| Brownimecia | |
|---|---|
 | |
| Brownimecia clavata holotype | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Hymenoptera |
| Family: | Formicidae |
| Subfamily: | †Brownimeciinae Bolton, 2003 |
| Tribe: | †Brownimeciini Bolton, 2003 |
| Genus: | †Brownimecia Grimaldi, Agosti & Carpenter, 1997 |
| Type species | |
| Brownimecia clavata Grimaldi et al., 1997 | |
| Species | |
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Brownimecia is anextinctgenus ofants, the only genus in thetribeBrownimeciini and subfamilyBrownimeciinae of theFormicidae. Fossils of the identified species,Brownimecia clavata andBrownimecia inconspicua, are known from theLate Cretaceous of North America. The genus is one of several ants described from Late Cretaceousambers ofNew Jersey.Brownimecia was initially placed in the subfamilyPonerinae, until it was transferred to its own subfamily in 2003; it can be distinguished from other ants due to its unusualsickle-like mandibles and other morphological features that makes this ant unique among the Formicidae.B. clavata is also small, measuring 3.43 millimetres (0.135 in), and a stinger is present in almost all of the specimens collected. The morphology of the mandibles suggest a high level of feeding specialization.
Brownimecia clavata is known from three adult fossils: theholotype—specimen number AMNH NJ-667—collected by Yale Goldman; theparatype; and a third described in 2005.[1] At the time of the genus description, the type specimens were residing in theAmerican Museum of Natural History, in New York City.[2] All the described specimens areworker caste adult females which have been preserved asinclusions in transparent chunks ofNew Jersey amber. The amber specimens were recovered from deposits of the South Amboy Fire Clay, part of theRaritan Formation. New Jersey amber has been dated to approximately 90 to 94mya, placing it in theTuronian of theLate Cretaceous. Analysis of the amber composition indicates it originated ascupressaceous resins which were deposited in lagoons and salt water marshes along the Cretaceous eastern seaboard.[2]Brownimecia clavata is one of several ant species described from New Jersey amber, the others beingSphecomyrma freyi,Sphecomyrma mesaki,Baikuris casei, andKyromyrma neffi.[1]
The type fossils were first studied by paleoentomologists David Grimaldi, Donat Agusti, and James Carpenter of the American Museum. The team's 1997type description of the new genus and species was published in the journalAmerican Museum Novitates.[2] The genus name was coined by them as apatronym honoring the ant systematist William L. Brown, Jr. who co-described the first Cretaceous ant genus and speciesSphecomyrma freyi. Thespecific epithetclavata was chosen as a reference to the distinctive clubbed antennae seen in the workers. Grimaldi, Agusti, and Carpenter placed the new genus into the extant ant subfamilyPonerinae, without tribal assignment, based on a slight constriction of thegaster. They also noted several features that are shared with ants of theamblyoponine group, then a part of Ponerinae. The workers havegenal spurs on the lower edge area under the small compound eyes. Workers also have narrow long mandibles, as do some amblyoponine genera. Placement in Ponerinae was unchanged until a revision of the subfamily was published in 2003 bymyrmecologistBarry Bolton. In that paper the subfamily was shown to be aparaphyletic grouping and many of the included genera were moved to separate subfamilies, including the amblyoponines andBrownimecia. Due to the unique combination of morphological features found inBrownimecia, Bolton erected the new subfamily Brownimeciinae for the genus. Bolton notes that its sickle-like mandibles which lack teeth are not usual for ants and are often associated with dulotic, orslave-making, behavior in extant genera. In contrast to stem group ants such as the sphecomyrmines, thescapes ofBrownimecia workers are more elongated like those ofcrown group ants.[1][3] In his 2007 phylogenetic examination of Formicidae, entomologist Philip Ward notes the possibility thatBrownimecia is a crown group genus and placed the subfamily into the informal "poneroid" grouping in his phylogony.[4]
Both theBrownimecia holotype worker and the 2005 worker are complete and fully preserved in curled positions and have their stings extended.[2][1] The paratype worker is very incomplete; the amber in which it is encased is highly likely to have been at least partlytumble polished in a rock causing the ant to be exposed and portions of the head, left antenna, mid legs, hind legs, and all of the right antennae and forelegs are gone. The exposure allowed the interior cavity of the fossil to be examined underscanning electron microscope after being coated in a layer ofgold.[2]
The holotype has an overall body length of approximately 3.43 millimetres (0.135 in) with finely scatteredsetae on all parts except thenotum andpropodeum. The head is large with small roundedcompound eyes composed of about one hundredommatidia. The holotype does not clearly show whether theocelli are present or absent, but they are clearly absent in the 2005 specimen. The mandibles arescimitar-shaped with no teeth present on the interior sides and almost the length of the head. The mandibles cross each other near their mid-length and the oral surfaces bear approximately thirty short needle-like setae.[2] Theclypeus is short but wide, crossing almost the whole width of the head.[2] Perpendicular crenelations run along the upper margin of the clypeus on the 2005 specimen.[1] Thegena have a distinct tooth-like structure on the lower sides. The eleven segmentedantennae are distinct in having a definite clubbed tip, a feature not seen in any other described Cretaceous ants. The apicalflagellomere segment is nearly twice the width of the other segments, while the third to the sixth segments are the shortest and the second flagellomere is slightly swollen.[2]
Themetathoracic spiracles are raised on small cones projecting from thealitrunk, while themetapleural gland orifices are not notably raised, having a ridge leading to them. All of the alitrunk gland and spiracle orifices are to some degree obscured on the holotype by froths of bubbles that escaped them soon after the worker was entombed in the sap.[2] The petiole top forms a pointed apex instead of a more rounded dome. There is a covering of finemicrotrichia hairs on the petiole and a pair of small setae are situated near the apex. At the front of the petiole there is a narrow attachment area to the propodeum, while the rear is flared into a large attachment to the gaster. The helcium, a small exoskeleton plate between the petiole and gaster, is developed and shows crenelations on the rear edge. There is a small but distinct constriction between the first and second segments of the gaster. Both the holotype and 2005 specimens have a fully preserved gaster tip showing the extended sting, while the paratype is missing the tip area.[2][1]
Due to the unusual morphology of the mandibles, scientists have suggested thatBrownimecia may have had a high level offeeding specialization.[5]
Media related toBrownimecia clavata at Wikimedia Commons