Suckers (Fish, Catostomidae) from the Eocene of China account for the family’s current disjunct distributions

Abstract

Unequivocal Eocene suckers from China are for the first time reported here. This discovery demonstrates that catostomids of the Eocene Epoch (some 55 35 Ma ago) are scattered widely on mainland Asia as well as western North America. The present day disjunct distribution pattern of catostomids, with 68 extant species widespread in North America and the northern part of Middle America and only two in the restricted areas of Asia, is the result of their post-Eocene decline in Asia due to the competitive pressure from cyprinids, their Late Cenozoic radiation in North America, and the vicariant and dispersal events triggered by the changed biogeographic landscape. All of these prove to be a historical product of the geological, biological, and climatic changes throughout the Cenozoic.Keywords: China, catostomids, Eocene, biogeography.Suckers (Catostomidae) are now one type of the most widespread freshwater fishes in North America, with a southern extension into Mexico and Guatemala. Among the family's 69 extant species [1,2] , only two occur elsewhere: one in northeastern corner of Siberia and the other in the Yangtse River and Minjiang River (Fujian Province), China [3,4] . This disjunct distribution ( fig. 1(a)) has long puzzled ichthyologists and biogeographers alike. Although Darlington's [5] scenario of eastern Asian origin of catostomids and their subsequent dispersal routes gained acceptance [6 8] , it is currently considered problematic because it lacked a robust phylogenetic analysis and an adequate fossil record. Surprisingly, with an almost blank record of fossil suckers in east Asia but quite a few from the then so-called "Oligocene" and "Miocene" in North America [9 11] , Darlington [5] postulated that "catostomids originated in eastern Asia, moved primarily from Asia to North throughout western North America [12,13] ( fig. 1(b)). They were all referred to the genus †Amyzon [15 18] ( fig. 2(b)), though the monophyly of the genus [17] and the validity of some included species [19] were questioned. Suckers belonging to modern genera did not appear until the middle or lateMiocene (approximately 15 Ma ago); once they did, they occurred on both sides of the Continental Divide of North America [13,20,21] ( fig. 1(b)).Prior to this report, fossil suckers were conspicuously absent from China except a few disarticulated operculars and vertebrae assigned as Catostomus sp. from the middle Eocene of Inner Mongolia, China [1,22] . In fact, the fossil record of suckers from Asia as a whole was sketchy. Sytchevskaya [7] described a late Eocene or early Oligocene sucker, †Vasnetzovia, from the Far East coastal area of Russia but did not mention its pharyngeal teeth. Other fossil suckers described by the same author from the early-middle Eocene and early Oligocene of Zaysan Basin, East Kazakhstan, were based on detached pharyngeal teeth alone. Among her findings, all but an ictiobine, †Vasnetzovia, were dismissed by Smith [1] . Besides, their occurrences were restricted to northern Asia [7] . Systematic...

A new Eocene catostomid (Teleostei: Cypriniformes) from northeastern China and early divergence of Catostomidae

“…Paratypes: IVPP V 12572.2, a well-preserved right pharyngeal bone with teeth, described in Chang et al [5] ; IVPP V 15711. Diagnosis: See the generic diagnosis.…”

“…†Amyzon hunanensis, IVPP V 1102, a nearly complete fish lacking caudal fin, the holotype of the species described by Cheng [11] ; IVPP V 12571.1, a complete fish, the specimen mentioned by Chang et al [5] .…”

“…The teeth in the well-preserved right pharyngeal bone IVPP V 12572.2 (see Chang et al [5] , Figure 3) are arranged in a single row. On the specimen, 40 teeth were counted on its ventral half, and spaces for more than 10 missing teeth could be estimated on its dorsal half.…”

“…The maximum body depth is at the origin of the dorsal fin and measures 156 mm. Thus, the body depth is approximately half of the standard length, much more than that in †Amyzon (0.21 -0.44) [5,40,41] and †Vasnetzovia (0.33) [4] . Judged from the preserved part of the cleithrum in the holotype, the depth of the head must be much smaller than that of the body.…”

“…She also erected several new species belonging to †Amyzon and Recent genera in the same paper, which were later invalidated [1,8] . The first unambiguous report of catostomid from China was †Amyzon hunanensis (Cheng, 1962) that was initially referred to cyprinids [5,11] .…”