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TheFirstTwisted-WingParasitoids(Insecta:Strepsiptera)fromtheEarlyEoceneGreenRiverFormationofColorado

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The First Twisted-wing Parasitoids (Insecta: Strepsiptera) from the Early Eocene

Green River Formation of ColoradoGwen S. Antell1 and Jeyaraney Kathirithamby2

1 Corresponding author: Peabody Museum of Natural History and Department of Geology and Geophysics, Yale University,

P.O. Box 208109, New Haven, CT 06520-8109 USA—email: gwenantell@gmail.com

2 Department of Zoology, Oxford University, Oxford, OX1 3PS, United Kingdom—email: jeyaraney.kathirithamby@zoo.ox.ac.uk

ABSTRACT

Strepsiptera is a clade of entomophagous parasitoid insects with fewer than 30 previously reportedfossils. Two new species of Caenocholax (Strepsiptera: Myrmecolacidae) described here representthe first reported adult strepsipterans preserved as organic compression fossils. Their occurrencein the Early Eocene (about 50 Ma) Green River Formation (Colorado, USA) is the northernmostNew World record of Myrmecolacidae and the oldest record of Caenocholax. Caenocholaxbarkleyi sp. nov. and Caenocholax palusaxus sp. nov. are each known from one adult male. Theaedeagus of C. barkleyi lacks a median projection and terminates in two hooks, an apomorphy ofthe species. Caenocholax palusaxus has distinctly intermediate wing vein density and a larger ratioof antennomere 6 to antennomere 7 than any other species of Caenocholax. The fossils reportedhere expand the known insect biota of the formation in taxonomic richness as well as the fossilrecord of Strepsiptera in space and time. Moreover, the Eocene specimens hint at an unappreci-ated fossil diversity of endoparasitic insects.

KEYWORDS

Myrmecolacidae, organic compression fossils, lacustrine preservation, Ypresian, endoparasitoidinsects, New World distribution

Bulletin of the Peabody Museum of Natural History 57(2):165–174, October 2016.© 2016 Peabody Museum of Natural History, Yale University. All rights reserved. • http://peabody.yale.edu

Introduction

In pinned and fossil entomology collections Strep-siptera is one of the rarest cosmopolitan insecttaxa, yet study of this small clade of tiny parasiteshas revolutionized our understanding of insectevolution. Sometimes called the twisted-wing par-asites, Strepsiptera includes a few more than 600recognized species, but fewer than 30 of thesewere described from fossils (Kathirithamby, inpress). Only adult males and first-instar larvae(and in the basal clade Mengenillidia, last-instarlarvae) live outside a host; older instar larvae,pupae and adult females live as obligate endopar-asites in other insects (Kathirithamby 1989). Adultfemales lack wings, legs and eyes, and they remainin their larval host while producing hundreds tohundreds of thousands of offspring through

haemocoelous viviparity (Kathirithamby 1989;Maeta et al. 1998). Adult males emerge withmembranous hind wings and live only longenough to track pheromones to females, no morethan a few hours (Kathirithamby et al. 2015). Evo-lutionary biologists have studied Strepsiptera notonly for the uniqueness of its life-history traits, butalso for the similarity of its morphology with cer-tain other arthropods.

Morphological convergences with otherendopterygote insect clades and with trilobitesmake Strepsiptera of paleontological and phylo-genetic importance. The eyes of adult male strep-sipterans represent the closest modern analoguein function and structure to those of schizochroaltrilobites (Horváth et al. 1997; Buschbeck et al.2003). Facets of these eyes are well separated, andin Strepsiptera are called “eyelets” (Buschbeck

et al. 2003). Forewings of adult male Strepsipteraare reduced to halteres, which appear to aid inflight stabilization, as do the hind wing halteres ofDiptera (Pix et al. 1993). Halter similarity withDiptera contributed to decades of fierce debateover the phylogenetic affinity of Strepsiptera,which recent morphological and genetic studieshave resolved as a sister-clade relationship withColeoptera (Niehuis et al. 2012; Boussau et al.2014). The shared ancestry of Strepsiptera andColeoptera implies that forewing halteres and ely-tra are homologous in these taxa. The ancestralstate of the forewing remains speculative, as noMesozoic transitional fossils have been found yet.

