Sphecomyrma mesaki, 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 : 7-9

Genus † Sphecomyrma Wilson and Brown

† Sphecomyrma Wilson and Brown, In Wilson et al., 1967: 8 . Type species: † Sphecomyrma freyi Wilson and Brown, 1967 , monobasic and original designation.

DIAGNOSIS: Scape short; funiculus long and filiform, about four times length of scape; promesothoracic suture complete and well developed; trochantellus absent; petiole with distinct, domed node widely separated from propodeum and remainder of metasoma by deep constrictions; cuticle without sculpturing, superficial microscopic relief, with scattered and sparse setae.

COMMENTS: The genus, which is defined largely by plesiomorphies, is doubtfully monophyletic. It contains three species: † Sphecomyrma canadensis Wilson in Canadian amber, and † S. freyi Wilson and Brown and a new species in New Jersey amber (vide infra). In addition, we provide information from newly identified material of † S. freyi .

Key to Species of † Sphecomyrma (based on the worker caste)

1. Anterior margin of clypeus with short, broad extension, surface with two, long setae at most; compound eye round.......... 2

— Anterior margin of clypeus with long, medial lobe (fig. 5), surface with numerous, long setae; compound eye oval [New Jersey amber].................................. † S. mesaki Engel and Grimaldi , n.sp.

2. Third antennal article slightly more than twice as long as second article [New Jersey amber]...................................... † S. freyi Wilson and Brown

— Third antennal article about as long as second article [Canadian amber]............................. † S. canadensis Wilson

† Sphecomyrma mesaki , new species

Figure 5

DIAGNOSIS: Distinguished from all other species of the genus by the median portion of the clypeus having a long ventral lobe, length of the clypeus through the lobe is 0.463 the greatest width of clypeus; clypeus setose; and scape very short (1.23 the length of longest funicular article). The species can be further distinguished from † S. freyi (the other species of the genus in New Jersey amber) by broad, shallow scrobes at base of antennae; an eye that is approximately 1/3 larg­ er and oval (vs. almost perfectly round in † S. freyi ); and a large head (length of head/ length of mesosoma 5 0.83, vs. 0.65 in † S. freyi ).

DESCRIPTION: Petiole and gaster not preserved, so only head, mesosoma, and legs preserved. Head. Large, length of head slightly less than length of alitrunk. Length of head 2.20 mm (with mandibles closed); width of head 1.95 mm; length of eye 0.66 mm. No microsculpture on cuticle of head. Vertex with fine, sparse pilosity, setae ca. 0.2 mm long. Ocelli present, median ocellus situated just above dorsal tangent of compound eyes. Face bare. Bases of antennae situated in shallow, broad scrobes; length of scrobe about equal to length of scape and articulating base. Eyes well developed, bare, situated well above bases of antennae; gena deep. Lateral portions of clypeus quadrate; median portion distended into long ventral lobe that extends to ventral margin of closed right mandible. Clypeus setose, except on middle part. Mandibles simple, with only two teeth. Antennae of moderate length, with scape short, funicular article I (pedicel) shortest antennal article, funicular article II the longest article of funiculus. Lengths of antennal articles (in mm): scape 0.53, pedicel (funicular article [fa] I) 0.20, faII 0.43, faIII 0.35, faIV 0.30, faV 0.23, faVI 0.23, faVII 0.30, faVIII 0.22, faIX 0.26, faX 0.30, faXI 0.33. Mesosoma. Mesosomal length 2.66 mm; without microsculpturing, except at posterolateral margin of promesonotal suture, where eight fine grooves occur. Dome of promesonotum setose; several fine setae on dorsal surface of metanotum and propodeum. Coxae large, inflated, ventrally setose. Attachment of petiole to propodeum not particularly thick; thickness (measured in lateral view) of anterior end of petiolar peduncle 0.3x greatest depth of propodeum. Metapleural gland opening (MGO) and MG bulla obvious, situated on posterolateral part of propodeum just above metacoxa. MGO small, with groove running between it and extended almost to vental margin of propodeum. Legs moderate length. Foreleg with tarsomere I slightly longer than combined length of more distal tarsomeres; tarsomere I with ‘‘antennal cleaner’’ (strigil) a velvety notch on ventral margin of proximal end; calcar present, length slightly longer than greatest width of femur, ventral margin with row of fine teeth and (apically) hairs. Stiff setae on ventral surface of protarsomeres: tarsomere I with 7 pairs, II with 3 pairs, III with 3 small pairs, IV with 2 small pairs. Pretarsal claw with subapical tooth. Metasoma not preserved.

