18:16Новый ископаемый вид муравьёв с необычным ротовым аппаратом - Zigrasimecia
A New Genus of Highly Specialized Ants in Cretaceous Burmese Amber (Hymenoptera: Formicidae).
PHILLIP BARDEN & DAVID GRIMALDI
Zootaxa. 2013 год, том 3681 (4): 405–412 (published: 24 Jun. 2013)
Из Бирманских меловых янтарей (Мьянма, Юго-Восточная Азия) описан новый уникальный специализированный вид и род ископаемых муравьёв Zigrasimecia tonsora Barden and Grimaldi n.sp. Возраст янтарей около 99 млн лет. Род Zigrasimecia очень близок к другому ископаемому меловому муравью Sphecomyrmodes Engel and Grimaldi, based in part on the shared possession of a comb of pegs on the clypeal margin, as well as mandible structure. Highly specialized features of Zigrasimecia include extensive development of the clypeal comb, a thick brush of setae on the oral surface of the mandibles and on the labrum, and a head that is broad, flattened, and which bears a crown of blackened, rugose cuticle. Mouthparts are hypothesized to have functioned in a unique manner, showing no clear signs of dentition representative of "chewing” or otherwise processing solid food. Although all ants in Burmese amber are basal, stem-group taxa, there is an unexpected diversity of mouthpart morphologies and probable feeding modes.
Среди почти 13000 видов описанных муравьёв a handful of rare and enigmatic taxa from the Cretaceous. Датирование на основании молекулярных часов показало, что crown-group ants diverged from their wasp-like ancestors between 115–135 (Brady et al. 2006) and 140–168 million years ago (Moreau et al. 2006), the oldest definitive ant fossils are approximately 100 myo, despite numerous older insect-yielding deposits (Nel et al. 2004). In amber deposits where ants are found, formicid inclusions from the Upper Cretaceous comprise between <1 and 3% of the total number of individual insects (LaPolla et al. 2013), a palpable contrast to much younger Miocene deposits where ant prevalence is as high as 24–36% (Grimaldi and Engel 2005; Dlussky and Rasnitsyn 2007). While younger amber deposits typically contain species that are readily placed in extant lineages (Dlussky and Rasnitsyn 2003), only one species of crown-group ant (a formicine) has been definitively identified before the Campanian (Grimaldi and Agosti 2000). The rest of the, proposed stem-group, Cretaceous taxa possess an array of unique morphologies that renders them unrecognizable with regard to modern groups and their relationship to living species is poorly explored. Ants from the Upper Cretaceous therefore act as valuable portholes, providing otherwise unknowable details at a critical time in the history of these small insects that now dominate terrestrial environments across the world.
Ископаемые муравьи обычно идентифицируются на основании ключевых муравьиных признаков, таких как наличие метаплевральных желёз, petiole, and an enlarged antennal scape. While the possession of one individual character does not imply that the insect in question is indeed a member of crown-group or stem-group ants, different combinations of the presence and absence among these characters have been the basis for taxonomic assignment. The metapleural gland, visible as a small opening on the posterior region of the mesosoma, is now known to function as a form of toxic defense and sanitation (Yek and Mueller 2011). Although it has been lost in many extant species, it is not present in any other groups of insects, and therefore is probably the most reliable defining character of ants. The vast majority of Cretaceous ants have been placed in the extinct subfamily Sphecomyrminae, their placement owing largely to this gland. Sphecomyrmine ants possess a metapleural gland, along with a petiole, but not the characteristic "elbowed antennae” that modern ants exhibit and so this subfamily is widely recognized as a stem-group of all other Formicidae (e.g., Ward 2007). Подсемейство Sphecomyrminae включает 8 родов и 15 видов (LaPolla et al. 2013), and, while there is no phylogenetic evidence to suggest the subfamily is monophyletic, one analysis has shown it may be a member of the group that is sister to all modern ants (Grimaldi et al. 1997).
Zigrasimecia Barden And Grimaldi, new genus
ДИАГНОЗ, самка: Based on unique dealate specimen. Similar to Sphecomyrmodes based on structure of the mandible (with only two large teeth: one apical, one subapical); ocelli large, scape very short (slightly less than twice the length of pedicel), 12 antennomeres, eyes relatively small, and clypeal margin with row of peg-like denticles. Differs from Sphecomyrmodes by the flattened, broad head with irregular posterodorsal margin; very
broad, concave clypeal margin with many more (ca. 30) denticles, plus two shorter rows of denticles ventrally; mandibles about half the length, with dense brush of spicule-like setae on oral surface; setae-coated labrum; presence of raised toruli and shallow lateral antennal scrobes; vertex of head with pair of oval, melanized, rugose patches.
ТИПОВОЙ ВИД. Z. tonsora, new species.
ЭТИМОЛОГИЯ. Patronym, for Mr. James Zigras, and –mecia, a common suffix for ant genera. In acknowledgment of Mr. Zigras’ generosity in loaning this and many other rare and scientifically valuable specimens from his collection of Burmese amber.
Zigrasimecia tonsora, Barden and Grimaldi, new species
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