Holdenius

Holdenius; Temporal range: Famennian PreꞒ Ꞓ O S D C P T J K Pg N
	Artist's reconstruction of Holdenius holdeni and its prey, an unidentified Ctenacanth chondrichthyan
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	†Placodermi
Order:	†Arthrodira
Suborder:	†Brachythoraci
Clade:	†Eubrachythoraci
Clade:	†Pachyosteomorphi
Clade:	†Aspinothoracidi
Genus:	†Holdenius; Dunkle and Bungart, 1942
Type species
	Holdenius holdeni; Dunkle and Bungart, 1942

Holdenius is an extinct genus of arthrodire placoderm fish which lived during the Late Devonian period.

Description

Holdenius was a large arthrodire, reaching lengths of around 3 m (9.8 ft).^[1] This placoderm is known only from isolated jaw bones,^[2] and little is known about it except that it is relatively morphologically similar to its more famous relative Dunkleosteus, with which it shared a spatial and temporal range.

Holdenius was a piscivorous animal that used its sharp shearing gnathal plates to seize and cleave its prey into manageable pieces. One articulated specimen of this placoderm from the Upper Devonian Cleveland Shale was preserved adjacent to the remains of its prey; a Ctenacanth chondrichthyan, which had been bitten in half. Considering its prey was over half its size, it can be inferred that Holdenius was an exceptionally aggressive nektonic predator. An anterior dorsal spine from the ctenacanth was found lodged in the palate and extending into the braincase of the Holdenius, likely killing it instantly.^[3]

Holdenius is a monospecific genus. Previously classified as belonging to the family Dunkleosteidae, it is now considered to be a member of Aspinothoracidi, the sister clade to Dunkleosteoidea.^[4]

References

^ M. C. Hansen and R. H. Mapes, “A Predator–Prey Relationship between Sharks and Cephalopods in the Late Paleozoic,” in Evolutionary Paleobiology of Behavior and Coevolution , Ed. by A.J. Boucot (Elsevier, London, 1990), pp. 189–199.
^ Carr, Robert. (2009). THE VERTEBRATE FAUNA OF THE CLEVELAND MEMBER (FAMENNIAN) OF THE OHIO SHALE.
^ Brett, Carlton & Walker, Sally. (2002). Predators and Predation in Paleozoic Marine Environments. Paleontological Society Papers. 8. 10.1017/S1089332600001078.
^ Carr, R.K.; Hlavin, W.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)". Zoological Journal of the Linnean Society. 159 (1): 195–222. doi:10.1111/j.1096-3642.2009.00578.x.

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[1] M. C. Hansen and R. H. Mapes, “A Predator–Prey Relationship between Sharks and Cephalopods in the Late Paleozoic,” in Evolutionary Paleobiology of Behavior and Coevolution , Ed. by A.J. Boucot (Elsevier, London, 1990), pp. 189–199.

[2] Carr, Robert. (2009). THE VERTEBRATE FAUNA OF THE CLEVELAND MEMBER (FAMENNIAN) OF THE OHIO SHALE.

[3] Brett, Carlton & Walker, Sally. (2002). Predators and Predation in Paleozoic Marine Environments. Paleontological Society Papers. 8. 10.1017/S1089332600001078.

[Carr2010-4] Carr, R.K.; Hlavin, W.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)". Zoological Journal of the Linnean Society. 159 (1): 195–222. doi:10.1111/j.1096-3642.2009.00578.x.

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