labeled as ?Darwinopterus by Steel (2012) and illustrated (Steel, 2012: fig. 3) in the same paper.

    Rauhut, O.W.M. 2012. Ein “Rhamphodactylus” aus der Mörnsheim-Formation von Mühlheim. Freunde der Bayerischen Staatssammlung für Paläontologie und Historische Geologie e.V., Jahresbericht und Mitteilungen, 40: 69-74.

    Steel, L. 2012. The pterosaur collection at the Natural History Museum, London, UK: an overview and list of specimens with description of recent curatorial developments. Acta Geologica Sinica, 36: 1340-1355.

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    1. You are exactly right, I was actually thinking Rhamphocephalus and about Mike’s work when I made that comment. I completely forgot about Rhamphodactylus. Either way, my comment remains the same – I don’t know much about it! In fact, I know even less… Hopefully we’ll get a formal description of the Painten pterodactyloid soon!

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