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The cranial anatomy of the neornithischian dinosaur Thescelosaurus neglectus.

Boyd CA - PeerJ (2014)

Bottom Line: Published phylogenetic hypotheses of neornithischian dinosaur relationships often differ in the placement of the North American taxon Parksosaurus, with some recovering a close relationship with Thescelosaurus and others with the South American taxon Gasparinisaura, but never both at the same time.The new morphological observations presented herein, combined with re-examination of the holotype of Parksosaurus, suggest that Parksosaurus shares a closer relationship with Thescelosaurus than with Gasparinisaura, and that many of the features previously cited to support a relationship with the latter taxon are either also present in Thescelosaurus, are artifacts of preservation, or are the result of incomplete preparation and inaccurate interpretation of specimens.Additionally, the overall morphology of the skull and lower jaws of both Thescelosaurus and Parksosaurus also closely resemble the Asian taxa Changchunsaurus and Haya, though the interrelationships of these taxa have yet to be tested in a phylogenetic analysis that includes these new morphological data for T. neglectus.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Geology and Geological Engineering Sciences, South Dakota School of Mines and Technology , Rapid City, SD , USA.

ABSTRACT
Though the dinosaur Thescelosaurus neglectus was first described in 1913 and is known from the relatively fossiliferous Lance and Hell Creek formations in the Western Interior Basin of North America, the cranial anatomy of this species remains poorly understood. The only cranial material confidently referred to this species are three fragmentary bones preserved with the paratype, hindering attempts to understand the systematic relationships of this taxon within Neornithischia. Here the cranial anatomy of T. neglectus is fully described for the first time based on two specimens that include well-preserved cranial material (NCSM 15728 and TLAM.BA.2014.027.0001). Visual inspection of exposed cranial elements of these specimens is supplemented by detailed CT data from NCSM 15728 that enabled the examination of otherwise unexposed surfaces, facilitating a complete description of the cranial anatomy of this species. The skull of T. neglectus displays a unique combination of plesiomorphic and apomorphic traits. The premaxillary and 'cheek' tooth morphologies are relatively derived, though less so than the condition seen in basal iguanodontians, suggesting that the high tooth count present in the premaxillae, maxillae, and dentaries may be related to the extreme elongation of the skull of this species rather than a retention of the plesiomorphic condition. The morphology of the braincase most closely resembles the iguanodontians Dryosaurus and Dysalotosaurus, especially with regard to the morphology of the prootic. One autapomorphic feature is recognized for the first time, along with several additional cranial features that differentiate this species from the closely related and contemporaneous Thescelosaurus assiniboiensis. Published phylogenetic hypotheses of neornithischian dinosaur relationships often differ in the placement of the North American taxon Parksosaurus, with some recovering a close relationship with Thescelosaurus and others with the South American taxon Gasparinisaura, but never both at the same time. The new morphological observations presented herein, combined with re-examination of the holotype of Parksosaurus, suggest that Parksosaurus shares a closer relationship with Thescelosaurus than with Gasparinisaura, and that many of the features previously cited to support a relationship with the latter taxon are either also present in Thescelosaurus, are artifacts of preservation, or are the result of incomplete preparation and inaccurate interpretation of specimens. Additionally, the overall morphology of the skull and lower jaws of both Thescelosaurus and Parksosaurus also closely resemble the Asian taxa Changchunsaurus and Haya, though the interrelationships of these taxa have yet to be tested in a phylogenetic analysis that includes these new morphological data for T. neglectus.

No MeSH data available.


