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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

Skull of NCSM 15728 in right lateral view.(A) diagram highlighting the contacts between the bones on the right side of skull; (B) illustration of right side of skull; (C) photograph of right side of skull. In (A) and (B), grey regions indicate the presence of matrix on the specimen. Abbreviations: an, angular; asor, accessory supraorbital; bo, basioccipital; de, dentary; eo, fused opisthotic/exoccipital; fr, frontal; ju, jugal; la, lacrimal; mx, maxilla; na, nasal; pd, predentary; pf, prefrontal; pm, premaxilla; po, postorbital; pop, paroccipital process; qj, quadratojugal; qu, quadrate; sor, supraorbital; sq, squamosal; su, surangular. Scale bars equal 10 cm.
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fig-1: Skull of NCSM 15728 in right lateral view.(A) diagram highlighting the contacts between the bones on the right side of skull; (B) illustration of right side of skull; (C) photograph of right side of skull. In (A) and (B), grey regions indicate the presence of matrix on the specimen. Abbreviations: an, angular; asor, accessory supraorbital; bo, basioccipital; de, dentary; eo, fused opisthotic/exoccipital; fr, frontal; ju, jugal; la, lacrimal; mx, maxilla; na, nasal; pd, predentary; pf, prefrontal; pm, premaxilla; po, postorbital; pop, paroccipital process; qj, quadratojugal; qu, quadrate; sor, supraorbital; sq, squamosal; su, surangular. Scale bars equal 10 cm.

Mentions: NCSM 15728 was collected in 1999 from Hell Creek Formation sediments in Harding County, South Dakota. This specimen includes much of the axial skeleton, part of the appendicular skeleton (largely from the right side), and a three-dimensionally preserved skull missing only part of the left quadratojugal (Fig. 1). Despite the excellent condition of this specimen and the poor understanding of the cranial anatomy of Thescelosaurus, prior research on NCSM 15728 focused on the possible preservation of soft tissue structures in the specimen (Fisher et al., 2000; Rowe, McBride & Sereno, 2001; Russell et al., 2001; Cleland, Stoskopf & Schweitzer, 2011) and the histology, morphology, and osteogenesis of de novo ossifications associated with the anterior dorsal ribs (Boyd, Cleland & Novas, 2011). NCSM 15728 was originally referred to Thescelosaurus neglectus by Fisher et al. (2000) based on general similarity to the types, and Boyd et al. (2009) noted that the cranial morphology of NCSM 15728 was consistent with the paratype of T. neglectus and distinct from the holotype of T. assiniboiensis. However, Boyd et al. (2009) referred NCSM 15728 to Thescelosaurus incertae sedis because it could not be sufficiently compared to the type material of T. garbanii (LACM 33542).


The cranial anatomy of the neornithischian dinosaur Thescelosaurus neglectus.

Boyd CA - PeerJ (2014)

Skull of NCSM 15728 in right lateral view.(A) diagram highlighting the contacts between the bones on the right side of skull; (B) illustration of right side of skull; (C) photograph of right side of skull. In (A) and (B), grey regions indicate the presence of matrix on the specimen. Abbreviations: an, angular; asor, accessory supraorbital; bo, basioccipital; de, dentary; eo, fused opisthotic/exoccipital; fr, frontal; ju, jugal; la, lacrimal; mx, maxilla; na, nasal; pd, predentary; pf, prefrontal; pm, premaxilla; po, postorbital; pop, paroccipital process; qj, quadratojugal; qu, quadrate; sor, supraorbital; sq, squamosal; su, surangular. Scale bars equal 10 cm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig-1: Skull of NCSM 15728 in right lateral view.(A) diagram highlighting the contacts between the bones on the right side of skull; (B) illustration of right side of skull; (C) photograph of right side of skull. In (A) and (B), grey regions indicate the presence of matrix on the specimen. Abbreviations: an, angular; asor, accessory supraorbital; bo, basioccipital; de, dentary; eo, fused opisthotic/exoccipital; fr, frontal; ju, jugal; la, lacrimal; mx, maxilla; na, nasal; pd, predentary; pf, prefrontal; pm, premaxilla; po, postorbital; pop, paroccipital process; qj, quadratojugal; qu, quadrate; sor, supraorbital; sq, squamosal; su, surangular. Scale bars equal 10 cm.
Mentions: NCSM 15728 was collected in 1999 from Hell Creek Formation sediments in Harding County, South Dakota. This specimen includes much of the axial skeleton, part of the appendicular skeleton (largely from the right side), and a three-dimensionally preserved skull missing only part of the left quadratojugal (Fig. 1). Despite the excellent condition of this specimen and the poor understanding of the cranial anatomy of Thescelosaurus, prior research on NCSM 15728 focused on the possible preservation of soft tissue structures in the specimen (Fisher et al., 2000; Rowe, McBride & Sereno, 2001; Russell et al., 2001; Cleland, Stoskopf & Schweitzer, 2011) and the histology, morphology, and osteogenesis of de novo ossifications associated with the anterior dorsal ribs (Boyd, Cleland & Novas, 2011). NCSM 15728 was originally referred to Thescelosaurus neglectus by Fisher et al. (2000) based on general similarity to the types, and Boyd et al. (2009) noted that the cranial morphology of NCSM 15728 was consistent with the paratype of T. neglectus and distinct from the holotype of T. assiniboiensis. However, Boyd et al. (2009) referred NCSM 15728 to Thescelosaurus incertae sedis because it could not be sufficiently compared to the type material of T. garbanii (LACM 33542).

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