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Supplementary cranial description of the types of Edmontosaurus regalis (Ornithischia: Hadrosauridae), with comments on the phylogenetics and biogeography of Hadrosaurinae

View Article: PubMed Central - PubMed

ABSTRACT

The cranial anatomy of the flat-skulled hadrosaurine Edmontosaurus regalis (Ornithischia: Hadrosauridae) is extensively described here, based on the holotype and paratype collected from the middle part of the Horseshoe Canyon Formation in southern Alberta. Focus is given to previously undocumented features of ontogenetic and phylogenetic importance. This description facilitates overall osteological comparisons between E. regalis and other hadrosaurids (especially E. annectens), and revises the diagnosis of E. regalis, to which a new autapomorphy (the dorsal half of the jugal anterior process bearing a sharp posterolateral projection into the orbit) is added. We consider the recently named Ugrunaaluk kuukpikensis from the upper Campanian/lower Maastrichtian of Alaska a nomen dubium, and conservatively regard the Alaskan material as belonging to Edmontosaurus sp.. A phylogenetic analysis of Hadrosauroidea using maximum parsimony further corroborates the sister-taxon relationship between E. regalis and E. annectens. In the strict consensus tree, Hadrosaurus foulkii occurs firmly within the clade comprising all non-lambeosaurine hadrosaurids, supporting the taxonomic scheme that divides Hadrosauridae into Hadrosaurinae and Lambeosaurinae. Within Edmontosaurini, Kerberosaurus is posited as the sister taxon to the clade of Shantungosaurus + Edmontosaurus. The biogeographic reconstruction of Hadrosaurinae in light of the time-calibrated cladogram and probability calculation of ancestral areas for all internal nodes reveals a significantly high probability for the North American origin of the clade. However, the Laramidia–Appalachia dispersals around the Santonian–Campanian boundary, inferred from the biogeographic scenario for the North American origin of Hadrosaurinae, are in conflict with currently accepted paleogeographic models. By contrast, the Asian origin of Hadrosaurinae with its relatively low probability resulting from the biogeographic analysis is worth seriously considering, despite the lack of fossil material from the Santonian and lower Campanian of Asia. Extra fossil collecting in appropriate geographic locations and stratigraphic intervals of Asia and Europe will help to clarify the biogeographic dynamics of hadrosaurine dinosaurs in the near future.

No MeSH data available.


Anterior region of the neurocranium of Edmontosaurus regalis (CMN 2289) in left anterolateral (A) and right anterolateral (B) views. Posterior region of the neurocranium of Edmontosaurus regalis (CMN 2289) in left lateral (C) and right lateral (D) views.
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pone.0175253.g015: Anterior region of the neurocranium of Edmontosaurus regalis (CMN 2289) in left anterolateral (A) and right anterolateral (B) views. Posterior region of the neurocranium of Edmontosaurus regalis (CMN 2289) in left lateral (C) and right lateral (D) views.

Mentions: Orbitosphenoid–presphenoid complex (Figs 4, 10–12 and 15). The presphenoid and orbitosphenoid are fused into a single unit in CMN 2288 and CMN 2289. The two bones form the anterodorsal part of the lateral wall of the braincase, and enclose most of the ventral region of the prosencephalon. The left and right presphenoids converge ventromedially to meet each other along the sagittal plane, and produce a reniform anterior exit of the olfactory nerve, together with the paired frontals. The ventral half of the orbitosphenoid is pierced by a large, oval foramen for the optic nerve (CN II), just above its nearly horizontal, weakly sinuous suture with the basisphenoid–parasphenoid complex. The posteroventral corner of the orbitosphenoid is slightly notched to form the anterodorsal margin of the circular foramen for the occulomotor nerve (CN III) and abducens nerve (CN VI). This foramen is located immediately laterodorsal to the pituitary fossa formed by the basisphenoid. In CMN 2288, the paired presphenoids contact the median cultriform process of the parasphenoid ventrally along the straight lateral sutures; the dorsal region of the orbitosphenoid is perforated by a small foramen that probably conducted the trochlear nerve (CN IV).


