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''Sphecomyrma'' is an extinct genus of
ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of ...
s which existed in the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
approximately 79 to 92 million years ago. The first specimens were collected in 1966, found embedded in
amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In ...
which had been exposed in the cliffs of
Cliffwood, New Jersey Cliffwood is an Local government in New Jersey#Unincorporated communities, unincorporated community located within Aberdeen Township, New Jersey, Aberdeen Township in Monmouth County, New Jersey, Monmouth County, New Jersey, United States. The a ...
, by Edmund Frey and his wife. In 1967, zoologists
E. O. Wilson Edward Osborne Wilson (June 10, 1929 – December 26, 2021) was an American biologist, naturalist, entomologist and writer. According to David Attenborough, Wilson was the world's leading expert in his specialty of myrmecology, the study of an ...
, Frank Carpenter and William L. Brown, Jr. published a paper describing and naming ''Sphecomyrma freyi''. They described an ant with a mosaic of features—a mix of characteristics from modern ants and aculeate wasps. It possessed a
metapleural gland Metapleural glands (also called metasternal or metathoracic glands) are secretory glands that are unique to ants and basal in the evolutionary history of ants. They are responsible for the production of an antibiotic fluid that then collects in a ...
, a feature unique to ants. Furthermore, it was wingless and had a petiole which was ant-like in form. The
mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
s were short and wasp-like with only two teeth, the gaster was constricted, and the middle and hind legs had double tibial spurs. The antennae were, in form, midway between the wasps and ants, having a short first segment but a long flexible funiculus. Two additional species, ''S. canadensis'' and ''S. mesaki'', were described in 1985 and 2005, respectively. The genus is among the earliest known ants to roam the earth and at the time was considered to be the evolutionary link between ants and wasps. It was suggested that ants diverged from tiphiid wasp ancestors, but later studies show that they originate from a different clade. It shows resemblance to extant primitive ants such as '' Nothomyrmecia'' and members of the tribe Aneuretini. Some scientists, however, doubted the nature of these ants and believed they were wasps due to the possible absence of the metapleural gland in ''Sphecomyrma'' and short scapes which are key diagnostic traits for ants. Additional specimens collected proved ''Sphecomyrma'' was an ant as the metapleural gland was identified. Further fossil evidence, along with its slender body and large
compound eyes A compound eye is a visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidia, which are tiny independent photoreception units that consist of a cornea, lens, and photoreceptor cells which distin ...
, suggest that they were epigaeic, foraging socially above ground and out in open areas. The sphecomyrmines, including these ants, most likely vanished by the end of the
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
.


