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The endocranial anatomy of therizinosauria and its implications for sensory and cognitive function - PubMed

The endocranial anatomy of therizinosauria and its implications for sensory and cognitive function

Stephan Lautenschlager et al. PLoS One. 2012.

Abstract

Background: Therizinosauria is one of the most enigmatic and peculiar clades among theropod dinosaurs, exhibiting an unusual suite of characters, such as lanceolate teeth, a rostral rhamphotheca, long manual claws, and a wide, opisthopubic pelvis. This specialized anatomy has been associated with a shift in dietary preferences and an adaptation to herbivory. Despite a large number of discoveries in recent years, the fossil record for Therizinosauria is still relatively poor, and cranial remains are particularly rare.

Methodology/principal findings: Based on computed tomographic (CT) scanning of the nearly complete and articulated skull of Erlikosaurus andrewsi, as well as partial braincases of two other therizinosaurian taxa, the endocranial anatomy is reconstructed and described. The wider phylogenetic range of the described specimens permits the evaluation of sensory and cognitive capabilities of Therizinosauria in an evolutionary context. The endocranial anatomy reveals a mosaic of plesiomorphic and derived characters in therizinosaurians. The anatomy of the olfactory apparatus and the endosseous labyrinth suggests that olfaction, hearing, and equilibrium were well-developed in therizinosaurians and might have affected or benefited from an enlarged telencephalon.

Conclusion/significance: This study presents the first appraisal of the evolution of endocranial anatomy and sensory adaptations in Therizinosauria. Despite their phylogenetically basal position among maniraptoran dinosaurs, therizinosaurians had developed the neural pathways for a well developed sensory repertoire. In particular olfaction and hearing may have played an important role in foraging, predator evasion, and/or social complexity.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. In-situ endocranial elements of the described therizinosaurian taxa displayed in their phylogenetic context.

Bone rendered transparent to reveal endocranial anatomy. (Phylogeny modified from [4]).

Figure 2
Figure 2. Sagittal sections through the individual braincases.

(A) Erlikosaurus andrewsi (IGM 100/111), (B) Nothronychus mckinleyi (AZMNH-2117), (C) Falcarius utahensis (holotype specimen, UMNH VP 15000), (D) Falcarius utahensis (referred specimen, UMNH VP 15001), all in medial view. All braincases are oriented with the lateral semicircular canal aligned horizontally, as indicated by the position of the left endosseous labyrinth. The sagittal sections show the variable degree of endocast angulation and flexure caused by the outline of the braincase floor and the position of the foramen magnum.

Figure 3
Figure 3. Cranial endocast of Erlikosaurus andrewsi (IGM 100/111).

In (A) left lateral, (B) dorsal, (C) ventral, (D) rostral, and (E) caudal view. Abbreviations: cer, cerebral hemisphere; cvcm, caudal middle cerebral vein; fl, floccular lobe; if, interhemispherical fissure; lab, endosseous labyrinth; ob, olfactory bulbs; otc, olfactory tracts; V1, ophthalmic branch of the trigeminal nerve canal; V2, maxillary branch of the trigeminal nerve canal; V3, mandibular branch of the trigeminal nerve canal; VII, facial nerve canal; VIII, vestibulocochlear nerve canal; IX–XI, shared canal for the glossopharyngeal, vagus and spinal accessory nerve; XII, hypoglossal nerve canal.

Figure 4
Figure 4. Braincase of Erlikosaurus andrewsi (IGM 100/111).

Sagittal sections in (A) and (B) in rostromedial view. Lateral braincase wall in (C) and (D) in right lateral view with squamosal, postorbital, quadrate and quadratojugal digitally removed (based on a digital reconstruction of the cranial anatomy). Bone in (C) and (D) rendered transparent to reveal endocranial elements. Abbreviations: bsp, basisphenoid; cc, columellar canal; ed, endolymphatic duct; exoc, exoccipital and paroccipital process; ff, floccular fossa; fo, foramen; pro, prootic; V2, maxillary branch of the trigeminal nerve canal; V3, mandibular branch of the trigeminal nerve canal; VII, facial nerve canal; VIII, vestibulocochlear nerve canal; IX–XI, shared canal for the glossopharyngeal, vagus and spinal accessory nerve; XII, hypoglossal nerve canal.

