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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

Posterior jaw elements of NCSM 15728 derived in part from CT scans.(A) photograph of the right post-dentary jaw elements in natural position; (B) left angular in lateral view; (C) left angular in medial view; (D) left angular in ventral view; (E) left surangular in lateral view; (F) left surangular in medial view; (G) left surangular in dorsal view; (H) left surangular in ventral view. The directional arrows indicate the orientation of the specimen in each view. Abbreviations: aa, articulation surface for angular; an, angular; ant, anterior; bo, basioccipital; ca, articulation surface for coronoid; cp, coronoid process; da, articulation surface for dentary; de, dentary; dor, dorsal; ju, jugal; lat, lateral; lds, lateral depression of surangular; lpf, lateral process foramen; lps, lateral process of surangular; med, medial; mps, medial process of surangular; paa, prearticular articulation surface; post, posterior; qj, quadratojugal; qu, quadrate; rp, retroarticular process; sas, splenial articulations surface; sf, surangular foramen; su, surangular; vent, ventral. Scale bar in (A) equals 5 cm. Scale bars in (B) through (H) equal 1 cm.
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fig-15: Posterior jaw elements of NCSM 15728 derived in part from CT scans.(A) photograph of the right post-dentary jaw elements in natural position; (B) left angular in lateral view; (C) left angular in medial view; (D) left angular in ventral view; (E) left surangular in lateral view; (F) left surangular in medial view; (G) left surangular in dorsal view; (H) left surangular in ventral view. The directional arrows indicate the orientation of the specimen in each view. Abbreviations: aa, articulation surface for angular; an, angular; ant, anterior; bo, basioccipital; ca, articulation surface for coronoid; cp, coronoid process; da, articulation surface for dentary; de, dentary; dor, dorsal; ju, jugal; lat, lateral; lds, lateral depression of surangular; lpf, lateral process foramen; lps, lateral process of surangular; med, medial; mps, medial process of surangular; paa, prearticular articulation surface; post, posterior; qj, quadratojugal; qu, quadrate; rp, retroarticular process; sas, splenial articulations surface; sf, surangular foramen; su, surangular; vent, ventral. Scale bar in (A) equals 5 cm. Scale bars in (B) through (H) equal 1 cm.

Mentions: The anterior portion of the surangular is slightly medially deflected in dorsal view (Fig. 15G), mediolaterally thin, and was situated medial to the dentary (Fig. 15A). The anterior two-thirds of the ventral margin angles medioventrally and was overlapped laterally by the lateral wall of the angular (Fig. 15H). The dorsal margin of the surangular is convex in lateral view (Fig. 15E), which is the basal ornithischian condition. The dorsal-most portion of the surangular is triangular in lateral view, is convex medially, and forms the posterodorsal portion of the coronoid eminence (Fig. 16A). The anterodorsal margin contacted the dentary along its lateral half and the coronoid along its medial half.


The cranial anatomy of the neornithischian dinosaur Thescelosaurus neglectus.

Boyd CA - PeerJ (2014)

Posterior jaw elements of NCSM 15728 derived in part from CT scans.(A) photograph of the right post-dentary jaw elements in natural position; (B) left angular in lateral view; (C) left angular in medial view; (D) left angular in ventral view; (E) left surangular in lateral view; (F) left surangular in medial view; (G) left surangular in dorsal view; (H) left surangular in ventral view. The directional arrows indicate the orientation of the specimen in each view. Abbreviations: aa, articulation surface for angular; an, angular; ant, anterior; bo, basioccipital; ca, articulation surface for coronoid; cp, coronoid process; da, articulation surface for dentary; de, dentary; dor, dorsal; ju, jugal; lat, lateral; lds, lateral depression of surangular; lpf, lateral process foramen; lps, lateral process of surangular; med, medial; mps, medial process of surangular; paa, prearticular articulation surface; post, posterior; qj, quadratojugal; qu, quadrate; rp, retroarticular process; sas, splenial articulations surface; sf, surangular foramen; su, surangular; vent, ventral. Scale bar in (A) equals 5 cm. Scale bars in (B) through (H) equal 1 cm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig-15: Posterior jaw elements of NCSM 15728 derived in part from CT scans.(A) photograph of the right post-dentary jaw elements in natural position; (B) left angular in lateral view; (C) left angular in medial view; (D) left angular in ventral view; (E) left surangular in lateral view; (F) left surangular in medial view; (G) left surangular in dorsal view; (H) left surangular in ventral view. The directional arrows indicate the orientation of the specimen in each view. Abbreviations: aa, articulation surface for angular; an, angular; ant, anterior; bo, basioccipital; ca, articulation surface for coronoid; cp, coronoid process; da, articulation surface for dentary; de, dentary; dor, dorsal; ju, jugal; lat, lateral; lds, lateral depression of surangular; lpf, lateral process foramen; lps, lateral process of surangular; med, medial; mps, medial process of surangular; paa, prearticular articulation surface; post, posterior; qj, quadratojugal; qu, quadrate; rp, retroarticular process; sas, splenial articulations surface; sf, surangular foramen; su, surangular; vent, ventral. Scale bar in (A) equals 5 cm. Scale bars in (B) through (H) equal 1 cm.
Mentions: The anterior portion of the surangular is slightly medially deflected in dorsal view (Fig. 15G), mediolaterally thin, and was situated medial to the dentary (Fig. 15A). The anterior two-thirds of the ventral margin angles medioventrally and was overlapped laterally by the lateral wall of the angular (Fig. 15H). The dorsal margin of the surangular is convex in lateral view (Fig. 15E), which is the basal ornithischian condition. The dorsal-most portion of the surangular is triangular in lateral view, is convex medially, and forms the posterodorsal portion of the coronoid eminence (Fig. 16A). The anterodorsal margin contacted the dentary along its lateral half and the coronoid along its medial half.

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