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Gesamtherstellung: Verlagsdruckerei Ph. C.W. Schmidt, 8530 Neustadt a.d. Aisch

Stuttgarter Beiträge zur Naturkunde

MUÜJS, COM +
. |

CEDC ENG:
SEP9 1981

Herausgeber:
HARVARD

Staatliches Museum für Naturkunde, Schloss Rosenstein, 7000Sturtgart=E:ı 7

| Stuttgarter Beitr. Naturk. | Ser. B | Nr. 67 | 10S. | Stuttgart, 15. 12. 1980 |

The Ant Genus Gnamptogenys
ın Dominican Amber

(Amber Collection Stuttgart: Hymenoptera, Formicidae. IV: Eetatommini)

By Cesare Baron: Urbani, Basel

Wıth 9 Figures

Summary

Two new Gnamptogenys species in Dominican amber (Early Miocene) are described from a
single specimen each. One of them (G. pristina) shows clear relationships with those Recent
Central American species which occur also on the Greater Antilles. The second one — (G.
levinates) — also matches some Recent relatives in several characters, but it strikingly differs
from all of them by the lack of gastral costulation. It is argued that this character might not
have an important evolutionary value. These first Neotropical fossils of Gnamptogenys throw
a new light on the palaeogeography of the genus and especially on the past distribution of
Recent Caribbean Gnamptogenys species.

Zusammenfassung

Die ersten fossilen Arbeiter der Ameisengattung Gnamptogenys werden aus dem Domini-
kanischen Bernstein (Unter-Miocän) beschrieben. G. pristina n. sp. zeigt Beziehungen zu
rezenten mittelamerikanischen Arten, die auch auf den Antillen vorkommen. G. levinates n.
sp. zeigt Ähnlichkeiten mit einigen Rezenten, weicht jedoch durch das Fehlen von Furchen
auf dem Gaster deutlich ab; diesem Merkmal wird indessen keine größere Bedeutung für die
Evolution beigemessen. Die Funde werfen ganz neues Licht auf die Paläogeographie der
Gattung und insbesondere auf die Verbreitungsgeschichte der heutigen karibischen Gnampto-
genys-Arten.

1. Introduction

The ant genus Gnamptogenys, nowadays Neotropical and Indomalayan in
distribution, is here recorded from amber from the Dominican Republic. These are
the first fossil records of the worker caste of this genus, the sexual castes having
already been recorded from Baltic amber. No other fossils of the tribe Ectatommini
are known.

2 STUTTGARTER BEITRÄGE ZUR NATURKUNDE Ser. B, Nr. 67

2. Material and methods

The two species described in this paper are represented by a single specimen each.
Each specimen is embedded in a different small piece of amber and both belong to
the State Museum of Natural History, Stuttgart. The amber specimen Do-
1172-K-1 is yellowish ın colour and, apart from the ant here described as Gnampto-
genys prıistina, only one additional inclusion, a small coccid, can be detected. The
fragment is crossed by one major diagonal fissure and a few minor ones which do not
prevent detailed observation. The amber specimen Do-929-K-1 is more reddish in
colour, with somewhat greenish reflexes under certain angles of light, and it is also
crossed by one oblique, ırregular fissure.

Although the preservation conditions are not the best available in Dominican
amber, they can be considered as good. For this reason, the drawings presented in
this paper can be regarded as very accurate and realistic. Using different optical
techniques, every detail has been seen. In order to obtain the figures reproduced
here, only a few trivial expedients have been necessary, like drawing the left antenna
(missing in G. pristina) exactly equal to the right one, or supposing the sculpture on
a whole sclerite to be uniform when part of it was not clearly visible.

3. Gnamptogenys pristina n. sp.
Fig. 1—4
Holotype: Worker (unique) in Dominican amber bearing the number Do-1172-K-1 in
the collection of the State Museum of Natural History, Stuttgart (Department of Phylogene-

tic Research). Left antenna almost entirely missing, otherwise complete.
Derivatıo nominis: From Latin „pristinus“ (= primitive).

