Distribution of
Insects in the
Northern Hemisphere:
Continental Drift: and
Epicontinental Seas
Gerald R. Noonan
I
nthe past ca. 30 years, three important paradigms have
become available for study of the biogeography of insects.
Plate tectonics has become a generally accepted hypothesis
for determining past continental positions and configurations.
The similarly general acceptance of the principles of cladistics
(as proposed by Hennig [1966J and summarized by Wiley [1981]
and other papers) has provided a conceptually rigorous method
for recognizing related groups of insects. And finally, the concept of vicariance biogeography (as set forth in Platnick [1976],
Platnick & Nelson [1978], Nelson & Rosen [1981], and Olher
80
papers) has provided a method for testing whether the presence
of cladistically related groups on the opposite sides of barriers,
such as oceans, is because their ancestor was vicariated when
the barrier developed.
Geological and paleontological data show that the lands of
the Northern Hemisphere were once strikingly different than
those of today. In the Late Cretaceous and the Early Tertiary, the
two large land masses were Euramerica, composed of eastern
North America and Europe, and ASiamerica, consisting of western North America and Asia (Cox 1974, Hallam 1981). This
BULLETIN
Of
THE ESA
paper summarizes
data ahout these and other past geological
changes in £111.' Northern Hemisphere
and considers the vicariann' dfccrs of such changes on insects. In the discussion below,
1 have uSl'd the time scale in Palmer (1983) to estimate approximate ages, in tl'rms of millions
of years, when geological
references
have cited only relative ages such as periods
or
epochs. These estimated ages are cited in parenthesis
as "mya"
without further rderence
to Palmer.
Euramerica and Asiamerica resulted from geophysical changes
that may he viewed, for this discussion,
as dating back to the
Paleozoic. The past lands had come together during the Paleozoic to form the super-continent
of Pangaea (Cox 1974). The
sim ilarity of reptile fossi Is thous:ll1ds of kilometers apart suggests
that during the Triassic (208 .. 24'5 mya) there were no major
geographical
or climatic barriers
(epicontinental
seas, major
mountain
chains, or deserts)
within Pangaea, even between
l.aurasia and Gondwanaland
(Cox 197"*).
During the Jurassic (l'H208 mya), seas began to divide the
land masscs (Cox 1974). Thc Tcthys Sca started to develop and
hy approximately
the end of the Jurassic (144 mya) had separatcd Pangaea into thc northern
land mass of Laurasia and the
southern one of Gondwanaland
(Schweickert
1981). The Turgai
Straits began [() transgrcss across Eurasia, and by the Callovian
Agc of thc late Middle Jurassic (163-169 mya) this epicontinental sea scparated the land in Asia from that in Europe (Hallam
1981l.
Thesl' .Jurassic changes resulted
in the land configurations
shown in the figure ahove (Cox 197-1). Euramerica
included
much of present North America, Greenland,
various Atlantic
islands, portions of thc British Isles, and lands now submerged
(Cox I 9~·t). Asia comprised
much of present Siberia and Asia
proper along with the Indo-Australian
Archipelago
and lands
now suhmergl'd
alongside
the Archipelago
(Cox 1974). Both
Asia and Euramcrica
wcrc possibly connected
via high paleoIal itude lands betweell
present day Alaska and Siberia (Cox
I()"7·t l.
By thc Early Crctaccous
(97.'5-144 mya), Euramerican
lands
includcd part of wcstcrn Europe (Cox 197"*, Hallam 1981). The
Mid-Contincntal
Scaway began [0 transgress across the middle
of North Amcrica. This epicontinental
seaway bisected
North
America in the Cenomanian
Age of the Late Cretaceous
(9197.5 mya) and did not withdraw until about 70 million years ago
(Hallam 1981). The Mid-Continental
Seaway together with the
Turgai Straits isolated two large land masses in the Northern
Hemisphere:
Asiamerica (Asia plus western North America, with
the connection
between them being lands between present-day
Alaska and Siberia); and Euramerica
(eastern
North America
plus Europe) (Cox 1974, lIallam 1981).
During a span of ca. 21-27 million years (from the complete
bisecting of North America by the Mid-Continental
Seaway 9197.5 mya to the withdrawal of this seaway ca. 70 mya), the two
large land masses in the Northern Hemisphere
were Euramerica
and Asiamerica (Cox 1974, Hallam 1981). Land configurations
began to shift toward those of today with the retreat of the Turgai
Straits from Asia (about 30 million years ago in the Oligocene
[Hallam 1981]) and the opening of the North Atlantic between
Europe and North America.
