A new Myrmecarchaea (Araneae: Archaeidae) species from Oise amber (earliest Eocene, France)

Abstract

Archaeidae spiders have long been known to occur in Oise amber (Ypresian, early Eocene, MP7). However, they are not abundant, 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 describe 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.

Figure 1 from: Wood HM, Singh H, Grimaldi DA (2021) Another Laurasian connection in the Early Eocene of India: Myrmecarchaea spiders (Araneae, Archaeidae). ZooKeys 1071: 49-61. https://doi.org/10.3897/zookeys.1071.72515

“…1D, F with fig. 2 from Carbuccia et al 2020). The pedicel seems slightly longer than in non-Myrmecarchaea archaeids, but not as extreme as the pedicel of M. petiolus and M. pediculus.…”

Another Laurasian connection in the Early Eocene of India: Myrmecarchaea spiders (Araneae, Archaeidae)

“…1D, F with fig. 2 from Carbuccia et al 2020 ). The pedicel seems slightly longer than in non- Myrmecarchaea archaeids, but not as extreme as the pedicel of M. petiolus and M. pediculus .…”

“…pediculus Wunderlich, 2004 (Fig. 2; pedicel is obscured in the single known specimen of M. antecessor Carbuccia et al, 2020). There are other palpimanoid genera with elongated legs, including both extinct (e.g., Planarchaea Wunderlich, 2015) and extant members (e.g., Eriauchenius workmani Pickard-Cambridge, 1881, although with only leg I elongated).…”

“…The pedicel seems slightly longer than in non- Myrmecarchaea archaeids, but not as extreme as the pedicel of M. petiolus and M. pediculus . The ratio of cephalothorax length to pedicel length can be used to compare these shape differences: M. pediculus = 1.2; M. petiolus = 1.4; M. antecessor = 2.3 (estimated from figures in Carbuccia et al 2020 ); E. workmani = 4.3. This ratio should be treated with caution because measurements were taken from different views for the different species out of necessity due to inconsistencies in fossil preservation.…”

Figure 2 from: Wood HM, Singh H, Grimaldi DA (2021) Another Laurasian connection in the Early Eocene of India: Myrmecarchaea spiders (Araneae, Archaeidae). ZooKeys 1071: 49-61. https://doi.org/10.3897/zookeys.1071.72515

“…The pedicel seems slightly longer than in non-Myrmecarchaea archaeids, but not as extreme as the pedicel of M. petiolus and M. pediculus. The ratio of cephalothorax length to pedicel length can be used to compare these shape differences: M. pediculus = 1.2; M. petiolus = 1.4; M. antecessor = 2.3 (estimated from figures in Carbuccia et al 2020); E. workmani = 4.3. This ratio should be treated with caution because measurements were taken from different views for the different species out of necessity due to inconsistencies in fossil preservation.…”