Diagnosis: A small Gnamptogenys of the regularis species group with much
more dense costulation than in other known species and with a seta interrupting the
pectinate area of the fore tarsı.

Description: Worker (Holotype). Total length 3.8 mm; maximum length of
head capsule 0.85 mm; maximum width of head behind eyes 0.73 mm; maximum
width between frontal carınae 0.42 mm; scape length 0.62 mm; maximum diameter of
eyes 0.18 mm; hind femur length 0.83 mm; petiole length 0.42 mm; petiole maximum
width 0.45 mm; tergum I of gaster (postpetiole) length 0.52 mm; tergum I of gaster
maximum width 0.69 mm.

Colour dark blackish brown nearly uniform, but with slightly paler legs and
articulations. Integument shining. Mandibles finely striate longitudinally. Head,
alitrunk, petiole, gaster, and, to a minor extent, also the coxae, heavily striate
longitudinally or costulate. Ca. 30 longitudinal striae are recognizable between the
frontal carınae and ca. 60 between the eyes. Number of longitudinal striae of the
trunk about 54 at maximum mesonotum width converging anteriorly. Pleural striae
of the trunk longitudinal, but converging transversely on the pronotum. Petiole with
longitudinal striae of equal length diverging posteriad from the anterior face;
maxımum number of striae on the dorsal face ca. 32. Gaster even more densely and
finely striate. Antennae and legs very superficially punctato-rugose or shining. Very
long, suberect, dark, robust, and acuminate hairs sparsely distributed on the whole
body, mostly Aroradiehe oral region and the occipital angles of the head; shorter on
the sides of the trunk and on the propodeal declivity; longer and more curved on the
petiolar sides; more abundant and conspicuous on the gaster. Subpetiolar process
smooth and hieime, Mandibles with thin hairs on the internal margins, but with very
short, robust pubescence externally. Antennae with comparatively short, subdecum-
bent, robust pubescence. Legs covered with moderately short subdecumbent haırs,

BARONI URBANI, GNAMPTOGENYS IN DOMINICAN AMBER 3

Figs. 1—2. Gnamptogenys pristina n. sp., worker, holotype. — Fig. 1. Habitus, dorsal view.
— Fig. 2. Habitus, lateral view. Photomicrographs by W. SUTER.

longer on tibiae and tarsi. The fore tarsı bear a long pectinate area on the internal
margin which is interrupted in the first 4th by a relatively long, dark seta (Fig. 3).

Head as shown in Figs. 1 and 3, subrectangular, with slightly curved, nearly
parallel sides and very rounded posterior corners. Occipital border very slightly
emarginate, nearly straight. Anterior clypeal border straight and wide, very slightly
projecting. Eyes large and convex, situated at about 2/3 along cephalic sides.
Mandibular blades elongated and subtriangular; masticatory margin curved, mostly
edentate, but with a small row of at least 5 spaced denticles in the basal halt; basal
border ca. 20%, longer than the masticatory margin and forming an ill-defined obtuse
angle with it. Clypeal suture obsolete. Frontal carinae short and straight, practically
without frontal lobes. Antennal scape continuously incrassated toward the apex and
very little curved; reclined posteriad, it doesn’t reach the occipital border by at least
once its maximum diameter. Funicular segments moniliform and incrassated, but
always longer than broad. Last funicular joint slightly shorter than the sum of the
two preceding ones.

Alitrunk (Figs. 3 and 4) broad, with a flat superior face separated from the pleural
regions by a marked rounded angle. Superior outline interrupted by a marked trace
of promesonotal suture. Propodeal suture absent on the dorsum but visible on the
pleurae. Pronotum rounded and depressed anteriorly, continuing indistinctly into
the declivity by a rounded angle. Petiole broader than long, narrower in front than
behind; sides scarcely convex; nearly flat superiorly. Subpetiolar process bilobed and
ventrally prominent. Tergum I of gaster anteriorly narrowly truncate, broader than
long. Anterior lobe of sternum I entire and robust. Gastrie somite II moderately
vaulted superiorly, but with a very reduced sternal portion.

