GEOLOGICA CARPATHICA, DECEMBER 2005, 56, 6, 473—481
www.geologicacarpathica.sk
Mass mutations of insects at the Jurassic/Cretaceous
boundary?
PETER VRŠANSKÝ
Geological Institute, Slovak Academy of Sciences, Dúbravská cesta 9, P.O. BOX 106, 840 05 Bratislava 45, Slovak Republic;
geolvrsa@savba.sk
Arthropoda Laboratory, Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya 123, 117868 Moscow, Russian
Federation; lab@palaeoentomolog.ru
Department of Zoology, Faculty of Natural Sciences, Comenius University, Mlynská dolina, 842 15 Bratislava, Slovak Republic;
vrsansky@nic.fns.uniba.sk
(Manuscript received May 12, 2005; accepted in revised form October 6, 2005)
Abstract: Diverse fossil insect assemblages near the Jurassic / Cretaceous transition from the Shar-Teg in Mongolia
comprise frequent deformed species. These (first known) mass fossil animal deformities, expressed as fusions of
veins changing the wing geometry, probably represent heritable mutations. They accumulated as a result of a changed
structure of selective pressure, and are unique in showing how individual variations may be fixed to form higher taxa,
significantly contributing to the process of evolution. Similar deformities were also recorded in recent ecosystems
undergoing elevated environmental stress. The occurrence of deformities indicate a long-lasting (100 kyr—1 Myr)
ecological stress in the continental environment before the J / K boundary and a biotic character of the changes: high
evolutionary tempo and consequent radiation of newly evolved taxa forming new control mechanisms including
social decompositors and new predators, resulted in temporary more or less destabilized ecosystems and uncon-
trolled, rapid evolution of its elements. Accordingly, ecosystems with higher diversity stabilized and some of their
elements remained virtually unchanged for over 30-million-years at least in Laurasia. Notably, occurrences of true
flowering plants and some advanced insects during the lowermost Cretaceous are limited to the region.
Key words: evolutionary mechanisms, modern ecosystems, boundary events, mass mutations, deformities.
Introduction
Variability extended by mutations, and natural selection in
the widest sense (comprising factors influencing fitness and
sexual selection) are essential premises for some of the evolu-
tionary processes eventually resulting in self-organization.
Deformities of the insect wings presented in this paper
provide indication of occurrence of mass mutations in cer-
tain periods such as during some boundary times when rap-
id evolution and / or radiation might have taken place.
It is hypothesized that during these comparatively short
time sections, significant mutations might result even in the
origin (and / or rapid evolution) of new higher taxa such as
those at the family and / or higher rank.
The origin of new control mechanisms, including social de-
compositors near the J / K boundary, display strong conver-
gence with recent activities of humans, which apparently also
represent new control mechanisms, temporarily destabilizing
ecosystems.
Material and methods
170 mostly fragmentary specimens (Table 1) of geologi-
cally different age from the Upper Jurassic sediments of
the Shar-Teg in Mongolia (Fig. 1) were studied: the near
J / K transition dating is based on the distribution of fos-
sil plants, gastropods, bivalves, ostracods, conchostracans,
insects, chelycerates, fishes, labyrintodont amphibians, tur-
tles, crocodiles, dinosaurs and mammals (Gubin & Sintza
1996; Vršanský 2004).
Specimens are compared with over 3000 insect speci-
mens of Mesozoic and Paleozoic insects world-wide: re-
sults from the Carboniferous specimens from Germany and
the Permian specimens from the Boskovice in Czech Re-
public are based on the drawings made by Schneider
(1978, 1980ab, 1982) and on my unpublished observa-
tions. The figures of the Upper Triassic insects of Mady-
Fig. 1. Paleogeographical map of the Tithonian, with the location
(rectangle) of the Shar-Teg in Mongolia. Notably, occurrences of all
the lowermost Cretaceous assemblages with flowering plants and
some advanced insects are limited to Asia – regions adjacent to
Shar-Teg. Coastlines after Smith et al. (1994).
474
VRŠANSKÝ
gen in Kirgizia originated from drawings made by Vish-
niakova (1998) and by my unpublished materials. The
data obtained from Dobbertin in Germany (Late Jurassic)
were based on observation by Vršanský & Ansorge (in
print). The figures of the Middle Jurassic material from
the Bakhar in Mongolia and the Kimmeridgian speci-
mens of Karatau in Kazakhstan are based on my unpub-
lished materials (in preparation). The Baissa material
originates from the Berriasian or Valanginian (Lower
Cretaceous) sediments of Siberia (Vršanský 1998b); fig-
ures of the Spanish material (Valanginian or Hauterivi-
an Lower Cretaceous insects of Montsec) originate from
unpublished materials (based on the material collected
by J. Ansorge and X. Martínez-Delclós respectively). Mon-
golian material from the Bon Tsagaan (Barremian or Aptian
Lower Cretaceous) has been described by Vršanský (2003).