This opening
was a complex
process and apparently
commenced 90-95 million years ago in the Middle Cretaceous when
a line of opening developed
from the Azores-Gibraltar
Ridge
northward into the Rockall Trough (Hallam 1981). During early
phases of the opening of the North Atlantic, a rift apparently
formed between Greenland
and Labrador, resulting in Greenland, the Rockall Plateau, and Europe being a single land mass
isolated by ocean from North America (Heirtzler
1973). Land
connections
between
Europe and eastern North America may
have remained,
via one or more northern
routes, until ca. 38
million years ago (Hallam 1981).
Climatic data and fossil vertebrate
and plant distributions
suggest that Euramerica
and Asiamerica
each had distinctive
insect faunas. Climate during the Cretaceous was much warmer
than today; during its warmest times a wide zone of temperatures
comparable
with modern tropical to subtropical
conditions
extended to at least 45' Nand 55' S in most of the world (Frakes
1979). Polar climates, thus, probably did not bar movements
of
terrestrial organisms across Euramerica or even across the possibly far northern connections
between western North America
and Asia. Temperatures
in the Northern
Hemisphere
did not
cool severely until approximately
the Eocene/Oligocene
boundary (ca. 36 mya) (Buchardt
1978, Frakes 1979, Norris 1982,
7cfN
1O'S
Super-continent
of Pangaea,
the Late Permian-Triassic.
(Past
and shaded areas, respectively;
dicated for reference purposes;
SllMMER
19H6
showing land configurations
of
lands and seas denoted by white
present boundaries
of lands inadapted from Cox [1974]).
Land configurations
of the Jurassic. (EA, Euramerica; T, Turgai
Straits; lands and seas denoted as in opposite
figure; adapted
from Cox [1974]).
81
Land configurations of the Late Cretaceous. (EA, Euramerica;
MCS,the Mid-Continental Seaway; T, the Turgai Straits; lands and
seas denoted as in first figure; adapted from Cox [1974]). Postulated northern land connections between Asia and western North
America are not shown since geologists do not agree on the past
configurations or latitudes of these connections.
Wolfe 1978). Until about the Middle or Late Eocene (ca. 36-52
mya) lands now well within or close to the Arctic Circle apparently had temperate to warm temperate climates (Frakes 1979,
West & Dawson 1978, R. West, personal communication). Vertebrate fossils show that both Asiamerica and Euramerica had
distinctive dinosaur faunas in the Cretaceous (Cox 1974). Plant
fossils show that each of these lands had distinctive floras in the
Cretaceous (Hallam 1981, Wolfe 1975) and in the early Tertiary
(Wolfe 1975).
Fossil data suggest that terrestrial faunal and floral relationships shifted in the Tertiary toward those of the present. Records
of mammal fossils from western Europe and western North
America show a high degree of faunal resemblance 49-53 million years ago in the early Eocene followed by a sudden decrease
in the latter part of the Eocene 38-49 million years ago (West
& Dawson 1978). Plant fossils suggest that the importance of
Beringia as a major floristic pathway declined from the Miocene
(5.3-23.7 mya) onward (Wolfe 1975).
In summary, geological and fossil data demonstrate that for
ca. 21-27 million years the Northern Hemisphere had tWOlarge
land masses, Euramerica and Asiamerica. These lands had distinctive fossil plants and vertebrates. The terrestrial faunas of
North America and Eurasia shifted toward present patterns in
the Tertiary, with such shift accelerated by the rupture of land
connections between Europe and eastern North America. It
seems logical to assume that groups of insects must once have
been endemic to Euramerica or to Asiamerica as were past plants
and vertebrates.
Many of these endemic insects probably had tropical adaptations because of the warm climates of the Cretaceous and early
Tertiary. However, data on paSt climates suggest that temperate
environments existed in northern lands before land configurations shifted completely toward those of the present.
Temperate environments apparently existed in the Northern
Hemisphere by the early Tertiary. Paleocene (57.8-66.4 mya)
mammal, insect, and plant fossil assemblages from Montana
suggest a lowland, humid, warm-temperate climate (Wilson
1978). Northern lands such as Spitzbergen and Ellsmere Island
82
apparently had warm temperate to temperate climates by the
Paleogene (23.7-66.4 mya) (Dawson et al. 1976, West & Dawson
1978). Similar climates apparently occurred in the Mackenzie
Delta region of northern Canada during the Middle and Late
Eocene (36.6-52 mya) (Norris 1982). Plant fossils suggest alternating cooler and warmer intervals of climate in the early Middle
Eocene (ca. 52 mya) and the early Late Eocene (ca. 40 mya)
(Wolfe 1985). Tropical forests apparently retreated southward
of 50' N during the cooler intervals and extended northward
during the warmer periods (Wolfe 1985). However, these northward extensions of tropical environments were less than during
the Early Eocene (52-57.8 mya), and belts of mixed coniferous
forest remained in the north during the warmer periods (Wolfe
1985). By the Eocene, western North America had uplands with
climates presumably cooler than in adjacent lowlands (Wolfe
1985).
