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. 2016 Aug 30:4:e2311.
doi: 10.7717/peerj.2311. eCollection 2016.

A Jurassic pterosaur from Patagonia and the origin of the pterodactyloid neurocranium

Laura Codorniú  1 , Ariana Paulina Carabajal  2 , Diego Pol  3 , David Unwin  4 , Oliver W M Rauhut  5
Affiliations

A Jurassic pterosaur from Patagonia and the origin of the pterodactyloid neurocranium

Laura Codorniú et al. PeerJ. .

Abstract

Pterosaurs are an extinct group of highly modified flying reptiles that thrived during the Mesozoic. This group has unique and remarkable skeletal adaptations to powered flight, including pneumatic bones and an elongate digit IV supporting a wing-membrane. Two major body plans have traditionally been recognized: the primitive, primarily long-tailed paraphyletic "rhamphorhynchoids" (preferably currently recognized as non-pterodactyloids) and the derived short-tailed pterodactyloids. These two groups differ considerably in their general anatomy and also exhibit a remarkably different neuroanatomy and inferred head posture, which has been linked to different lifestyles and behaviours and improved flying capabilities in these reptiles. Pterosaur neuroanatomy, is known from just a few three-dimensionally preserved braincases of non-pterodactyloids (as Rhamphorhynchidae) and pterodactyloids, between which there is a large morphological gap. 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 µCT 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. These results suggest that, while modularity may play an important role at one anatomical level, at a finer level the evolution of structures within a module may follow a mosaic pattern.

Keywords: Cañadón Asfalto; Chubut; Middle Jurassic; Patagonia; Pterosauria.

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Conflict of interest statement

The authors declare there are no competing interests.

Figures

Figure 1
Figure 1. Selected skeletal elements of Allkaruen koi.
(A–C), Holotype braincase (MPEF-PV 3613) in left lateral (A), dorsal (B) and posteroventral (C) views. (D, E), Mandible (MPEF-PV 3609) in dorsal (D) and right lateral (E) view. (F, G), Cervical vertebra (MPEF-PV 3615) in ventral (F) and right lateral (G) view. Abbreviations: ag, alveolar groove; alv, alveoli; atr, anterior tympanic recess; bo, basioccipital; btr, basipterygoid recess; bpt, basipterygoid process; bs, basisphenoid; bt, basal tuber; cmv, caudal middle cerebral vein foramen; co, condyle; ct, crista tuberalis; d, dentary; eo-op, exoccipital/opisthotic; f, frontal; fm, foramen magnum; lts, laterosphenoid; mf, metotic foramen; nc, nuchal crest; np, nasal process; ns, neural spine; oc, occipital condyle; p, parietal; pf, pneumatic foramen; poz, postzygapophysis; pro, prootic; prz, prezygapophysis; ptf, posttemporal fenestra; ptr, posterior tympanic recess; sc, sagittal crest. Roman numerals indicate cranial nerves. Scale bars are 10 mm.
Figure 2
Figure 2. Surface-rendered CT-based reconstructions of the cranial endocast and endosseous labyrinth of the holotype of Allkaruen koi, in dorsal (A), right lateral (B), ventral (C) and dorsolateral (D) views.
Abbreviations: asc, anterior semicircular canal; cer, cerebral hemisphere; de, dorsal expansion ; floc, flocculus; fm, foramen magnum; lag, lagena; med, medulla oblongata; lsc, lateral semicircular canal; ob, olfactory bulb; pit, pituitary body; psc, posterior semicircular canal; V, XII, cranial nerves. Scale bar is 1 cm.
Figure 3
Figure 3. Inner ear anatomy.
Digital reconstruction of the left inner ear of Allkaruen koi, based on the CT scan of the holotype in lateral (A), dorsal (B), anterior (C) and posteromedial (D) views. Reconstructed sections are in light-blue. Abbreviations: am, anterior ampula; asc, anterior semicircular canal; ct, common trunk; lag, lagena; lsc, lateral semicircular canal; psc, posterior semicircular canal. Scale bar is 0.5 cm.
Figure 4
Figure 4. Volume-rendered CT-based reconstruction of the braincase of the holotype of Allkaruen koi, in left laterodorsal view.
The bone is rendered solid (A), and semi-transparent (B). Pneumatic recesses are shown in yellow in (B). Abbreviations: bpt, basipterygoid process; f, frontal; fm, foramen magnum; nc, nuchal crest; oc, occipital condyle; p, parietal; pf, pneumatic foramen; pop, paroccipital process; pn.f, frontal pneumaticity; pn.eo-op, exoccipital-opisthotic pneumaticity; sc, sagittal crest. Scale bar is 1 cm.
Figure 5
Figure 5. Strict consensus of the 360 most parsimonious trees with major nodes of Pterosauria labelled.
Numbers at the nodes represent the Bremer support value and Bootstrap frequencies for each of the nodes present in the strict consensus tree.
Figure 6
Figure 6. Cranial endocast and comparison of brain anatomy in pterosaurs.
(A, B), Volume-rendered CT-based reconstruction of the braincase of the holotype of Allkaruen koi, in dorsal (A) and left lateral (B) views (the bone is rendered semitransparent to show the cranial endocast and the inner ear). (C–H), schematic drawings of brain anatomy in Rhamphorhynchus (C, F), Allkaruen (D, G), and Anhanguera (E, H) in dorsal (C–E) and lateral (F–H) views. Colors (C–H) indicate equivalent brain regions (blue, cerebrum; green, optic lobe; yellow, cerebellum; red, floccular process of cerebellum; pink, semicircular canals). The horizontal black line shows the relationship between the dorsal expansion of the anterior semicircular canal and the forebrain. Abbreviations: asc, anterior semicircular canal; cer, cerebral hemisphere; de, dorsal expansion; f, frontal; floc, floccular process of cerebellum; lab, labyrinth of inner ear; lsc, lateral semicircular canal; lag, lagena; ob, olfactory bulb; oc, occipital condyle; ol, optic lobe; pbt, basipterygoid process; pit, pituitary body; psc, posterior semicircular canal; sc, sagittal crest. Roman numerals indicate cranial nerves. Brain anatomy of Rhamphorhynchus and Anhanguera modified from Witmer et al. (2003). Scale bars are 10 mm.
Figure 7
Figure 7. Phylogenetic position of Allkaruen koi calibrated against geological time.
The topology is based on the strict consensus and summarizes the relationships among basal pterosaurs (“rhamphorhynchoids”) and major groups of Pterodactyloidea (collapsed into clades). Grey bar represents ghost lineage leading to Monofenestrata and schematic endocast drawings represent the condition of “rhamphorhynchoids,” Allkaruen, and pterodactyloids. Further phylogenetic information is given in the Supplemental Materials.
See this image and copyright information in PMC

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