The Ant Aphaenogaster Dlusskyana Sp. Nov. (Hymenoptera, Formicidae) from the Sakhalin Amber—The Earliest Described Species of an Extant Genus of Myrmicinae A
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ISSN 00310301, Paleontological Journal, 2016, Vol. 50, No. 9, pp. 936–946. © Pleiades Publishing, Ltd., 2016. The Ant Aphaenogaster dlusskyana sp. nov. (Hymenoptera, Formicidae) from the Sakhalin Amber—the Earliest Described Species of an Extant Genus of Myrmicinae A. G. Radchenko and E. E. Perkovsky Schmalhausen Institute of Zoology, National Academy of Sciences of Ukraine, ul. Bogdana Khmel’nitskogo 15, Kiev, 01601, Ukraine email: [email protected], [email protected] Received April 10, 2015 Abstract—The earliest member of an extant ant genus of the subfamily Myrmicinae, Aphaenogaster dlussky ana sp. nov., from the Sakhalin amber (Russia, Middle Eocene, 43–47 Ma) is described. Fossil representa tives of the genus Aphaenogaster are critically analyzed and it is proposed to transfer many of these to the fossil morphotaxon Paraphaenogaster. The morphology, distribution, and possible evolutionary trends of the genus Aphaenogaster are reviewed and it is suggested that this genus appeared in the territory currently occupied by the Palearctic not later than the Early Eocene (over 50 Ma). Aphaenogaster dlusskyana can be considered the oldest described representative of an extant genus of the subfamily Myrmicinae, although earlier, as yet unde scribed, records of extant genera of Myrmicinae belong to the Early Eocene. Keywords: Myrmicinae, Aphaenogaster, Paraphaenogaster, ants, paleontology, taxonomy, evolution, Middle Eocene, Sakhalin amber DOI: 10.1134/S0031030116090136 INTRODUCTION (Danian, 56–59 Ma) to Middle Eocene (42–47 Ma). Dlussky (1988) tentatively dated this amber as Pale In 1972 a team from the Paleontological Institute ocene and in all subsequent publications on fossil ants, of the USSR Academy of Sciences collected large the Sakhalin amber was dated as Paleocene (Dlussky material from amber deposits in the vicinity of the vil and Fedoseeva, 1988; Archibald et al., 2006; Dlussky lage of Starodubskoe on the eastern coast of southern and Rasnitsyn, 2007; Aria et al., 2011; Dubovikoff, Sakhalin Island, which included 838 insect specimens 2012; LaPolla et al., 2013; and others). Eskov (2002) (Zherikhin, 1978). These included ten ants (1.2% of also accepted this dating. However, as early as the end the total number of insects), based on which Dlussky of the 20th century, Kodrul (1999), based on geologi (1988) described five extinct genera and seven species, cal and paleobotanical data, convincingly substanti assigned to the extant subfamilies Ponerinae (Proto ated the Middle Eocene age of the Naibuchi Forma pone Dlussky), Aneuretinae (Aneuretellus Dlussky), tion, in which the Sakhalin amber was found in situ Dolichoderinae (Eotapinoma Dlussky, Zherichinius (see also Baranov et al., 2015). Dlussky), and Formicinae (Chimaeromyrma Dlussky). The age of the deposits of the Ventana Formation in It is interesting that representatives of the two genera Argentina, from which Ameghinoia piatnizkyi Viana et of Dolichoderinae described from the Sakhalin amber Haedo Rossi was described based on imprints (this were later found in the much older deposits of Alberta species was later placed in the genus Archymyrmex (Canada, Upper Cretaceous, Campanian, 78–79 Ma) Cockerell of the subfamily Myrmeciinae; see Dlussky (Eotapinoma macalpini Dlussky) (Dlussky, 1999) and and Perfilieva, 2003), has been debatable for many in a younger Late Eocene Bitterfeld (=Saxonian) decades. Originally, these beds were dated as Late amber (35–37 Ma) (as yet undescribed species of Eocene–Early Oligocene (Viana et al., 1957), but, Zherichinius) (Dlussky and Rasnitsyn, 2009; Dubo later, these deposits were dated as Late Eocene (Rossi vikoff, 2012), whereas seven new species of the genus de Garcia, 1983), or were dated within a wide range Protopone were described from the Middle Eocene from the Late Paleocene to Early Oligocene (Petrulev (Lutetian) shale in Germany (Grube Messel, 47 Ma) icius, 1999); Dlussky previously considered this spe (Dlussky and Wedmann, 2012). cies Paleocene (Dlussky and Fedoseeva, 1988). The age of the Sakhalin amber was debated for a Finally, in the last decade, the Ventana Formation was long time. Zherikhin (1978), based on indirect evi dated as Middle Eocene (Early Lutetian, 47–48 Ma) dence, dated it over a wide range from Paleocene (Wilf et al., 2005; Dlussky, 2012). Previously, the Ølst 936 THE ANT APHAENOGASTER DLUSSKYANA SP. NOV. (HYMENOPTERA, FORMICIDAE) 937 Formation (Denmark) was dated Upper Paleocene– Not all morphological elements could be measured Lower Eocene (Dlussky and Rasnitsyn, 2007) with in the specimen studied; hence, measurements are numerous remains of Ypresiomyrma rebekkae (Rust et only given for structures