Biases in preservation mode, geography andtaxonomy characterize the fossil record of mostendoparasites. The small size of first-instar larvae,the short life span of adult males and the endopar-asitic lifestyle of all other life stages limit the fos-silization of Strepsiptera in particular. All but threepreviously described Strepsiptera fossils occur inamber. A Formicidae specimen preserved in Mid-dle Eocene oil shale and hosting two pupae of maleMyrmecolacidae (Lutz 1990) and a taxonomicallyunplaced first instar in Eocene Brown coal(Kinzelbach and Lutz 1985) are the only nonamberStrepsiptera fossils known besides those describedhere. All but four amber Strepsiptera fossils werecollected in the Dominican Republic or the Balticregion. Fossils collected outside these regions arethe Cretaceous Cretosylops engeli Grimaldi andKathirithamby, 2005 (Cretosylopidae) (in Grimaldiet al. 2005), Kinzelbachilla ellenbergeri Pohl andBeutel, 2016 (Kinzelbachillidae) and Phthanoxenosnervosus Engel et al., 2016 (Phthanoxenidae) fromBurmese amber, and the Eocene Kronomyrmeco-lax fushunicus Wang et al., 2015 (Myrmecolacidae)from Chinese (Fushun) amber. About half ofextinct Strepsiptera species belong to Myrmeco-lacidae, and about half of those (including the twodescribed here) are assigned to Caenocholax(Kathirithamby, in press). Kronomyrmecolax fushu-nicus is the oldest described myrmecolacid at 50 to53 Ma (Wang et al. 2014).

Myrmecolacidae differs from other Strep-siptera taxa in host affinity and geographic dis-tribution. Each sex in this basal clade of stylopidstrepsipterans parasitizes a different insect clade(a condition termed heterotrophic heteronomy):males parasitize Formicidae (Hymenoptera),and females parasitize orthopteroid insects

(Kathirithamby and Hamilton 1992; Kathiri-thamby 2009). All Strepsiptera clades traditionallyranked as families exhibit cosmopolitanism inextant species distributions except Bahiaxenidae,Bohartillidae and Myrmecolacidae. Each of thesefirst two taxa is represented in the Recent by onespecies: Bahiaxenos relictus in Brazil (Bravo et al.2009) and Bohartilla megalognatha in CentralAmerica (Kathirithamby and Grimaldi 1993;Cook 2015). Myrmecolacidae includes 80 extantspecies, all of which are restricted to tropical andsubtropical latitudes, up to Texas and North Car-olina in the New World (Kathirithamby, in press).The clade’s host taxa live worldwide.

Here we report two new species of Caeno-cholax. The specimens are preserved as compres-sion fossils in thinly bedded limestone from theEarly Eocene Green River Formation of RioBlanco County, Colorado. The fossils describedbelow are the first strepsipterans reported fromthe Green River Formation, the first adult strep-sipterans preserved as compression fossils and theoldest and northernmost occurrences of fossil orextant Caenocholax in the New World.

Materials and Methods

Jim Barkley collected the specimens in Rio BlancoCounty, Colorado, and donated them to the Divi-sion of Invertebrate Paleontology of the PeabodyMuseum of Natural History, Yale University, NewHaven, Connecticut, USA. The fossils are pre-served as organic compressions in thinly beddedlimestone. We immersed specimens in alcoholwhile photographing them with a Leica MZ-16microscope and Leica Application Suite software(Leica Microsystems, Buffalo Grove, Illinois;www.leica-microsystems.com/), and we z-stackedimages with Helicon Focus, v. 5.3 (Helicon Soft2012) to generate a single composite image of eachspecimen. We prepared line drawings from z-stacked images with Adobe Photoshop CS4(Adobe Systems 2008). For the line drawing ofYPM IP 320328, which has a part and counter-part slab, we horizontally reversed the image ofone plate and superimposed it on the image of theother plate. We measured specimen anatomy witha Zeiss STEMI 2000-CS microscope (Carl ZeissMicroscopy, Thornwood, New York; www.zeiss.com), a QImaging Micropublisher 5.0 RTV cam-era and QCapture Pro 7 (QImaging 2010). We