The Shar-Teg material has been collected by the Arthro-
poda Laboratory, Paleontological Institute of the Russian
Academy of Sciences, Russia, where it is deposited.
The contemporary material originating from Equador, Laos,
Malaysia, Madagascar, Israel, Slovakia and Croatia is deposit-
ed in the Slovak National Natural History Museum, Bratislava
and in the Zoological Institute, Slovak Academy of Sciences.
The wing deformities are present as teratological fu-
sions of competent veins. These are abbreviated as: R – ra-
dial system; M – medial system; Cu – cubital system
and A – anal system.
Results
In the Shar-Teg, the deformities – which change the ge-
ometry of wings – are expressed as fusion of vein to an-
other vein (R-M Fig. 2d—e), mutual fusion of two veins
(M-M Fig. 2a or M-R Fig. 2b), lost of a (M) branch
(Fig. 2c), additional branches among cross-veins (Fig. 2f),
as blind veins with unfinished growth (Fig. 2g) or as wid-
ened, lentiform, veins (Fig. 2h). Fused veins are present
mostly between the medial and radial systems which vein
distribution is highly correlated (Vršanský 1997, 2000), or
within the medial system. Unfinished growth of veins is
additionally recorded within the anal system.
The deformities in fossil caddis flies are recorded as
lentiform thickening of the radial vein. Appropriately
named Bullivena Novokshonov et Sukacheva, 1995 and
Oncovena Sukacheva et Novokshonov, 1995 (O. sharate-
gensis Ivanov et Novokshonov, 1995) from the families
Hydrobiosidae and Dysoneuridae respectively (Novoks-
honov et al. 1995) possess virtually identical types of
teratology.
Thus, the wing venation deformities are recorded in
primitive and derived insects. Such environmentally in-
duced changes occur in cockroaches and mantises such
as Juramantis initialis Vršanský, 2002, the oldest man-
tis known to date. Rich venation of the both groups en-
able tracking of the deformities in the fossil record.
Cockroaches and mantids are additionally considered
to be a stratigraphic tool for high temporal resolution
(Vršanský et al. 2002).
Among Dictyoptera, five independent lineages were
affected. Two of the family Blattulidae, namely Blat-
tula Handlirsch, 1906 (B. mongolica Vršanský, 2004) and
Elisama Giebel, 1856 (E. pterostigmata Vršanský, 2004),
which are diurnal species inhabiting shorefaces. The third
has been found in the Mesoblattinidae (Mongolblatta ac-
curata Vršanský, 2004), which is predominantly a forest
species. The fourth among the new family (Shartegoblatti-
na elongata Vršanský, 2004) presumably of crepuscular
habits; and lastly in the predatory mantid of the family Ju-
ramantidae (Juramantis initialis Vršanský, 2002). These
above-mentioned occurrences indicate a great variety of
niches affected by environmental stress. Of these five taxa,
8 of 69 specimens bear deformities approximating the ratio
of affected individuals in the habitat to 15—20 % (the high-
er approximated ratio resulting from highly fragmentary
material, damaged by predation (Vršanský 2004) – there-
fore not all deformities are preserved. For example, 17 %
of all preserved roaches are represented by isolated clavi.
This especially concerns larger species, where wing defor-
Fig. 2. Wing deformities from the Shar-Teg. a—f – Cockroaches.
a – Elisama pterostigmata Vršanský, 2004, PIN 4270 / 1916;
b—c – Mongolblatta accurata Vršanský, 2004, PIN 4270 / 1856;
d – PIN 4270 / 1827; e – Elisama mongolica Vršanský, 2004, PIN
4270 / 1798; f – Elisama pterostigmata, PIN 4270 / 1835. g – Man-
tis Juramantis initialis Vršanský, 2002, PIN 4270 / 1842. h – Cad-
dis-fly Bullivena grandis Novokshonov et Sukacheva, 1995 PIN,
4270 / 123. R – radial system, M – medial system, A – anal system.
475
MASS MUTATIONS OF INSECT AT THE JURASSIC / CRETACEOUS BOUNDARY?
mities occur more frequently as with the nocturnal Calob-
lattinidae, which are absent in the Shar-Teg assemblage.
