NativeEctobius(Blattaria: Ectobiidae) from the Early Eocene Green River Formation of Colorado and Its Reintroduction to North America 49 Million Years Later

Abstract

Ectobius kohlsi sp. n. and three undetermined species of the common Eurasian cockroach genus EctobiusStephens, 1835 are reported from the lower middle Eocene of North America. This species indicates a cosmopolitan distribution of the genus during the mid Paleogene, and supports its current relict distribution in modern north-temperate and African ecosystems. When compared with the living species, E. kohlsi was either neutral or plesiomorphic in all characters, but exhibited a close relationship to the extant Ectobius kraussianusRamme, 1923 Species Group in the identical structure of the pronotum. E. kohlsi also was similar to extant Ectobius ticinusBohn, 2004, in the character of its wing venation (see Bohn 2004), in particular the forewing vein M, and to extant Ectobius vittiventris (Costa 1847) in details of forewing coloration. These latter two species are members of the Ectobius sylvestris Species Group (Bohn 1989). Ectobius balticusGermar et Berendt, 1856 —a conspicuously dominant cockroach from mid-Eocene Baltic amber—also appears plesiomorphic in all characters despite being a few million years younger than E. kohlsi. One reason for the complete disappearance of this dominant genus from North America is the peculiar consequence that, after 49 million years, a cool-adapted Ectobius lapponicus (L.) was capable of being reintroduced to a significantly cooler North America than that its antecedents which inhabited North America during a warmer European Eocene. Modern E. lapponicus is synanthropic in North America, even though no synanthropism is recorded for this species in its native habitat throughout Europe.

Fossil calibrations for the cockroach phylogeny (Insecta, Dictyoptera, Blattodea), comments on the use of wings for their identification, and a redescription of the oldest Bla

“…Phylogenetic justification. Vršanský et al (2014) place this fossil as a member of either the Krasussianus or Sylvestris species group. This is supported by a number of morphological characters.…”

“…This node represents the basal divergence within Ectobius Stephens, 1835. Labandeira, 2014 (in Vršanský et al, 2014). Specimen number.…”

“…All these features support the association of this species with extant subgenus Ectobius (Ectobius) Stephens, 1835, as opposed to the subgenus Ectobius (Ectobiola) Uvarov, 1940, which has dark spots on the tegmina and is lacking punctae. Vršanský et al (2014) suggested that Ectobius (Ectobiola) may not be sister to Ectobius (Ectobius) but is a member of the Lapponicus species group of Ectobius. Vršanský et al (2014) also differentiate this fossil from other Ectobius species groups in that they are lacking the pronotal ridges, have different coloration on the pronotum or tegmina, have different punctae patterns, have different shape of cerci, and have different gland morphology.…”

“…Vršanský et al (2014) suggested that Ectobius (Ectobiola) may not be sister to Ectobius (Ectobius) but is a member of the Lapponicus species group of Ectobius. Vršanský et al (2014) also differentiate this fossil from other Ectobius species groups in that they are lacking the pronotal ridges, have different coloration on the pronotum or tegmina, have different punctae patterns, have different shape of cerci, and have different gland morphology. Because the sister taxon to the Krasussianus and Sylvestris species groups of Ectobius are not known, this fossil should be used to calibrate the basal split in Ectobius.…”

“…Fortunately, there are a few cases where bodies with diagnostic characters have been pre-served in amber or impression fossils (e.g., Shelford, 1910;Vršanský et al, 2014). Age calibrations can be reliable if they utilize fossils such as these.…”