that could be measured (with Andersen), but now it is clear that these remains the precision to 0.01 mm), in particular: (HL) head belong to the very beginning of the Ypresian (Lower length from the top of the occipital margin to anterior Eocene, ca. 54 Ma) (Archibald et al., 2006). margin of the clypeus; (HW) maximum head width behind the eyes; (SL) scape length in profile; (ML) Two imprints of ant wings were found in the length of the mesosoma in profile from the anterodor Tadushi Formation previously assigned to the Pale sal margin of the pronotum to the posterior margin of ocene (SikhoteAlin, Russian Far East). They were the propodeal lobes; (ED) maximum eye diameter; previously assigned to unidentifiable taxa from the (MDL) mandible length; (MML) masticastory mar subfamily Formicinae (Dlussky and Fedoseeva, 1988; gin of mandible length ; (HTL) hind tibia length; (PL) Dlussky and Rasnitsyn, 2007), but they were later petiole length; (PH) petiole height; (PPL) postpetiole placed in the morphotaxon Donisthorpe Leucotaphus length; (PPH) postpetiole height; (PSL) propodeal (Dlussky and Perfilieva, 2014). The Tadushi Forma spine length; (GL) gastral length. Ratios calculated tion is currently dated as the end of the Early Eocene based on the measurements are given below. (about 50 Ma) (Makarkin, 2014); hence occurrences of Paleocene ants are currently limited to two uniden tified incomplete imprints from the Pascapoo Forma SYSTEMATIC PALEONTOLOGY tion (Alberta, Canada; Mitchell and Wighton, 1979). Subfamily Myrmicinae Lepeletier, 1835 Genus Aphaenogaster Mayr, 1853 MATERIAL AND METHODS Type species. Aphaenogaster sardoa Mayr, 1853. In 2012 one of us (EP) found in the collections of Species composition. Altogether over the Borissiak Paleontological Institute of the Russian 180 described species and about 45 infraspecific forms Academy of Sciences (PIN) a small piece (less than 1 g) of Aphaenogaster (Bolton, 2014; Borowiec and Salata, of amber collected in Starodubskoe in 1972 and con 2014). The geographical range of this genus is interest taining an earliest known representative of an extant ing. The overwhelming majority of species (around genus of Myrmicinae from the Sakhalin amber, which is 100) inhabit the western Palearctic, over 80 of these described below as Aphaenogaster dlusskyana sp. nov. occur in the Mediterranean; four species with three subspecies are known from Madagascar; around ten Inclusion state. The Sakhalin amber experienced species are found in Australia, six are in New Guinea, high temperatures and pressure after fossilization, around 40 are in Central Asia, south of the eastern resulting in deformation of the shape and proportions Palearctic, and in the Oriental Zoogeographic Realm, of various body parts of the included insects (Dlussky, and fewer than 30 occur in America, from southern 1988). This applies to the specimen of the species Canada to northern Columbia. Aphaenogaster is described below. In particular, the mesosoma is com absent in subSaharan Africa (Fig. 1). pressed strongly laterally, especially the mesothorax At present, about 20 fossil Aphaenogaster species and propodeum, so the mesopleural cuticle has are known, but some of these cannot be reliably become fragmented and pulled upward and somewhat assigned to this genus (see below). forward to form what appear to be small “horns,” D i a g n o s i s. Worker monomorphic; body 4.5– which clearly were not present in the intact specimen; 7 mm long, from yellow to black, but bicolored species the propodeum evidently had been strongly elevated very rare. Head variously shaped, always longer than and rimmed laterally and dorsally with sharp keels. As wide, rectangular, oval, in some species strongly elon a result of the compression, the anterior part of the gated, without occipital corners, tapering posteriorly pronotum was also elongated to form a long, thin forming “collar”. Eyes welldeveloped, but not large, “neck.” The gaster is compressed slightly dorsoven approximately at midpoint of lateral head margin, trally, so that it appears relatively flat. The shape of the ocelli absent. Mandibles elongated triangular, not waist and the propodeal spines were apparently only widened, masticatory margin with sharp (up to 10) slightly changed. A photograph of the specimen is teeth. Palp formula 5, 3. Antennae 12segmented; given below as well as a drawing based on this photo scape gently bent at base, without angle, long or very graph and reconstructions of the body and its separate long, always projecting beyond occipital margin, parts, aiming to show the original body shape of this funiculus terminating in 4–5segmented club, some species. times club absent. Frontal lobes partly covering anten The photographs were taken using a Leica M165 nal sockets. Frontal carinae straight or slightly curved. stereomicroscope with a Leica DFC425a camera,