Palaeopsychops is an extinct genus of lacewing in the moth lacewings family Ithonidae. The genus is known from Early Eocene fossils found in Europe, and North America and is composed of ten species. The ten species can be informally separated into two species groups based on veination of the forewings, the "European" and "North American" groups. When first described, the genus was placed in the family Psychopsidae, but later was moved to Polystoechotidae, which itself is now considered a subgroup of the moth lacewings.
Distribution and age
The European species of Palaeopsychops are all known from the Early Eocene Fur Formation along the western Limfjord coast of Denmark. Most of the thick formation is diatomites with an interspersed sequence of approximately 179 ash layers. Argon–argon radiometric dating of ash layer "+19", which is slightly lower in the strata then the "insect beds", has determined a age.
Palaeopsychops species have been recovered from three locations in the Okanagan highlands, the Horsefly shales near Horsefly, British Columbia, the Coldwater Beds Quilchena site near Quilchena, British Columbia and the Klondike Mountain Formation in Republic, Washington, northern Ferry County, Washington. The Okanagan highlands are aged between for the Quilchena site to for the Klondike Mountain Formations Tom Thumb Tuff member.
Archibald and Makarkin (2006) suggested the Turgai Sea which separated western Europe and Asia from the Cretaceous to Oligocene prevented the spread of polystoechotid group lacewings into Asia from Europe. The disjunct distribution of Palaeopsychops between Denmark and the Okanagan Highlands may have been enabled by rising crust elevations in the northern Atlantic region and subsequent increase in landmass during the Late Paleocene which linked Northern Europe with Greenland until at least the Early Eocene. Several land bridge routes may have acted as migration corridors for biotic interchange, the northern De Geer land bridge from Fennoscandia to North America via northern Greenland, and the southern Thulean land bridge from northern Britain though the Faroe Islands and then Greenland and North America. Other insect genera that share a similar disjunct distribution include the mecopteran Cimbrophlebia, the green lacewing Protochrysa and the bull dog ant Ypresiomyrma.
Paleoenvironment
The Fur formation represents a marine depositional environment of the inland water body which is ancestral to the North Sea. While the ancestral water body had an occasional opening to the Atlantic, it was entirely or almost entirely enclosed by land. The Fur formation outcrop is of a site that is an undetermined distance from the paleoshoreline with the preserved terrestrial flora and fauna suggested to have been carried from a shoreline to the north of the site by winds or drifting. Analysis of the δ18O/δ16O isotope ratio found in mollusc shells in the formation indicates paleotemperatures were of a low megathermal mean annual temperature, though the presence in the paleobiota of thermophilic taxa could indicate a lower mean annual temperature combined with a higher coldest month mean temperature.
All three Okanagan Highlands sites represent upland lake systems that were surrounded by a warm temperate ecosystem with nearby volcanism. The highlands likely had a mesic upper microthermal to lower mesothermal climate, in which winter temperatures rarely dropped low enough for snow, and which were seasonably equitable. The paleoforest surrounding the lakes have been described as precursors to the modern temperate broadleaf and mixed forests of Eastern North America and Eastern Asia. Based on the fossil biotas the lakes were higher and cooler then the coeval coastal forests preserved in the Puget Group and Chuckanut Formation of Western Washington, which are described as lowland tropical forest ecosystems. Estimates of the paleoelevation range between higher than the coastal forests. This is consistent with the paleoelevation estimates for the lake systems, which range between , which is similar to the modern elevation , but higher.
Estimates of the mean annual temperature have been derived from climate leaf analysis multivariate program (CLAMP) analysis of the Republic and Quilchena paleofloras, and leaf margin analysis (LMA) of all three paleofloras. The CLAMP results after multiple linear regressions for Republic gave a mean annual temperature of approximately , with the LMA giving . CLAMP results from Quilchena returned the higher which was supported by the returned from the LMA. LMA of the Horsefly flora returned a mean annual temperature of . These are lower than the mean annual temperature estimates given for the coastal Puget Group, which is estimated to have been between . The bioclimatic analysis for Republic, Quilchena, and Horsefly suggest mean annual precipitation amounts of and respectively.
History and classification The genus was first described by Andersen (2001) from a series of 31 fore and hind wing part-counterpart fossils plus three partial body fossils found in the Fur Formation. Andersen chose the genus name as a combination of the psychopsid families nominal genus Psychops, itself a combination of the Greek words psyche and opsis meaning "butterfly" and "appearance", with the Latin word palaeo meaning "old". Andersen designated Palaeopsychops latifasciatus as the type species, and named three other species in the same paper, Palaeopsychops abruptus, Palaeopsychops angustifasciatus, and Palaeopsychops maculatus. Of the study material, the holotype specimens of all four species, along with paratypes for P. abruptus and P. angustifasciatus were deposited in the Geological Museum, University of Copenhagen. The four holotypes plus P. abruptus paratype 1 were all declared by Andersen as danekræ, specimens of high scientific value to the Danish. Additional paratype fossils were spread out between a number of collections including the Fur Museum on Fur Island, the Moler Museum on Mors Island and private collections in Nykøbing Mors Denmark and in Germany.
