Abstract
Extant Archaeidae, also known as pelican or assassin spiders, have an Austral distribution (South Africa, Madagascar and Australia), but were present in Eurasia during the Mesozoic and Cenozoic, as attested by fossils from Cretaceous Burmese amber (Ross A. 2019. Burmese (Myanmar) amber checklist and bibliography 2018. Palaeoentomology 2(1): 22–84) and Eocene European ambers (Wunderlich J. 2004. Fossil spiders in amber and copal: conclusions, revisions, new taxa and family diagnoses of fossil and extant taxa. Hirschberg-Leutershausen: Ed. Joerg Wunderlich, 1893 p.). They have been known to occur in Oise amber (Ypresian, early Eocene, MP7), from northern France. However, they are not abundant in Oise amber, and have been the subject of few studies until now. Here, we describe the only well-preserved, almost complete, archaeid fossil specimen. This adult male is described as Myrmecarchaea antecessor sp. nov, based on the presence of unique morphological features. The elongate petiolus and extremely long legs are characteristic of the genus Myrmecarchaea from the Middle Eocene Baltic amber. However, unique traits such as the thick, stout petiolus and the extremely elongated, posteriorly tapering cephalothorax distinguish it from the other species of Myrmecarchaea. This specimen is of high interest, as besides being a new species, it is also the first documented adult male in the genus, allowing us to observe sexual characters for the first time. Furthermore, it is the first occurrence of this genus outside Baltic amber, showing affinities between Oise and Baltic ambers, which are, otherwise, very different in their faunistic compositions, and further extends the known past range of the archaeid spiders.
Highlights
Oise amber (Ypresian, reference level MP7, 55–53 Ma) is one of the oldest known Cenozoic fossil resins (Penney, 2010), and, with more than 20,000 identified inclusions (Brasero et al, 2009), is the best-known deposit from the sparsely recorded earliest Eocene
Oise amber is situated in geological time at a thermal optimum, between the PETM (Paleocene-Eocene Thermal Maximum) and the EECO (Early Eocene Climatic Optimum), two short, but extreme (Röhl et al, 2007; Zachos et al, 2008) global warming events that allowed the existence of paratropical environments, with taxa that would later become restricted to intertropical zones (Saupe et al, 2019) occurring high latitudes
Because of the geographic proximity of Oise and Baltic ambers, one would expect the taxa in the families shared by both of these sites to be somewhat closely related. This seems to be the case with the adult male Archaeidae from Oise amber that we describe here
Summary
Oise amber (Ypresian, reference level MP7, 55–53 Ma) is one of the oldest known Cenozoic fossil resins (Penney, 2010), and, with more than 20,000 identified inclusions (Brasero et al, 2009), is the best-known deposit from the sparsely recorded earliest Eocene. A more recent study (Carbuccia et al, in press) yielded 23 families, including the ones identified by Penney (2006, 2007a, 2007b), and a new species in the family Segestriidae. The assemblage of Oise amber spiders, in its composition, is markedly different (Carbuccia et al, in press) from the geographically close, albeit more recent, Central European Palaeogene ambers (Baltic, Bitterfeld and Rovno ambers). Differences between these assemblages are not surprising, as the global climate underwent some quick and drastic climatic shifts during the terminal Paleocene and early Eocene (Röhl et al, 2007; Zachos et al, 2008). The younger Baltic amber forests seem to have been a much cooler, mesothermal environment (Wolfe et al, 2015; Sadowski et al, 2017)
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