Novjitates PUBLISHED by the AMERICAN MUSEUM of NATKTIUA-1ISTORY CENTRAL PARK WEST at 79TH STREET, NEW YORK, N.Y
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AMERICANt MUSEUM NovJitates PUBLISHED BY THE AMERICAN MUSEUM OF NATKTIUA-1ISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 3208, 43 pp., 24 figures, 1 tables October 23, 1997 New and Rediscovered Primitive Ants (Hymenoptera: Formicidae) in Cretaceous Amber from New Jersey, and Their Phylogenetic Relationships* DAVID GRIMALDI,1 DONAT AGOSTI,2 AND JAMES M. CARPENTER' ABSTRACT All Cretaceous records of ants are reviewed, worker are external and even some internal fea- and evidence originally given for their placement tures of the metapleural gland-a definitive for- is evaluated. Cretaceous Formicoidea preserved in micid synapomorphy-which are described in de- rocks lack preservation of critical ant synapomor- tail for the first time. This specimen is designated phies like the metapleural gland, which are pre- as a neotype to replace the disintegrated holotype served in specimens in amber. For this reason, the of this species. One complete male specimen is Armaniidae Dlussky, from the Cretaceous of Rus- tentatively assigned to Sphecomyrma, which sia, are placed here as Formicoidea incertae sedis, would be the first known male of the genus. One not in the Formicidae proper. The oldest amber complete and one partial male, both from the with ants is from New Jersey. same piece of amber, are a new, plesiomorphic Seven complete and partial specimens of For- species of Baikuris Dlussky (Baikuris casei, n. micidae, recently discovered in Turonian (92 Ma) sp.), the genus previously known only from upper amber from central New Jersey, are described and Cretaceous (Santonian) amber of Taymyr, north- discussed. The specimens consist of four males ern Siberia. Two workers represent a new genus and three workers. One complete and well-pre- and species of Cretaceous Formicidae, Browni- served worker is Sphecomyrma freyi Wilson and mecia clavata n. gen., n. sp., based on distinc- Brown 1967, known previously from two workers tively clubbed antennae, proportions of the anten- in a piece of Turonian amber from Cliffwood nal articles, and thin mandibles that lack teeth and Beach, New Jersey. Well preserved in the new extensively cross, and a ponerine-like constriction * Paleontology of New Jersey amber, Part VI. ' Curator, Department of Entomology, American Museum of Natural History. 2 Research Scientist, Department of Entomology, American Museum of Natural History. Copyright C American Museum of Natural History 1997 ISSN 0003-0082 / Price $5.60 2 AMERICAN MUSEUM NOVITATES NO. 3208 between abdominal segments M and IV (gaster crepencies with the cladograms of Baroni Urbani segments I and II). Brownimecia is more closely et al. (1992) are discussed. Including the fossil related to extant Formicidae than are Sphecomyr- taxon Formiciinae Lutz (compressed remains minae, the genus being the earliest known mem- from the Eocene of Germany) in the cladistic ber of the extant subfamily Ponerinae. The fourth analysis, as done by Baroni Urbani et al., imparts male belongs to a third genus, undescribed. These too many missing values for meaningful analysis. are the oldest definitive ants. Sphecomyrma, not discussed by Baroni Urbani et Composition, monophyly, and systematic po- al., retains its basal position in the Formicidae in sition of the subfamily Sphecomyrminae are dis- the present analysis. Discovery of new and exclu- cussed. Modifications were made to the data of sively primitive ants in upper Cretaceous ambers Baroni Urbani et al. (1992) and reanalyses were indicates an origin of the ants probably in the low- made of the basal relationships of the Formicidae ermost Cretaceous, but no older, contrary to a re- including Sphecomyrma and Brownimecia. Dis- cent molecular hypothesis. INTRODUCTION The ants can arguably be said to be the son and Brown, in Cretaceous amber from ecologically and numerically dominant fam- New Jersey. The piece of amber that con- ily of insects-perhaps of all organisms-on tained two workers was discovered in 1966 earth. As Holldobler and Wilson (1990) dis- by an amateur collector, Edmund Frey, who cussed, ants are so abundant that approxi- found it in strata of the Raritan-Magothy For- mately 3 million exist in a hectare of Ama- mations exposed in bluffs at Cliffwood zonian forest soil, and they represent some Beach, New Jersey. It was studied and re- 10-15% of the entire animal biomass in ter- ported by Wilson et al. (1967a, 1967b). De- restrial ecosystems. On this basis alone, the spite such a sensational find, little attention origins of the ants would be important for was paid to New Jersey amber other than by understanding the evolution of modem ter- another fossil collector, Gerard R. Case. Case restrial biological communities. collected Cretaceous amber from at least a The outstanding hallmark of the ants is that dozen localities between 1962 and 1986, all all species are eusocial, which is what probably of it found in rather trace quantities on the caused their