Additionally, on some wings, multiple deformities occur.
The small species also change the ratio of affected indi-
viduals since damage in its wing would affect their flight
abilities and thus their chance of being preserved).
Discussion
The preserved deformities are highly variable in loca-
tion and thus this mutation(s) most probably affects
general regulatory control. This supports the appear-
ance of wing deformities of different insects including
cockroaches caused by the application of general
growth regulator (IGR – hydroprene) (Arthur 2003).
The supportive function of the fusion is insignificant
because this function is provided by cross-veins.
According to Bartlett & Staten (1996), a recessive
mutation and genetic changes in a single gene could
lead to wing deformities and thus to decreased fitness if
the gene could be forced into the native population in
large numbers.
In addition to deformities, variability of undeformed
cockroaches at the Shar-Teg might differ from the gen-
eral trend of their decreasing variability of the total
number of veins as determined by study from the Penn-
sylvanian to the Recent (Vršanský 2000). Consequent-
ly, it is possible that similar or identical regulatory
genes are responsible for the control of regular spacing
of veins, a developmental process that apparently failed
in the specimens described above.
Notably the most common cockroach at the Shar-Teg
lacked these deformities, which would indicate that
they were not affected by environmental stress. A possi-
ble explanation for the lack of the deformities in the
common species is its small size and therefore low num-
ber of veins which results in more strict selective con-
trol of each individual vein as reported for fossil
cockroaches by Vršanský (1998a). Nevertheless, it is
most probable that the deformity in such small individ-
uals would influence their flying abilities and thus limit
the preservation potential.
The heritable character of wing deformities is also
shown by Eldon et al. (1994) from different Drosophila
genes (e.g., mutation in 18 w resulting from improper
eversion of imaginal discs).
Similar deformities affected different phylogenetic
lineages, which can serve as the evidence for a stabi-
lized and heritable mechanism for acquisition of these
changes, resulting in a reduction of fitness. In such
a case, these mutations of developmental genes, which
are debilitating and potentially lethal, are effectively
lost from populations. Such heritable wing deformities
can serve as markers to important genetic traits like fit-
ness (Suszkiw 2005).
The stability of the total number of veins at the wing
margin and the constant vein number / wing surface ratio
in spite of deformities since the Pennsylvanian indi-
cates that the developmental control mechanisms dur-
ing wing growth must have been evolved since the first
fossil appearance of the Dictyoptera lineage.
By comparison with the Mesozoic sites, vein fusion
appears more common in some Paleozoic sites such as
in the Permian sediments of the Bohemian Massif,
where 3 of 29 forewings are deformed, which might be
facilitated by the larger size of Paleozoic cockroaches
and the higher number of veins, each of lesser selective
control, but also by the destabilization of the ecosys-
tems at the beginning of the Permian. In spite of that, in
the Carboniferous sediments of Germany, only 4 of 256
forewings bear deformities.
In Mesozoic localities, both younger and older than
Shar-Teg, vein fusion is considerably rarer. In the Trias-
sic sediments of Madygen in Kirgizia no deformities are
recorded among more than 100 studied specimens. In
the Middle Jurassic sediments of Bakhar in Mongolia
only 5 of over 500 forewings bear deformities, a similar
ratio is known for Eurasian Lower Cretaceous sites:
6 / 673 at Bon Tsagaan in Mongolia, 2 / 121 at Montsec
in Spain and 3 of about 400 in Siberian Baissa.
A comparatively higher number, even much less than
those of the Shar-Teg, ratio (3 / 52) occurs in the Lower
Jurassic sediments of Dobbertin in Germany which orig-
inated in island areas and thus characterize low diversity
ecosystems destabilized to some degree (Vršanský &
Ansorge in print). These occurrences appear to be sup-
ported with the data from Recent habitats (see below).
Even though, fusion ratio from Shar-Teg is dispropor-
tionally high particularly for a modest diversity – 7 gen-
era, 8 species and 170 specimens. In the more diverse
Karatau in Kazakhstan of a comparable (Kimmeridgian)
age, a single deformity is recorded among 668 studied
specimens comprising about 60 species.
