Abstract
Well-preserved specimens of an undescribed species of arthrodiran placoderm, Groenlandaspis howittensis sp. nov. (Middle Devonian of Victoria, Australia), reveals previously unknown information on the dermal skeleton, body-shape and tooth arcade of the wide-spread genus Groenlandaspis. The new material includes, dual pineal plates, extrascapular plates, and cheek bones cheek bones showing the presence of cutaneous sensory organs. The anterior supragnathal, usually a paired element in arthrodires, is a fused medial bone in G. howittensis sp. nov. It is positioned anterior to the occlusion of the mouth between the lower jaw (infragnathals) and upper jaw (posterior supragnathals) bones, indicating a specialised feeding mechanism and broadening the known diversity of placoderm dental morphologies. G. howittensis sp. nov. differs from all other groenlandaspidids by a less pronounced posterior expansion of the nuchal plate; the shape of the posterior dorsolateral plate and the presence of a short accessory canal on the anterior dorsolateral plate. A new phylogenetic analysis positions Groenlandaspididae in a monophyly with the phlyctaeniid families Arctolepidae and Arctaspdidae, however, the specific intrarelationships of groenlandaspidids remain poorly resolved.
Competing Interest Statement
The authors have declared no competing interest.
Institutional Abbreviations
- NMV
- Museum of Victoria, Melbourne, Australia
- AMF
- Australian Museum, Sydney, Australia
- ANU
- Australian National University, Canberra, Australia
Anatomical Abbreviations
- ab
- annular bourrelet
- a.c
- aberrant canal
- acc
- accessory canal
- ADL
- anterior dorsolateral plate
- af
- anal fin
- AL
- anterior lateral plate
- AMV
- anterior median ventral plate
- APi
- anterior pineal plate
- ASG
- anterior supragnathal
- AVL
- anterior ventrolateral plate
- C
- central plate
- cf.ADL
- contact face for the anterior dorsolateral plate
- cf.AMV
- contact face for the anterior median ventral plate
- cf,MD
- contact face for the median dorsal plate
- cf.PDL
- contact face for the posterior dorsolateral plate
- cf.IL
- contact face for the interolateral plate
- cf.PMV
- contact face for the posterior median ventral plate
- cf.PVL
- contact face for the posterior ventrolateral plate
- cf.Sp
- contact face for the spinal plate
- csc
- central sensory canal
- cr.PNu
- paranuchal crista
- cuso
- cutaneous sensory organ
- df
- dorsal fin
- end.d
- endolymphatic duct
- Esc
- extrascapular plates
- Esc.c
- extracapsular plate canal
- if.pt
- infranuchal pit
- IG
- infragnathal
- IL
- interolateral plate
- il.proc
- iliac process of the pelvic gridle
- ioc
- infraorbital canal
- kd
- articular condyle
- lc
- lateral canal
- l.infsp
- infraspinal lamina
- MD
- median dorsal plate
- mpl
- median pit line
- Nu
- nuchal plate
- oa.AVL
- overlap area for the anterior ventrolateral plate
- oa,C
- overlap area for the central plate
- oa.IL
- overlap area for interolateral plate
- oa.M
- overlap area for the marginal plate
- oa.N
- overlap area for the nuchal plate
- oa.PL
- overlap area for the posterior lateral
- oa.PVL
- overlap area for the posterior ventrolateral plate
- occ
- occipital cross commissure
- orb
- orbit
- pap
- para-articular process
- PDL
- posterior dorsolateral plate
- pdl
- posterior descending lamina
- pect.f
- pectoral fin
- pelv
- basal plate of the pelvic girdle
- pelv.f
- pelvic fin
- PL
- posterior lateral plate
- PPi
- posterior pineal plate
- ppl
- posterior pit line
- ppt
- pineal pit
- psoc
- post suborbital canal
- PM
- post marginal plate
- pmc
- postmarginal canal
- pms
- post median scute
- PMV
- posterior median ventral plate
- PNu
- paranuchal plate
- PrO
- preorbital plate
- PSG
- posterior supragnathal
- PSO
- post suborbital plate
- Psph
- parasphenoid
- PtO
- postorbital plate
- PVL
- posterior ventrolateral plate
- R
- rostral plate
- SM
- submarginal
- SO
- suborbital
- soc
- supraorbital canal
- sorc
- supraoral canal
- Sp
- spinal plate
- suo.v
- supra orbital vault
- symph.s
- symphysial surface
- v.gr
- ventral groove.