Bulletin of the Peabody Museum of Natural History 57(2) • October 2016166

compared the slabs containing specimens againstthe Munsell Rock Color Chart (Munsell Color,Grand Rapids, Michigan; munsell.com) todescribe shale color.

The wing venation abbreviations used in thetext and figures follow standard entomology con-ventions: C, cubitus; CuA, anterior cubitus; R,radius; and Sc, subcubitus. Subscripts indicatewing vein branches, with the first branch definedas most proximal. Other anatomical terms areabbreviated in figures: a, antennomere; ab,abdominal segment; ae, aedeagus; e, eye; fb, fla-bellum; fm, femur; h, halter; hd, head; le, leg; s,seta; tb, tibia; ts, tarsus. Antennal and abdominalsegments are numbered from proximal to distal.

Institutional abbreviations used here are asfollows: USNM, National Museum of NaturalHistory, Smithsonian Institution, Washington,DC, USA; YPM IP, Division of Invertebrate Pale-ontology, Peabody Museum of Natural History,Yale University, New Haven, Connecticut, USA.

The nomenclatural acts below have been reg-istered with Zoobank: urn:lsid:zoobank.org:pub:340F120E-9B88-4B48-B6DD-3C94B1C4380E

Geologic Setting

The Green River Formation is a series of pondedbasins, including lakes in what now forms north-west Colorado, northeast Utah and southwest

Wyoming. The lakes formed as a result ofdrainage into areas of Late Cretaceous forelandbasins deformed by the Laramide Orogeny (Dick-inson et al. 1988). Diverse animal and plant fossilsabound in the Green River Formation, a famousEocene lacustrine Lagerstätte (Grande 1984,2013). The fossils discussed here come from theformer eastern shore of Lake Uinta, the largest ofthe Green River lakes, in the southeast part of theformation. Six members of Lake Uinta sedimentshave been identified; this material belongs to theParachute Creek Member in the Piceance CreekBasin (Grande 2013). The Parachute Creek Mem-ber is thought to have formed in an evaporativeevent 49 to 50 Ma, during the Ypresian (EarlyEocene) (Smith et al. 2008).

The fossils described here came from twoadjacent properties in Rio Blanco County, Col-orado (Figure 1). YPM IP 320328 was collected atsite B in Dayvault et al. (1995), in a quarry collo-quially known as Gus’ Pit. The coordinates for thislocality are 39°43�38.10�, –107°58�34.14�, approx-imately 2 miles (3 km) west of the Rio Blancotown store. YPM IP 389335 was collected at aranch neighboring the quarry, at 39°43�38.13�,–107°58�34.17�. Both sites lie approximately 45 mbelow the Mahogany Bed, at 2,180 m elevation.

Consistent with environmental reconstructionsfor other localities in the Green River Formation,the flora and fauna associated with the collection

The First Twisted-wing Parasitoids from the Green River Formation • Antell and Kathirithamby 167

FIGURE 1. Collection localities of Caenocholax. Filled circles indicate collection localities of modern specimens;open circles indicate fossil localities. Fossils from the Baltic region and the Dominican Republic are preserved inamber; fossils from the United States are preserved as organic compressions and described here.

area indicate a low-energy wetland environment,possibly a lagoon. Equisetaceae, Typhaeceae andalgae are present (J. Barkley, pers. comm., 18 Sep-tember 2015), as well as insects in aquatic life stages.Some rock slabs exhibit ripple marks, but theseslabs have not been found to contain fossils. Thebeds are rich in iron, with limonite and pyrite com-monly occurring. Slabs with fossil insects also fre-quently contain pyrite, as well as aluminum oxideclays; dolomite and amber are present occasionally.