Figure 5
Figure 5. Cranial endocast and braincase of Nothronychus mckinleyi (AZMNH-2117).

In (A) and (B) in left lateral, (C) caudal, (D) dorsal, and (E) ventral view. Bone in (B) rendered transparent. Abbreviations: car, cerebral carotid artery canal; cvcm, caudal middle cerebral vein; fl, floccular lobe; lab, endosseous labyrinth; pfo, pituitary (hypophyseal) fossa; V1, ophthalmic branch of the trigeminal nerve canal; V2, maxillary branch of the trigeminal nerve canal; V3, mandibular branch of the trigeminal nerve canal; VI, abducens nerve canal; VII, facial nerve canal; IX–XI, shared canal for the glossopharyngeal, vagus and spinal accessory nerve; XII, hypoglossal nerve canal.

Figure 6
Figure 6. Cranial endocast and braincase of Falcarius utahensis (holotype, UMNH VP 15000).

In (A) and (B) in left lateral, (C) and (D) in caudal, (E) dorsal, and (F) ventral view. Bone in (B) and (D) rendered transparent. Abbreviations: car, cerebral carotid artery canal; cvcm, caudal middle cerebral vein; fc, fenestra cochleae; fl, floccular lobe; fv, fenestra vestibuli; lab, endosseous labyrinth; pfo, pituitary (hypophyseal) fossa; V1, ophthalmic branch of the trigeminal nerve canal; V2, maxillary branch of the trigeminal nerve canal; V3, mandibular branch of the trigeminal nerve canal; VI, abducens nerve canal; VII, facial nerve canal; IX–XI, shared canal for the glossopharyngeal, vagus and spinal accessory nerve; XII, hypoglossal nerve canal.

Figure 7
Figure 7. Cranial endocast and braincase of Falcarius utahensis (referred specimen, UMNH VP 15001).

In (A) and (B) in left lateral, (C) and (D) in caudal, (E) dorsal, and (F) ventral view. Bone in (B) and (D) rendered transparent. Abbreviations: car, cerebral carotid artery canal; cvcm, caudal middle cerebral vein; fl, floccular lobe; lab, endosseous labyrinth; pfo, pituitary (hypophyseal) fossa; V1, ophthalmic branch of the trigeminal nerve canal; V2, maxillary branch of the trigeminal nerve canal; V3, mandibular branch of the trigeminal nerve canal; VI, abducens nerve canal; IX–XI, shared canal for the glossopharyngeal, vagus and spinal accessory nerve; XII, hypoglossal nerve canal.

Figure 8
Figure 8. Endosseous labyrinths (right side).

(A) Erlikosaurus andrewsi (IGM 100/111), (B) Nothronychus mckinleyi (AZMNH-2117, portions reconstructed from the left side shown in different color), (C) Falcarius utahensis (holotype specimen, UMNH VP 15000), (D) Falcarius utahensis (referred specimen, UMNH VP 15001). From left to right in lateral, dorsal, rostral and caudal view. Abbreviations: c, cochlear duct; crc, crus communis; csc, caudal semicircular canal; csca, ampulla of the caudal semicircular canal; fc, fenestra cochleae; ed, endolymphatic duct; fv, fenestra vestibuli; lsc, lateral semicircular canal; lsca, ampulla of the lateral semicircular canal; rsc, rostral semicircular canal; rsca, ampulla of the rostral semicircular canal.

Figure 9
Figure 9. Reptile encephalization quotient of Erlikosaurus andrewsi in comparison to several extant and extinct archosaurs.

Supplemented by data from , .

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Grants and funding

SL is supported by a doctoral fellowship by the Volkswagen Foundation (Volkswagen Stiftung), Hannover. LMW acknowledges funding support from the United States National Science Foundation (IBN-9601174, IBN-0343744, IOB-0517257, IOS-1050154) and the Ohio University Heritage College of Osteopathic Medicine. The Ohio Supercomputing Center also provided support. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.