Eastmanosteus

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Eastmanosteus
Temporal range: Middle to Late Devonian
Eastmanosteus calliaspis.JPG
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Placodermi
Order: Arthrodira
Suborder: Dunkleosteoidea
Family: Dunkleosteidae
Genus: Eastmanosteus
Type species
Eastmanosteus pustulosus
(Eastman 1897)

Eastmanosteus ("Eastman's bone") is a fossil genus of dunkleosteid placoderms. It was closely related to the giant Dunkleosteus, but differed from that genus in size, in possessing a distinctive tuberculated bone ornament, a differently shaped nuchal plate and a more zig-zagging course of the sutures of the skull roof.[1]

Species of Eastmanosteus had powerful jaws with sharp cutting edges and were likely active predators. Fossils have been found in many parts of the world in marine sediments dating from the Middle to Late Devonian. They were medium-to-large fish, with specimens E. pustulosus and E. licharevi approaching a total length of 3 metres. Complete exoskeletons with soft-tissue traces of E. calliaspis from Australia make this one of the best known dunkleosteids.

Species[edit]

Eastmanosteus calliaspis Dennis-Bryan 1987[edit]

From the Frasnian Gogo Formation of northwestern Western Australia. This is the best known member of the genus with many articulated skulls and trunk armours in museum collections.[2] Evidence of muscle fibres, circulatory structures and nerve tissue have been preserved representing some of the oldest known gnathostome soft tissue.[3] The largest known skull is 272mm in length suggesting a total body length of roughly 1.5m. It was one of the largest fish in the Gogo assemblage.[4] A reexamination of the family Dunkleosteidae posits the Late Emsian Xiangshuiosteus as E. calliaspis' sister taxon, and further implicates that E. calliaspis differs enough from other members of this genus to merit placement with its own genus.[5]

E. licharevi (Obrucheva 1956)[edit]

A poorly known species from Russia, originally described from an isolated nuchal plate from the Frasnian of Timman with additional material from the Famennian of Lipetsk.[6]

E. lundarensis Hanke, Stewart and Lammers 1996[edit]

A medium sized species from the Eifelian of south-central Manitoba, Canada. One of the earliest and most completely known members of the genus.[7]

E. magnificus (Hussakof & Bryant 1918)[edit]

Based on a single almost complete head shield from the Late Devonian of New York State, USA. Has previously been assigned to Dinichthys and Dunkleosteus.[8]

E. pustulosus (Eastman 1897)[edit]

This is the type species and was originally placed in the genus Dinichthys. It was a large and widely distributed form, with fossil material from the Middle-Late Devonian of the USA (Wisconsin, Iowa, Michigan, New York State) and the Frasnian of Poland.[9]

E. yunnanensis (Wang 1982)[edit]

Originally assigned to Dunkleosteus. From the Middle Devonian of Yunnan Province, China.[10]

Eastmanosteus species 1 Janvier[edit]

An undescribed species based on relatively well preserved material from the Frasnian of Kerman, East Iran.[11]

Other species[edit]

Many other species have been included within this genus based on material from Russia, Morocco, and the USA. Most of these are either indeterminate dinichthyids or are now placed in different genera.[12]

References[edit]

  • Dennis-Bryan, K (1986) A new species of eastmanosteid arthrodire (Pisces: Placodermi) from Gogo, Western Australia, Zoological Journal of the Linnean Society Volume 90 Issue 1, Pages 1 – 64.
  • Long, J.A. (2007) Swimming in Stone: The Amazing Gogo Fossils of the Kimberley, Fremantle Arts Centre Press