Parallel fusion and unfinished growth of veins has
not been recorded throughout the 325 Myr history of
the Dictyoptera. This indicates that errors in growth and
failure of control in wing development represent a fail-
ure in communication between respective venial sys-
tems and individual vein systems, which normally have
constant distance between veins. Although these un-
common changes affected the genetic variability of the
population through enhancing the diversity of the ve-
nation pattern, the most stable taxonomic character of
the wing venation – the total number of veins appears
unaffected. Thus the ratio of the wing surface to the to-
tal number of veins appear constant and control of the
total number of veins at the wing margin (with coeffi-
cient of variation around 5—10) was at least partially
functional. Nevertheless, selective absence of deformi-
ties in smaller individuals allows a conclusion that the
malformations did affect the function of the wings.
Deformities of this sort were not recorded in Dicty-
optera in the intact contemporary rainforests of the
Equador (0 / 120) and they are extremely rare (apparent
as a simple fusion of veins) in primeval forests of Laos
(1 / 272) and Malaysia (1 / 180). On the other hand they
are common in damaged areas of the rainforests in
476
VRŠANSKÝ
Madagascar (4 / 32), SE Asia (12 / 102) or deserts of Isra-
el (10 / 98). It is also important that in extant desert
cockroaches, as well as in the Paleozoic Blattaria, defor-
mities are mostly restricted to larger species with an in-
creased number of veins (and possibly reduced flight
abilities), while in the Shar-Teg, they also affect small,
apparently actively flying species. Partition of deformi-
ties differs even within the same modern genera – while
in native forest areas of Slovakia, deformities of Ecto-
bius are extremely rare (4 / 568), this ratio is higher in
the Mediterranean (4 / 112).
The presence of virtually identical deformities in differ-
ent lineages of caddis-flies indicates a genetic basis. Ap-
parently, this is supported by the presence of similar
structures about as stable morphotype in living Conoesu-
cidae from Australia (Mosely & Kimmins 1953; Neboiss
1977). Only four specimens (belonging to different fami-
lies) of thousands of known fossil caddis-fly species bear
such structures. Two of them (of about 20 caddis-flies) be-
longing to different species, genera and even families are
present in Shar-Teg and therefore it can be concluded they
represent individual variability. Stabilization of this mor-
photype in a continent different to Eurasia represented by
the Shar-Teg deposits may possibly indicate global occur-
rence of the changes and mass mutations at the whole
boundary, not limited to surroundings of the Shar-Teg.
However, the appearance of virtually modern ele-
ments of ecosystems such as flowering plants and some
modern insects during the earliest Cretaceous is limited
to Asia, regions more or less adjacent to Shar-Teg. The
Shar-Teg, where the mass mutation appeared, is the old-
est locality of the Cretaceous type, which might indi-
cate a regional character of the changes resulting in
origin of modern particles of ecosystems.
Similar wing deformities indicate a similarity of Re-
cent changes across the food web in these habitats.
The cause of the mass deformities at Shar-Teg is ob-
scure. Volcanic activity which modified pollen (Krassi-
lov 2003) and insects (2 of 3 cockroaches and a single
preserved ice-crawler are deformed at the Nedubrovo lo-
cality in Russia) at the P / T boundary, has hardly been
involved. Shar-Teg deposits do not contain any volca-
nic particles, minerals etc. (unpublished observation).
Similar changes of the venation are recorded for organ-
isms in the area around the Ukrainian city of Chernobyl
after the nuclear power-plant accident of April 26, 1986.
Nuclear isotopic radiation affects the insect genome
(e.g., Williams et al. 2001) by penetrating an insect
through two relatively independent trophic chains: (1) car-
bon dioxide from consumption of foliar material, and
graphite through the ingestion of microfungi, protozoans
and other insects (Kovaliukh et al. 1998). Nevertheless,
radiation as a reason for changes in the cockroach spe-
cies at Shar-Teg may be excluded, attributable to the ab-
sence of an effect on species living in different time (the
layers containing deformities differ in the scale of dozens
of thousands years – see Table 1), the radiation needs to
be global (more global than, for example, the natural re-
actor in Oklo which had started the fusion in a result of
concentration of radioactive elements by protists. Never-
theless, nothing like that is known in history.). Notwith-
standing, some Shar-Teg layers containing samples with
deformities are free of radiation (e.g., the Bed 451 / 3), the
others are slightly radioactive, most probably as a result
of post-burial contamination (see Table 1). For comparison,
the post-Chernobyl radiation of insects was much higher
( ± 5.000 Bq / kg) even in the Central Sweden (Dahl & Gri-
mas 1987). Considerably elevated radiation is necessary to
modify or kill insect cells: the 80 % lethal dose for insect
cells is 60 Gy (Grey) and for cockroaches 900—1000 Gy
requiring weeks of exposure is necessary (Koval 1983).
