Plourdosteus

Plourdosteus is an extinct genus of placoderm arthrodire which was relatively widespread in Euramerica during the Givetian to Frasnian ages of the Devonian.^[1] It was a small placoderm, with P. canadensis specimen MNHM 2-177 measuring 37.5 cm (14.8 in) long.^[2]

Plourdosteus Temporal range: Devonian: Givetian–Frasnian, 391.8–374.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Various species of Plourdosteus, from Late Devonian of Canada, Russia and Baltic countries
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	†Placodermi
Order:	†Arthrodira
Suborder:	†Brachythoraci
Family:	†Panxiosteidae
Genus:	†Plourdosteus Ørvig, 1951
Species
Plourdosteus canadensis (Woodward, 1892) Plourdosteus livonicus (Eastman, 1896) Plourdosteus mironovi (Obruchev, 1933) Plourdosteus trautscholdi (Eastman, 1897)

Artist's reconstruction of Plourdosteus trautscholdi

Etymology

The name Plourdosteus commemorates the Plourde family at Miguasha National Park.^[3]

Taxonomy

Plourdosteus was previously assigned to the family Plourdosteidae within the Coccosteomorphi. However, subsequent studies found the family Plourdosteidae to be polyphyletic and should be dismissed. Plourdosteus was then proposed to be a member of Panxiosteidae.^[4][5] In the 2010 Carr & Hlavin phylogenetic study, Panxiosteidae was recognized as the sister taxon to the family Dunkleosteidae, which together comprised the superfamily Dunkleosteoidea (one of the three major clades of Eubrachythoraci).^[4]

The phylogeny of Plourdosteus within Panxiosteidae is shown in the cladogram below from the 2013 Zhu & Zhu study:^[5]

Eubrachythoraci	Coccosteomorphi Coccosteus cuspidatus Harrytoombsia elegans Mcnamaraspis kaprios Incisoscutoidea Compagopiscis croucheri Incisoscutum ritchiei Incisoscutum sarahae Camuropiscidae Latocamurus coulthardi Camuropiscis laidlawi Rolfosteus canningensis Tubonasus lennardensis Fallacosteus turneri Aspinothoracidi Dinichthys herzeri Hadrosteus rapax Gorgonichthys clarki Heintzichthys gouldii Selenosteidae Stenosteus angustopectus Gymnotrachelus hydei Rhinosteus parvulus Pachyosteus bulla Dunkleosteoidea Westralichthys uwagedensis Protitanichthys rockportensis Panxiosteidae Panxiosteus ocullus Janiosteus timanicus Plourdosteus canadensis Dunkleosteidae Eastmanosteus calliaspis Xiangshuiosteus wui Eastmanosteus pustulosus Kiangyousteus yohii Golshanichthys asiatica Dunkleosteus amblyodoratus Dunkleosteus terrelli Dunkleosteus raveri	Pachyosteomorphi

However, the subsequent 2016 Zhu et al. study using a larger morphological dataset recovered Panxiosteidae well outside of Dunkleosteoidea, instead within Coccosteomorphi and then Coccosteoidea as the sister group of Coccosteidae, as shown in the cladogram below:^[6]

Eubrachythoraci

Coccosteomorphi Coccosteoidea Coccosteidae Millerosteus minor Coccosteus cuspidatus Dickosteus threiplandi Watsonosteus fletti Protitanichthys rockportensis Panxiosteidae Plourdosteus canadensis Panxiosteus ocullus Janiosteus timanicus Incisoscutoidea Harrytoombsia elegans Torosteus tuberculatus Torosteus pulchellus Mcnamaraspis kaprios Compagopiscis croucheri Trematosteus fontanellus Camuropiscidae Incisoscutum ritchiei Incisoscutum sarahae Rolfosteus canningensis Tubonasus lennardensis Fallacosteus turneri Camuropiscis laidlawi Latocamurus coulthardi Pachyosteomorphi Rhachiosteus pterygiatus Dunkleosteoidea Eastmanosteus calliaspis Eastmanosteus pustulosus Kiangyousteus yohii Golshanichthys asiatica Westralichthys uwagedensis Dunkleosteus raveri Dunkleosteus terrelli Dunkleosteus amblyodoratus Heterostiidae Heterosteus ingens Yinosteus major Aspinothoracidi Tapinosteus heintzi Bullerichthys fascidens Kendrickichthys cavernosus Bruntonichthys multidens Dinichthys herzeri Hadrosteus rapax Gorgonichthys clarki Selenosteidae Heintzichthys gouldii Pachyosteus bulla Gymnotrachelus hydei Stenosteus angustopectus Brachyosteus dietrichi Melanosteus occitanus Rhinosteus parvulus