Etymology:.

Derived from the Maya word maat- (means “amber”) and -idesmus, which is a common suffix in the Chelodesmidae.

Diagnosis:.

As for the only known species below.

Type species:.

Maatidesmus paachtun Riquelme et Hernández sp. nov.

Designated by monotypic species. Fig. 2–3, 5A. Movie S1.

ZooBank LSID: urn:lsid:zoobank.org:act:AFA5FAA8-12E3-4D0E-A09D-62078F640DF3.

Etymology:.

The specific epithet paachtun means “stony-backed”, composed from the Maya elements: paach-: “back” plus tun: “stone”, refers to conspicuous, lobulated dorsal sculpture in collum and metatergite in rings 2–5.

Holotype:.

LZ.MALM28, and only known specimen. An entire adult female, three-dimensionally preserved (Fig. 2–3.).

Horizon and locality:.

The amber-bearing beds at the Guadalupe Victoria site, Latitude 17° 07′ 58′ ´N, Longitude 92° 48′ 19′ ´ W (Fig. 1), near the town of Simojovel, State of Chiapas, México. These rocks belong to Mazantic shale and Balumtum sandstone strata dated as early-middle Miocene, ca. 23-15 Ma [11]–[15].

Diagnosis:.

Large-sized chelodesmid, adult female, with head+19 rings, 35.5 mm total length. Head wider than collum, vertex moderately granulated, with a deep vertigial sulcus extending from the top of antennal sockets; antenna clavate, long and robust, antennomere length relationships: (2, 6) > (3) > (4, 5) > (1, 7). Collum with a convex dorsum covered with margin lobations, metatergite in rings 2–5 heavily lobulated in three transverse rows arrangement; whereas metatergite in rings 6 and 7 with an asymmetric pattern of swellings rather than truly-lobed. Differs from extant representatives of the Chelodesmidae by its conspicuous, coarsely lobulated dorsal sculpture in collum and metatergite in rings 2–5. Paranota on all rings short, inflated, subrectangular, dorsally roughened, tilted toward the body midline, with tick, minute, acute margins. In the longitudinal direction, dorsally, paranota+metatergite in rings 2–3, 17, 18 and 19 distinctly narrower than width of the rest of the rings. Epiproct wide, short, triangular, with caudal edged broadly blunt. Monotypic.

Description:.

– General characteristics: Fossil specimen LZ.MALM.28 represents an adult female with the entire trunk and head preserved (Fig. 2A–B). Distinguished by its conspicuous, coarse, lobulated dorsal sculpture in collum and metatergite in rings 2–5 (Fig. 2C, 3B–H, and 5A). Head wider than collum (Fig. 3G–I). Trunk composed of 19 segments with paranota and telson, ca. 35.5 mm in length, 7.9 mm in maximum width, and W/L ratio of 22.2% (Fig. 3A–D). Rings 2–5 equal to collum in overall width, whereas posterior ring widths slightly increasing gradually to ring 17, thence gently narrowing over the last rings and telson (Fig. 3C–D, 3K, and 3J); Paranota inflated, subrectangular, dorsally roughened, tilted toward the body midline (Fig. 2B–C and 3A–G). Epiproct wide, short, triangular (Fig. 3C). Since amber is cloudy around female genitalia and this is a tiny structure, it cannot be clearly assessed.

Taphonomic features:.

a partial dorsal portion of rings 18–19 were accidentally scraped during amber polishing by collectors; accordingly, the preanal ring was scarcely altered in dorsal view, affecting the epyproct surface dorsally. The head is ventrally bent as seen in a defensive position. The body decay was dramatically interrupted by rapid polymerization of plant resin, which preserved intact soft tissues inside the fossil as shown in a cross section of inner body layers from the reconstructed X-ray tomography (Fig. 3G); although the cuticle is slightly recrystallized due to reacting with amber, it also preserves colored morphology. Copious embedded biodebris along and around the body, mostly insect parts from mosquitos and ants; there are also plant fragments and soil particles. The piece of amber is golden to orange yellow with translucent to cloudy glossiness, internally recrystallized with abundant transverse, small fractures (Fig. 2).

Coloration preserved in amber:.

Ground color in head and rings creamy white to nut-brown splatter (Fig. 2). All rings show slightly dissolved and recrystallized portions of cuticle as crystal-white patches, probably calcium carbonate salts. Head and antenna white. Collum whitish colored, most of the lobes nut-brown. Paranota generally from crystalline to creamy white, metaterga also nearly white with nut-brown lobes; upper part of prozona white and lower side creamy gray to nut-brown (Fig. 2C). Sterna pale to nut-brown. Legs white, ending in a nut-brown splashes (Fig. 2C).

