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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

Left fused opisthotic/exoccipital, left prootic, and the fused basisphenoid/parasphenoid of NCSM 15728 derived from CT scans.(A) left fused opisthotic/exoccipital in posterior view; (B) left fused opisthotic/exoccipital in anterior view; (C) left fused opisthotic/exoccipital in lateral view; (D) left fused opisthotic/exoccipital in medial view; (E) left prootic in lateral view; (F) left prootic in medial view; (G) fused basisphenoid/parasphenoid in dorsal view; (H) fused basisphenoid/parasphenoid in ventral view; (I) fused basisphenoid/parasphenoid in left lateral view; (J) fused basisphenoid/parasphenoid in posterior view; (K) fused basisphenoid/parasphenoid in anterior view. The directional arrows indicate the orientation of the specimen in each view. Abbreviations: alp, anterolateral processes of basisphenoid; bpp, basipterygoid process; bpro, boss for articulation with proatlas; ci, crista interfenestralis; cn, cranial nerve; cpr, crista prootica; ct, crista tuberalis; cup, cutriform process; dor, dorsal; fm, foramen metoticum; fo, fenestra ovalis; fs, fossa subarcuata; lat, lateral; med, medial; oc, occipital condyle; pop, paroccipital process; post, posterior; prp, preotic pendant; sel, sella turcica; vcd, groove for the vena capitis dorsalis; vcms, groove for the vena cerebralis media secunda; ve, vestibule; vent, ventral. Scale bars equal 1 cm.
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fig-13: Left fused opisthotic/exoccipital, left prootic, and the fused basisphenoid/parasphenoid of NCSM 15728 derived from CT scans.(A) left fused opisthotic/exoccipital in posterior view; (B) left fused opisthotic/exoccipital in anterior view; (C) left fused opisthotic/exoccipital in lateral view; (D) left fused opisthotic/exoccipital in medial view; (E) left prootic in lateral view; (F) left prootic in medial view; (G) fused basisphenoid/parasphenoid in dorsal view; (H) fused basisphenoid/parasphenoid in ventral view; (I) fused basisphenoid/parasphenoid in left lateral view; (J) fused basisphenoid/parasphenoid in posterior view; (K) fused basisphenoid/parasphenoid in anterior view. The directional arrows indicate the orientation of the specimen in each view. Abbreviations: alp, anterolateral processes of basisphenoid; bpp, basipterygoid process; bpro, boss for articulation with proatlas; ci, crista interfenestralis; cn, cranial nerve; cpr, crista prootica; ct, crista tuberalis; cup, cutriform process; dor, dorsal; fm, foramen metoticum; fo, fenestra ovalis; fs, fossa subarcuata; lat, lateral; med, medial; oc, occipital condyle; pop, paroccipital process; post, posterior; prp, preotic pendant; sel, sella turcica; vcd, groove for the vena capitis dorsalis; vcms, groove for the vena cerebralis media secunda; ve, vestibule; vent, ventral. Scale bars equal 1 cm.

Mentions: The braincase of NSCM 15728 is slightly transversely crushed (Fig. 4), and demonstrates a lack of fusion between most of the individual bones (Fig. 11), with a few exceptions. Each opisthotic is fused indistinguishably with its exoccipital (Figs. 11A, 11B, 13A–13D), as is the general case in basal ornithischians (Norman et al., 2004), and the parasphenoid and the basisphenoid are indistinguishably fused (Figs. 11A, 11B, 11D, 13G–13I), which occurs in nearly all dinosaurs (Currie, 1997). The left opisthotic/exoccipital is slightly inset medially from its normal position (Fig. 11E), while the right opisthotic/exoccipital is displaced anteriorly and slightly medially (Fig. 4). The prootics, laterosphenoids, and the supraoccipital are all slightly displaced anteriorly, so that small gaps are present between each of these bones and most of their adjacent bones (Figs. 11A and 11B). There is no evidence of an ossified orbitosphenoid or presphenoid in NCSM 15728. The presence of an orbitosphenoid was noted in Parksosaurus (Galton, 1973: Figs. 2 and 3); however, its placement and morphology suggest that this is actually a slightly damaged palatine (C Boyd, pers. obs., 2011). This observation is supported by the fact that this bone was reconstructed in the same position the palatine occupies in NCSM 15728 (Galton, 1973: Fig. 5). Thus, the lack of an ossified orbitosphenoid in NCSM 15728 is not unexpected. In TLAM.BA.2014.027.0001 there are some fragmentary pieces of bone positioned anterior to the dorsal half of the right laterosphenoid that may represent part of an ossified orbitosphenoid, but exact identification of those fragments is difficult given their poor preservation.


The cranial anatomy of the neornithischian dinosaur Thescelosaurus neglectus.

