Table Of ContentPUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3612, 19 pp., 11 figures June 16, 2008
Insects from the Upper Miocene Grubstake
Formation of Alaska
DAVID A. GRIMALDI1 AND DON M. TRIPLEHORN2
ABSTRACT
Well-preservedinsectwingsarereportedinweaklyconsolidatedlacustrineshalefromtheGrubstake
Formation,UpperMioceneofSuntranaCreek,centralAlaska.40Ar/39Ardatingofanimmediately
overlying volcanic ash indicates an age of slightly more than 6.7 6 0.1Ma, or approximately one
millionyearsbeforetheopeningoftheBeringlandbridge.Theinsectsincludefourgeneraandtwo
subfamilies of ants (Hymenoptera: Formicidae: Myrmicinae and Dolichoderinae), a species of
Ichneumonidae (Hymenoptera), three genera and families of flies (Diptera: Chironomidae [genus
indet.], Bibionidae [Bibio] and Lonchaeidae [Dasiops]), and the elytra of curculionid and carabid
beetles. Extant distributions of the flies and possibly the ichneumonid include northerly latitudes
around Suntrana. The ants are attributable to the extant genera Dolichoderus or Tapinoma
(Dolichoderinae), Solenopsis or Erebomyrma (Myrmicinae), as well as Veromessor and Novomessor
(Myrmicinae), indicating extensive biogeographic contraction to more southern latitudes of North
America today. These finds are consistent with evidence from a slightly younger deposit from the
uppermostMiocene(5.7Ma)oftheSewardPeninsula,Alaska.Implicationsarediscussedregarding
thedifferentialeffectsofclimatechangeandlandbridgesonthedispersalofvariousinsecttaxa.
INTRODUCTION (summarized by Elias, 1994), very few
Tertiary deposits are known, and only one
Despiteanareaof570,374squaremilesand significant Cretaceous deposit is known,
remarkablyvariedgeology,Alaskaboastsfew which is based on several minute insects in
reports thus far of Tertiary insects. While Late Cretaceous amber from the Arctic
there are actually more than 30 sites through- Coastal Plain (Hurd et al., 1958; Langenheim
outAlaskawhereinsectsfromtheQuaternary et al., 1960; Usinger and Smith, 1957;
(1.64 Ma to present) have been excavated Muesebeck, 1963). The largest deposit of
1DivisionofInvertebrateZoology,AmericanMuseumofNaturalHistory,CentralParkWestat79thSt.,NewYork,
NewYork10024-5192([email protected]).
2DepartmentofGeologyandGeophysics,UniversityofAlaska,Fairbanks,Alaska99775.
CopyrightEAmericanMuseumofNaturalHistory2008 ISSN0003-0082
2 AMERICAN MUSEUMNOVITATES NO. 3612
Tertiary insects is the so-called Lava Camp understandingthephylogenyofinsects,though
site from near Deering, northern Seward they are germane to issues on the lifespan of
Peninsula, a Late Miocene assemblage of speciesaswellasbiogeography.Insectremains
well-preserved remains of a flood plain forest asyoungasthePleistoceneandQuaternary,in
(Hopkins et al., 1971; Matthews, 1970, 1976, fact, often indicate extensive range contrac-
1977, 1978). These authors reported mega- tions, and have provided abundant data on
fossil plants, several dozen pollen types, and paleoclimatic fluctuations (Coope, 1962, 1970,
various orders of arthropods in 15 families 1973,1995).Grimaldi(1992)andGrimaldiand
and nearly 100 species. The flora was identi- Engel(2005)discussedaswelltheimplications
fiable to generic and often to species/species- of extralimital fossils for biogeographic hy-
group levels, and was dominated by spruce potheses. The ants preserved in these new
(Picea) and birch (Betula), with at least 10 Alaskan collections reveal extensive biogeo-
species of conifers. Well-sclerotized arthro- graphiccontractions,andtheinsectscollective-
pods were preserved as original cuticular ly contribute paleoclimatological data for
remains, albeit completely disarticulated, in- Alaska during a time period of considerable
cluding, for example, beetle elytra and prono- significance,namelyjustpriortoopeningofthe
ta (e.g., Matthews, 1970, 1976), oribatid mite Bering land bridge and mixing of the Arctic
carapaces, and even some sclerotized portions andNorthPacificoceans.
of male beetle genitalia (the last being highly
useful for comparison to modern species).