Taxonomy

Before the discovery of the first ''Sphecomyrma'' fossils, there were no fossil records of any ants from
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In ...
and the oldest social insects at the time extended back to the
Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...
epoch; the earliest known ant at the time was described from a forewing found in the
Claiborne Formation The Claiborne Formation or Claiborne Group is a geologic formation in Arkansas, Illinois, Kentucky, and Texas. It preserves fossils dating back to the Paleogene period . See also * List of fossiliferous stratigraphic units in Kentucky Thi ...
in Tennessee. The great diversity of ant fossils found in the
Baltic amber The Baltic region is home to the largest known deposit of amber, called Baltic amber or succinite. It was produced sometime during the Eocene epoch, but exactly when is controversial. It has been estimated that these forests created more than ...
and Florissant shales of the Oligocene and in the Sicilian amber of the
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 ...
have prompted entomologists to search for ants of Cretaceous age that may link ants and non-social wasps together. Such a link may shed light on the early origins of ants, but no fossils of any social insect existed before ''S. freyi'' was discovered, thus the early evolution of ants remained a mystery. Only a single hymenopterous
Upper Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', th ...
fossil has been the subject of possible significance to the evolution of aculeate wasps and ants. A single forewing was discovered in Siberia and described in 1957 as '' Cretavus sibiricus'', with the author noting that the wing venation closely resembles those of bethylid or scoliid wasps, of which these families of wasps have close connections with the origin of ants. However, there were several problems: as the fossil was only a single wing, scientists could not explain or answer whether or not the insect had key diagnostic body traits that would even place it within the subclade Aculeata. In 1966, the first fossils of ''S. freyi'' were collected by Edmund Frey and his wife during a trip collecting
mineralogical Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the p ...
specimens in the Magothy exposure near Cliffwood Beach in
Raritan Bay Raritan Bay is a bay located at the southern portion of Lower New York Bay between the U.S. states of New York and New Jersey and is part of the New York Bight. The bay is bounded on the northwest by New York's Staten Island, on the west by Per ...
, New Jersey. They found a large deep red piece of amber embedded in clay containing a number of insects, including some Diptera flies. The approximate age of the fossils dates back to the Cretaceous, 92 million years ago. Donald Baird of
Princeton University Princeton University is a private research university in Princeton, New Jersey. Founded in 1746 in Elizabeth as the College of New Jersey, Princeton is the fourth-oldest institution of higher education in the United States and one of the ...
first notified Carpenter about the recent discovery, and David Stager of the
Newark Museum The Newark Museum of Art (formerly known as the Newark Museum), in Newark, Essex County, New Jersey, United States, is the state's largest museum. It holds major collections of American art, decorative arts, contemporary art, and arts of Asia, A ...
arranged to transfer the specimens to be studied and examined. At the time, the existence of ants of Cretaceous age was significant, but the ants were most likely not detected as much of the amber around the site was previously collected. The discovery of the ants confirmed the existence of Cretaceous ants, and the appearance of the workers closely matched the speculations of what
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
ants looked like. As a result of these finds,
E. O. Wilson Edward Osborne Wilson (June 10, 1929 – December 26, 2021) was an American biologist, naturalist, entomologist and writer. According to David Attenborough, Wilson was the world's leading expert in his specialty of myrmecology, the study of an ...
and colleagues erected the new subfamily
Sphecomyrminae Sphecomyrminae is an extinct subfamily of ants in family Formicidae known from a series of Cretaceous fossils found in North America, Europe, and Asia. Sphecomyrminae contains eight genera, divided into two tribes Sphecomyrmini and Zigrasimec ...
and designated the genus ''Sphecomyrma'' (meaning "wasp ant") as the type genus in an article they published in 1967 in the journal ''
Science Science is a systematic endeavor that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earli ...
''. The published paper included the first description of ''S. freyi'', which was named after Edmund Frey and his wife. A
holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...
and a
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 nor a syntype). O ...
of the species were collected and moved to the
Museum of Comparative Zoology A museum ( ; plural museums or, rarely, musea) is a building or institution that cares for and displays a collection of artifacts and other objects of artistic, cultural, historical, or scientific importance. Many public museums make thes ...
