Dunkleosteus amblyodoratus Carr & Hlavin 2010, SP. NOV.
Creators: name: Carr, Robert K.
name: Hlavin, William J.
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Placodermi
Arthrodira
Dunkleosteidae
Dunkleosteus
Dunkleosteus amblyodoratus

description: DUNKLEOSTEUS AMBLYODORATUS SP. NOV.  (FIGS 6, 7)  
 Diagnosis: A Dunkleosteus species possessing a tapered prehypophysial region of the parasphenoid, with anterolateral contact faces for posterior processes of the anterior superognathals.   
 Holotype: UM 101105 (Figs 6, 7), an isolated nuchal plate, with the transverse thickened portion of the left paranuchal plate and an incomplete parasphenoid plate.   
 Etymology: From amblys meaning blunt and doratos meaning spear (Greek); referring to the form of the prehypophysial region of the parasphenoid plate.   
 Occurrence and stratigraphy: Collected from Ontario, Canada (Fig. 2A). The exact locality data are not available, but the specimen was recovered from the Kettle Point Formation (Upper Devonian, but the exact stratigraphic level was not recorded; Fig. 2B). The specimen was found within a carbonate concretion that is typical for the Kettle Point Formation.   
SKULL ROOF AND PARASPHENOID  
 Dunkleosteus amblyodoratus sp. nov. is known only from fragmented parasphenoid, nuchal, and paranuchal plates. The external surface of the skull roof is worn. Tubercles are visible only in one area of the paranuchal plate where an outer layer is missing, revealing tubercles on a deeper surface (representing an earlier generation of tubercles). The punctate tubercles are evenly spaced.   
The nuchal plate (Nu; Fig. 6) outline is trapezoidal with a transverse anterior margin, with reduced indentations forming a shallow W-shape (suggesting an interdigitation with the central plates). The exact nature of this shape is unclear because of some weathering. The internal surface possesses a transverse occipital thickening (th.occ; Fig. 6A) that is continuous with that of the paranuchal plate. Double pits (pt.u; Fig. 6A) are present and bounded anteriorly by the nuchal thickening (th.n; Fig. 6A), and posteriorly by a well-developed transverse ridge (p.tr.r; Fig. 6A). Individual pits are separated by a median septum (m.sept; Fig. 6A) that does not cross the posterior transverse ridge. A posterior process (p.pr; Fig. 6A, C) is present, and is bounded laterally by shallow paired fossae (f.lv; Fig. 6B).  
Only the transverse occipital thickening of the paranuchal plate is preserved (PNu; Fig. 6). The thickening is massive and continues to the lateral articular fossa (laf; Fig. 6C). Only a portion of the left fossa remains, but it suggests the presence of a large and well-developed ginglymoid articulation between the head and thoracic armour.  
The parasphenoid (Psp; Fig. 7) is incomplete, with only its anterior half preserved. The prehypophysial region (pre.reg; Fig. 7) is tapered, and is as long as it is wide. The lateral edges of the prehypophysial region are thickened, providing possible contact facets for the anterior superognathal plates (cf.ASG; Fig. 7).
description: Published as part of Carr, Robert K. & Hlavin, William J., 2010, Two new species of Dunkleosteus Lehman, 1956, from the Ohio Shale Formation (USA, Famennian) and the Kettle Point Formation (Canada, Upper Devonian), and a cladistic analysis of the Eubrachythoraci (Placodermi, Arthrodira), pp. 195-222 in Zoological Journal of the Linnean Society 159 (1) on pages 204-205, DOI: 10.1111/j.1096-3642.2009.00578.x, http://zenodo.org/record/10114686