TYPE MATERIAL: Holotype. AMNH NJ­ 1023 , an incompletely preserved worker in a piece of amber barely larger than the ant, from Sayreville , New Jersey (Middlesex Co.), White Oaks outcrop, coll. Bob Mesak (fig. 5). The amber is an irregularly shaped drop, 7 3 5 3 4 mm, made of clear yellow amber. Portions of some appendages are breached at the surface, and the petiole and gaster were similarly lost at the surface. Since very little amber exists between the ant and surface of the amber piece, no trimming or polishing was possible. Still, details through the rough surface are highly visible by immersing the piece in glycerine.

ETYMOLOGY: The specific epithet is a patronymic for Bob Mesak, who collected and donated this valuable specimen to the AMNH.

† Sphecomyrma freyi Wilson and Brown

Figure 6

† Sphecomyrma freyi Wilson and Brown, In Wilson et al., 1967: 8 . Grimaldi et al., 1997: 12 (redescription of some features, new specimens, neotype).

MATERIAL: AMNH NJ­943 , in amber from New Jersey: Middlesex Co., Sayreville, White Oaks outcrop, collected by Keith Luzzi (fig. 6). The piece is transparent yellow, originally much larger than now; was embedded and trimmed to 14 3 15 3 4 mm. The piece contains two workers of † S. freyi .

DESCRIPTIVE NOTES: Both workers are largely but not completely preserved. Specimen A has the frontal half of the head missing; most of the antenna is present except for bases of the scapes; the entirety of the remainder of the body is preserved and the sting appears largely or fully extruded. Specimen B has the dorsal and apical part of the gaster missing, as well as portions of the right hind leg; the anterior third of the head is obscured by Schimmel and a bubble.

Measurements of body: Width of head (specimen B), 1.03 mm; length of head (B, approximate), 1.20 mm; length of mesosoma 1.39 mm (B), 1. 40 mm (A); length of petiole 0.29 mm (B), 0.33 mm (A); length of gaster (A) 1.72 mm; length of extruded portion of sting (A), 0.33 mm. Measurements of antennal articles (as measured for right antenna in A, left antenna in B) presented in table 2. Measurements of leg segmentation (as measured on specimen A) presented in table 3.

COMMENTS: The discovery of this piece of amber is highly significant and addresses questions of the social behavior of primitive ants like † Sphecomyrma . As reviewed in Grimaldi et al. (1997), Dlussky (1987, 1988), and Poinar et al. (1999) questioned whether † Sphecomyrma was a true ant since it had such a short scape [but see response to Poinar et al. (1999) by Grimaldi and Agosti (2000b)]. With such a short scape, Dlussky argued that it would be impossible for † Sphecomyrma to antennate, and therefore it was considered highly unlikely for † Sphecomyrma to have been social. Among the approximately 1700 fossiliferous pieces of New Jersey amber in the AMNH collection thus far, four pieces contain worker or male sphecomyrmine ants. These ants are (and probably originally were) exceedingly rare, and the probability that two workers would be preserved in one piece by chance alone is extremely remote. It is most parsimonious to explain the occurrence of two workers in the same piece as a result of social behavior.

Figures

Fig. 5. Holotype worker of †Sphecomyrma mesaki, new species (AMNH NJ­1023); lateral habitus and facial view.

Fig. 6. Two workers of †Sphecomyrma freyi Wilson and Brown preserved in a single piece of New Jersey amber (AMNH NJ­943).