Some insects retrieved from the Chernobyl event pos-
sess more significant deformities (Hesse—Honegger 2002),
although if such deformities occurred at Shar-Teg, they
would have affected the ability of insects to fly and thus
their chance of burial.
Calibration to sediment accumulation rate shows that the
Shar-Teg fossil insects are preserved in strata of slightly
different age (Vršanský 2004). Age differences between
successive beds are minimally 100 kyr (about 90 m). An
abrupt reversal in climate change such as a pronounced
change of temperature and / or aridification may have
caused such ecological stress. It is notable that even
short, only an hour lasting temperature shock of —10 °C
is reported to cause wing deformities in flies (Milkman
1962; Hegdekar 1971; Rinehart et al. 2000). Insects are
Species/
Bed
? 423/5 423/6 423/9 434/2 441/4 442/2 443/1 443/2 451/3 452/2 465/2 Total
Shartegoblattina elongata
2
1
10–1*
1
1
2
17
Breviblattina minor
4
1
5
Mongolblatta accurata
1
2
1
13–2*
1
18
Elisama pterostigmata
5
5–1*
1
1
1
14–2*
2
29
Blattula mongolica
1
1
2
1*
5
Blattula vidlickai
3
1
7
7
1
22
1
1
43
Elisamoides mantiformis
3
3
gen. et sp. indetermined
2
1
3
Juramantis initialis
1*
1
Unidentifiable
6
2–1*
2
3
28–2*
4
1
46
SUM
18
1
17–2*
2
12
2
4
98–8*
6
7–1*
2 1
170
Table 1: Distribution of the Dictyoptera from the Shar-Teg representing the common fauna throughout the section. Specimens with vein
fusions are marked with “*“. Isotopic radiation of samples: PIN 4270 / 1798 (451 / 3) – 4.4602 g –
238
U less than 33 Bq / kg;
232
Th less
than 72; PIN 4270 / 1835 (443 / 1) – 5.3305 g –
238
U 92 ± 19 Bq / kg what is ca. 7.5 ppm or 7.5 mg
238
U / 1kg;
232
Th less than
55 Bq / kg). ?= unknown bed.
477
MASS MUTATIONS OF INSECT AT THE JURASSIC / CRETACEOUS BOUNDARY?
sensitive to temperature stress because of their small size
and ectothermy. A global temperature perturbation at the
Jurassic / Cretaceous boundary would have been enabled
regionally by the continental crust uplift caused by the
Kimmeridgian orogenesis and thus of change of mon-
soon currents in Asia. During intervals of prolonged
aridification, deformities might have accumulated, as it
is present in extant xeric habitats (see below) and also
during the dry Permian Period (see above). Deformities
are also common in humid areas of exploited rainforest,
but exclusively in areas where the deforestation causes
arid microclimate. Nevertheless, also there, the cause of
deformities needs to be sought within the habitat
changes rather than in common local climate changes: a
long lasting climate change would probably have
caused a change of fauna that would have changed the
taxonomic composition. However, this composition is
identical throughout the section. Therefore the climate
must had been very stable at the scale of kyr, most
probably considerably longer then 100 kyr. During the
temperature and / or humid oscillations, the assemblage
would have changed. Also it is necessary to consider
that within habitat, the fossils come from near the water
body, that is, from a humid area (although influence of
dry air could not be excluded definitely). Also, there is
no apparent indication of aridity of the Shar-Teg depos-
its and biota.
The age of Shar-Teg may also correspond to an inter-
val of damaged ionosphere or ozone layer (possibly
caused by the burst of gamma-ray in the milky way as
shown by Thomas et al. (2005), which analogically may
have caused extinction in the Ordovician), or an unusu-
ally long-lasting magnetic reversal resulting in the ab-
sence of the Van Allen radiation belts. This hypothesis
appears to be the least probable because of an insuffi-
cient effect of a polarity change on biota evolution. A
lack of association between the frequency of polarity
change and the tempo of evolution cannot explain nu-
merous changes during the Middle and Upper Jurassic
which are shown by Gradstein et al. (2004) when insect
evolutionary tempo was low; and few changes during the
end of the Early Cretaceous to beginning of the Late Cre-
taceous. However an unusually long lasting (20 kyr and
possibly more) low-intensity polarity period resulting in a
period of low intensity of the geomagnetic field, may have
affected the genome. (The last polarity change prior to the
Jurassic / Cretaceous boundary [magnetozone M19 r 445 ka
( ± 5 kyr) (Houša et al. 1999, 2004)].)
