Among Antarctic amphipods of the genus Eusirus, a highly distinctive clade of giant species is characterized by a dorsal, blade-shaped tooth on pereionites 5–7 and pleonites 1–3. This lineage, herein named ‘crested Eusirus’, includes two potential species complexes, the Eusirus perdentatus and Eusirus giganteus complexes, in addition to the more distinctive Eusirus propeperdentatus. Molecular phylogenies and statistical parsimony networks (COI, CytB and ITS2)of crested Eusirus are herein reconstructed. This study aims to formally revise species diversity within crested Eusirus by applying several species delimitation methods (Bayesian implementation of the Poisson tree processes model, general mixed Yule coalescent, multi-rate Poisson tree processes and automatic barcode gap discovery) on the resulting phylogenies. In addition, results from the DNA-based methods are benchmarked against a detailed morphological analysis of all available specimens of the E. perdentatus complex. Our results indicate that species diversity of crested Eusirus is underestimated. Overall, DNA-based methods suggest that the E. perdentatus complex is composed of three putative species and that the E. giganteus complex includes four or five putative species. The morphological analysis of available specimens from the E. perdentatus complex corroborates molecular results by identifying two differentiable species, the genuine E. perdentatus and a new species, herein described as Eusirus pontomedon sp. nov. ADDITIONAL KEYWORDS: alpha taxonomy – cryptic species – genetics – molecular systematics – phylogenetic systematics.
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RBINS Staff Publications 2020
The Paleocene in general and in Europe in particular, is generally considered as an epoch with high endemism and few intercontinental dispersals of mammals, although some faunal interchange is known between Asia and North America, mainly from the Tiffanian-Clarkforkian boundary. Up to now, however, faunal interchange between Europe and North America during the Paleocene has almost never been demonstrated. The study of the early Paleocene fauna of Hainin (Belgium) reveals high endemism in European mammals at the end of the Danian (early Paleocene). The age of the fauna of Walbeck (Germany) is reevaluated and is likely to be Selandian (middle Paleocene), significantly older than previously suggested. Therefore, Walbeck is closer in age to Hainin than to the typical late Paleocene fauna of Cernay (France). However, the faunas from Walbeck and Cernay share many common genera that are not present in Hainin, showing a faunal turnover around the Danian-Selandian boundary in Europe, marked by the first occurrence of Plesiadapis, Arctocyon and Adunator in Walbeck, and of neoplagiaulacid multituberculates and Dissacus in Cernay. The three genera present in Walbeck are abundant and diversified in North America from the beginning of the Tiffanian, i.e., older than the expected age of Walbeck. Therefore, it is inferred that these genera dispersed from North America to Europe around the Danian–Selandian boundary, corresponding roughly to the Torrejonian–Tiffanian boundary. The absence of multituberculates in the fauna of Walbeck does not allow the drawing of definite conclusions about the moment of their dispersal, but it is likely that it happened at the same time as Plesiadapis and Arctocyon, because neoplagiaulacids are abundant and diversified during the whole Paleocene in North America. Similarly, Dissacus is very rare in Cernay, and could also have dispersed at the same time as others, but remained unnoticed because of its rarity. The Clarkforkian in North America is marked by massive arrival of taxa from Asia, among which are rodents, carnivorans, and tillodonts. The recent discovery of the latest Paleocene fauna of Rivecourt (France), where typical Paleocene taxa cohabit with rodents and a carnivoran, indicates that the large-scale dispersal event marking the Paleocene–Eocene boundary began in Europe about at the same time as in North America, with the arrival of rodents and carnivorans. The morphology of the new carnivoran species suggests that this group dispersed separately from Asia to Europe and from Asia to North America.
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