Systematics

Strepsiptera Kirby, 1813Stylopidia Kinzelbach, 1969

Myrmecolacidae Saunders, 1872Caenocholax Pierce, 1909

Type species. Caenocholax fenyesi Pierce, 1909; USNM 10081.

Included species. Caenocholax barkleyi sp. nov.; C. brodzin-skyi Kathirithamby and Grimaldi, 1993; C. dominicensisKathirithamby and Grimaldi, 1993; C. fenyesi Pierce, 1909; C.groehni Kathirithamby and Henderickx, 2008; C. palusaxus sp.nov.

Diagnosis. Median and two lateral spines, or median spine only,on dorsally hooked aedeagus; abdominal segment X with

enlarged lobate plate partially overlapping abdominal segmentIX; hind wing R3 absent (Kathirithamby and Johnston 1992).

Discussion. Synapomorphies of crown Strepsiptera present inCaenocholax barkleyi and C. palusaxus include a dorsallyattached antenna, shortened coronal suture and eye with well-separated eyelets (Pohl and Beutel 2016). Flabella on the third ofseven antennomeres and the absence of CuA2 place the newspecies in Myrmecolacidae, the basalmost lineage of Stylopidiaexcluding Corioxenidae (McMahon et al. 2011). Caenocholaxbarkleyi and C. palusaxus are attributable to Caenocholax, sisterclade to all other myrmecolacids, because each lacks R3 and hasa curved aedeagus with at least one hooked projection(McMahon et al. 2011).

Of the four previously described Caenocholax species, onlyC. fenyesi is extant. Genetic analysis indicates a substantial,unrecognized diversity within C. fenyesi, however. As many as 10lineages within Recent C. fenyesi were found consistent with dis-crete species according to the evolutionary species concept(Hayward et al. 2011). In addition to genetic differences amonglineages, females’ host choice is diagnostic, and male morphol-ogy differs subtly in several but not all of these lineages (Hay-ward et al. 2011).

Caenocholax barkleyi Antell and Kathirithamby, sp. nov.

http://zoobank.org/urn:lsid:zoobank.org:act:935B3915-B23E-4E93-80D3-36C233D1BD63

Figures 2 and 3

Bulletin of the Peabody Museum of Natural History 57(2) • October 2016168

FIGURE 2. Caenocholax barkleyi sp. nov., holotype (YPM IP 389335). A, Full body, image composed of stackedphotographs at different depths of field. B, Schizochroal eyes, showing the separate eyelets. C, Aedeagus, show-ing the two recurved hooks and lack of central projection.

Fossil material. Holotype, YPM IP 389335, Green River Forma-tion (Early Eocene; about 50 Ma), Rio Blanco, Colorado, USA.Adult male preserved in left lateral aspect on a single slab 25 by29 mm. The right wing is extended, but the distal leg segmentsand mouthparts are obscured. The lithology is pale yellowishbrown, with a grayish orange blush on the edge of the plate clos-est to the specimen.

Etymology. The species is named after Jim Barkley, who col-lected the holotypes described in this paper.

Diagnosis. May be distinguished from other species in Caeno-cholax by the following combination of character states: (1)aedeagus with two dorsal spines (lacking central projection pres-ent in C. fenyesi [Kathirithamby and Johnston 1992]); (2) pres-ence of R4 (absent in C. dominicensis [Kathirithamby andGrimaldi 1993]); (3) small ratio of antennomere 5/flabellum(smaller than in C. brodzinskyi holotype [0.66] [Kathirithambyand Grimaldi 1993], C. dominicensis [0.75] [Kathirithamby andGrimaldi 1993] or C. fenyesi [0.60] [Kathirithamby and Johnston1992]); and (4) ratio of antennomeres 6/7 (smaller in C. brodzin-skyi holotype [0.56] [Kathirithamby and Grimaldi 1993] or C.groehni [0.55] [Kathirithamby and Henderickx 2008]; larger in C.dominicensis [0.71] [Kathirithamby and Grimaldi 1993] and C.fenyesi [equal length] [Kathirithamby and Johnston 1992]).