Geological and paleontological data discussed earlier show
that three important vicariance events either ended or began
within the Tertiary. The Turgai Straits continued to bisect Eurasia
until ca. 30 million years ago. There may have been land connections between Europe and eastern North America as recently
as 38 million years ago. And last, plant fossils suggest that
interchange across the Bering area declined from the Miocene
(5.3-23.7 mya) onward. All three events, thus, occurred after
temperate climates existed in the Northern Hemisphere.
Geological and paleontological data do not offer much basis
for concluding whether the Mid-Continental Seaway affected
temperate-adapted insects. This epicontinental sea retreated in
the Late Cretaceous. I have been unable to find references
establishing temperate climates in the Northern Hemisphere
before the end of the Cretaceous, but Wolfe (1975) inferred
from past plant distributions that climates at higher latitudes
may have been "more temperate" than those at more southerly
locations.
It seems probable that populations of the ancestors (whether
tropical or temperate adapted) of some of our extant temperate
insects in the Northern Hemisphere were split by 1) the COI11plete opening of the North Atlantic, 2) the deterioration of the
Bering area as a path for faunal interchange between Asia and
western North America, 3) the Turgai Straits, and 4) the MidContinental Seaway.
From the above geophysical changes we might expect tWO
biogeographical patterns.
1. Groups present in Europe mid eastern Nortb America, hut
not elsewbere. The anceStors of these groups were presumably
present in Euramerica and subsequently underwent vicariance
with the opening of the North Atlantic.
2. Groups present ill anI)' temperate Asia and western Nortb
America. The ancestors of these groups were presumably pres·
ent in Asiamerica and subsequently underwent vicariance when
land connections were interrupted by ocean or by the development of polar climates.
Recognition of these patterns may be obscured in some groups
by dispersal of descendants away from eastern North America,
western North America, Europe, or temperate Asia. However,
vicariance biogeography techniques such as those used by Platnick (976) may permit identification of dispersal and recognition of vicariance.
A survey of biogeographical literature on all insect orders
(done by searching the Zoological Record for the last 40 years
and by using computerized data bases extending from the pres·
ent back through 1969) reveals more than 20 groups with
biogeographical patterns suggesting that Euramerican ancestors
were split by the opening of the North Atlantic. The same survey
BULLETIN OF THE ESA
yields only five cxamplcs of groups with biogeographical patterns suggcsting that ancestors werc split by severing of connections betwet'n Asia and western North America. (A detailed
reading of all taxonomic papers and catalogs about insects of
the Northern Hemisphcre would probably reveal additional
instanCl's of groups showing one or both biogeographical patterns_) Examples of both types of patterns are summarized
below.
Groups with Presumed Euramerican Ancestors
Schaefer & Calabrese (1980) studied amphi-Atlantic species
pairs in Gerris and Lilll//oporus (Gerridae) and decided that the
closest relative of a to[al of four Nearctic water striders is another
species in the Palaearctic. Each pair consists of one member in
western or central Europe and another in North America, with
only one of thc North American forms occurring west of the
Rocky Mountains_ Four ancestral species were apparently prest'nt in Euramerica, and the opening of the North Atlantic apparently isolated populations that produced the present speciespairs.
The tribe Callaphidini of the family Aphididae has 24 genera,
is widespread througholll the Northern Hemisphere, and has
groups that show geographical distributions suggesting Euramerican ancestors (Richards 1965). For example, the therioaphidinc group has two gencra, Monelliopsis in eastern North
AmcriCI, and Tberioapbis restricted to the western Palaearctic.
Thc bectle family Carabidae has several groups with presumed
Euramerican ~lI1cestors, two of which are noted here. Jeannel
(19·12) concluded that those Nearctic genera of the tribe Trechini with all or many species restricted to cave habitats are
morl' closcly related to montane-dwelling European genera than
the)' are to mhcr North Amcrican trechines. Allen (1980, 1983)
analyzed the cladistics and biogeography patterns of the subtribe
Myadi (tribc l'terostichini). The five genera of the subtribe occur
in three disjunct areas: northeastern North America, the western
Palal'arcric from southern Europe to northern parts of the Middle
East, and tcmperate Asia. Allen concluded that the opening of
the North Atlantic split a Euramerican lineage and led to the
evolution of the European lH)'as cbal)'baeus and the three species of the North American sister genus Neomyas.
