Allkaruen koi was overlooked as a proto-Pterodaustro

A new pterosaur described by Codorniú et al. 2016
somehow escaped my notice until today. Allkaruen koi (Figs. 1,3,4) is the new genus. It was originally nested between basal (long-tailed) pterosaurs and the Darwinopterus clade + ‘Pterodactyloidea’ using an antiquated cladogram modified from Lü e al 2010, itself modified from Unwin 2003. We’re going to critically examine this paper, applying logic, creating reconstructions, calling on overlooked data and including more than a few previously excluded taxa.

Figure 1. Allkaruen elements as originally published.

Figure 1. Allkaruen elements as originally published. Some of the scale bars are different by 94% and 117%, resized to the same scale below in figure 3. Why couldn’t they all be drawn to the same scale, and in relation to one another? You’ll see how well that works in figure 3.

The holotype of Allkaruen koi includes:

  1. MPEF-PV 3613 (Museo Paleontológico Egidio Feruglio)  braincase,
  2. MPEF-PV 3609 mandible
  3. MPEF-PV 3615 cervical vertebrae (Fig. 1)

The stratigraphic horizon
in which Allkaruen was found was labeled by Codorniú et al.: “latest Early-early Middle Jurassic.” Let’s just call it “Middle Jurassic.”

From the Codorniú et al. abstract
“Here we report on a new Jurassic pterosaur from Argentina, Allkaruen koi gen. et sp. nov., remains of which include a superbly preserved, uncrushed braincase that sheds light on the origins of the highly derived neuroanatomy of pterodactyloids and their close relatives. A mCT ray-generated virtual endocast shows that the new pterosaur exhibits a mosaic of plesiomorphic and derived traits of the inner ear and neuroanatomy that fills an important gap between those of non-monofenestratan breviquartossans (Rhamphorhynchidae) and derived pterodactyloids.”

The diagnosis:
“Small pterosaur diagnosed by the following unique combination of skull characters present in the holotype (autapomorphies marked with asterisk):

  1. frontal with large pneumatic foramen on the postorbital process
  2. dorsal occiput faces posterodorsally and occipital condyle faces posteroventrally
  3. long, rod-like basipterygoid processes diverging at approximately 20–25 degrees.

The referred mandibular and vertebral materials also show a unique combination of characters that include:

  1. a long lower jaw with a concave profile in lateral view
  2. four-five large, septated, and well-separated anterior alveoli followed by a posterior alveolar groove*;
  3. mid-cervical vertebrae elongate with low neural arch and blade-like neural spine; pneumatic foramina on lateral surface of the centrum and peduncle of the neural arch
  4. reduced diapophyseal process lacking articular surface
  5. absence of accessory zygapophyseal processes.”
Codornií cladoram nesting Allkaruen between basal pterosaurs and derived pterosaurs.

Figure 2. Codornií cladoram nesting Allkaruen between basal pterosaurs and derived pterosaurs. Note that a dinosaur is the outgroup here. There are 59 taxa above. Note the close relationship of Dorygnathus and Allkaruen and Pterodaustro in this cladogram. It gets even closer in figure 6.

The Codorniú et al. phylogenetic analysis
Codorniú et al. added Allkaruen to the cladogram of Lü et al 2003 (the Darwinopterus study) based on Unwin 2003. They recovered Allkaruen basal to their ‘Monofenestrata, which was basal to their ‘Pterodactyloidea’. Both clades were found to be invalid in the large pterosaur tree.

Figure 3. Reconstruction of Allkaruen atop a more complete Pterodaustro to the same scale demonstrating a close match-up of elements.

Figure 3. Reconstruction of Allkaruen atop a more complete Pterodaustro to the same scale demonstrating a close match-up of elements that was somehow overlooked by the original authors. The amount of material missing between the mandibles and the cranium is unknown. See figure 4 for a closer look at the cranium. Note the tooth grooves and anterior alveoli in the top view of the dentary.

