Myanmyrma, ENGEL & GRIMALDI, 2005

ENGEL, MICHAEL S. & GRIMALDI, DAVID A., 2005, Primitive New Ants in Cretaceous Amber from Myanmar, New Jersey, and Canada (Hymenoptera: Formicidae), American Museum Novitates 3485, pp. 1-24 : 13-17

† Myanmyrma , new genus

TYPE SPECIES: † Myanmyrma gracilis , new species.

DIAGNOSIS: Gracile ‘‘poneroid’’ ant with extremely long legs; mandibles nearly equal to length of head, sickle­shaped, with a long, apical sharp tooth and blunt subapical one; clypeal margin bilobate, denticulate; long, spatulate genal process; antennal sockets inclined, antennal funiculus very long, second article longest; articles slightly shorter apically; integument of head spinose; clypeus deeply incised along anterior margin and with distinct peglike setae; eyes and ocelli not apparent (but may be present); pretarsal claws with minute tooth; petiole with distinct nodus; gastral constriction distinct; sting well developed. Easily distinguished from † Haidomyrmex , another highly modified ant in Burmese amber, by the mandibular and clypeal structure, head microsculpturing, metasomal constriction, long genal processes, and very long legs.

ETYMOLOGY: Taken directly from Myanmar, the country of the amber’s origin; and– myrma, a common suffix for ant genera. The name is feminine.

† Myanmyrma gracilis , new species

Figures 1 , 9

DIAGNOSIS: As for the genus (vide supra).

DESCRIPTION: Specimen has been compressed, but body form was clearly extremely gracile, with very long legs. Head. Proportions difficult to determine due to compression; length ca. 1.76 mm. Front of head with pair of carinae diverging dorsally; blunt spines on ridges of carinae and on frons; spines absent below ventral limit of carinae, with irregular cuticular foveae on clypeus. Ventral margin of clypeus with deep median emargination; clypeus with two lobes, margin of two lobes with row of ca. 14 minute denticles on each lobe, labrum similarly bilobed and denticulate. Lateral portion of clypeus lobed, without denticles. Gena with spatulate process, exact length difficult to discern, but ca. 0.33 length of mandible. Mandibles long, 1.61 mm. (right one), nearly equal to length of head, sickle­shaped; apical tooth long, sharp; blunt subapical tooth, no other teeth. No fine setae apparent. Apex of right mandible longer than left, especially apical tooth. Eyes well developed (difficult to observe since they are sunken in a cavity), length ca. 0.253 length of head. Antenna very long (7.2 mm); scape fairly short, with wide base; funicular article (fa) 1 shortest, fa2 longest; lengths of antennal articles (in mm): scape 0.63, funicular article (fa) [pedicel] I 0.44, faII 1.05, faIII 0.62, faIV 0.53, faV 0.61–faVI 0.45, faVII 0.40, faVIII 0.41, faIX 0.48, faX 0.48, faXI 0.65. Mesosoma. Elongate, not deep, length ca. 3.52 mm; small opening to metapleural gland (MPG) apparent just above hind coxa. Legs extremely long (vide measurements in table 4); trochantellus apparently absent. Protibia with dorsal, preapical brush of fine setae; one large, two finer apical spurs; ventral surface of probasitarsus with fine pilosity, six pairs of stiff setae; all tarsomeres with four apical spines; each pretarsal claw with median tooth. Mesotibia with pair of ventroapical spurs; ventral surface of mesobasitarsus with three rows of 10 stiff setae each; metatibia with pair of apical spurs, one larger and pectinate; ventral surface of metabasitarsus with fine pilosity, 10 pairs of setae. Metasoma. Petiole attachment to second metasomal segment narrow; petiole with high, narrow node; length of petiole 1.26 mm; posterior portion of petiole narrow, tubular; deep constriction between second and third metasomal segments. Metasoma overall quite small, ca. 0.3x length of body (excluding antennae). Terga and sterna telescoped in specimen, as shown in figure 9; gaster (i.e., metasoma excluding petiole) approximately 2.95 mm long. Sting well developed, only partly extruded but internally visible; pygidium with long fine setae.

HOLOTYPE: AMNH Bu­014, a worker, in amber from northern Myanmar (Burma) (figs. 1, 9). Collected in Kachin state, Tanai village, on Ledo Road, 105 km NW Myitkyna, via Leeward Capital Corp., 1999. The ant is in a transparent yellow piece of amber, which was originally more than 20 mm in diameter and 30 mm in length. The piece was occluded with fractures and debris, so it required epoxy embedding and then trimming to better observe the ant. The piece is now rhomboid­shaped, 17 3 22 3 4 mm, the broad surfaces being parallel to the lateral surface of the ant. A flat edge also permits a frontal view of the head. Other inclusions in the piece are numerous frass pellets and wood fragments, further suggestive (besides body form) of arboreal/wood nesting habits of the ant. The ant specimen shows a great deal of distortion due to compression. The cuticle is transparent, facilitating observation of some internal structures (such as unextruded portions of the sting), but some compressed surfaces could easily be mistaken for flanges and other structures.