, but the holotype was accidentally destroyed. However, a
neotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...
specimen numbered AMNH-NJ-112 was collected from the Sunrise Landing site near Brunswick in 1994, and was subsequently donated to the museum. The holotype was destroyed because the amber was accidentally cracked in half, separating the two workers from each other and later stored in a wooden cabinet in an uncovered drawer with other fossil insects for 30 years; the piece eventually deteriorated, appearing more dark and fractured. Although the hypothesised description of what Mesozoic ants looked like was somewhat accurate when compared to actual specimens, some characteristics were inaccurate. They believed that ant-like
mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
s first appeared before the development of an ant-like petiole, but such case was proven false when it was opposite on ''S. freyi'' specimens (ant-like petiole first appeared before the development of ant-like mandibles). Based on drawings, it was suggested that Mesozoic ants had long mandibles with multiple teeth, toothed tarsal claws and a broadly jointed petiole. Examination of collected specimens, however, shows that these ants had very short mandibles, toothless tarsal claws and a separated petiole. ''S. freyi'' remained as the sole member of ''Sphecomyrma'' until a fossil closely resembling the species was collected in Canadian amber deposits in 1985. Wilson provided the first description of the fossil, naming it ''S. canadensis''. He notes that the close resemblance of the fossils to ''S. freyi'' in key characteristics strongly support its inclusion in Sphecomyrminae. He further notes that the specimens are the first ants recorded in Canadian amber, but a vast diversity of insects have been found in the amber prior to the discovery, stretching as far back as the 19th century. The discovery of the specimens from Canada indicates that the subfamily was widespread through much of the northern hemisphere during the late Cretaceous. In 2005, new fossils of an undescribed ''Sphecomyrma'' ant and ''S. freyi'' were collected in the White Oaks
outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Features Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficia ...
in Sayreville, New Jersey. The specimens were later donated to the American Museum of Natural History and studied by palaeoentomologists Michael Engel and David Grimaldi, who both provided the first description of the undescribed ant in an ''American Museum Novitates'' journal article, naming it ''Sphecomyrma mesaki''. The age of these fossils are estimated at 79 to 92 million years. In 1987, Russian palaeoentomologist Gennady M. Dlussky elevated the subfamily at family level, renaming it as Sphecomyrmidae to accommodate ''Sphecomyrma'' and other fossil insects he studied throughout the Soviet Union. This placement was only short-lived as Wilson, with new morphological evidence, elevated the family back to subfamily level and all studied Cretaceous ants were put into ''Sphecomyrma'' or '' Cretomyrma''. However, Dlussky and Russian palaeoentomologist Elena B. Fedoseeva retained their classification and ''Sphecomyrma'' remained under Sphecomyrmidae. Their reasons were that the first segments of the antenna were too short to be geniculate (elbowed), and the structure of the mandibles. As geniculate antennae allow brood and food manipulation, or even sociality, it is impossible to classify ''Sphecomyrma'' and relatives as ants. Despite the authors' notes, they did not cite any study as to how ants manipulate items and such with their antennae, but he may have implied that the apices, a feature found on the antenna, may have been too far away from the mandibles. The close distance of the apices from the mandibles would allow manipulation of food or antennation with other nestmates. Another issue was whether or not a
metapleural gland Metapleural glands (also called metasternal or metathoracic glands) are secretory glands that are unique to ants and basal in the evolutionary history of ants. They are responsible for the production of an antibiotic fluid that then collects in a ...
was present, a unique feature only found in ants. Despite this and previous claims made by Dlussky saying that sphecomyrmines including ''Sphecomyrma'' were most likely solitary or semi-communal, the confirmed existence of the metapleural gland through newly collected fossils confirms that ''Sphecomyrma'' and relatives were definitely social. The evidence against Dlussky eventually reinstated ''Sphecomyrma'' and the subfamily as members of Formicidae in 1997, although some sources published before 1997 did not formally recognise Sphecomyrminae at family level. Additional doubts surrounding the nature of ''Sphecomyrma'' and relatives emerged when a 1999 paper concluded that the fossil ants found in Cretaceous amber in New Jersey were closer to wasps than they were to ants. This was quickly dismissed due to overwhelming evidence supporting their placement within the Formicidae, and the fact the authors cited unpublished cladograms and disregarded the key diagnostic traits ( synapomorphies) found in the ants.


