M. dicki. Distinguishing Characteristics: • Poorly developed lateral corners on the anterior median dorsal plate • Ornamentation on thoracic consists of tubercles fused into distinct lines • Breadth/Length ratio of 100 of anterior median dorsal plates Microbrachius chuandongensis This species is endemic to the Late Emsian-aged (393.3 Ma) Late Early Devonian Chuandong Formation in Qujing, China. M. chuandongensis was named by Wang in 1999 and is known from several articulated specimens that have poor preservation. This species is currently recognized as the oldest member of the genus. Distinguishing Characteristics : • Mixilateral plate overlapping the anterior median dorsal plate • Anterior median dorsal plate does not have an anterior ventral pit • Lateral plates quite broad • Breadth/length ratio of 100 of anterior median dorsal plates • Posterior median dorsal plate much shorter and smaller than the anterior median dorsal plate • Ornamentation consists of isolated tubercles in no arrangement Microbrachius kedoae A small species known from a single incomplete specimen from the upper Givetian strata of Belarus . It was discovered in Gavrilchitsy Core 45 (rock core sample) taken by A. Gursenko in 1954 located near village of Gavrilchitsy, Belarus along with unidentifiable osteolepid remains. The specimen was recently described in March 2018 as a new species of Microbrachius closely related to M. dicki. The specimen was from a single siltstone sample located at a depth of 225.25-228.95m. This siltstone correlates to the Moroch Beds of the Polotsk Region Stage. Dating of the Moroch Beds puts M. kedoae in the Late Middle Devonian during the late Givetian stage approximately 385 Ma. M. kedoae is currently recognized as the youngest member of the genus along with M. dicki that occurs in laterally correlative beds. Distinguishing Characteristics: • Mixilateral plate is overlapped by the anterior median • Anterior ventro-lateral plate has a crista postbranchialis developed • Lateral plates narrow • Denticles on the mesial edge of the distal segment of the pectoral appendage are fairly blunt • Anterior median dorsal plate does have an anterior ventral pit • Ornamentation consists of isolated tubercles in no arrangement • Well developed lateral corners on the anterior median dorsal plate Sexual dimorphism and mating Claspers (male sex organs) in living vertebrates (sharks, few fish) are used for internal fertilization and penetrative sex. Most modern fish and amphibians fertilize externally by releasing their gametes into the water, where fertilize. M. dicki is the earliest placoderm