ADDITIONAL MATERIAL: Two additional, fragmentary specimens are perhaps representative of † M. gracilis ; however, because of their poor preservation, we hesitate to designate them as paratypes. Both are preserved in amber from northern Myanmar and with the same collection data as the holotype . AMNH Bu­225, a poorly preserved worker but very similar to holotype in observable traits . AMNH Bu­1509, a badly compressed worker preserved in yellow amber; head mostly crushed and difficult to discern, metasoma similarly compressed; somewhat

TABLE 4 Leg Measurementsa of Holotype Worker of † Myanmyrma gracilis (in mm)

smaller than holotype and Bu­225 but still exhibiting the same elongate, slender legs, constriction in first gastral segments, etc., this individual may represent a minor worker.

ETYMOLOGY: The specific epithet is the Latin word gracilis , meaning ‘‘slender’’, as a reference to elongate legs and structure of this ant.

COMMENTS: Constriction of the metasoma indicates the specimen is a ‘‘poneroid’’, which is the third and oldest Cretaceous record of this paraphyletic grade of primitive ants (the poneroid grade includes the poneromorph and myrmeciomorph subfamilies of Bolton, 2003). The other Cretaceous ‘‘poneroids’’ are † Brownimecia clavata (in New Jersey amber: Turonian), and † Canapone dentata Dlussky (in Canadian amber: Campanian). It is interesting that † Myanmyrma is only the fourth record of ants in Burmese amber, but two of these records are for highly modified species. † Burmomyrma rossi Dlussky is based on a single, alate, incomplete specimen, with head and portion of the alitrunk missing. The most distinctive feature of † Burmomyrma is the wing with highly reduced venation; thus, the taxonomic concept of this genus is not entirely comparable with that of the other two Burmese amber genera. † Burmomyrma , as discussed again later (vide infra), has been tentatively placed in the Aneuretinae ( Dlussky, 1996; Bolton, 2003). Both † Haidomyrmex and † Myanmyrma are extremely gracile and relatively large ants, with large, highly modified mouthparts and genae. The extremely long legs and slender body are analogous to Leptomyrmex (Dolichoderinae) and Oecophylla (Formicinae) , the latter of which is entirely arboreal. † Haidomyrmex and † Myanmyrma presumably had similar habits. † Haidomyrmex and † Myanmyrma are clearly not closely related, the former placed in the †Sphecomyrminae by Dlussky. The type and only specimen of † Haidomyrmex , however, has only the second metasomal (i.e., first gastral) segment preserved, so the lack of a constriction posterior to this segment is suggested, not definitive (vide supra).

The lengths of basal articles of the antenna of † Myanmyrma are highly significant. Funicular article 2 is the longest article in the funiculus, as is the case for most †Sphecomyrminae (except † S. canadensis Wilson ). This condition does not exist in the other Cretaceous ‘‘poneroids’’, † Brownimecia and † Canapone . A long funicular article 2 was proposed by Grimaldi et al. (1997: 8) as one of only two or three possible synapomorphies for the †Sphecomyrminae. If truly apomorphic, the long funicular article 2 would have been independently derived in † Myanmyrma . If a long funicular article 2 was plesiomorphic, the monophyly of the †Sphecomyrminae would be seriously doubtful. Outgroup evidence from closely related aculeate families suggests that, indeed, this feature is symplesiomorphic for basal ants, including † Myanmyrma .

Placement of † Myanmyrma in a subfamily is challenging. As noted, the metasomal constriction implies placement among the poneroid grade where it best approximates species of the Ponerinae (poneromorph) or the Myrmeciinae (myrmeciomorph). Neither placement is entirely satisfactory, but we believe inclusion in the latter subfamily is more likely (although we tentatively retain the genus as subfamily incertae sedis). Like myrmeciines, † Myanmyrma has a metasomal constriction, the antennal sockets inclined to nearly a vertical position, 12­segmented antennae, pectinate inner metatibial spur, and elongate mandibles. Unlike typical myrmeciines, however, the the new genus has mandibles that are sickle­shaped, with dentition only at the apices; has a deeply incised clypeal margin, with distinct spicules on the lobes; has a spinose integument on the head; has gracile legs; and elongate genal processes. These traits are, however, autapomorphic and do not preclude placement in Myrmeciinae . Within Myrmeciinae , † Myanmyrma would appear to be closest to the tribe Myrmeciini (sensu Bolton, 2003; Ward and Brady, 2003) as evidenced by the elongate second funicular segment and distinctly twosegmented waist. The latter trait is likely plesiomorphic as it occurs in Myrmecia and weakly so in † Prionomyrmex , perhaps being apomorphically lost in Nothomyrmecia . The presence of spicules along the clypeal margin in † Myanmyrma is an interesting and enigmatic feature that should be further explored for its systematic implications.

This is the species that is referred to by Grimaldi and Engel (2005) as ‘‘undescribed Myrmeciinae ?’’

SUBFAMILY ANEURETINAE ? EMERY

Figures

Figs. 1–3. Three Cretaceous amber ants. 1. †Myanmyrma gracilis, new genus and species (AMNH Bu­014) in Burmese amber. 2. †Cananeuretus occidentalis, new genus and species (TMP 8.89.7) in Canadian amber. 3. †Sphecomyrmodes orientalis, new genus and species (AMNH Bu­351) in Burmese amber.

Fig. 9. Holotype worker of †Myanmyrma gracilis, new genus and species (AMNH Bu­014); facial view and general habitus.