Drepanaspis (from Greek: δρεπάνη drepánē 'sickle' and Greek: ἀσπίς aspís 'shield') is an extinct genus of primitive jawless Ostracoderms from the Early Devonian (approximately 416 - 397 mya) that belonged to the phylum Chordata, infraphylum Agnatha, class Pteraspidomorphi, and the subclass Heterostraci.[1] Drepanaspis are assumed to have lived primarily in marine environments and is most commonly characterized by their ray-like, heavily armored bodies, along with their lack of paired fins and jaws.[2][3]
The first fossils of the genus Drepanaspis, scientifically known as D. gemuendenensis of Schlüter, were found in 1887 from the Gemünden slate in the Hunsrück lagerstätte of Rhineland, Germany and was first described by Clemens August Schlüter.[2][4] These fossils were also most notably studied and described by Scottish palaeoichthyologist Ramsay H. Traquair who created the first outline restorations from articulated specimens of Drepanaspis.[2][4]
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 Ardenne Massif in Belgium and Luxembourg, specifically within the Emsian Oesling, by Alain Bleick and his team.[1] This discovery would lead to a new geographical record of the genus, dating to the middle-upper Emsian period.[1]
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]