tremendous success. The wingless surface of lignitic exposures. Many of his workers can easily penetrate minute niches. samples were given to Princeton University Their array of glands and secretions enables (Dept. of Geology) where they were exam- sophisticated chemical communication, such ined for inclusions. (The other samples were that they can rapidly recruit workers for se- given to the AMNH [American Museum of questering food; defend the colony, especially Natural History] in 1992.) The only piece with soldiers and stinging workers; and even with inclusions was found in 1966-the prey. Eusociality has actually subdue large same year as the Sphecomyrma discovery- 12 in the Hymenoptera: once in evolved times in the Such Clay Pits in Parlin, New Jersey. the ants, and all other times in the Vespoidea It contained a ceratopogonid and two chiron- (social/paper wasps) and the Apoidea s.s. revealed that (bees). It was the ants that became predomi- omid midges. Case's collections nant, though, because they are thought to have amber in New Jersey was actually wide- been the earliest, perhaps the first, eusocial in- spread in appropriate Cretaceous exposures, sect predators on the ground (Holldobler and and that other insects existed in the amber Wilson, 1990). Clearly, knowing the earliest besides Sphecomyrmna. These collections re- history of the ants can allow much better un- mained largely unnoticed for more than 20 derstanding of the unparalleled success of this years, and even the ceratopogonid wasn't de- remarkable group. It is a history that began in scribed until 1986, as Culicoides casei. the late Mesozoic. In 1976 Gerard Case brought Robert Lan- genheim (University of Illinois, Champagne- SPHECOMYRMA AND NEW JERSEY AMBER Urbana) to several of the amber localities in The first Mesozoic ant to be discovered Sayreville and adjacent towns in New Jersey, and described was Sphecomyrma freyi Wil- where they collected samples. Langenheim 1997 GRIMALDI ET AL.: PRIMITIVE ANTS IN CRETACEOUS AMBER 3 had worked on the stratigraphy of late Oli- deep deposits of the South Amboy Fire Clay gocene amber from Mexico and Cretaceous (Tlronian). The peats are the stranded re- amber from Alaska. No results were reported mains of deltaic deposits, probably formed from those samples from New Jersey. From by coastal cedar swamps. Inclusions of leafy 1986-1989 the senior author resumed the shoots and fibrous bark indicate that the bo- collection of amber from various Cretaceous tanical origin of the amber is not Araucan- exposures in New Jersey, some of them vis- aceae, as originally proposed based on chem- ited 20 years earlier by Case. The samples istry (Langenheim, 1969; Grimaldi et al., collected by Grimaldi were used in a strati- 1989), but in the Cupressaceae. A detailed graphic and chemical study of the amber account of the stratigraphy, taphonomy, and (Grimaldi et al., 1989), and only one piece paleoecology of the amber sites is provided was found to contain an insect inclusion (a elsewhere (Grimaldi, 1997). partial midge). By 1986, some sites had been Approximately 70% of the amber is vir- developed and were no longer accessible. tually opaque, due to a thick suspension of The bluffs at Cliffwood Beach-type locality particulate debris and bubbles. The transpar- for Sphecomyrma freyi-for example, were ent pieces are mostly very brittle and fracture covered in 1974-75 with boulders and a skin easily. To trim and polish a window in this of cyclone steel fencing onto which concrete amber with an orientation crucial for obser- was poured. All collecting done in New Jer- vation, a technique of vacuum-embedding sey up until 1989 uncovered small amounts needed to be developed. The technique is de- of amber, and the likelihood of discovering scribed in more detail elsewhere (Silverstein pieces with insects seemed so remote that and Nascimbene, 1997), but involves embed- prospecting was then abandoned. ding the amber in a synthetic casting resin of In 1992 Gerard Case brought to Grimaldi's low viscosity and refractive index (see also attention two remarkable new deposits from appendix). While the resin is still fluid, the central New Jersey rich in fossiliferous Cre- preparation is subjected to a reduced pressure taceous amber. They lay between some of the of approximately 4 psi in a bell jar attached sites prospected earlier that were only a few to a vacuum pump. This removes air from miles apart. Exact locations and maps are the fine cracks and allows resin to seep in. available through the senior author, but they Filling cracks not only cements the fragile correspond most closely to site number five piece, but allows one to see through cracks on the map in Grimald et al. (1989), approx- where the air would otherwise cause a crack imately 7 km NW of Cliffwood Beach. Since to be like a small mirror. November 1992, excavations by dedicated Work on the manuscript was as follows: AMNH volunteers (see below) have amassed Grimaldi did the final trims and polishing of several hundred pounds of amber and hun- specimens for observation, did sketches and dreds of inclusions.