The Deposit
Flight wings were not preserved. Elias and
Matthews (2002) reviewed LateTertiaryfossil ThelocalityisatSuntranaCreek,anorthern
Coleoptera from northern Alaska and the tributary of Healy Creek, about 4.8 km above
Canadian high Arctic, and discussed the thejunctionofthelatterwiththeNenanaRiver
paleoclimatic implications. near the town of Healy in central Alaska
Here we report another occurrence of fossil (63u519N, 148u589W) (fig. 1). A description
insects from Alaska, recently discovered in of the general geology was provided by
lacustrine shales from the basal Grubstake Wahrhaftig (1987). The insect specimens oc-
Formation of Suntrana Creek in central curred in a gray, weakly consolidated, poorly
Alaska. This deposit is overlain by a volcanic stratified lacustrine shale less than one meter
ash that recently has been dated to 6.7 6 below a prominent white volcanic ash 10 me-
0.1 Ma, or Late Miocene (see below). Like ters above the base of the Grubstake For-
most compression fossil insects, these are mation, uppermost unit of the Usibelli Group
preserved as wings only, but with a venation (fig. 1). Exact derivation of specimens in the
sufficiently well preserved to allow identifica- shalesequenceisuncertain,becausespecimens
tion to family and generic levels. Studies of wererareandcouldbefoundonlybyremoving
complete, finely preserved insects in Early to and splitting weathered shale fragments.
mid-Miocene amber (20–15 Ma; Iturralde- Repeated attempts to collect additional speci-
Vinent and MacPhee, 1996) from the mens were not very successful, probably
Dominican Republic indicate that remarkably becausetheexposurewasactivelyundercutby
modern taxa existed at that time, some two- the creek and yielded relatively fresh material
thirdsofthespeciesbelongingtoextantgenera that did not readily split along weak bedding
(Grimaldi, 1995, unpubl.). Some studies of planes to reveal the insect remains. Future
insects in Dominican amber, in fact, have collecting will rely on the availability of
revealed species extremely similar to modern weathered,unearthedmatrix.
species (e.g., Krishna and Grimaldi, 1991; The overlying volcanic ash has been corre-
Kathirithamby and Grimaldi, 1993), and the lated (Wahrhaftig et al., 1969) with the
greatproportionofspeciesintheLateTertiary Tatlanika Creek ashes 60 km northeast of
(latest Miocene through Pliocene) of the the Suntrana locality. At Suntrana the ash is
Western Hemisphere Arctic appears to be not air-fall material, but was transported as
Recent species (Elias and Matthews, 2002). sediment by rivers and streams into a broad,
Thus,LateMioceneinsectshavelittlevaluefor shallow lake. Recent 40Ar/39Ar dating of
2008 GRIMALDI AND TRIPLEHORN: INSECTS FROM THEGRUBSTAKE FORMATION 3
Fig.1. MapsshowinglocationofGrubstakeFormationwhereinsectfossilswerecollected,alongwitha
generalizedLateTertiarystratigraphyofthearea.Ageswithdecimalpointsareradiometricagecontrols(see
Triplehorn etal.,1999). Arrowindicates approximate level offossil insects.
biotite, hornblende, and plagioclase from the nematoceranDiptera).Specimensaredeposited
Tatlanika ash gives a weighted mean mineral intheUniversityofAlaska,FairbanksMuseum
age of 6.7 6 0.1 Ma (Triplehorn et al., 1999), of Paleontology, for which UAF numbers (GS
which indicates a Late Miocene age for the [Grubstake]1toGS32)areprovided.
underlying insect fauna.
Order HYMENOPTERA Linnaeus, 1758
The Insects
Family Formicidae Latreille, 1802
Thirty-two isolated insect wings were pre-
Thewingsofalateantsarethemostcommon
served as dark brown, brittle membranous
insectremainsfromSuntrana,withatotalof22
remains on the matrix (e.g., figs. 2, 4, 6, 7).
ant forewings out of 30 identifiable insect
Theyappeartohavesomeoriginalcuticle,since
specimens. Represented are three genera, pos-
theyaredarkbrownwithadegreeofreliefand
siblythreespecies,ofmyrmicinesandaspecies
shine, typical of wings and other external
of dolichoderine. In discussion of wing vena-
cuticular parts of insects. To facilitate observa-
tion the terminology used is that presented in
tion in somecases, 70% ethanolwasappliedto
Ho¨lldobler and Wilson (1990), as labeled in
thesurfacetoincreasethecontrastbetweenthe
figure 3.Creighton(1950)servedastheprima-
veins and remaining areas. Venation was
ry reference for identification to genus and
illustratedwithadrawingtubeonaZeissSV-8
summariesofextantdistributions.