Evolution

Ants of this genus are considered to be the most primitive within the family Formicidae. The body presents a wasp-like structure but with several ant-like characteristics. These ant-like characteristics, however, are primitive compared to more modern ants, and thus it is intermediate with other primitive ants and aculeate wasps. The presence of the metapleural gland, the nodiform (a structure resembling a node, which is a segment found between the
mesosoma The mesosoma is the middle part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the metasoma. It bears the legs, and, in the case of winged insects, the wings. In hymenopterans of ...
and gaster, the bulbous posterior portion of the
metasoma The metasoma is the posterior part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the mesosoma. In insects, it contains most of the digestive tract, respiratory system, and circul ...
), the structure of the petiole and its general physical appearance of an ant concludes ''Sphecomyrma'' species are ants rather than wasps; the absence of the metapleural gland would mean that it is most likely a wasp instead of an ant. It is not exactly known which group of wasps are the ancestors of ''Sphecomyrma'', but members of the family
Thynnidae The Thynnidae (also known as thynnid wasps or flower wasps) are a family of large, solitary wasps whose larvae are almost universally parasitoids of various beetle larvae, especially those in the superfamily Scarabaeoidea. Until recently, the co ...
, particularly those in the genus ''
Methocha ''Methocha'' is a genus of parasitoid wasps in the family Thynnidae. The species of this genus are found worldwide except in Australia, and attack the larvae of tiger beetles. Females are wingless, and can be mistaken for ants, while males are w ...
'' are strikingly similar to ''Sphecomyrma''. Wilson placed the genus closest to the Tiphiidae among extant wasps, but a later study published in 1975 derived the ants from a later clade and not to the Tiphiidae. More recently, ants (including ''Sphecomyrma'') are considered to have evolved from a lineage within the aculeate wasps, and a 2013 study suggests that they are a sister group of the
Apoidea The superfamily Apoidea is a major group within the Hymenoptera, which includes two traditionally recognized lineages, the " sphecoid" wasps, and the bees. Molecular phylogeny demonstrates that the bees arose from within the traditional " Crabroni ...
, and the sister group to this lineage is likely the
Scoliidae The Scoliidae, the scoliid wasps, are a family of about 560 species found worldwide. They tend to be black, often marked with yellow or orange, and their wing tips are distinctively corrugated. Males are more slender and elongated than females, wi ...
. ''Sphecomyrma'' may hold a close relationship with extant primitive ants. The Australian dinosaur ant (''Nothomyrmecia macrops'') is recognised as the most primitive living ant today, and both ants closely resemble each other. The Eocene genera of Aneuretini also resemble ''Sphecomyrma'' ants, which are believed to be the ancestors of
Dolichoderinae Dolichoderinae is a subfamily of ants, which includes species such as the Argentine ant (''Linepithema humile''), the erratic ant, the odorous house ant, and the cone ant. The subfamily presents a great diversity of species throughout the wor ...
. The subfamily
Myrmeciinae Myrmeciinae is a subfamily of the Formicidae, ants once found worldwide but now restricted to Australia and New Caledonia. This subfamily is one of several ant subfamilies which possess gamergates, female worker ants which are able to mate a ...
was thought to be the ancestor of Aneuretini because the elongated mandibles (a well-known feature in Myrmeciinae ants), were considered primitive and short mandibles were derived. This theory was proven false after ''Sphecomyrma'' specimens had small mandibles. Currently,
phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
analyses recognise ''Sphecomyrma'' as a
sister A sister is a woman or a girl who shares one or more parents with another individual; a female sibling. The male counterpart is a brother. Although the term typically refers to a family, familial relationship, it is sometimes used endearingly to r ...
group to modern living ants, meaning that is a
stem-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...
formicid. This means that it is more closely related to the ants in contrast to any other organism, but the
crown-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...
formicids (as in the
most recent common ancestor In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA) or concestor, of a set of organisms is the most recent individual from which all the organisms of the set are descended. The ...
of modern ants and their descendants) are more closely related to each other and distantly related to ''Sphecomyrma''. By the end of the Mesozoic, the sphecomyrmines including these ants vanished.


Description

''Sphecomyrma'' ants can be distinguished from other ants by their extremely primitive body structure, small, narrow wasp-like mandibles, short scapes (the basal segment of the antenna) and the exceptionally long funiculus, which is four times longer than the scape. The suture (a pattern of shallow grooves on the head) is well developed and the trochantellus (the
proximal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
end of the
femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...
) is absent. The node (a segment between the mesosoma, the middle part of the body, and gaster) of the petiole is noticeably dome-shaped and is separated from the
propodeum The propodeum or propodium is the first abdominal segment in Apocrita Hymenoptera (wasps, bees and ants). It is fused with the thorax to form the mesosoma. It is a single large sclerite A sclerite (Greek , ', meaning " hard") is a hardened bod ...
, the first abdominal segment, and parts of the metasoma, the posterior part of the body, by several constrictions. The cuticle (outer exoskeleton of the body) is not sculptured and is covered with either scattered or spare
seta In biology, setae (singular seta ; from the Latin word for " bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. ...
e, which are different types of
bristle A bristle is a stiff hair or feather (natural or artificial), either on an animal, such as a pig, a plant, or on a tool such as a brush or broom. Synthetic types Synthetic materials such as nylon are also used to make bristles in items such as ...
or hair-like structures. The body structure shows that ''Sphecomyrma'' ants were medium-sized formicids. Workers are known to have stingers.


''S. canadensis''

''S. canadensis'' was described from a holotype and paratype specimen, one of which is from Canadian amber and the other, the paratype, is poorly preserved and was collected from Medicine Hat amber. The holotype and paratype specimens, numbered CAS 330 and CAS 205 respectively, are currently preserved in the Biosystematics Research Institute in Ottawa, Canada. Its body is similar to ''S. freyi'', but it has a narrower head than ''S. canadensis'' (the head of ''S. freyi'' is wide). The mesosoma is more robust and the third funicular segment is extremely short and as long as the second segment, while it is twice as long in ''S. freyi''. The width and length of the head are the same at and the scapes measure The length of the mesosoma varies in the holotype and paratype, ranging from .


