Limits...
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.


Left and right jugals of Edmontosaurus regalis (CMN 2289) in lateral (A, B) and medial (C, D) views. Close-ups of the jugal anterior process of CMN 2288 in lateral (E) and posterolateral (F) views. Left and right quadratojugals of Edmontosaurus regalis (CMN 2289) in lateral (G, H) and medial (I, J) views. The sharp posterolateral projection of the jugal along the orbital margin is indicated by an arrow.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5383305&req=5

pone.0175253.g008: Left and right jugals of Edmontosaurus regalis (CMN 2289) in lateral (A, B) and medial (C, D) views. Close-ups of the jugal anterior process of CMN 2288 in lateral (E) and posterolateral (F) views. Left and right quadratojugals of Edmontosaurus regalis (CMN 2289) in lateral (G, H) and medial (I, J) views. The sharp posterolateral projection of the jugal along the orbital margin is indicated by an arrow.

Mentions: Jugal (Figs 3, 4 and 8). As in other hadrosauroids, the jugal is bowed laterally and mediolaterally compressed between its contacts with the maxilla anteriorly and quadratojugal posteriorly [38, 39]. This triradiate bone has a dorsoventrally expanded, asymmetrically spade-shaped anterior process that tapers anteriorly to a stout triangular apex. In CMN 2288, the maxilla-lacrimal contact is laterally covered by the jugal. The anterior apex occurs within the dorsal half of the anterior process as in Gryposaurus (e.g. MOR 478-6-10-87-2), Kundurosaurus (e.g. AENM 2/921-2), and Prosaurolophus (e.g. CMN 2870), but is slightly shorter than that of these taxa. By contrast, the extremely elongate anterior apex is located at the mid-height of the subtriangular anterior process of the jugal in Acristavus, Maiasaura, and Brachylophosaurus. Posterior to the apex, the anterodorsal surface of the anterior process in both CMN 2288 and CMN 2289 is modestly anteroventrally inclined and transversely narrow, forming an angle of 40° with the horizontal. The surface is gently excavated to receive the lacrimal. The posterodorsal part of the anterior process broadens mediolaterally and deepens dorsoventrally, where it is remarkably flared posterolaterally to form a sharp projection that invades the orbital margin. In lateral view, the convex ventral edge of the anterior process is shallowly arcuate, and is comparable to that in Saurolophini. Medially, the rugose contact surface for the maxilla is posteriorly delineated by the prominent, dorsoventrally oriented, weakly wavy posteromedial margin of the anterior process. The dorsal half of the margin is formed by the narrow, strip-like palatine sutural surface that contrasts with the relatively wide, lunate equivalent in many lambeosaurines, such as Amurosaurus riabinini [40].


Supplementary cranial description of the types of Edmontosaurus regalis (Ornithischia: Hadrosauridae), with comments on the phylogenetics and biogeography of Hadrosaurinae
Left and right jugals of Edmontosaurus regalis (CMN 2289) in lateral (A, B) and medial (C, D) views. Close-ups of the jugal anterior process of CMN 2288 in lateral (E) and posterolateral (F) views. Left and right quadratojugals of Edmontosaurus regalis (CMN 2289) in lateral (G, H) and medial (I, J) views. The sharp posterolateral projection of the jugal along the orbital margin is indicated by an arrow.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0175253.g008: Left and right jugals of Edmontosaurus regalis (CMN 2289) in lateral (A, B) and medial (C, D) views. Close-ups of the jugal anterior process of CMN 2288 in lateral (E) and posterolateral (F) views. Left and right quadratojugals of Edmontosaurus regalis (CMN 2289) in lateral (G, H) and medial (I, J) views. The sharp posterolateral projection of the jugal along the orbital margin is indicated by an arrow.
Mentions: Jugal (Figs 3, 4 and 8). As in other hadrosauroids, the jugal is bowed laterally and mediolaterally compressed between its contacts with the maxilla anteriorly and quadratojugal posteriorly [38, 39]. This triradiate bone has a dorsoventrally expanded, asymmetrically spade-shaped anterior process that tapers anteriorly to a stout triangular apex. In CMN 2288, the maxilla-lacrimal contact is laterally covered by the jugal. The anterior apex occurs within the dorsal half of the anterior process as in Gryposaurus (e.g. MOR 478-6-10-87-2), Kundurosaurus (e.g. AENM 2/921-2), and Prosaurolophus (e.g. CMN 2870), but is slightly shorter than that of these taxa. By contrast, the extremely elongate anterior apex is located at the mid-height of the subtriangular anterior process of the jugal in Acristavus, Maiasaura, and Brachylophosaurus. Posterior to the apex, the anterodorsal surface of the anterior process in both CMN 2288 and CMN 2289 is modestly anteroventrally inclined and transversely narrow, forming an angle of 40° with the horizontal. The surface is gently excavated to receive the lacrimal. The posterodorsal part of the anterior process broadens mediolaterally and deepens dorsoventrally, where it is remarkably flared posterolaterally to form a sharp projection that invades the orbital margin. In lateral view, the convex ventral edge of the anterior process is shallowly arcuate, and is comparable to that in Saurolophini. Medially, the rugose contact surface for the maxilla is posteriorly delineated by the prominent, dorsoventrally oriented, weakly wavy posteromedial margin of the anterior process. The dorsal half of the margin is formed by the narrow, strip-like palatine sutural surface that contrasts with the relatively wide, lunate equivalent in many lambeosaurines, such as Amurosaurus riabinini [40].

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.