Eulithomyrmex Rugosus
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''Eulithomyrmex'' is an
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
ant Ants are Eusociality, eusocial insects of the Family (biology), family Formicidae and, along with the related wasps and bees, belong to the Taxonomy (biology), order Hymenoptera. Ants evolved from Vespoidea, vespoid wasp ancestors in the Cre ...
in the formicid subfamily
Agroecomyrmecinae Agroecomyrmecinae is a subfamily of ants containing two extant and two fossil genera. The subfamily was originally classified in 1930 by Frank M. Carpenter as Agroecomyrmecini, a Myrmicinae tribe. Barry Bolton, Bolton raised the tribe to subfami ...
. The genus contains two described species, ''Eulithomyrmex rugosus'' and ''Eulithomyrmex striatus''. ''Eulithomyrmex'' is known from a group of
Late Eocene The Priabonian is, in the International Commission on Stratigraphy, ICS's geologic timescale, the latest age (geology), age or the upper stage (stratigraphy), stage of the Eocene epoch (geology), Epoch or series (stratigraphy), Series. It spans ...
fossils which were found in
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
.


History and classification

When described the genus ''Eulithomyrmex'' was known from over forty separate fossils preserved as impressions in fine
shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...
s of the
Florissant formation The Florissant Formation is a sedimentary geologic formation outcropping around Florissant, Teller County, Colorado. The formation is noted for the abundant and exceptionally preserved insect and plant fossils that are found in the mudstones an ...
in Colorado. The formation is composed of successive lake deposits which have preserved a diverse assemblage of insects. The insects and plants suggest a climate similar to modern Southeastern North America, with a number of taxa represented that are now found in the subtropics to tropics and confined to the Old World. When ''Eulithomyrmex'' was described, the Florissant formation was considered to be
Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
in age, based on the flora and fauna preserved. Successive research and fossil descriptions moved the age older and by 1985 the formation had been reassigned to an
Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...
age. Further refinement of the formation's age using radiometric dating of sanidine crystals has resulted in an age of 34 million years old. This places the formation in the Eocene Priabonian stage. At the time of description the
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
and three
paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype (biology), isotype ...
s of ''E. rugosus'' plus the holotype and single paratype of ''E. striatus'' were deposited in the
Museum of Comparative Zoology The Museum of Comparative Zoology (formally the Agassiz Museum of Comparative Zoology and often abbreviated to MCZ) is a zoology museum located on the grounds of Harvard University in Cambridge, Massachusetts. It is one of three natural-history r ...
paleontology collections at
Harvard University Harvard University is a Private university, private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the History of the Puritans in North America, Puritan clergyma ...
. One additional paratype specimen, number 17,019a, was part of the collections of the
University of Colorado The University of Colorado (CU) is a system of public universities in Colorado. It consists of four institutions: the University of Colorado Boulder, the University of Colorado Colorado Springs, the University of Colorado Denver, and the U ...
. The fossils were first studied by paleoentomologist Frank M. Carpenter of the Museum of Comparative Zoology. His 1930 type description of the new species was published in the ''Bulletin of the Museum of Comparative Zoology''. Carpenter described the genus under the name ''Lithomyrmex'', with the two species respectively as ''Lithomyrmex rugosus'' and ''Lithomyrmex striatus''. Carpenter designated ''L. rugosus'' as the type species for the genus. At the time of Carpenter's description, the generic name ''Lithomyrmex'' had already been used in 1929 for a modern ant species '' Lithomyrmex glauerti''. As a result, Carpenter moved the two species to the new genus ''Eulithomyrmex''. When described Carpenter noted the similarity between ''Eulithomyrmex'' and the genus ''Agroecomyrmex'' known from
Baltic amber Baltic amber or succinite is amber from the Baltic region, home of its largest known deposits. It was produced sometime during the Eocene epoch, but exactly when is controversial. It has been estimated that this forested region provided the re ...
fossils and described in 1910 and placed both into the tribe
Agroecomyrmecini Agroecomyrmecinae is a subfamily of ants containing two extant and two fossil genera. The subfamily was originally classified in 1930 by Frank M. Carpenter as Agroecomyrmecini, a Myrmicinae tribe. Barry Bolton, Bolton raised the tribe to subfami ...
. A third genus was added to the group in 1968 with the description of the living genus ''
Tatuidris ''Tatuidris'', or armadillo ant, is a rare genus of ants consisting of a single species, ''Tatuidris tatusia''. The ants are small in size and inhabit the leaf litter of Neotropical forests in Central and South America, from Mexico to Brazil ...
'' found in Central and South America. Placement of the group has changed several times, with the genera being placed in the
Myrmicinae Myrmicinae is a subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily ...
tribe Agroecomyrmecini from 1930 until 2003. The placement of the tribe was challenged in 2003 by
Barry Bolton Barry Bolton is an English myrmecologist, an expert on the classification, systematics, and taxonomy of ants, who long worked at the Natural History Museum, London. He is known especially for monographs on African and Asian ants, and for encyclop ...
who suggested a closer relationship between the group and the "poneromorph" subfamilies. In addition to the suggested relationship, Bolton moved the tribe from Myrmicinae to a new subfamily,
Agroecomyrmecinae Agroecomyrmecinae is a subfamily of ants containing two extant and two fossil genera. The subfamily was originally classified in 1930 by Frank M. Carpenter as Agroecomyrmecini, a Myrmicinae tribe. Barry Bolton, Bolton raised the tribe to subfami ...
.


Description

In general the two ''Eulithomyrmex'' are considered very similar to ''Agroecomyrmex duisburgi'' and the two genera can be separated based on the features of the head, with ''Agroecomyrmex'' displaying larger mandibles and a smaller antennal club. Overall ''Eulithomyrmex'' species have a nearly square head sporting small mandibles and short antennae composed of twelve total segments in the females and thirteen segments in the males. From the head across the thorax and down to the
pedicel Pedicle or pedicel may refer to: Human anatomy *Pedicle of vertebral arch, the segment between the transverse process and the vertebral body, and is often used as a radiographic marker and entry point in vertebroplasty and kyphoplasty procedures ...
, the exoskeleton has coarse sculpturing, and the fore wings have two cubital cells. ''E. rugosus'' was described from four
alate Alate (Latin ''ālātus'', from ''āla'' (“wing”)) is an adjective and noun used in entomology and botany to refer to something that has wings or winglike structures. In entomology In entomology, "alate" usually refers to the winged form of ...
females and one male with Carpenter noting at least forty specimens of the species were known to him. Overall it is estimated the females would have been around long while the male was smaller at about . Males are also distinguished by their head, which is broader then it is long, while in females the head is longer than broad. Unlike ''E. rugosus'', ''E. striatus'' was described from only two specimens, an adult worker and an alate female. They are identical in features and only differ in the size of worker, at , while the queen is . ''E. striatus'' is noted for having a smaller head with longer antennae segments than ''E. rugosus'', plus a smaller postpetiole and lack of sculpturing on the gaster.


References

{{Taxonbar, from=Q14447775 Agroecomyrmecinae Fossil ant genera Priabonian insects Prehistoric insects of North America Florissant Formation Fossil taxa described in 1935 Taxa named by Frank M. Carpenter