Supplementary cranial description of the types of Edmontosaurus regalis (Ornithischia: Hadrosauridae), with comments on the phylogenetics and biogeography of Hadrosaurinae
Anterior region of the neurocranium of Edmontosaurus regalis (CMN 2289) in left anterolateral (A) and right anterolateral (B) views. Posterior region of the neurocranium of Edmontosaurus regalis (CMN 2289) in left lateral (C) and right lateral (D) views.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383305&req=5

pone.0175253.g015: Anterior region of the neurocranium of Edmontosaurus regalis (CMN 2289) in left anterolateral (A) and right anterolateral (B) views. Posterior region of the neurocranium of Edmontosaurus regalis (CMN 2289) in left lateral (C) and right lateral (D) views.
Mentions: Orbitosphenoid–presphenoid complex (Figs 4, 10–12 and 15). The presphenoid and orbitosphenoid are fused into a single unit in CMN 2288 and CMN 2289. The two bones form the anterodorsal part of the lateral wall of the braincase, and enclose most of the ventral region of the prosencephalon. The left and right presphenoids converge ventromedially to meet each other along the sagittal plane, and produce a reniform anterior exit of the olfactory nerve, together with the paired frontals. The ventral half of the orbitosphenoid is pierced by a large, oval foramen for the optic nerve (CN II), just above its nearly horizontal, weakly sinuous suture with the basisphenoid–parasphenoid complex. The posteroventral corner of the orbitosphenoid is slightly notched to form the anterodorsal margin of the circular foramen for the occulomotor nerve (CN III) and abducens nerve (CN VI). This foramen is located immediately laterodorsal to the pituitary fossa formed by the basisphenoid. In CMN 2288, the paired presphenoids contact the median cultriform process of the parasphenoid ventrally along the straight lateral sutures; the dorsal region of the orbitosphenoid is perforated by a small foramen that probably conducted the trochlear nerve (CN IV).

View Article: PubMed Central - PubMed

ABSTRACT

The cranial anatomy of the flat-skulled hadrosaurine Edmontosaurus regalis (Ornithischia: Hadrosauridae) is extensively described here, based on the holotype and paratype collected from the middle part of the Horseshoe Canyon Formation in southern Alberta. Focus is given to previously undocumented features of ontogenetic and phylogenetic importance. This description facilitates overall osteological comparisons between E. regalis and other hadrosaurids (especially E. annectens), and revises the diagnosis of E. regalis, to which a new autapomorphy (the dorsal half of the jugal anterior process bearing a sharp posterolateral projection into the orbit) is added. We consider the recently named Ugrunaaluk kuukpikensis from the upper Campanian/lower Maastrichtian of Alaska a nomen dubium, and conservatively regard the Alaskan material as belonging to Edmontosaurus sp.. A phylogenetic analysis of Hadrosauroidea using maximum parsimony further corroborates the sister-taxon relationship between E. regalis and E. annectens. In the strict consensus tree, Hadrosaurus foulkii occurs firmly within the clade comprising all non-lambeosaurine hadrosaurids, supporting the taxonomic scheme that divides Hadrosauridae into Hadrosaurinae and Lambeosaurinae. Within Edmontosaurini, Kerberosaurus is posited as the sister taxon to the clade of Shantungosaurus + Edmontosaurus. The biogeographic reconstruction of Hadrosaurinae in light of the time-calibrated cladogram and probability calculation of ancestral areas for all internal nodes reveals a significantly high probability for the North American origin of the clade. However, the Laramidia–Appalachia dispersals around the Santonian–Campanian boundary, inferred from the biogeographic scenario for the North American origin of Hadrosaurinae, are in conflict with currently accepted paleogeographic models. By contrast, the Asian origin of Hadrosaurinae with its relatively low probability resulting from the biogeographic analysis is worth seriously considering, despite the lack of fossil material from the Santonian and lower Campanian of Asia. Extra fossil collecting in appropriate geographic locations and stratigraphic intervals of Asia and Europe will help to clarify the biogeographic dynamics of hadrosaurine dinosaurs in the near future.

No MeSH data available.