Related in: MedlinePlus

Squamosal and quadrate of Thescelosaurus neglectus(A) left squamosal of NCSM 15728 in lateral view; (B) right squamosal of NCSM 15728 in dorsal view; (C) right quadrate of TLAM.BA.2014.027.0001 in medial view; (D) right quadrate of TLAM.BA.2014.027.0001 in lateral view; (F) close up of the pterygoid wing on the left quadrate of NCSM 15728; (F) contact between the left squamosal and postorbital of NCSM 15728 in dorsal view; (G) foramen between the right quadrate and quadratojugal of NCSM 15728 in posterolateral view. The directional arrows indicate the orientation of the specimen in each view. Abbreviations: ant, anterior; aqj, articulation for quadratojugal; asq, articulation surface for squamosal; c, concretion; d, damage; dor, dorsal; dsq, dorsal projection of the anterior process of squ amosal; ju, jugal; jw, jugal wing; lat, lateral; lp, lateral process of posterior process of postorbital; med, medial; mp, medial projection of the posterior process of the postorbital; po, postorbital; pop, paroccipital process; poq, postquadratic process of squamosal; post, posterior; prq, prequadratic process; pw, pterygoid wing; pwf, pterygoid wing fossa; pwg, pterygoid wing ventral groove; qf, quadrate foramen; qj, quadratojugal; qu, quadrate; rsq, ventral ridge on squamosal; sed, sediment; so, supraoccipital; sq, squamosal; vent, ventral; vsq, ventral projection of the anterior process of the squamosal. Scale bars equal 1 cm.
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fig-8: Squamosal and quadrate of Thescelosaurus neglectus(A) left squamosal of NCSM 15728 in lateral view; (B) right squamosal of NCSM 15728 in dorsal view; (C) right quadrate of TLAM.BA.2014.027.0001 in medial view; (D) right quadrate of TLAM.BA.2014.027.0001 in lateral view; (F) close up of the pterygoid wing on the left quadrate of NCSM 15728; (F) contact between the left squamosal and postorbital of NCSM 15728 in dorsal view; (G) foramen between the right quadrate and quadratojugal of NCSM 15728 in posterolateral view. The directional arrows indicate the orientation of the specimen in each view. Abbreviations: ant, anterior; aqj, articulation for quadratojugal; asq, articulation surface for squamosal; c, concretion; d, damage; dor, dorsal; dsq, dorsal projection of the anterior process of squ amosal; ju, jugal; jw, jugal wing; lat, lateral; lp, lateral process of posterior process of postorbital; med, medial; mp, medial projection of the posterior process of the postorbital; po, postorbital; pop, paroccipital process; poq, postquadratic process of squamosal; post, posterior; prq, prequadratic process; pw, pterygoid wing; pwf, pterygoid wing fossa; pwg, pterygoid wing ventral groove; qf, quadrate foramen; qj, quadratojugal; qu, quadrate; rsq, ventral ridge on squamosal; sed, sediment; so, supraoccipital; sq, squamosal; vent, ventral; vsq, ventral projection of the anterior process of the squamosal. Scale bars equal 1 cm.

Mentions: TLAM.BA.2014.027.0001 (Figs. 8C, 8D; Table 1): Relatively complete, slightly transversely crushed skull missing the supraorbitals, accessary supraorbitals, right postorbital, right quadratojugal, most of the right jugal (anterior-most process preserved), and the entire lower jaws. Preserved postcranial elements consist of the left antlantal neural arch, the atlantal intercentrum, eight dorsal vertebrae, the sacrodorsal, three sacral vertebrae (all unfused), forty-three caudals, six partial dorsal ribs, nine chevrons, left scapulocoraoid, partial right and left pubes, right ischium, partial proximal right tibia, incomplete distal ends of right and left tibiae, partial right astragulus, right calcaneum, distal ends of right metatarsals III and IV, eight pedal phalanges, and additional unidentified material.


The cranial anatomy of the neornithischian dinosaur Thescelosaurus neglectus.

Boyd CA - PeerJ (2014)

Squamosal and quadrate of Thescelosaurus neglectus(A) left squamosal of NCSM 15728 in lateral view; (B) right squamosal of NCSM 15728 in dorsal view; (C) right quadrate of TLAM.BA.2014.027.0001 in medial view; (D) right quadrate of TLAM.BA.2014.027.0001 in lateral view; (F) close up of the pterygoid wing on the left quadrate of NCSM 15728; (F) contact between the left squamosal and postorbital of NCSM 15728 in dorsal view; (G) foramen between the right quadrate and quadratojugal of NCSM 15728 in posterolateral view. The directional arrows indicate the orientation of the specimen in each view. Abbreviations: ant, anterior; aqj, articulation for quadratojugal; asq, articulation surface for squamosal; c, concretion; d, damage; dor, dorsal; dsq, dorsal projection of the anterior process of squ amosal; ju, jugal; jw, jugal wing; lat, lateral; lp, lateral process of posterior process of postorbital; med, medial; mp, medial projection of the posterior process of the postorbital; po, postorbital; pop, paroccipital process; poq, postquadratic process of squamosal; post, posterior; prq, prequadratic process; pw, pterygoid wing; pwf, pterygoid wing fossa; pwg, pterygoid wing ventral groove; qf, quadrate foramen; qj, quadratojugal; qu, quadrate; rsq, ventral ridge on squamosal; sed, sediment; so, supraoccipital; sq, squamosal; vent, ventral; vsq, ventral projection of the anterior process of the squamosal. Scale bars equal 1 cm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4232843&req=5