Description.

Adult male. Eye very large; maximum width across eyes 0.72mm; with at least 17 eyelets. Antenna with 7 segments and 1 fla-bellum (0.75 mm) on flagellomere 3. Antennomere lengths: 5 �

0.41 mm; 6 � 0.19 mm; 7 � 0.30 mm. Ratios: antennomere5/flabellum � 0.55; antennomeres 6/7 � 0.63. Wing venation:R2 short; R3 and R5 not apparent; R4 1.11 mm. Wing expanse:maximum width 1.53 mm. Halter length 0.56 mm. Thoraxhumped: maximum width 0.64 mm at mesothorax. Maximumwidth of abdomen 0.31 mm. Aedeagus terminating in two sym-metric, recurved spines. Aedeagus length 0.15 mm; widthbetween apices of spines 0.13 mm. Total length 1.64 mm (meas-ured from anterior-most visible part of vertex to end ofabdomen, excluding aedeagus).

Remarks. Although the eyes of the holotype appear to be touch-ing or nearly touching, this configuration is likely an artifact oftwo-dimensional preservation. While surrounding sedimentcompressed and dewatered, the specimen was angled on its rightside, so the left eye appears to overlap the right eye. In life, thevertex may have separated the eyes as in all other Caenocholax.Similarly, although only 17 eyelets are visible in the holotype,several more eyelets may be present ventrally and obscured byrock matrix. We interpret the venation as having an absent R5;in all other Caenocholax the R5 is present. In the C. barkleyi holo-type a short vein lies posterior to the R4 in the distal portion ofthe wing, however, and it is possible that this fragment repre-sents the R5.

Caenocholax palusaxus Antell and Kathirithamby, sp. nov.

http://zoobank.org/urn:lsid:zoobank.org:act:5870F130-716B-49DF-B3BF-00B4EFB87AE4

Figures 4 and 5

Fossil material. Holotype, YPM IP 320328, Green River Forma-tion (Early Eocene; about 50 Ma), Rio Blanco County, Colorado,USA. Adult male preserved on two slabs 33 by 48 mm (part andcounterpart). The rock is pale yellowish brown. The strep-sipteran is exposed in dorsal aspect with the left wing extendedand the right wing folded, obscuring abdominal segment X andsome of the aedeagus. Rock matrix conceals maxillae, mandiblesand tarsi on ventral side of specimen.

Etymology. The new species epithet is a combination of thenoun saxum (Latin, meaning rock), referring to the novelpreservation medium of the holotype, and the root palu (Latin,meaning swamp or marsh), indicating a habitat in which thespecies may have lived and the low-energy lacustrine environ-ment that facilitated its preservation.

Diagnosis. May be distinguished from other species in Caeno-cholax by the following combination of character states: (1) ratioof antennomeres 6/7 (smaller in all other Caenocholax species);(2) ratio of antennomere 5/flabellum (smaller in C. barkleyi[0.55]; larger in C. brodzinskyi [0.66] [Kathirithamby andGrimaldi 1993] and C. dominicensis [0.75] [Kathirithamby andGrimaldi 1993]); and (3) C, Sc and R1 present and R4 extendingto wing margin (wing venation more reduced in C. barkleyi, C.dominicensis and C. groehni).

Description.