A reconstruction
missing from the original paper, but provided here (Fig. 3) provides an overlooked answer to the affinities of Allkaruen. This Middle Jurassic taxon closely matches Albian (latest Early Cretaceous) Pterodaustro, the only other South American pterosaur with a dorsally concave dentary (#1), an alveolar groove (#2), similar mid-cervical vertebrae (#3) and maybe traits #4 and #5, (hard to tell from the available data). The dorsal appearance of the cranium of Allkaruen also closely matches that of another ctenochasmatid, Gnathosaurus. Most to all Pterodaustro specimens are preserved in lateral view, so the dorsal appearance must be gained from closely related taxa. like Gnathosaurus, by phylogenetic bracketing.

Figure 4. Closeup of the cranium and brain scan of Allkaruen atop a ghosted to scale image of Pterodaustro demonstrating a close affinity that was somehow overlooked originally.

Figure 4. Closeup of the cranium and brain scan of Allkaruen atop a ghosted to scale image of Pterodaustro to scale demonstrating a close affinity that was somehow overlooked originally with that short taxon list.

Pterodaustro is distinct from other ctenochasmatids
in that it has typical tetrapod vertically oriented mandibles, rather than flattened (wider than tall) mandibles typical of other ctenochasmatids (Fig. 7). In addition Pterodaustro has upwardly curved jaw tips, a trait documented in Allkaruen, in which we can see the transition from a toothy dentary to one with grooves to accommodate the hundreds of needle-like filter teeth found in Pterodaustro. Not sure why, but this similarity was overlooked by Codorniü et al. It’s doubly puzzling because Dr. Codorniú has published extensively on Pterodaustro. The only time Pterodaustro was mentioned by Codorniú et al. was when they wrote, “The cavities that invade the basicranium are also large, equivalent to those observed in pterodactyloids such as Pterodaustro.”

Figure 4. Chronological evolution of Pterodaustro via Allkaruen, Angustinaripterus (Early Jurassic) and Dorygnathus (late survivor in the Middle Jurassic).

Figure 5. Chronological evolution of Pterodaustro via Allkaruen, Angustinaripterus (Early Jurassic) and Dorygnathus (late survivor in the Middle Jurassic).

The pterosaur phylogeny presented
by the large pterosaur tree (LPT, subset Fig. 5) provides a fast track evolution from derived dorygnathids, already demonstrating a wide radiation in the Early Jurassic, to ctenochasmatids like Allkaruen (Middle Jurassic) and Ctenochasma (Late Jurassic) that does not include the Darwinopterus clade as transitional taxa. In the LPT four clades evolved a complete set of pterodactyloid-grade traits. Two other clades, Anurognathidae and Wukongipteridae, independently evolved an incomplete set of pterodactyloid-grade traits. These led to invalid claims by Andres, Clark and Xu 2014 that anurognathids were basal to pterodactyloids and Unwin 2003 + Lü et al. 2010 that wukongopterids were basal to pterodactyloids. These claims were made with short, incomplete taxon inclusion lists that were shown to be lacking in pertinent taxa by the LPT.

Fig. 5. Subset of the LPT focusing on Dorygnathus clades that evolved to become ctenochasmatids and azhdarchids. This is what you get when don't exclude taxa the way Codorniú did.

Fig. 6. Subset of the argePT focusing on Dorygnathus clades that evolved to become ctenochasmatids and azhdarchids. This is what you get when don’t exclude taxa the way Codorniú did.

It’s no surprise that Allkaruen has transitional traits.
In the LPT it represents a transitional stage in the evolution of Pterodaustro from Angustinaripterus ancestors. Allkaruen nests with Pterodaustro in the LPT, but due to the headless D2514 ‘not Eosipterus‘ specimen adding Allkaruen creates a polytomy (Fig. 6). As earlier, no claim of ‘mosaic evolution‘ can be made by Codorniú et al. ‘Mosaic evolution’ has not been shown to exist in large gamut cladograms. Such claims by Codorniú et al. and others are the result of small cladograms grossly lacking in pertinent taxa.