Hind coxae bearing a distinct basidorsal spine. All tibiae with a single pectinate
spur. Claws dentate.

Relationships: For the size, colour, costulation, size and position of the eyes,
general habitus, etc., this species clearly resembles G. regularis Mayr (S. Mexico to
Paraguay). However, G. pristina differs from regularis in a set of important
characters. Firstly, there are differences in the number of striae as follows:

Between Between At maxımum On
frontal carınae the eyes mesonotum width petiolar dorsum
G. regularıs 16—18 ca. 30 20—22 18— 20

G. prıstina a0 ca. 60 ca. 54 Cay32

4 STUTTGARTER BEITRÄGE ZUR NATURKUNDE Ser. B, Nr. 67

Fig. 3. Gnamptogenys pristina n. sp., worker. Dorsal view. Drawing by Armın Corar.

BARONI URBANI, GNAMPTOGENYS IN DOMINICAN AMBER 5

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|
Y

imm

Fig. 4. _ Gnamptogenys pristina n. sp., worker. Lateral view of trunk and gaster. The shaded
areas represent non-visible parts covered by the legs or by amber impurities.
Drawing by Armın Coray.

Moreover, the propodeum of pristina is much more rounded in profile, the
mandibular dentition much more reduced and the petiolar costulation converges on
the anterior face, as much as in G. horni SANTSCHI (Panama, Trinidad to Bolivia).
But the latter also differs from G. pristina ın the other previously mentioned
characters and is, moreover, lighter in colour and smaller in size.

Finally, the peculiar seta interrupting the pectinate area of the fore tarsı in
pristina is missing from all the Recent Gnamptogenys species which I have been able
to examine, although some morphologically non-related species possess more or less
abundant setae by the side of the pectinate area. Such setae are absent in G. regularıs
and horni.

4. Gnamptogenys levinates n. sp.
Figs. 5—8
Holotype: Worker (unique) in Dominican amber bearing the number Do-926-K-1 ın
the collection of the State Museum of Natural History, Stuttgart (Department of Phylogene-
tic Research). Tarsomeri 3—5 of the right posterior leg missing, otherwise complete.

Derivatio nominis: From Latin „levis“ (=smooth) and „nates“ (=buttocks), to
underline the lack of gastric costulation.

Diagnosis: A small Gnamptogenys not very different from pristina or from
continua in morphology, but differing from all known related species for the entire
lack of costulation of the gaster.

Description: Worker (Holotype). Total length 4.2 mm; maximum length of
head capsule 0.94 mm; maximum width of head behind eyes 0.77 mm; maxımum
width between frontal carinae 0.39 mm; scape length 0.81 mm; maxımum diamerer of
eyes 0.09 mm; hind femur length 0.94 mm; petiole length 0.36 mm; petiole maximum
width 0.29 mm; tergum I of gaster (postpeuiole) length 0.55 mm; tergum I of gaster
maxımum width 0.56 mm.

Colour brown with lighter gaster and appendages. In the single available
specimen the coxae, part of the legs, and some of the antennal joints show
infuscations of various degrees which are probably alterations due to the embedding
in amber. Integument shining. Mandibles longitudinally striate. Head, alitrunk
superiorly, petiole and coxae very finely and regularly longitudinally costulate. The
costulae less impressed and somewhat less regular than in G. pristina. Ca. 25
longitudinal striae are recognizable between the frontal carinae and ca. 60 between
the eyes. Number of longitudinal striae of the trunk about 36 at maximum
mesonotumwidth, converging anteriorly. Petiole somewhat more finely longitudinal-

6 STUTTGARTER BEITRÄGE ZUR NATURKUNDE Ser. B, Nr. 67

Figs. 5—6. Gnamptogenys levinates n. sp., worker, holotype. — Fig. 5. Habitus, dorsal
view. — Fig. 6. Habitus, lateral view. Photomicrographs by W. SUTER.

ly striate with the striae diverging posteriad from the anterior face. Maximum
number of striae on the dorsal face ca. 22. Gaster deeply punctate and shining.
Remaining surfaces less deeply punctate, but equally shining. Rare, elongated, and
pointed yellowish hairs, mostly subdecumbent, on the body, erect and longer around
the oral and anal regions. T'he remainder being very short, sparse, obsolete on the
cheeks, on the sides of the humeri, and on the superior sides of the propodeal
declivity; more abundant and longer on the sides of the gaster and of the petiole.
Antennae and legs essentially with sparse and inconspicuous subdecumbent hairs
increasing in size and density towards the extremities. A few very short and tiny
bristles on the external mandibular border. Pectinate area of the internal face of fore
tarsı without setae.

