Myerslopiidae, Evans, 1957

Szwedo, Jacek, 2004, An annotated checklist of Myerslopiidae with notes on the distribution and origin of the group (Hemiptera: Cicadomorpha), Zootaxa 425 (1), pp. 1-15 : 6-7

Distribution of Myerslopiidae

Biogeographers have long been attracted by disjunct distributions of organisms, and transoceanic disjunctions seem to be particularly favoured. Extant Myerslopiidae have an “Antarctic” or “Gondwanan” distributional pattern ( Nielson 1996, Nielson & Knight 2000). This pattern of distribution ( Fig. 1 ) is frequently regarded as evidence of antiquity of recent fauna. It also suggests a transantarctic dispersal route, which is believed impossible for flightless arthropods after the Lower Cretaceous break up of Gondwanaland. Only a few family­group taxa have so limited an austral distribution as Myerslopiidae , e.g., the caddisflies Rhynchopsychidae ( Ross 1967) and Kokiridae (Eskov & Golovatch 1989). More common are families found in Chile, New Zealand, New Caledonia, Tasmania, and mainland Australia (Eskov & Golovatch 1989, Hamilton 1999). The origin of recent trans­ Pacific disjunctions is discussed in detail by Eskov (1987) and Eskov & Golovatch (1989), while various points of view and hypotheses are also discussed in Humphries & Parenti (1999). The most famous case is that of the flightless coleorrhynchan hemipterans Peloridiidae ; the origin and evolution of this group is discussed in Popov & Shcherbakov (1996).

Regarding Myerslopiidae and distribution of extant forms, I agree with Hamilton and others, that Myerslopiidae are a very old group. On the other hand, recent forms, even if retaining primitive characters, seem to be highly specialized. I subscribe to the view that Myerslopiidae originated in former Gondwanaland during the Mesozoic. The question whether the Ovojassini were true ancestors of Myerslopiidae needs further research to collect more data on fossils from the southern hemisphere. I suppose that in Mesozoic­Early Cenozoic times, Myerslopiidae had a wider distribution in the austral zone, but due to geologic and climatic events they are recently highly restricted in distribution. Before the glaciation in the Miocene­Pliocene was complete, Antarctic peripheries might have served as effective stepping­stones between New Zealand and Chile for ancestors of recent Myerslopiidae . Myerslopiidae , like Peloridiidae , seem to be connected with Nothofagus forests. The history of Nothofagus is rather well documented by fossil pollen, leaves, and wood ( Romero 1986, Tanai 1986). Its biogeography was recently analysed by Linder & Crisp (1995) and the results discussed by Ladiges, Nelson & Grimes (1997). One of the reasons for limited distribution of Myerslopiidae could be the fact that intensive glaciation of Antarctica, as well as the uplift of the Andes, caused aridization in Patagonia and most of Australia, and hence a probable reduction (extinction in some areas?) of Myerslopiidae about the Middle Miocene. On the other hand, some forms living at this time in Antarctica could be preadapted to the severe conditions of glaciation and migrated northwards. It is worth noting that during the Pliocene the orogenesis started in New Zealand and that Pleistocene glaciations covered New Zealand as well as southern parts of Chile, so the ancestors of recent taxa of Myerslopiidae could survive in particular conditions in New Zealand and South America or migrate northwards in the latter. I believe that New Zealand species are descendants of survivors from the ice age(s) and that the diversity of species in the genus Pemmation may be a result of post­glaciation speciation. By contrast, species of the genera Myerslopia in New Zealand and Mapuchea in Chile are limited to refugial areas.

A similar view that southern hemisphere trans­oceanic disjunctions have resulted from Mesozoic integrity of the southern continents and their subsequent fragmentation and drift is regarded as common­place. Still, Eskov (1992) criticizes this statement on the ground of both facts and methodology. According to him, disjunct ranges have resulted from an extinction of “intermediate links” in the northern continents, which he believes to be a fundamental regularity among terrestrial and freshwater invertebrates ( Eskov 1992). He proposes a mechanism which implies a gradual reduction of the pancontinental range to a bipolar (amphitropical) range and, in consequence, to a “Gondwanan” distribution due to the disappearance of the northern “semicircle” ( Eskov 1984, 1992; Eskov & Golovatch 1986). However, this concept of “ousted relicts” cannot be applied to Myerslopiidae . There is no record of fossil Myerslopiidae in the northern hemisphere, and the only supposed fossils of this group are known from Lower Cretaceous strata of Brazil ( Hamilton 1990).

Figures

FIGURE 1. Recent distribution of Myerslopiidae and fossil site where Ovojassini have been found.