Occurrences at the Jurassic / Cretaceous boundary were
not as catastrophic as the events at the Permian / Triassic
or even as the Triassic / Jurassic boundaries. Biota change
at the J / K boundary was possibly caused by internal eco-
logical reasons. Evidence is a long-lasting change, result-
ing in the absence of correlated boundary sections
throughout the world and according diversification of
the calcareous nannoplankton and stratification of the
water in oceans, with consequent climate change in con-
tinents. This shift included a change of air-currents
(e.g., the monsoonal climate replaced by more zonal pa-
leoclimate (Weissert & Mohr 1996)), temperature de-
crease (Francis & Frakes 1993), global fall in sea level
(Ruffel & Rawson 1994), start of the change to more
arid climate (Allen 1981) and decrease in the C org / C
carb burial possibly related to reorganization of the
global climate system also resulting in decrease of reef
growth (Weissert & Mohr 1996).
The biotically driven character of the changes is sup-
ported by the fact that although the Shar-Teg is the old-
est assemblage of the modern type, its diversity is only
moderate (Vršanský 2004). This phenomenon is less ex-
pressed at the family level (3000 specimens with 200 in-
sect families (Gubin & Sinitza 1996; Ponomarenko
1998)) comparing with low diversity from the Lower Ju-
rassic sediments of Germany (3821 specimens of about
120 families (Ansorge 2003, unpublished materials)) and
high diversity from the Late Jurassic of Kazakhstan (18 000
specimens of at least 450 families (Panfilov 1968)).
Appearance of a new predator might cause destabili-
zation of whole assemblages (e.g., newly evolved man-
todeans or the like) even if their taxonomical composition
would remain more or less stable. The radiation of mantids
was possibly the result of a necessary control of the just-
appeared plant-eaters attacking foliage.
The hypothesis of biotically driven changes seems to
be the most promising since the faunal contact caused by
the invasion of new predatory species, and ecosystem
damage in the regions of the modern tropical forest also
results in destabilization of morphological standard and
increase of alleles creating deformities (see above).
Parasitoids may cause the abundant deformities on
non-adapted insects of that time. The number of living
insects influenced by parasitoids causing wing deformi-
ties contribute up to 4 % (Thompson 1986; Naranjo
2001). A higher ratio (up to 11 %) is reported only for
lepidopteran Ephestia kuehniella parasitized by Tri-
chogramma brassicae (Babendreier et al. 2003).
Nutrient deficiency also may cause wing deformities
(Reddy & Chippendale 1972) in a frequency 17—27 %
even if the population of insects is supported by antibi-
otic packages (Qureshi et al. 2004). The lack of free fat-
ty acids (oleic, linoleic acids) may also cause wing
deformities in insects, but this is not the case for the
Shar-Teg since the absence of food in such long period
would be hardly explainable.
Another possible agent might be bacterial, viral or
protist infections which may cause wing deformities in
bees (Fujiyuki et al. 2004; Chen et al. 2005) when at-
tacking larvae. The induction of wing deformities by
viruses (DWV – deformed wing virus) is also used for a
Polymerase Chain Reaction detection (Tentcheva et al.
2004). Bacterial infection may also cause a production
of toxic substances which may cause wing deformities
preventing successful mating and reproduction (Naran-
jo & Prabhaker 2000). The same effect is known to be
caused by a non-steroidal ecdysone agonist RH-5992
tebufenozide (Sundaram et al. 2002).
Protozoans such as Trypanosoma rangeli may regulate
the whole populations of insects and the partition of
478
VRŠANSKÝ
wing deformities may reach up to 50 % as evidenced in
hemipteran Rhodnius domesticus (Guarneri et al. 1997).
Wing deformities may also be caused by products of
some plants such as azadirachtin contained in the neem
tree, Azadirachta indica (Martinez & van Emden 2001).
The Jurassic / Cretaceous boundary falls within the evo-
lution of new plant taxa such as angiosperms, which
possibly might have been able to produce such insecti-
cides, but even in such case, their influence on predators
seems unlikely.
Thus, the most probable hypothesis is the destabiliza-
tion of the whole ecosystem, which might have been
a result of the appearance of new taxa such as new foli-
age-eaters, social decompositors and predators (Vršan-
ský 2002, 2004). As the dating of the Shar-Teg locality
shows (Gubin & Sintza 1996), this appears to have oc-
curred before the boundary.