Head as shown in Figs. 5 and 7, subrectangular, with curved sides, and narrower
behind than in front. Occipital border slightly emarginate. Anterior clypeal border
produced into a median lobe with the anterior margın slightly curved. Clypeal suture
visible. Eyes much smaller than in G. pristina, more flat, but equally situated at
about , of the head sides. Mandibular blades subtriangular, elongated, and remarka-
bly curved on their major axıs. Masticatory margin subdentate with a trace of
diastema before the apical tooth. The internal margin passes through a continuous
curve into the chewing margin and is shorter than the latter. Frontal carinae short
and greatly curved; their distance slıghtly greater than /, of head width. Antennal
scape orten incrassated towards the apex and curved; reclined posteriad, it
exceeds the occipital border by about '/, of its maximum diameter. Funicular
segments moniliform, nearly always longer than broad, only segment IX (antennal
joint X) slightly broader than long. Last funicular joint slightly shorter than the sum
of the two preceding ones.

Alıtrunk (Figs. 6 and 8) relatively slender and with the flat superior face separated
from the pleural regions by a smooth, rounded angle. Superior outline clearly
interrupted by the promesonotal suture. Mesonotum continued forwards into the
pronotum by a gentle slope. Humeral angles rounded and nearly obsolete. Propodeal
sutures absent on the dorsum. Superior face of the propodeum about twice as long as
the declivity and forming with it an angle of about 100 . Propodeal declivity
sagittally concave and costulate on the sides. Petiole longer than broad, narrower in
front than behind, with convex sides converging cranially and rounded superiorly.
Subpetiolar process bilobed and ventro-caudally proeminent. Tergum I of gaster
inconspicuously truncated anteriorly, subequal in length to width and with relatively

BARONI URBANI, GNAMPTOGENYS IN DOMINICAN AMBER

Fig. 7. _ Gnamptogenys levinates n. sp., worker. Dorsal view. Drawing by Armın Coray.

8 STUTTGARTER BEITRÄGE ZUR NATURKUNDE Ser. B, Nr. 67

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—

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Fig. 88 _Gnamptogenys levinates n. sp., worker. Lateral view of trunk and gaster. The

shaded areas represent non-visible parts covered by the legs or by amber impurities.
Drawing by ArmIn Coray.

curved sides converging anteriorly. Anterior lobe of sternum I small and dentiform.
Gastric somite II nearly straight.

Hind coxae with trace of the basidorsal spine. All tibiae with a single pectinate
spur. Claws dentate.

Relationships: On the general habitus, size, and morphology, there is no
doubt that the new species belongs to Gnamptogenys and to the large group of
species formerly included into this genus s. str. On the basis of the fine and dense
longitudinal costulation, ıt can be compared with G. continua Mayr (from Vera
Cruz in $. Mexico and Jamaica to Brazil) or, due to its larger size, with the related
species interrupta Mayr (about the same distribution as continua), but besides
numerous minor details, one important character of G. levinates does not match any
of the known living species formerly included in the genera Gnamptogenys s. str. or
Holcoponera; ı. e. the entire lack of costulate striation on the gaster. A non
costulated gaster is frequent ın several other Gnamptogenys species groups formerly
considered separate genera such as Stictoponera, Rhopalopone, etc. However, I
believe that G. levinates shows a too typical „Gnamptogenys s. str.“ habitus to be
considered as a stem taxon for both costulate and non-costulate species groups.