fig-8: Squamosal and quadrate of Thescelosaurus neglectus(A) left squamosal of NCSM 15728 in lateral view; (B) right squamosal of NCSM 15728 in dorsal view; (C) right quadrate of TLAM.BA.2014.027.0001 in medial view; (D) right quadrate of TLAM.BA.2014.027.0001 in lateral view; (F) close up of the pterygoid wing on the left quadrate of NCSM 15728; (F) contact between the left squamosal and postorbital of NCSM 15728 in dorsal view; (G) foramen between the right quadrate and quadratojugal of NCSM 15728 in posterolateral view. The directional arrows indicate the orientation of the specimen in each view. Abbreviations: ant, anterior; aqj, articulation for quadratojugal; asq, articulation surface for squamosal; c, concretion; d, damage; dor, dorsal; dsq, dorsal projection of the anterior process of squ amosal; ju, jugal; jw, jugal wing; lat, lateral; lp, lateral process of posterior process of postorbital; med, medial; mp, medial projection of the posterior process of the postorbital; po, postorbital; pop, paroccipital process; poq, postquadratic process of squamosal; post, posterior; prq, prequadratic process; pw, pterygoid wing; pwf, pterygoid wing fossa; pwg, pterygoid wing ventral groove; qf, quadrate foramen; qj, quadratojugal; qu, quadrate; rsq, ventral ridge on squamosal; sed, sediment; so, supraoccipital; sq, squamosal; vent, ventral; vsq, ventral projection of the anterior process of the squamosal. Scale bars equal 1 cm.
Mentions: TLAM.BA.2014.027.0001 (Figs. 8C, 8D; Table 1): Relatively complete, slightly transversely crushed skull missing the supraorbitals, accessary supraorbitals, right postorbital, right quadratojugal, most of the right jugal (anterior-most process preserved), and the entire lower jaws. Preserved postcranial elements consist of the left antlantal neural arch, the atlantal intercentrum, eight dorsal vertebrae, the sacrodorsal, three sacral vertebrae (all unfused), forty-three caudals, six partial dorsal ribs, nine chevrons, left scapulocoraoid, partial right and left pubes, right ischium, partial proximal right tibia, incomplete distal ends of right and left tibiae, partial right astragulus, right calcaneum, distal ends of right metatarsals III and IV, eight pedal phalanges, and additional unidentified material.

Bottom Line: Published phylogenetic hypotheses of neornithischian dinosaur relationships often differ in the placement of the North American taxon Parksosaurus, with some recovering a close relationship with Thescelosaurus and others with the South American taxon Gasparinisaura, but never both at the same time.The new morphological observations presented herein, combined with re-examination of the holotype of Parksosaurus, suggest that Parksosaurus shares a closer relationship with Thescelosaurus than with Gasparinisaura, and that many of the features previously cited to support a relationship with the latter taxon are either also present in Thescelosaurus, are artifacts of preservation, or are the result of incomplete preparation and inaccurate interpretation of specimens.Additionally, the overall morphology of the skull and lower jaws of both Thescelosaurus and Parksosaurus also closely resemble the Asian taxa Changchunsaurus and Haya, though the interrelationships of these taxa have yet to be tested in a phylogenetic analysis that includes these new morphological data for T. neglectus.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Geology and Geological Engineering Sciences, South Dakota School of Mines and Technology , Rapid City, SD , USA.

ABSTRACT
Though the dinosaur Thescelosaurus neglectus was first described in 1913 and is known from the relatively fossiliferous Lance and Hell Creek formations in the Western Interior Basin of North America, the cranial anatomy of this species remains poorly understood. The only cranial material confidently referred to this species are three fragmentary bones preserved with the paratype, hindering attempts to understand the systematic relationships of this taxon within Neornithischia. Here the cranial anatomy of T. neglectus is fully described for the first time based on two specimens that include well-preserved cranial material (NCSM 15728 and TLAM.BA.2014.027.0001). Visual inspection of exposed cranial elements of these specimens is supplemented by detailed CT data from NCSM 15728 that enabled the examination of otherwise unexposed surfaces, facilitating a complete description of the cranial anatomy of this species. The skull of T. neglectus displays a unique combination of plesiomorphic and apomorphic traits. The premaxillary and 'cheek' tooth morphologies are relatively derived, though less so than the condition seen in basal iguanodontians, suggesting that the high tooth count present in the premaxillae, maxillae, and dentaries may be related to the extreme elongation of the skull of this species rather than a retention of the plesiomorphic condition. The morphology of the braincase most closely resembles the iguanodontians Dryosaurus and Dysalotosaurus, especially with regard to the morphology of the prootic. One autapomorphic feature is recognized for the first time, along with several additional cranial features that differentiate this species from the closely related and contemporaneous Thescelosaurus assiniboiensis. Published phylogenetic hypotheses of neornithischian dinosaur relationships often differ in the placement of the North American taxon Parksosaurus, with some recovering a close relationship with Thescelosaurus and others with the South American taxon Gasparinisaura, but never both at the same time. The new morphological observations presented herein, combined with re-examination of the holotype of Parksosaurus, suggest that Parksosaurus shares a closer relationship with Thescelosaurus than with Gasparinisaura, and that many of the features previously cited to support a relationship with the latter taxon are either also present in Thescelosaurus, are artifacts of preservation, or are the result of incomplete preparation and inaccurate interpretation of specimens. Additionally, the overall morphology of the skull and lower jaws of both Thescelosaurus and Parksosaurus also closely resemble the Asian taxa Changchunsaurus and Haya, though the interrelationships of these taxa have yet to be tested in a phylogenetic analysis that includes these new morphological data for T. neglectus.

No MeSH data available.


Related in: MedlinePlus