A selection of valid Ctenochasma skulls

Figure 7. A selection of valid Ctenochasma skulls together with the two interpretations of Sos 2179 (in gray below). Note the phylogenetic miniaturization following Angustinaripterus.

Professional bias among paleontologists
and a refusal to test competing hypotheses of relationships (Peters 2000, 2007) led to the phylogenetic disaster presented by Codorniú et al. 2016. No one will ever be convinced that pterosaurs arose from Euparkeria + HerrerasaurusWorkers who do so open themselves up to ridicule. We don’t want that. It makes us all look bad. Adding taxa should solve the phylogenetic problems found in Codorniú et al. The LRT and LPT offer suggestions, but workers must put forth the effort. In Peters 2000 Cosesaurus, Sharovipteryerx and Longisquama were documented to demonstrate closer relationships to pterosaurs than dinosaurs and archosaurs can offer.

Was Allkaruen transitional between basal pterosaurs and pterodactyloids?
No. There is no valid monophlietic clade of pterodactyloids. At present, the best we can say is: Middle Jurassic Allkaruen is (time wise) transitional between Early Jurassic Angustinaripterus and Early Cretaceous Pterodaustro (Fig. 5). Allkaruen is a ctenochasmatid, plain and simple. It points to an earlier radiation of ctenochasmatids than the Solnhofen Late Jurassic. The cranial elements of Allkaruen might someday be matched to post-cranial elements now represented by the lower Yixian D2514 specimen wrongly attributed (by Lü et al. 2006) to Eosipterus. Or not. A complete specimen (crania + post-crania) would settle this  issue.

I can’t be the first pterosaur worker to notice
the Allkaruen/Pterodaustro connection. If others preceded me, please let me know so I can congratulate and confirm them.

Everyone, including Codorniu et al., is looking for
that one transitional taxon, that ‘missing link’ between long-tailed pterosaurs and short-tailed pterosaurs. Andres, Clark and Xu 2014 failed when they mistook small parts of a skinny dorygnathid for a much smaller pterodactyloid. Lü et al. 2010 failed when they added Darwinopterus to a small gamut cladogram. Codorniú et al. failed when they promoted Allkaruen to that position. The authority to state that these PhDs failed comes from a large gamut cladogram, the LPT, that tests their short taxon lists with a much larger taxon list. The LPT documents four appearances of pterodactyloid-grade clades and so will competing studies when they expand their lists, create reconstructions and have a third party certify their scores are correct.

Ironically, no one’s looking for
that one transitional taxon, that ‘missing link’ between pre-volant pterosaur ancestors and basal pterosaurs. Do you wonder why that is? I can only suppose no one wants to confirm the published work of an amateur from 17 years ago (Peters 2000). There’s no reward in it for PhDs. No one wants to admit they were wrong and needlessly parochial for 17 years.

References
Andres, B, Clark J and Xu X 2014. The Earliest Pterodactyloid and the Origin of the Group. Current Biology. 24: 1011–6.
Codorniú L, Carabajal AP, Pol D, Unwin D and Rauhut OWM 2016.
 A Jurassic pterosaur from Patagonia. and the origin of the pterodactyloid neurocranium. PeerJ 4:e2311; DOI 10.7717/peerj.2311
Lü J-C, Gao C-L, Meng Q-J, Liu J-Y, Ji Q 2006. On the Systematic Position of Eosipterus yangi Ji et Ji, 1997 among Pterodactyloids. Acta Geologicia Sinica 80(5):643-646.
Lü J, Unwin D, Jin X, Liu Y, Ji Q 2010. Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proceeding of the Royal Society B 273:383389.
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007. The origin and radiation of the Pterosauria. Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27.
Unwin DM 2003. On the phylogeny and evolutionary history of pterosaurs. In:Buffetaut E, Mazin J-M, eds. Evolution and Paleobiology of Pterosaurs, vol. 217. London: Geological Society, Special Publications, 139190.

wiki/Allkaruen

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