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

Lautenschlager S, Rayfield EJ, Altangerel P, Zanno LE, Witmer LM - PLoS ONE (2012)

Bottom Line: This specialized anatomy has been associated with a shift in dietary preferences and an adaptation to herbivory.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.In particular olfaction and hearing may have played an important role in foraging, predator evasion, and/or social complexity.

View Article: PubMed Central - PubMed

Affiliation: School of Earth Sciences, University of Bristol, Bristol, United Kingdom. glzsl@bristol.ac.uk

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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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.
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pone-0052289-g004: 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.

Mentions: In Erlikosaurus (Figure 3A–C), the forebrain region–most notably the olfactory apparatus and the cerebral hemispheres–is well differentiated and clearly demarcated. The olfactory tracts and bulbs are preserved only in Erlikosaurus. However, due to the lack of preserved or ossified sphenethmoid and mesethmoid elements [42] (compare Figure 4), the ventral extent of the olfactory apparatus is uncertain and has been reconstructed only tentatively as far as possible, tracing the ventral margins of frontal bones. The olfactory tracts are elongate and extend relatively far from the cerebral hemispheres and the actual brain. They are slightly downturned, following the shape of the skull roof. The olfactory bulbs are only moderately indicated by shallow impressions on the ventral surface of the frontals. They are of moderate size, as in other Maniraptoriformes (Struthiomimus altus, Deinonychus antirrhopus), for which endocranial casts are available [21]. In Falcarius, two incomplete frontals (UMNH VP 14524, 12525; [43]) show preserved, although only partial, impressions of olfactory tracts. Olfactory bulb size and tract length cannot be ascertained, but a considerable expansion of the olfactory apparatus is evident.


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

Lautenschlager S, Rayfield EJ, Altangerel P, Zanno LE, Witmer LM - PLoS ONE (2012)

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.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3526574&req=5

pone-0052289-g004: 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.
Mentions: In Erlikosaurus (Figure 3A–C), the forebrain region–most notably the olfactory apparatus and the cerebral hemispheres–is well differentiated and clearly demarcated. The olfactory tracts and bulbs are preserved only in Erlikosaurus. However, due to the lack of preserved or ossified sphenethmoid and mesethmoid elements [42] (compare Figure 4), the ventral extent of the olfactory apparatus is uncertain and has been reconstructed only tentatively as far as possible, tracing the ventral margins of frontal bones. The olfactory tracts are elongate and extend relatively far from the cerebral hemispheres and the actual brain. They are slightly downturned, following the shape of the skull roof. The olfactory bulbs are only moderately indicated by shallow impressions on the ventral surface of the frontals. They are of moderate size, as in other Maniraptoriformes (Struthiomimus altus, Deinonychus antirrhopus), for which endocranial casts are available [21]. In Falcarius, two incomplete frontals (UMNH VP 14524, 12525; [43]) show preserved, although only partial, impressions of olfactory tracts. Olfactory bulb size and tract length cannot be ascertained, but a considerable expansion of the olfactory apparatus is evident.

Bottom Line: This specialized anatomy has been associated with a shift in dietary preferences and an adaptation to herbivory.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.In particular olfaction and hearing may have played an important role in foraging, predator evasion, and/or social complexity.

View Article: PubMed Central - PubMed

Affiliation: School of Earth Sciences, University of Bristol, Bristol, United Kingdom. glzsl@bristol.ac.uk

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.

Show MeSH