''S. freyi''

''S. freyi'' ants are small, measuring . The mandibles are wasp-like, its 12- segmented antennae are far apart from each other and the second funicular segment is longer than all the other segments. This is unusual for ants, but such case occurs in ''Nothomyrmecia macrops''. The scapes are very short at . The
compound eyes A compound eye is a visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidia, which are tiny independent photoreception units that consist of a cornea, lens, and photoreceptor cells which distin ...
are very long and convex, situated on the middle side of the head. The clypeus (one of the
sclerite A sclerite (Greek , ', meaning " hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonly ...
s that make up the "face" of an arthropod or insect) is broad and convex and the
ocelli A simple eye (sometimes called a pigment pit) refers to a form of eye or an optical arrangement composed of a single lens and without an elaborate retina such as occurs in most vertebrates. In this sense "simple eye" is distinct from a multi-l ...
( photoreceptors) are well developed. The mesosoma is slender and closely resembles those of '' Methocha malayana'', measuring . The mesonotum is also long and slender with a distinct convexed
scutum The ''scutum'' (; plural ''scuta'') was a type of shield used among Italic peoples in antiquity, most notably by the army of ancient Rome starting about the fourth century BC. The Romans adopted it when they switched from the military formati ...
and scutellum, but these two features are separated from each other by an axillary region. Spiracles are present on the metathorax, but they are situated just below the scutellum. The petiole has a raised node and separated from the propodeum and the gaster. The gaster measures , and an acute protruding
stinger A stinger (or sting) is a sharp organ found in various animals (typically insects and other arthropods) capable of injecting venom, usually by piercing the epidermis of another animal. An insect sting is complicated by its introduction of ve ...
, measuring is present. The legs are long and slender with two tibial spurs present at each tibia, and the tarsal claws have a median tooth. The two worker specimens have little morphological differences, but they range in size. The head and segments of the antenna tend to be smaller in the holotype specimen while in the paratype they are slightly larger. The pubescence is short but scattered throughout the body, measuring . The colour of the specimens appears to be light-brown. The metapleural gland exhibits a notably wide and oval-shaped
orifice An orifice is any opening, mouth, hole or vent, as in a pipe, a plate, or a body * Body orifice, any opening in the body of a human or animal *Orifice plate, a restriction used to measure flow or to control pressure or flow, sometimes given specia ...
, (openings into the body). The separation between the orifice and the posterior portion of the propodeum is twice the diameter than the orifice itself. The cuticle situated in the anterior portion (referring to what is in front) of the orifice is thinner in contrast to the cuticle surrounding the mesosoma, where it is notably transparent. An oddly shaped chamber can be seen beneath the cuticle, but this is most likely the atrium (chamber with a hardened, thickened wall). The gland itself is covered in a whitish mass and is located in the anterodorsal region (meaning in front and toward the back) of the subcuticular chamber. The gland is said to be shrunken from its original size.


''S. mesaki''

''S. mesaki'' was found in a small piece of amber barely larger than the ant itself. The incomplete specimen numbered AMNH NJ-1023 is currently preserved at the American Museum of Natural History in New York City. The appendages breach the surface of the amber while the petiole and gaster are completely absent. Engel and Grimaldi coined the specific epithet after Bob Mesak, the original collector who donated the specimen to the museum. The species is discernible from the other species by a portion of the clypeus having an elongated ventral lobe. The broad but shallow scrobes of the antennae, the size of the head and oval-shaped eyes can further distinguish ''S. mesaki'' from other ''Sphecomyrma'' ants. The only body parts of the ant that are preserved are the legs, mesosoma and head. The head is notably large, but it is shorter than its mesosoma. The head is long and wide, with the eyes alone measuring . The
vertex Vertex, vertices or vertexes may refer to: Science and technology Mathematics and computer science *Vertex (geometry), a point where two or more curves, lines, or edges meet * Vertex (computer graphics), a data structure that describes the positio ...
is covered in sparse pilosity with setae. Ocelli are present on top of the ants' head, precisely located just above the dorsal tangent. The base of the antennae emerges from the scrobes, which are equally as long as the scape. The eyes are well developed and located above the bottom of the antennae. The clypeus is setose, meaning that it bears bristles or setae, except on the middle part. The mandibles are small and only contain two teeth. The antennae are moderately long, the scapes are very short but 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 ...
is even shorter. The mesosoma measures and is setose. Several setae are seen around the
metanotum The metathorax is the posterior of the three segments in the thorax of an insect, and bears the third pair of legs. Its principal sclerites ( exoskeletal plates) are the metanotum (dorsal), the metasternum (ventral), and the metapleuron (lateral) ...
(the dorsal sclerite) and propodeum. The coxae, the proximal segment and functional base of the leg, are setose (bearing bristle or setae), inflated and large. The metapleural gland opening is small and noticeable, located away from the propodeum and above the metacoxa (the hind of the coxa). The legs are moderately long. The forelegs first tarsomere (subsegments of the tarsus) is longer than the combined length of other tarsomeres more distant than the first subsegment. The number of stiff setae varies on each tarsomere: for example, the first tarsomere has seven pairs while the fourth tarsomere has only two pairs. The pretarsal claw has a single subapical tooth and the metasoma is absent.