Gagnl' (1981) rcvised the genus Trichonta (Mycetophilidae)
and analyzed the biogeography of its species and that of other
relatcd genera. He found that the insects' discernible characters
The geographical distribution of obligate cave-dwelling tre·
chine Carabidae in North America and the geographical distribution of their phylogenetic relatives in Eurasia.
did not permit proposal of detailed cladistic hypotheses, but he
was able to place species into general groups by similarities of
the male terminalia. He analyzed the geographical distributions
of these groups and proposed models for Holarctic Mycetophilidae whereby groups evolved in Euramerica and underwent
vicariance with the opening of the North Atlantic.
Fossil insects are poorly known compared with those of plants
and vertebrates. However, Baltic amber fossils show that some
groups of insects that are now restricted to the New World were
also once present in Europe. For example, Larsson (1978)
reponed that a fossil beetle in Baltic amber is apparently Megacephala (Tetracha) carolina. This species is today limited to
the Americas, from the southern United States southward into
South America, and in the West Indies (Blackwelder 1944, Boyd
1982). The genus Megacephala now occurs in tropical and warm
temperate areas of both the Old and New World (Basilewsky
1966). Hthe fossil has been correctly identified to species, then
M. carolina apparently once occurred in both Europe and the
Americas and died out in the former area. Even if the fossil is
another species of Megacephala, it suggests that the genus once
had a Euramerican distribution. Ross (953) noted that the
eastern Nearctic trichopteran genus Phylocentropus is also
known by a Baltic amber fossil practically conspecific with an
extant Nearctic species.
Groups of Asiamerican Origin
The geographical distribution of therioaphidine
SUMMER
19H6
aphids.
Relatively few groups of possible Asiamerican ongll1 are
known. Allen (1983) noted instances where H. H. Ross phylogenies for mountain Trichoptera contained dichotomies between
pairs of taxa, with one taxon in northern Asia and the other in
the western United States. Richards (1965) reported that the
genus Tuberculatus (Homoptera: Aphididae: tribe Callaphidini)
occurs in both western North America and northeastern Asia. He
suggested that morphological specializations of its species suggest origin of the genus in western North America, with a
subsequent extension into temperate Asia.
The relative paucity in the biogeographic literature of examples of probable Asiamerican groups is possibly explained by
many temperate Asian insects being much less well known than
those of Europe and eastern North America. Many groups of
insects in western North America are also less well known than
those of the latter two regions.
83
Only one of the examples cited above (pterostichine carabid
beetles analyzed by Allen [1980, 1983]) is based on relationships
of extant taxa analyzed by cladistic techniques. However, the
use of such cladistic techniques is essential for forming testable
biogeographical hypotheses (Ball 1975, Noonan 1979, Allen
1983, and other authors). The near absence of cladistic analyses
of temperate groups widespread in both Eurasia and North
America emphasizes the strong need for such studies. We know
little about the relative importance to major groups of insects of
four vicariance events that were important to other organisms:
1) the opening of the North Atlantic, 2) the severing of land
connections between western North America and Asia, 3) the
separation of western North America from eastern North America
by the Mid-Continental Seaway, and 4) the separation of Europe
from Asia by the Turgai Straits.
Analysis of the effects of these vicariances on insects is best
approached by studying insect groups with taxa in both the
Nearctic and Palaearctic Regions. These studies should parallel
those of Allen (1983) and Platnick (1976), with use of cladistics,
vicariance
biogeography,
and data about postulated
past geolog-
ical and climatic changes. Such research will greatly increase
our understanding of the origins of many insect groups in the
Northern Hemisphere.
Acknowledgment
Gary S. Casper, Peter M. Sheehan, Stanley A. Rewolinski,and Jack A.
Wolfe read the manuscript and provided useful suggestions. Peter M.
Sheehan, Robert M. West, and Jack A. Wolfe provided useful information
and discussions about past geological changes. Any misinterpretations
of data are, of course, m)' responsibility. This material is based upon
work supported by the National Science Foundation under Grant BSR-
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Noonan. G. R. 1979. The science of biogeography with relation to
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•
GERALDR. NOONANis Curator of Coleoptera in the Invertebrate
Zoology Section of the Milwaukee Public Museum. Since receiuing his Ph.D. from the Univ. of California, Riverside in ]97] he
has conducted research on the classiji'cation, evolution, and
biogeography of beetles of the family Carabidae. He has done
research work in North, Central, and South America. His current studies include analyses of the effects of continental drift
and epicontinental seas on the distributions of ItlSects in the
Northern Hemisphere. He is also studying past and present
montane refugia for animals in North and South America and
speciation processes.
BULLETIN OF TilE
ESA