stereomicroscope. For two specimens the pres-
ervation did not allow identification; a third
specimen (UAF-GS8) had some venation pre- Subfamily Dolichoderinae Forel
served, but lack of resolution of the branching
precludes unambiguous identification (it ap- SPECIMENS: The myrmicine wings are dis-
pears to be a chironomoid or some other tinguished from the dolichoderine wing based
4 AMERICAN MUSEUMNOVITATES NO. 3612
Fig. 2. Photomicrographs of ant forewings. A–B. Dolichoderinae: Dolichoderus/Tapinoma: A. UAF-
GS1; B. UAF-GS20. C.Solenopsis/Erebomyrma: UAF-GS19.
2008 GRIMALDI AND TRIPLEHORN: INSECTS FROM THEGRUBSTAKE FORMATION 5
on lack of a second submarginal cell; a Formica and Lasius. In these two genera,
discoidal cell that is small and trapezoidal in however, the apical forking of veins Rs-M is
shape; and presence of a deep first submar- distal to the 1st radial cell. The fossils, in fact,
ginal cell. Specimens UAF-GS1 and GS20 are most similar to the myrmecine genera
(figs. 2,3)veryclosely resembles Dolichoderus Solenopsis Westwood and Erebomyrma
(Hypoclinea) Mayr and Tapinoma Foerster by WheelerinalsohavingRs-Memergefromthe
the existence of 1st and 2nd submarginal cells middle of the ventral wall of the 1st submar-
andadiscoidalcell,aswellasbytheirrelative ginalcell.Thefossilscanbeascribedinornear
shapes and positions (Brown and Nutting, thesetwomyrmicinegenerawithconfidence.
1949;Creighton,1950).Thefossildiffersfrom DISCUSSION: In North America there are
thesetwogenerabytheabsenceofashortvein approximately 15 species of Solenopsis (many
connecting the 1st discoidal cell and R+Sc. more in the neotropics); only two species
Wing length is estimated to be 8 to 8.5 mm extend to southernmost Canada (S. molesta
(tip of wing is lost). [Say] and S. texana Emery. Solenopsis molesta
DISCUSSION: There are approximately 20 is an extremely minute ant, 1.0–1.5 mm body
speciesofdolichoderineantsinNorth America length, much smaller than the fossils (6–
belonging to seven genera: Dolichoderus Lund, 7.5 mm estimated wing lengths, based on
Dorymyrmex Mayr, Forelius Emery, Line- incomplete specimens). Erebomyrma consists
pithema Mayr, Liometopum Mayr, Tapinoma ofoneextantspecies(E.longiWheeler),known
Foerster, and Technomyrmex Mayr (Bolton, onlyfrom Texas.Solenopsishasbeen reported
1994; Creighton, 1950). These are distributed from the Oligocene of France (The´obald,
mostlyinthesouthernpartoftheU.S.,andonly
1937a, b), Miocene of Croatia (Pongra´cz,
onespecies extends to Manitoba, the northern-
1928), and Miocene amber of the Dominican
most distribution of the subfamily in North
Republic(Wilson,1985),butnotreportedfrom
America. Extant Dolichoderus and Tapinoma
the prolific uppermost Eocene volcanic shales
extend at best to the southernmost border of
of Florissant, Colorado (Carpenter, 1930).
Canada. Dolichoderus appears to have been
Erebomyrma has been reported from the Oli-
widespreadinthegeologicalrecord,havingbeen
goceneofAix-en-Provence,France(The´obald,
reported from the Miocene of Idaho (Lewis et
1937a,b), but many of the insect fossils from
al., 1990a), Washington state (Lewis et al.,
thisdepositrequirerevision.
1990b), Dominican Republic (Wilson, 1985),
and China (Zhang, 1989; Zhang et al., 1994),
from the Oligocene of Colorado (Carpenter, Species 2 (Aphaenogaster sp.)
1930), France (The´obald, 1937a, b), England
(Cockerell, 1915), and in Eocene Baltic amber SPECIMENS: UAF-GS23 and UAF-GS24
(Wheeler, 1914). Tapinoma does not have such (figs. 4, 5) are partial forewings with an
an extensive fossil record, and is recorded only estimated length of approximately 10 mm.
in Miocene amber from the Dominican They are most similar to species formerly
Republic (Wilson, 1985) and Sicily (Kohring assigned to Novomessor Emery (now in
and Schlu¨ter, 1989), as compressions from the Aphaenogaster Mayr), based on the lack of a
MioceneofChina(Zhang,1989),andinEocene discoidal and 2nd submarginal cell, and the
amber from Rovno, Ukraine (http://edna. factthatthe(apical)RsandMveinsconverge
palass-hosting.org/search.php). proximally at the tip of the 1st marginal cell
(thereisnostemtoRsandM),forminganX.