The presence of abundant mutations near the bound-
ary may explain the appearance of new taxa as a result
of increased variability. Actually, the happenings at the
Jurassic / Cretaceous boundary triggered a great success
of dictyopterans. Social termites and mantids radiate
immediately after the boundary, as well as the just ap-
pearing new families Blattellidae (relatives of the com-
mon synantrophic cockroach Blattella germanica), the
Holocompsidae and the beetle-like Umenocoleidae. Ad-
ditionally, advanced genera of the Mesozoic families
Blattelidae and Caloblattinidae appear, while no archa-
ic genera or families disappear from the fossil record at
that time. More than this, a revolutionary change occurs
in cockroaches – groups which lay ootheca radiate and
replace those laying single eggs, which had been com-
mon in the Mesozoic. The age of the origination of the
modern egg-eating midges is roughly estimated to the
Late Jurassic—Early Cretaceous (unpublished observa-
tion), and thus their role in the selection of the ootheca
producers could not be excluded.
It is notable that the Shar-Teg is probably the only
Mesozoic locality where presumably nocturnal Calob-
lattinidae are absent. Nevertheless other nocturnal in-
sects such as some neuropterans are common, which
may indicate the environmental stress was not especial-
ly expressed during the night. In spite of the enhanced
mutability and evolution and / or radiation of the mod-
ern groups, the Mesozoic groups of cockroaches show
unusual stability and pass through the boundary with-
out remarkable changes.
Additionally, a general coherence is worth mention-
ing: the evolutionary tempo of insects was significantly
rising near the end of the Jurassic which is connected
with the decreased extinction and higher diversification
rates, as seen among wasps and flies (Dmitriev & Pono-
marenko 2002; A.P. Rasnitsyn – personal communica-
tion); cockroaches, mantids and termites (Vršanský
2004). At least in the three latter groups, the evolution-
ary tempo at family level, was low after the Shar-Teg
times. It appears that the saturation of niches (sensu
Zherikhin & Rasnitsyn 1980; Zherikhin 1987; Rasnitsyn
1988) took place. The long, over 30-million-years last-
ing stability of ecosystems (until the paradoxical phase
of ecosystem change during the Albian) was apparently
caused by new control mechanisms, such as modern de-
compositors including social termites, predators, foliage
consumers and others, which radiate during that time.
The normal, stable ecosystem lowers the evolutionary
tempo of respective elements (Zherikhin 1978), thus
keeping the stability and regular tempo of evolution of
the whole ecosystem – possibly it regulates the num-
ber of available niches through the amount of energy
available for use by competent organisms. It appears
very probable that initially, the new control mecha-
nisms destabilized ecosystems, in which case the evolu-
tionary tempo of the respective elements, namely
species, is uncontrolled according to Zherikhin (1987)
and Rasnitsyn (1988). This caused population fluctua-
tions and change of other factors, among which the
most important was structural change of selective pres-
sure (as it is recognized in recent activities of humans),
allowing the accumulation of deformities. In the case
that the mass deformities represent mutations, the Shar-
Teg record might represent direct evidence for this com-
paratively rapid process at a scale of 100 kyr. The newly
organized stable complexes were braking the evolution
of respective taxa actively as shown by the standard
composition of decompositors, with lower diversity.
It is a significant fact that the new Cretaceous ecosys-
tems reached stability without using the elements most
characteristic of the living ecosystems, namely true
flowering plants and ants. Thus, they probably did not
exist during that time, but precursors of true flowers are
expected (Ren 1998). (The ecological role of angiosperm
plants was growing up slowly during the Cretaceous, in
contrast to their diversity (Dmitriev & Ponomarenko
2002) and the integration of the flowering plants-polli-
nating insects complexes caused the consequent changes
of ecosystems at the Early / Late Cretaceous and Mesozo-
ic / Cenozoic boundaries.)
The agent triggering change at the Jurassic / Creta-
ceous boundary, unlike changes at the K1 / K2 and K / T
boundaries, which were triggered by changes of the pri-
mary producers at the lower trophic levels causing de-
stabilization of whole succession and trophic structures
(Zherikhin 1978, 1987), might well be represented by
rapidly evolving insects as shown by deformities.
The social decompositors were integrated into newly
forming ecosystems, and radiated. In the case they were
common in the ecosystems (termites are known from the
Berriasian and common in the fossil record from the Hau-
terivian), they might have represented a major stabilizing
agent, which actively returned the organic carbon into the
ecosystems. Thus they might have also caused a sharp de-
crease in the Productivity / Biomass ratio, which is a main
trend in the evolution of ecosystems according to Krassilov
(1992). In the initial stages of their radiation, the change in
the cycle of organic Carbon might have destabilized the
primary producers especially in the early successive stages.
