Two Flat-Backed Polydesmidan Millipedes from the Miocene Chiapas-Amber Lagerstätte, Mexico

<div><p>Two species of fossil polydesmidan millipedes (Diplopoda: Polydesmida) embedded in amber are described from Miocene strata near Simojovel, in the Chiapas Highlands, Mexico. <i>Maatidesmus paachtun</i><b>gen. et sp. nov</b>., placed into Chelodesmidae Cook, 1895, and <i>Anbarrhacus adamantis</i><b>gen. et sp. nov</b>., assigned in the family Platyrhacidae Pocock, 1895. Morphological data from fossil specimens have been recovered using 3D X-ray micro-computed tomography and regular to infrared-reflected microscopy. Both fossil species are recognizable as new primarily but not exclusively, by collum margin modification and remarkable paranotal and metatergite dorsal sculpture.</p></div

<i>Maatidesmus paachtun</i> nov. gen. and sp., holotype.

<p>(A) General view, scale bar 5 mm. (B) Close dorsal view of first segments, scale bar 1 mm. (C) Close dorsal view of metatergite and paranota in mid-body rings, scale bar 5 mm. See anatomical abbreviations in the main text.</p

<i>Anbarrhacus adamantis</i> nov. gen. and sp., holotype.

<p>(A): General view, scale bar 5 mm. (B): Head, collum and antenna, scale bar 1 mm (C): Right antenna, scale bar 0.5 mm. (D): Antennomeres 6–8 and cones in right antenna, scale bar…mm. (E): Lateral view of rings 4–5, scale bar 0.5 mm. (F): Dorsal view of paranota and metatergite in 6–7 rings, scale bar 1 mm. (G): Lateral view of gonopods in 7 ring, scale bar 0.5 mm. (H): Legs, scale bar 0.5 mm. (I): Telson, scale bar 1 mm. See anatomical abbreviations in the main text.</p

Location of the amber sites: Guadalupe Victoria I and II, Municipality of Simojovel de Allende, Chiapas, southern Mexico.

<p>Location of the amber sites: Guadalupe Victoria I and II, Municipality of Simojovel de Allende, Chiapas, southern Mexico.</p

<i>Maatidesmus paachtun</i> nov. gen. and sp., schematic reconstruction, dorsal view.

<p>(A) collum, paranota and metatergite in rings 2–5 and mid-body rings. <i>Anbarrhacus adamantis</i> nov. gen. and sp., schematic reconstruction, dorsal view: (B) paranota and metatergite in rings 3–5. (C): inmature gonopods in ring 7. See anatomical abbreviations in the main text.</p

<i>Maatidesmus paachtun</i> nov. gen. and sp., holotype, 3D micro-CT reconstruction.

<p>(A–D): General view, scale bar 5 mm. E) Head, collum and first segments in lateral view, scale bar 5 mm. (F) Dorsal view of first segments, scale bar 2 mm. (G) Ventral view of head with a cross section of first segments, scale bar 2 mm. (H) Collum, metaterga and paranota in dorsal view, scale bar 3 mm. (I) Head and legs in dorsal view, scale bar 3 mm. (J) Last segments in ventral and dorsal view (K), respectively, scale bar 5 mm. All 3D images are expressed in virtual colors. See anatomical abbreviations in the main text.</p