Although the integumental costulation is highly characteristic and constant
through several different species, it is likely that this character represents a secondary
adaptation and appeared several times in the course of Gnamptogenys evolution as it
did also ın other not closely related genera (e. g. Diacamma).

It is interesting to recall, in this connection, that G. continua, the nearest living
relative of levinates, is peculiar for presenting populations with more or less shining
parts of the second gastric somite. Such a geographic variation also points against an
important evolutionary meaning of this structure.

5. Discussion

The genus Gnamptogenys, with about 90 described species, has a discontinuous
distribution in the Indomalayan and Neotropical regions (Fig. 9). Besides the two
new species described in this paper, a third fossil from Baltic amber, originally
described as Ectatomma europaeum by Mayr (1868) from a single female, the male
being described later by WHEELER (1915), has been transferred to Gnamptogenys by
Brown (1958). However, despite the different castes represented, the recognizable
characters leave no ground to suppose a strict relationship between the Baltic and the
Dominican fossils, as was to be expected.

BARONI URBANI, GNAMPTOGENYS IN DOMINICAN AMBER 9

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Recent records

Fig. 9. _Known distribution of the ant genus Gnamptogenys.

The Dominican amber is now referred to the lower part of Early Miocene
(BARONI URBANI & SAUNDERS, 1980), which corresponds to some 20—23 million
years B. P. and hence it ıs some 12—30 million years younger than the Baltic one.
While G. pristina does not differ in a very striking way from the Recent Central
American and Antillean representatives of the genus, G. levinates ıs much more
puzzling as far as the relationships are concerned. It might actually represent a
member of a phyletic line now extinct.

The fossils indicate a much wider distribution of the genus during Tertiary times
and the present astonishing lack of Gnamptogenys records on big and apparently
favourable land masses such as Africa, the major part of India, and Australia, has
been already tentatively explained by Brown (1958) as probably due to the invasıon
of these lands by better adapted competitors rather than to palaeogeographic events.
I entirely agree with this hypothesis which may be partly confirmed by my own
observations in the Indian states of Assam and Meghalaya and ın South Bhutan,
where G. bicolor is not uncommon in primary forests as well as in cultivated areas.
This relative abundance sharply contrasts with the apparently total absence of the
genus from very similar areas nearby in West Bengala and South Nepal.

In view of these facts and of the fossil records from Hispaniola reported in this
paper, some Caribbean records of the genus which had been considered as due to
Recent introduction, might be now regarded under an entirely new light. We know
in fact that the Greater Antilles constitute a unique land mass probably connected
with Florida during Early Miocene times (KHUDOLFY & MEYERHOFF, 1971), and,
through the fossil records described in this paper, that the genus was already present
on it with at least one species very similar to the Recent ones.

10 STUTTGARTER BEITRÄGE ZUR NATURKUNDE Ser. B, Nr. 67

References

BARONI ÜRBANI, ©. & SAUNDERS, J. (1980): The fauna of Dominican Republic amber: The
present status of knowledge. — Trans. IXth Caribbean geol. Conf.; Santo Domingo
(in press).

Brown, W. L. (1958): Contributions toward a reclassification of the Formicidae. II. Tribe
Ectatommini. — Bull. Mus. comp. Zool, 118: 175—362; Harvard.

KHuporery, K. M. & MEYERHOFF, A. A. (1971): Paleogeography and geological history of
Greater Antilles. — Geol. Soc. Amer., Mem. 129: XV + 199pp; Boulder.

Mayr, G. L. (1868): Die Ameisen des baltischen Bernsteins. — Beitr. Naturk. Preuss., 1:
IV + 108 pp., 5 pls.; Königsberg.

WHEELER, W.M. (1915): The ants of the Baltic amber. — Schrift. phys.ökonom. Ges.
Königsberg, 55: 1—142; Leipzig & Berlin.

Author’s address:

Dr. C. Baronı Urbani, Naturhistorisches Museum, Augustinergasse 2, CH-4000 Basel,
Switzerland.

Gesamtherstellung: Verlagsdruckerei Ph.C.W. Schmidt, 8530 Neausack ad Aisch

BERN

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