Control and thus a stabilized number of niches in the
decomposition chain at the J / K boundary is indicated by
479
MASS MUTATIONS OF INSECT AT THE JURASSIC / CRETACEOUS BOUNDARY?
considerably lower species diversity of cockroaches in
ecosystems of the Cretaceous compared to the Middle
and Late Jurassic. Nevertheless, it must be stressed that
the role of termites in ecosystems, as we know it today,
probably began only with the appearance of modern ter-
mite families during the Tertiary.
Structural changes in the decomposition chain are in-
dicated also by dominance of beetle Mesocinetes sp. (Eu-
cinetidae), which was a saprophagous forest inhabitant
according to A.G. Ponomarenko (personal communica-
tion). This, supported by the radiation of modern preda-
tors indicate a raised primary production of ecosystems.
The radiation at the same time of eusocial termites, pred-
atory mantids and modern cockroaches – groups be-
longing to one lineage – is notable.
Altogether, the J / K boundary might be characterized
as a preparation phase of the ecosystem change with
comparatively high extinction and higher appearance ra-
tios, which is supported by lack of short-living families
at the Shar-Teg and absence of relics. The next phases
might be characterized by true flowering plants, which
were initially rather common; almost completely absent
in the next, paradoxical phase, and common again from
the dramatic phase (Rasnitsyn 1988).
The current observation support a gradual change at
the J / K boundary, without indications of dramatic ex-
tinction at generic and higher levels. This indicates that
the period of destabilization lasted well under 1 Myr.
Conclusions
– Enhanced environmental stress during some periods
such as during the boundary times might have caused the
occurrence of mass mutations which significantly contrib-
ute to the variability of species. This might have resulted
in the origin and / or the rapid evolution of higher taxa.
– New control mechanisms such as modern decom-
positors including the social ones, predators and others,
temporarily destabilized and subsequently stabilized ec-
osystems near the J / K boundary. Accordingly, Laurasian
ecosystems remained stable for at least 30 Ma, with iden-
tical composition of some of its elements.
– The Shar-Teg deposits near the J / K transition in
Mongolia display mass insects deformities expressed as
fusion of wing veins which most probably represent heri-
table mutations.
– The partition of the modified individuals in some
groups reach 15—20 %. Their accumulation was allowed
by a changed structure of selective pressure during the
period of ecosystem destabilization.
– Deformed individuals are preserved in strata of
slightly different age (scale 100 kyr), indicating a long-
lasting environmental stress and biotic character of the
changes. On the other hand, the low extinction rates at
the generic and higher levels indicate that the period of
destabilization lasted considerably less than 1 Myr.
– Similar deformities are also recorded in the Recent
ecosystems undergoing elevated environmental stress
indicating similarity of Recent changes across the food
web in these habitats.
– Deformities of caddis-flies appear later fixed in taxa
of the family rank, thus supporting the heritable charac-
ter of the deformities and the significance of enhanced
mutability during the events for the process of evolution.
– The earliest Cretaceous assemblages of Asia are
characterized by the presence of flowering plants and
some modern insects, while in other continents they are
missing. The Shar-Teg, additionally characterized by
the presence of mass mutations, is the oldest locality of
the Cretaceous type.
Acknowledgments:
I thank to Prof. Alexandr P. Ras-
nitsyn (PIN, Moscow), to Dr. Conrad Labandeira (NMNH,
Washington, D.C.), to Prof. Ed Jarzembowski (MM,
Maidstone), to Dr. Jozef Michalík (GlU SAV, Bratislava) and
Prof. Anthony Hallam (SGEES, Birmingham) for review-
ing the manuscript; to Dr. ubomír Vidlička (ZIN SAV,
Bratislava), Dr. Alexandr G. Ponomarenko, Dr. Dmitrij
Shcherbakov, Dr. Irina D. Sukatsheva, Dr. Danilo Aristov
(PIN RAS, Moscow), Dr. Dušan Žitňan (ZIN SAV, Brat-
islava) and Juraj Kotulič (FU SAV) for fruitful consulta-
tions and technical support.
Supported by the UNESCO IGCP 458, VEGA 3135 and
6002 Grant Projects, Faculty of Natural Sciences, Come-
nius University, Bratislava and by the Literárny Fond,
Bratislava. Radiance has been measured at the Laboratory
of the Department of Nuclear Chemistry (CU, Bratislava).
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