Drepanaspis

Extinct genus of jawless fishes

Drepanaspis (from δρεπάνη drepánē 'sickle' and 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. 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.

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. were applied to Psammosteids, but proved not to be useful. 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 and another new species, along with the identification of radial ridges of dorsal and ventral plates of D. gemuendenensis as sensory line canals, were able to alleviate the issue and provide significant morphological information in the area. 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. 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. Interestingly, Drepanaspis also has a dorsal mouth opening which is a distinct feature that separates the genus from its other Heterostracan relatives.

The carapace of Drepanaspis is described to be broad, depressed, and very obtusely rounded at the front, consisting of a ventral and dorsal shield made up of several overlapping plates or scales. These scales, or tubercles, cover a large majority of the carapace in a characteristic v shape pattern, with approximately 8.5 tubercles per cm aligned naturally to the edge of the plate, which can be used to identify a specimen's symmetry plane. It can be seen in specimens, such as the one discovered from the Odenspiel quarry in Rhineland, Germany, that the lateral line sensory system lies under the dorsal plate of Drepanaspis, situated above its smooth and extremely thin basal layer. These slate deposits were estimated to be 4,000 meters in thickness and ran for about 150 kilometers from the northwest to southeast direction. 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 suction feeding. The suction feeding mechanism of Drepanaspis was likely a specialized adaptation for feeding on small, benthic invertebrates in shallow marine environments. The edges of the mouth opening is lined with small denticles which allowed for the grasping and retention of food during suction feeding.