Friday, 7 November 2014

Two new species of Flat-backed Millipede from Miocene Mexican amber.


Millipedes, Diplopoda, are highly successful soil dwelling Arthropods found in soil in all temperate and tropical regions. They are an ancient group, with a fossil record going back to the Silurian, but this is rather patchy as they appear to have poor preservational potential, and fossil Millipedes are typically only found in Lagerstätten deposits with exceptional preservation of small terrestrial animals, such as ironstone nodules and amber. Millipedes are thought to play a key role in soil formation, and to have played an important role in the development of ecological communities in the soil, so understanding the history of the group is considered important.

In a paper published in the journal PLoS One on 27 August 2014, a team of scientists led by Francisco Riquelme of Posgrado en Ciencias Biológicas and the Instituto de Física at the Universidad Nacional Autónoma de México, describe two new species of Flat-backed Millipedes from amber deposits in northern Chiapas State, Mexico. Chiapas Amber is thought to be between 23 and 15 million years old, and to have been produced in a Mangrove environment by trees of the genus Hymenaea. It is largely collected by artisanal miners.

The first new species is named Maatidesmus paachtun, where ‘Maat’ means ‘amber’ in Mayan, ‘-idesmus’ implies a Flat-backed Millipede and ‘paachtun’ means ‘stoney-backed’ in Mayan. The species is described from a single adult female specimen, preserved three dimensionally in amber.

Maatidesmus paachtun, general view, scale bar is 5 mm. Riquelme et al. (2014).

The specimen is 35.5 mm in length, and comprises the head and all 19 body segments. It has distinctive patterning on the dorsal surface of its body, comprising a large number of tiny lobes (which appear ‘stoney’ to Riquelme et al.), which is not seen in any close living relative.
 
 Maatidesmus paachtun, 3D micro-CT reconstruction. (A–D): General view, scale bar is 5 mm. (E) Head, collum and first segments in lateral view, scale bar is 5 mm. (F) Dorsal view of first segments, scale bar is 2 mm. (G) Ventral view of head with a cross section of first segments, scale bar is 2 mm. (H) Collum, metaterga and paranota in dorsal view, scale bar is 3 mm. (I) Head and legs in dorsal view, scalebar is 3 mm. (J) Last segments in ventral and dorsal view (K), respectively, scale bar is 5 mm. All 3D images are expressed in virtual colours.Anatomical Abbreviations: ant, antennae; cl, collum; ct, cuticle; cw, claw; ep, epiproct; hc, head capsule; hyp, hypoproct; its, inner tissues; l, leg; lgs, longitudinal sulcus of the head capsule; mt, metatergite; mz, metazonite; p, paranota; pap, paraproct; par, preanal ring; pz, prozonite; s, trunk segment;spm, suture between the prozonite and metazonite. Riquelme et al. (2014).

The second new species described is named Anbarrhacus adamantis, where ‘Ánbar’ is Arabic for ‘amber’, ‘-rhacus’ is a common suffix for Millipedes and ‘adamantis’ means ‘diamond’ in Latin, a reference to the rhomboidal sculpting on the dorsal surface of the body segments. The species is described from a single male specimen, 19.8 mm in length, with a head and 17 body segments, preserved three dimensionally in amber.

Anbarrhacus adamantis, general view, scale bar is 5 mm. Riquelme et al. (2014).

See also…

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