Boyd CA - PeerJ (2014)

Left fused opisthotic/exoccipital, left prootic, and the fused basisphenoid/parasphenoid of NCSM 15728 derived from CT scans.(A) left fused opisthotic/exoccipital in posterior view; (B) left fused opisthotic/exoccipital in anterior view; (C) left fused opisthotic/exoccipital in lateral view; (D) left fused opisthotic/exoccipital in medial view; (E) left prootic in lateral view; (F) left prootic in medial view; (G) fused basisphenoid/parasphenoid in dorsal view; (H) fused basisphenoid/parasphenoid in ventral view; (I) fused basisphenoid/parasphenoid in left lateral view; (J) fused basisphenoid/parasphenoid in posterior view; (K) fused basisphenoid/parasphenoid in anterior view. The directional arrows indicate the orientation of the specimen in each view. Abbreviations: alp, anterolateral processes of basisphenoid; bpp, basipterygoid process; bpro, boss for articulation with proatlas; ci, crista interfenestralis; cn, cranial nerve; cpr, crista prootica; ct, crista tuberalis; cup, cutriform process; dor, dorsal; fm, foramen metoticum; fo, fenestra ovalis; fs, fossa subarcuata; lat, lateral; med, medial; oc, occipital condyle; pop, paroccipital process; post, posterior; prp, preotic pendant; sel, sella turcica; vcd, groove for the vena capitis dorsalis; vcms, groove for the vena cerebralis media secunda; ve, vestibule; vent, ventral. Scale bars equal 1 cm.
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Related In: Results  -  Collection

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Show All Figures
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fig-13: Left fused opisthotic/exoccipital, left prootic, and the fused basisphenoid/parasphenoid of NCSM 15728 derived from CT scans.(A) left fused opisthotic/exoccipital in posterior view; (B) left fused opisthotic/exoccipital in anterior view; (C) left fused opisthotic/exoccipital in lateral view; (D) left fused opisthotic/exoccipital in medial view; (E) left prootic in lateral view; (F) left prootic in medial view; (G) fused basisphenoid/parasphenoid in dorsal view; (H) fused basisphenoid/parasphenoid in ventral view; (I) fused basisphenoid/parasphenoid in left lateral view; (J) fused basisphenoid/parasphenoid in posterior view; (K) fused basisphenoid/parasphenoid in anterior view. The directional arrows indicate the orientation of the specimen in each view. Abbreviations: alp, anterolateral processes of basisphenoid; bpp, basipterygoid process; bpro, boss for articulation with proatlas; ci, crista interfenestralis; cn, cranial nerve; cpr, crista prootica; ct, crista tuberalis; cup, cutriform process; dor, dorsal; fm, foramen metoticum; fo, fenestra ovalis; fs, fossa subarcuata; lat, lateral; med, medial; oc, occipital condyle; pop, paroccipital process; post, posterior; prp, preotic pendant; sel, sella turcica; vcd, groove for the vena capitis dorsalis; vcms, groove for the vena cerebralis media secunda; ve, vestibule; vent, ventral. Scale bars equal 1 cm.
Mentions: The braincase of NSCM 15728 is slightly transversely crushed (Fig. 4), and demonstrates a lack of fusion between most of the individual bones (Fig. 11), with a few exceptions. Each opisthotic is fused indistinguishably with its exoccipital (Figs. 11A, 11B, 13A–13D), as is the general case in basal ornithischians (Norman et al., 2004), and the parasphenoid and the basisphenoid are indistinguishably fused (Figs. 11A, 11B, 11D, 13G–13I), which occurs in nearly all dinosaurs (Currie, 1997). The left opisthotic/exoccipital is slightly inset medially from its normal position (Fig. 11E), while the right opisthotic/exoccipital is displaced anteriorly and slightly medially (Fig. 4). The prootics, laterosphenoids, and the supraoccipital are all slightly displaced anteriorly, so that small gaps are present between each of these bones and most of their adjacent bones (Figs. 11A and 11B). There is no evidence of an ossified orbitosphenoid or presphenoid in NCSM 15728. The presence of an orbitosphenoid was noted in Parksosaurus (Galton, 1973: Figs. 2 and 3); however, its placement and morphology suggest that this is actually a slightly damaged palatine (C Boyd, pers. obs., 2011). This observation is supported by the fact that this bone was reconstructed in the same position the palatine occupies in NCSM 15728 (Galton, 1973: Fig. 5). Thus, the lack of an ossified orbitosphenoid in NCSM 15728 is not unexpected. In TLAM.BA.2014.027.0001 there are some fragmentary pieces of bone positioned anterior to the dorsal half of the right laterosphenoid that may represent part of an ossified orbitosphenoid, but exact identification of those fragments is difficult given their poor preservation.

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