Adult male. Head length 0.38 mm. Eye large with at least 18 eye-lets; maximum distance across eyes 1.07 mm and minimumdorsal separation 0.18 mm. Antenna with 1 flabellum (0.93 mm)on flagellomere 3 and the following antennomere lengths: 5 �

0.56 mm; 6 � 0.35 mm; 7 � 0.43 mm. Ratios: antennomere5/flabellum � 0.60; antennomeres 6/7 � 0.81 mm. Wing vena-tion: C and Sc present, with Sc adjacent and parallel to C; R1, R2

The First Twisted-wing Parasitoids from the Green River Formation • Antell and Kathirithamby 169

FIGURE 3. Line drawing of Caenocholax barkleyi sp.nov., holotype (YPM IP 389335). Abbreviations: a,antennomere; ae, aedeagus; e, eye; fb, flabellum; fm,femur; h, halter; R, radius; Sc, subcubitus; tb, tibia; ts?,tarsus?

Bulletin of the Peabody Museum of Natural History 57(2) • October 2016170

FIGURE 4. Caenocholax palusaxus sp. nov., holotype (YPM IP 320328). A, Part slab. B, Counterpart slab.

and R4 nearly touching or touching wing margin; R3 not appar-ent. R4 1.74 mm in length. Wing expanse: broadest width 1.93mm. Halter length 0.56 mm (average of left and right halteres).Thorax symmetrically tapering anteriorly and posteriorly frommaximum width of 0.93 mm across metanotum. Aedeagusbroad, curved and with �1 hooked spine. Total length 2.42 mm(measured from anterior-most visible part of vertex to end ofabdomen, excluding aedeagus).

Remarks. Although less than 3 mm long, the holotype of Caeno-cholax palusaxus is nearly 50% larger in body length than C.barkleyi, C. dominicensis, C. fenyesi or C. groehni. Preservation ispoor in the wing region that contains the R5 in other Caeno-cholax.

Superimposing a horizontally reversed image of one slabon an image of the other allows better resolution of some fea-tures in the holotype compression fossil than do photographs ofeither slab alone. The spine on the aedeagus of the holotype isone such structure that is split across two slabs and revealed ingreater detail when slab images are superimposed.

Discussion

The two Early Eocene (about 50 Ma) adultstrepsipterans described here are the oldestMyrmecolacidae reported thus far, except for Kro-nomyrmecolax fushunicus from Fushun Coalfield

amber in northeastern China, which is coeval orup to 4 million years older (Wang et al. 2015). Theage of the Early Eocene Caenocholax speciesdescribed here lies within the range of divergencedates of stem Caenocholax estimated from a fossil-calibrated molecular dating of 44.0 to 55.0 Ma(95% highest posterior density) (Hayward et al.2011; McMahon et al. 2011). The Green River fos-sils restrict the origin of Caenocholax to at least 49Ma, however. Relationships of C. barkleyi and C.palusaxus to other Caenocholax species remainunresolved because phylogenies of Caenocholax todate are based exclusively on genetic data unavail-able in fossils (Hayward et al. 2011).

The preservation of extinct Caenocholaxbarkleyi and C. palusaxus in limestone differs fromthat of all previously described fossil strepsipterans,which, except for two male pupae parasitic in anant in oil shale (Lutz 1990) and a first-instar larva inbrown coal (Kinzelbach and Lutz 1985), occurexclusively in amber. The lithification of theseGreen River specimens gives further evidence forthe exceptional quality of preservation in the for-mation and for the high preservation potential of

The First Twisted-wing Parasitoids from the Green River Formation • Antell and Kathirithamby 171

FIGURE 5. Caenocholax palusaxus sp. nov., holotype (YPM IP 320328). Line drawing made from the image ofone plate reversed horizontally and superimposed on an image of the other plate. Abbreviations: a, antennomere;ae, aedeagus; C, cubitus; e, eye; fb, flabellum; h, halter; R, radius; Sc, subcubitus; tb, tibia; ts, tarsus.

insects in lacustrine environments in general(Smith 2012). Famous as both a Concentration andConservation Lagerstätte, the Green River Forma-tion has previously yielded 20 major clades ofinsects traditionally ranked as orders: Blattodea,Coleoptera, Dermaptera, Diptera, Ephemeroptera,Hemiptera, Hymenoptera, Isoptera, Lepidoptera,Mantodea, Mecoptera, Neuroptera, Odonata,Orthoptera, Plecoptera, Psocoptera, Raphid-ioptera, Siphonaptera, Thysanoptera and Tri-choptera (S. Butts, pers. comm., 5 February 2016;T. Karim, pers. comm.; Grande 2013). As the firstexamples of Strepsiptera reported from the for-mation, the fossils discussed here are a significantaddition to the known Green River paleobiota.

