A new Eocene catostomid genus and species,Plesiomyxocyprinus arratiae, is described from Huadian, Jilin Province, northeastern China. The materials include a nearly complete skeleton, dozens of pharyngeal bones with teeth, and a number of disarticulated bones. The new articulated specimen is large-sized and deep-bodied, with an estimated standard length of ca. 300 mm and body depth of 156 mm or about half of its standard length. The assignment of the fish to the Catostomidae is based on its falciform pharyngeal bone with one row of numerous (more than 50) compressed teeth, and the bone is much smaller than in cyprinids, especially given the size of the fish. The new fish distinguishes itself from all known catostomids (both extinct and extant) in its long anal fin with four unbranched and 17-18 branched rays, and its extremely short caudal peduncle that is only about one fourth of its depth. Plesiomyxocyprinus arratiae resembles the Eocene-Oligocene transpacific-distributed Amyzon in many general skeletal characters. However, it shows a few characters uniquely shared with the Recent catostomid Myxocyprinus asiaticus. Those include a very long dorsal fin with about 50 branched fin rays, the end of dorsal fin rays being close to the caudal fin base, and anal rays stretching posteriorly beyond the base of caudal fin. It is the first fossil catostomid that shows a close relationship to the endemic Myxocyprinus now living in the Yangtze River and Minjiang River, China. The discovery of Plesiomyxocyprinus arratiae, along with two previously described possible catostomid genera Jianghanichthys and Vasnetzovia, may indicate that the divergence of the Catostomidae started much earlier, in the middle Eocene or earlier, on the western side of the Pacific than on its eastern side.
The rapid development of molecular phylogenetic analysis has provided a new path to investigate the tempo of evolution.In this work,a rather complete molecular phylogeny of the East Asian gobionid fishes was constructed based on mtDNA cytochrome b gene sequences.Molecular clock analysis was then applied to investigate the speciation tempo of this group.The phylogenetic analysis revealed four major groups that were in agreement with previous studies.Lineage numbers plotted over time indicate that gobionid lineages increased in an exponential mode with the equation expressed as y=87.562×e 0.1141x,where y is the number of lineages and x represents the geological time,and 0 < x ≤ 30,1≤ y ≤ 65.The speciation rate of gobionid fishes calculated by LASER program was inconstant.Peaks of speciation were identified and found approximately to be coincident with East Asian geological events,such as uplifts of the Tibetan plateau and formation of the monsoon system.