The fifth species, Palaeopsychops dodgeorum, was described by Makarkin and Archibald (2003) two years later . The holotype hindwing was found at the Coldwater Beds Quilchena site in British Columbia. The only known specimen of the species, was included in the University of Alberta collections at the time of study. Archibald and Makarkin (2006) added five additional species in the genus, bringing to known species count to ten with one additional Danish species Palaeopsychops quadratus, and four Okanagan Highlands species. Palaeopsychops douglasae added a second species from Quilchena, while one species Palaeopsychops setosus was described from the more northern Horsefly shales site and two species Palaeopsychops marringerae and Palaeopsychops timmi were detailed from the southern most Klondike Mountain Formation in Washington.
Andersen (2001) placed the new genus into the family Psychopsidae based on the large size of the wings, the dense vein structure, and his interpretation that the subcosta (Sc), anterior radial trace (R1), and anterior sectoral trace (R2) veins merged near the wing apex forming a vena triplica structure. As such, Andersen placed the genus within the psychopsids, while noting at the time the species were larger than any other member species and notably similar to the Florissant Formation species Polystoechotites piperatus, which was placed in the psychopsid family at the time as "Propsychopsis" piperatus. Makarkin and Archibald (2003) called the psychopsid into question based on examination of the P. latifasciatus images in the type description and the venation of P. douglasae. While the R1 and Sc veins do merge into a single vein, they determined the R2 did not merge with them. Instead the R2 runs parallel to the other two and then to the fused vein and separately terminates at the wing margin. As such, it lacked the key venation character that unites the psychopsids. After examining all described neuropteran families they tentatively placed the genus within the "giant lacewing" family Polystoechotidae. With the addition of the 2006 species and description of the form genus Polystoechotites Archibald and Makarkin reaffirmed the placement of Palaeopsychops within the family Polystoechotidae and noted the fore-wing species fall into two informal groups the "European" and "North American" groups. They were hesitant to place strong weight on the groupings as the scattered crossveins uniting the three North American species is a character seen in other Ithonid genera from North America. Winterton and Makarkin (2010) documented phylogenetic and morphological analysis of the families Ithonidae and Polystoechotidae in which the two families were found to form a monophyletic clade. Due to several of the traditional ithonidae genera forming a sister group within the polystoechotid genera and a lack of characters specific to only one family or the other, Winterton and MAkarkin merged the two into a single expanded Ithonidae family. Subsequent to the expansion of Ithionidae an overview of the family was given by Zheng et al (2016) in which they informally grouped the genera into three genus groups, the Ithonid genus group, the Polystoechotid genus-group, and the Rapismatid genus group, with Palaeopsychops placed in the Polystoechotid genus-group.
Species Paleopsychops is distinguished from other polystoechotid group genera by a number of characters mainly seen in the fore-wings, though one character is distinct to the hind-wings. The fore-wings of Paleopsychops have a broadly subtriangular outline, while other genera are more elongated and have a length to width ratio of greater than 2.5. The rear margins of the fore-wings are not falcate, while the genus Fontecilla does have a falcate rear margin. Most genera have a MA vein which forks, but in Paleopsychops the basal end of the MA is fused with the Rs1. The MP vein of both the fore and hind-wings notably forks into multiple closely spaced elongate branches, a feature seen in the extinct Jurassic Pterocalla fore-wing, but rare in other genera. The fore-wings range between in length and between in width resulting in length/width ratios between 2.14 and 2.40. As with many neuropteran genera, trichosors are often present along the rear margins of the wings though preservation makes it hard to identify if it is specific to certain Paleopsychops species or uniform for the genus. None of the specimens described have a sufficiently preserved basal area of the wing to detect the absence or presence of a basal nygma, however in at least some of the species an apical nygma is present, located between the Rs1 and Rs2 veins. The hind-wings range between long and wide, giving a less subtriangular outline than the forewings. While the hind-wings do not show nygmata, there are trichosors and a coupling apparatus near the wing base typical of polystoechotid group species. The apparatus, used for gripping to the fore-wings in flight, has a frenulum composed of long setae.
Archibald and Makarkin (2006) made note of the possibility that some of the perceived species diversity found in Paleopsychops could be a result of species description from isolated wings combined with sexual dimorphism in wing colorpatterning. They noted specifically the Okanagan Highlands species pair P. dodgeorum + P. marringerae along with the Danish pairs P. latifasciatus + P. abruptus and P. angustifasciatus +'P. quadratus. Given the incomplete nature of the fossils however and that dimorphic color pattering is not known in the polystoechotid group genera, the likelihood of this possibility is small.
P. abruptus