The Colorado occurrence of Caenocholaxbarkleyi and C. palusaxus illuminates the biogeo-graphic history of Myrmecolacidae. Rio BlancoCounty is the northernmost New World record offossil or Recent Myrmecolacidae. Extant membersof the clade occupy a circumtropical distribution,with the northernmost range extent in North Car-olina (Figure 1) (Kathirithamby, in press). TheEocene presence of Caenocholax in Coloradoindicates the colonization and subsequent extinc-tion of Myrmecolacidae in the Green River region(approximately 40°N). From the Late Paleoceneto Early Eocene, the earth experienced a rapid risein global temperatures and CO2 concentrationstermed the Paleocene-Eocene Thermal Maxi-mum (PETM), in which megathermal climatesextended to high latitudes (Kennett and Stott1991; Greenwood and Wing 1995; Zachos et al.2003). Like members of several other animalclades adapted to warm climates, including stem-relatives of tsetse flies (Insecta: Diptera: Glossina)(Grimaldi 1992), diverse primates (Mammalia:Placentalia) (Ni et al. 2013), frigatebirds (Aves:Suliformes) (Olson 1977) and several clades ofcrocodilians (Reptilia: Archosauria: Crocodylia)(Selden and Nudds 2008), myrmecolacids lived inthe Green River region during the warmer andwetter conditions of the PETM but becamerestricted to lower latitudes by the Recent.

Conclusions

As for many entomophagous endoparasites, thefossil record of Strepsiptera is scarce and is biasedin taxonomy, geography and type of preservation.We describe two new species of myrmecolacid

strepsipterans from the Eocene Green River For-mation, extending the known New World geo-graphic distribution of the clade. The specimensdescribed here are also the only adult strepsipter-ans preserved in rock and the oldest fossils ofCaenocholax reported thus far. The detailedpreservation of tiny males, which live for nomore than a few hours as adults, highlights theexceptional preservation potential of lacustrineenvironments.

We encourage careful examination of insectcompression fossils to discover small but signifi-cant specimens, particularly parasites, whichmight otherwise remain unnoticed. Particularlypromising sites for future fossil parasite prospect-ing include those that, like the Green River, harborabundant insect compression fossils from lacus-trine environments. Examples of such sitesinclude Florissant, Grube Messel and the RubyPaper Shale (Monroe 1981; Wilson 1988; Schaaland Ziegler 1992). Further examination of insectfossils from these and other Conservation Lager-stätten may yield rarely preserved taxa that couldexpand our understanding of Paleogene ecologi-cal community composition and the evolution ofspecies interactions, including host–parasite inter-actions.

Acknowledgments

Jim Barkley collected, photographed and donatedthousands of Green River insect fossils to the YalePeabody Museum of Natural History, includingthe two described here. The Yale PeabodyMuseum Division of Invertebrate Paleontologysupported research on the specimens, and SeniorCollections Manager Susan Butts provided accessto the collections. Derek Briggs (Yale University),Jacques Gauthier (Yale University), James Lams-dell (Yale University) and Erin Saupe (Yale Uni-versity) commented on drafts. Eric Lazo-Wasem(Yale Peabody Museum) assisted with specimenmeasurement. Sam Heads (University of Illinois)confirmed the initial identification. Jerry Cook(Sam Houston State University, Texas) andDavid Grimaldi (American Museum of NaturalHistory, New York) provided detailed and help-ful reviews.

Received 11 March 2016; revised and accepted 20June 2016.

Bulletin of the Peabody Museum of Natural History 57(2) • October 2016172

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