Drepanaspis

Drepanaspis Temporal range: Early Devonian PreꞒ Ꞓ O S D C P T J K Pg N
Drepanaspis gemuendenensis reconstruction
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Infraphylum:	Agnatha
Class:	†Pteraspidomorphi
Subclass:	†Heterostraci
Order:	†Pteraspidiformes
Family:	†Psammosteidae
Genus:	†Drepanaspis
Type species
Drepanaspis gemuendenensis Schluter, 1887
Species
D. gemuendenensis D. sehrieli Gross, 1933 D. lipperti Gross, 1937 D. jaegeri Tarlo, 1964 D. earteri (McCoY, 1851) D. edwardsi Tarlo, 1964

Drepanaspis (from

A second species of Drepanaspis, D. sehrieli, would later be discovered, followed by a third species produced by the Clervaux Formation, D. lipperti, found near Zweifelscheid, and Willwerath, Germany.^[1] Both species were first described by Walter R. Gross in 1933 and 1937 respectively.^[1]

More specimens of Drepanaspis would later be uncovered in 2004, in the Lower Devonian subdivision of the 

Previously, the method of using specific arrangements of the lateral line sensory canals to identify the well characterized cyathaspidid and pteraspidid species^[5][6] were applied to Psammosteids, but proved not to be useful.^[7] At the time, Psammosteids were not well characterized morphologically due to a lack of specimens with distinct sensory canal features, but the discovery of sensory lines in a new Late Devonian Obrucheviid Psammosteid^[8] and another new species, along with the identification of radial ridges of dorsal and ventral plates of D. gemuendenensis as sensory line canals,^[9][10] were able to alleviate the issue and provide significant morphological information in the area.^[9][7]

It is important to note, however, that when the identification of radial ridges of dorsal and ventral plates of D. gemuendenensis as sensory line canals were made by W. Gross in 1963, it sparked some debate from paleontologists Obruchev and Halstead Tarlo.^[10][7] Obruchev and Halstead Tarlo argued that the interpretation of these structures were incorrect as they were too symmetrical and situated on the visceral surface of the plates.^[11] This debate would continue until the discovery of a specimen from the Odenspiel quarry in Rhineland, Germany that contained two incomplete dorsal plates, two branchial plates and several fragments of D. gemuendenensis pointing to Gross as the one with the correct observation.^[7]

Description

Drepanaspis was a small, flattened fish with a heavily armored body that ranged from 10 to 30 cm long in size.^[12] The presence of widely spaced eyes, sensory canals, and its flattened morphology suggests that these fish may have been bottom feeders that foraged the ocean floor for food.^[7][13] Interestingly, Drepanaspis also has a dorsal mouth opening which is a distinct feature that separates the genus from its other Heterostracan relatives.^[14]

Carapace

The

A large majority of the first Drepanaspis specimens were found in the Gemünden slate in the Hunsrück lagerstätte of Rhineland, Germany.^[2] The fauna of the Hunsrück lagerstätte consisted of trilobites, mailed fish, bivalves, cephalopods, and other Late Devonian marine lifeforms.^[2] The predominantly diverse range of marine fauna found within these slate formations strongly indicate that the members of Drepanaspis are of marine origin.

Hunsrück lagerstätte, the primary slate formation of which Drepanaspis is most commonly found, are of Early Devonian age, and is thought to have deposited during the Late Pragian to Early Esmian Ages in subsiding basins that were separated by swells.^[16] These slate deposits were estimated to be 4,000 meters in thickness and ran for about 150 kilometers from the northwest to southeast direction.^[16] It was estimated, through observations of well-developed eyes of arthropod and vertebrate specimens recovered from the slate formation, that the water depth of the offshore environment was estimated to be rather shallow, only ranging from 40–60 meters in depth.^[16] It was based on these sedimentary observations that the conclusion of Drepanaspis having lived in shallow water environments, such as shallow seas, coral reefs, or lakes, can be drawn.

Feeding Ecology

Members of Drepanaspis were most likely nektobenthic, or bottom dwellers, a conclusion based on its flattened morphology and dorsal positioning of its oral opening. With information inferred from extant jawless fish species, it is a common feeding strategy for bottom dwellers to be bottom feeders, suggesting that Drepanaspis may have likely been a bottom feeder.^[17]

This same conclusion can also be drawn by observing the anatomical features of its dorsal facing mouth. Due to the jawless nature of the mouth, Drepanaspis may have most likely utilized an aquatic feeding mechanism called

Drepanaspis belongs to the clade Drepanaspididae, a subdivision of the family Psammosteida. Psammosteida belongs to the order Pteraspidiformes and class Pteraspidomorphi, which is one of the major classes of the paraphyletic group Ostracoderm.^[18]

Gallery

• 
  Fossil of Drepanaspis sp. in the National Museum of Nature and Science, Tokyo, Japan
• 
  Fossil of Drepanaspis sp. in the Field Museum of Natural History
• 
  Fossil of Drepanaspis gemuendenensis at the American Museum of Natural History

See also

• Arandaspis – Extinct genus of jawless fishes
• Hemicyclaspis – Extinct genus of jawless fishes
• Sacabambaspis – Extinct genus of jawless fishes

References