Unplaced specimens

An additional specimen was described as a possible ''Sphecomyrma'' male, but it was never assigned to a specific species. The specimen numbered AMNH NJ-242 was collected from the White Oaks outcrop in 1995 and is currently preserved in the American Museum of Natural History. The entire body of the male specimen is completely preserved. As most ant genera are based on the morphology of workers, assigning males to a species or a genus is rarely done unless they are taken from a colony. However, its size, petiole structure, the absence of the trochantellus and basal antennal structure are similar to that of a ''Sphecomyrma'' worker. It is a small ant, measuring with three ocelli present on the vertex. Stiff hairs can be found on its
frons Insect morphology is the study and description of the physical form of insects. The terminology used to describe insects is similar to that used for other arthropods due to their shared evolutionary history. Three physical features separate insec ...
and vertex. It has large eyes and the face has two pairs of long setae along with smaller setae. The scape is short and is around the same length as the flagellomere (one of the three main segments of the antenna); the pedicel is only slightly longer than the flagellomere by 0.3 times, and the total length of the antenna is . Most of its mouthparts are covered in bubbles from the amber, but two palpals (a pair of appendages found near the mouth) are seen protruding. The mesosoma is in length and the petiole is , which has pairs of long setae on the apex of the nodus. Both tibias have a pair of setose and the apical spurs on the hind tibia is pectinate. The forewings measure and the hindwings are 0.7 times the length of the forewings. The shape of the wings is consistent with other formicids. The hindwings have seven hamuli but none is found around the anterior portions. The gaster is long and the first and second segments are equally as long as each other (these two segments alone cover two-thirds of the gaster). The terminalia (the last segments of the abdomen) is difficult to examine due to a layer of froth covering the area, but there are two pairs of setose lobes.


Ecology

As some scientists such as Dlussky believed ''Sphecomyrma'' was not an ant, they thought it was solitary and semi-communal. Further statements include that the morphology of sphecomyrmines would prevent workers from transporting larvae or engaging in
trophallaxis Trophallaxis () is the transfer of food or other fluids among members of a community through mouth-to-mouth ( stomodeal) or anus-to-mouth ( proctodeal) feeding. Along with nutrients, trophallaxis can involve the transfer of molecules such as pher ...
(transfer of food between two nestmates) with them. However, wasps with antennal proportions similar to sphecomyrmines are able to feed their own larvae. The presence of the metapleural gland also shows that ''Sphecomyrma'' was a
eusocial Eusociality (from Greek εὖ ''eu'' "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping gen ...
(the highest level of organisation of animal sociality) insect and lived in colonies, as this gland possibly acts as a disinfectant in order to nest in soil and leaf litter without infecting the colony's nestmates and brood. The large eyes, long appendages and thin exoskeleton suggests that workers were epigaeic, where they foraged above ground and out in the open. Fossil evidence further suggests that they foraged socially with other worker ants.


Notes


References


External links

* * {{Taxonbar, from=Q1450344 Sphecomyrminae Cretaceous insects Fossil ant genera New Jersey amber Fossil taxa described in 1967 Fossil taxa described in 1985 Fossil taxa described in 2005 Prehistoric insects of North America