Titanomyrma is a genus of prehistoric giant ant. The latest species to be discovered, T. lubei, was described in 2011, when a 49.5 million year old fossilized winged queen ant, comparable in size to hummingbirds, was found in Wyoming. This fossil is the first body of a giant ant found in the Western Hemisphere. The presence of Titanomyrma in North America is considered to indicate "the first reported cross-Arctic dispersal by a thermophilic insect group".[1] Another fossil species of this genus, T. giganteum, is the largest known fossil or extant species of giant ant in the world.
Discovery[]
The fossil ant Titanomyrma lubei was discovered in ancient lake sediments in the DMNS locality 784, Farson Fish Beds, Laney Member of the Green River Formation; Sweetwater County, Wyoming, USA by Louis Lube, the collector and donor of the holotype specimen.[2][3]
The fossil formed part of the collection of Denver Museum of Nature and Science and was discovered by Bruce Archibald and co-author and museum chief curator Kirk R. Johnson while casually going through storage drawers.[1] The fossil depicts the queen ant only and no fossils of workers have been found. With the discovery of Titanomyrma lubei and the description of the genus, two other species of giant ants, Formicium giganteum and Formicium simillimum, were reclassified into this genus.
Well preserved fossils of Titanomyrma giganteum and Titanomyrma simillimum were discovered in the Messel shales,[4] near the village of Messel, in the state of Hesse, 30 km south of Frankfurt am Main (Darmstadt Administrative District), in Germany. A related undescribed species has been found in the nearby Eckfeld Maar.
Etymology[]
The name of the genus is a derivative of the Greek Τιτάν (Titan), meaning 'one of prodigious size, strength, or achievement',[6] and alluding to the Titans of Greek mythology; and the Greek word μύρμηξ (myrmex) meaning 'ant',[7] gender feminine. The specific epithet of the new species is formed from the surname of the collector of the holotype, Louis Lube.
Taxonomy[]
Archibald et al. in 2011 erected the genus Titanomyrma, described the species Titanomyrma lubei and proposed two new combinations, T. gigantea (formerly Formicium giganteum Lutz, 1986) and T. simillima (formerly Formicium simillimumLutz, 1986). T. gigantea has been designated the type species for the genus.
The name of the genus is a derivative of the Greek Τιτάν (Titan), meaning 'one of prodigious size, strength, or achievement',and alluding to the Titans of Greek mythology; and the Greek word μύρμηξ(myrmex) meaning 'ant'.
The genus Titanomyrma is differentiated from others in the family by the shape of the gaster which is variable. In the three included species the gaster ranges from ovate to more slender or cylindrical. The A5 abdominal segment width relative to other gaster segments is variable and the relative lengths of A3–A7 are also variable.
The queens of the three Titanomyrma can be distinguished from those of other genera most easily by gaster characters. The gasters are more slender in Titanomyrma. Amongst the three species of Titanomyrma, the ratio between length to width of the queens of the three species is as follows, T. lubei – 2.14, T. gigantea – 1.40, and T. simillima – 1.50. The middle half of T. lubeiis roughly cylindrical while for other Titanomyrma species, it is ovate with the segment A5 being the widest. The segment A3 has a length about a quarter of the width while for other species it is about a third. The segment A4 is thrice as long as the length of segment A3 while that of A4 segments of other species is less than twice. The segment A5–6 of T. lubei is approximately half as long as it is wide while for other species it is about a third. A3 is not curved around the petiole at the junction.
T. gigantea is the largest giant ant ever found, larger than the biggest extant giant ants, which are the five-centimetre-long (2.0 in) driver ants of the genus Dorylus, found in Central and East Africa. The fossils indicate that the males grew up to 3 centimetres (1.2 in) and the queens grew to 7 centimetres (2.8 in). It had a wingspan of about 16 centimetres (6.3 in).
With the description of the genus Titanomyrma and the description T. lubei, two other species, Formicium giganteum and Formicium simillima, were reclassified into this genus, additional undescribed or unplaced specimens are also known.
T. giganteaedit[]
Titanomyrma gigantea queens and males are described from the Messel Formation,near the village of Messel, in the state of Hessen, 30 km (19 mi) south of Frankfurt am Main in Germany.
T. simillimaedit[]
Titanomyrma simillima, as with T. gigantea, are also only known from the Messel Formation, and is slightly smaller in size then the coeval species.
T. lubeiedit[]
The Titanomyrma lubei holotype was discovered by Louis Lube at DMNS locality 784, the Farson Fish Beds, in Sweetwater County, Wyoming, USA. The site works Early Eocene lake sediments of the Green River Formations Laney Member.
After discovery, Lube donated the fossil to the collections of the Denver Museum of Nature and Science where it was noticed by paleoentomologist Bruce Archibald and (then) museum chief curator Kirk R. Johnsonwhile they were going through storage drawers. The holotype is of a queen ant comparable in size to rufus hummingbirds, but no workers have been found. The specific epithet of the new species is formed from the surname of the collector of the holotype, Louis Lube., and was the first member of the genus known from North America. [[null|link=https://en.m.wikipedia.org/wiki/File:Titianomyrma_sp_BBM-PAL-2022-00001_Allenby_Formation_Fig1a.png%7Calt=%7Cleft%7Cthumb%7CTitianomyrma sp.Eocene Okanagan Highlands
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Unidentified speciesedit[]
An undescribed species has been reported from the Eckfeld Maar of Germany.Archibald, Mathewes, & Aase (2023) reported a Titanomyrma queen from the Allenby Formation, and noted the range extension for Formiciinae into the Eocene Okanagan Highlands, as the subfamily was previously considered a strictly thermophilicant group. Due to complications arising from preservational distortion during diagenesis, they were unable to determine the correct size of the queen in life. If the distortion was lateral, then compression to bilateral symmetry yielded an adult length of approximately 3.3 cm (1.3 in), placing it the same range as Formicium berryi and F. brodiei, known only from wings, and suggested as possible males. Conversely stretching the fossil to bilateral symmetry results in a larger 5 cm (2.0 in) length estimate, placing it as comparable to queens of T. lubei and T. simillima.