Thefossilsareratherlargeants,similarinsize
Subfamily Myrmicinae Lepeletier de Saint
to modern species of the genus. The fossil
Fargeau
differs from at least A. albisetosus (Mayr)
Species 1 becausethe1st submarginalcell isnotaslong
and slender.
SPECIMENS: Specimens UAF-GS2, 4, 5, DISCUSSION: There are two extant North
and 19 (figs. 2, 3) have submarginal and American species of Aphaenogaster formerly
discoidal cells that are similar in size and assigned to Novomessor: albisetosus (Mayr),
position to those in the formicine genera which ranges from southwestern Texas to
6 AMERICAN MUSEUMNOVITATES NO. 3612
Fig.3. Cameralucidadrawingsofantforewings:A.UAF-GS1(Dolichoderinae:Dolichoderus/Tapinoma).
B–D: Myrmicinae sp. 1 (Solenopsis/Erebomyrma). B. UAF-GS2. C. UAF-GS4. D. UAF-GS5. All to the
samescale.
2008 GRIMALDI AND TRIPLEHORN: INSECTS FROM THEGRUBSTAKE FORMATION 7
Fig.4. Photomicrographsofantforewings.A,B:Aphaenogastersp.A.UAF-GS23.B.UAF-GS24.C.
UAF-GS25, Messor(Veromessor)sp.
8 AMERICAN MUSEUMNOVITATES NO. 3612
Fig.5. Cameralucidadrawingsofantforewings.A,B:Aphaenogastersp.A.UAF-GS23(A,Btosame
scale).B. UAF-GS24. C,D:Messor (Veromessor) sp.C. UAF-GS25. D.UAF-GS11.
2008 GRIMALDI AND TRIPLEHORN: INSECTS FROM THEGRUBSTAKE FORMATION 9
Fig. 6. Camera lucida drawing and photomicrograph of Ichneumonidae forewing, UAF-GS12,
cf.Brachypimpla.
southern Arizona; and cockerelli (E. Andre´), They are most similar to the North American
foundinMexico,westernTexas,andsouthern speciesofMessorForelformerlyassignedtothe
Arizona. They are abundant, desert-dwelling genusVeromessorForel,basedonthepresence
ants that are omnivorous and nest in the ofadiscoidaland 1stsubmarginalcell,no 2nd
ground. submarginalcell,andthefactthatthe(apical)R
and M veins converge proximally at the tip of
Species 3 (Messor sp.) the1stmarginalcell(thereisbarelyastemtoR
and M), virtually forming an X. The fossil
SPECIMENS: UAF-GS25 and UAF-GS11 differsfromatleastM.andrei(Mayr)basedon
(figs. 4,5)arevirtuallycompleteforewingswith thesmallerdiscalcellandveinsRandMnotas
estimated lengths of approximately 5–7 mm. divergent.
10 AMERICAN MUSEUMNOVITATES NO. 3612
Fig. 7. Photomicrographs of Bibionidae (Bibio)wings.A. UAF-GS6. B. UAF-GS7.
DISCUSSION: There are five extant species victimize the larvae principally of Lepidop-
of Messor (Veromessor) ants, three of which tera, symphytan Hymenoptera, and Coleop-
occur exclusively in California or immediate tera. Their geological record begins in the
vicinity. The other two are M. lobognathus Cretaceous, but a great diversity of fossils
(Andrews) from Colorado, and M. andrei occurs in various Tertiary deposits (a catalog
(Mayr)—the most widespread species—from of those genera with fossil species is in
California into Oregon, Nevada, and south- Carpenter, 1992). Given the overwhelming
western Arizona. They are desert-dwelling, diversity of ichneumonids, identification of
seed-harvesting ants that build mounds. their fossils (particularly ones where just a
wing remains) would be daunting without
comprehensive work like the series of mono-
Family Ichneumonidae Latreille, 1802 graphs on the North American ichneumonids
by Townes et al. and published in Memoirs of
Theichneumonids,orichneumonflies,area the American Entomological Institute, which
very large cosmopolitan family (some 60,000 served as reference for the present study.
species globally) of parasitoid wasps, which Fortunately, ichneumonid wing venation