Head:.

convex, slightly wider than collum, with a vertex moderately granulated, and deep vertigial sulcus extending from the top of antennal sockets; sockets slightly impressed ventrolaterally; frons elevated above level of clypeus and labrum. Cardo, stipes and gnathal lobe are prominent. Antenna clavate, long and robust, thicker than legs; antennomeres length relationships: (2, 6) > (3) > (4, 5) > (1, 7), apical cones are hardly distinguished (Fig. 3G–E, and 3I).

Collum:.

strongly convex anteriorly in dorsal view, with anterior margins broadly rounded, not hiding the head in lateral view; dorsal surface conspicuously lobed posteriorly, with posterior margins angled (Fig. 3D–F, and 3H).

Trunk:.

composed of 19 rings with paranota and telson (Fig. 3A–D). In the transverse direction, rings 2–5 equal to collum in overall width, consecutive ring widths increase gradually to ring 16, thence gently narrow over the last rings (17–19) and telson (Fig. 3C, 3D, 3K, and 3J); In the longitudinal direction, dorsal view, paranota+metatergite in rings 2 and 3 distinctly narrower than width of paranota+metatergite in consecutive rings, which gradually increase reaching a maximum width in mid-region and moderately decrease to ring 16, thence in rings 17–19 are as narrow as 2 and 3; between metazonite and prozonite waist striated; the prozonite surface almost smooth, metazonite surface finely granulated. Paranota on all rings short, inflated, subrectangular, dorsally roughened, tilted toward the body midline, with thick, minute, acute margins, and distinctly but irregularly toothed (Fig. 2C, 3B–C, 5A). The mid-dorsal surface of metatergite with at most three transversal rows of lobes in rings 2–5, whereas rings 6 and 7 with swellings randomly located (Fig. 2C, 5A); pleural tubercles conspicuous; sternites surface moderately setose; ozopores opening laterally as seen in rings 5, 7, 9–10, 12–13, and 15–16; there are not differences between segments with pores and without pores. Legs extended ventrally in all rings, long, slender, with elongated femora and tarsi, ending in a short claw. The podomere length relationships: femur > tarsus >prefemur > (postfemur, tibia) (Fig. 2C, 3B, and 3I).

Telson:.

Epyproct wide, short, triangular, with caudal edge broadly blunt, not extended beyond paraprocts due to taphonomic alteration; paraprocts semicircular, surface finely granular but the edges are smoother and scaly; hypoproct triangular but sharply truncate, posterior margin convex, apex acute, with setae on each side of the midline (Fig. 3C and 3J–K).

Remarks:.

– After the Paradoxosomatidae, the family Chelodesmidae is one of the most diverse polydesmidan group comprising 230 extant genera with nearly 450 species [31], whose distribution now extends to Africa, Middle America and South America [28]. At the present time, there are five living species of the Chelodesmidae recorded in Mexico assigned to the genera Chondrodesmus, Rhaphandra and Eutyporhachis, the latter is also present in the Chiapas Highlands [32]–[33]. Maatidesmus paachtun gen. et sp. nov. has in common several characters with the living representatives of the Chelodesmidae, including the shape of collum, paranota and telson, but differs by the conspicuous, coarsely lobulated dorsal sculpture in collum and metatergite in rings 2–5 (Fig. 2C, 3B–H, 5A). M. paachtun is the first fossil species of this family from the Neogene of Middle America. Other fossil chelodesmid form has been previously known from Dominican amber based on headless specimen [10].

Etymology:.

Derived from the Arabic voice ánbar (means “amber”) and –rhacus, which is a common suffix in the Platyrhacidae.

Diagnosis:.

As for the only known species below.

Type species:.

Anbarrhacus adamantis Riquelme et Hernández sp. nov.

Designated by monotypic species. Fig. 4.

ZooBank LSID: urn:lsid:zoobank.org:act:DF667E57-51C8-4104-BC95-B2375DF3E5E4.

Etymology:.

The specific epithet adamantis is derived from adamantus (Latin): “diamond”, refers to dorsal sculpture in collum and metatergite with a rhomboidal-pattern (Fig. 4 and 5B–C).

Holotype:.

IGM.4544, and only known specimen. Stadium 7 male, three-dimensionally preserved, almost complete; only left antenna is partially missing (Fig. 4).

Horizon and locality:.

Amber-bearing beds at the Guadalupe Victoria site, Latitude 17° 07′ 58′ ´N, Longitude 92° 48′ 19′ ´ W, near Simojovel de Allende, State of Chiapas, Mexico (Fig. 1). These rocks belong to Mazantic shale and Balumtum sandstone strata dated as early-middle Miocene [11]–[15].

Diagnosis:.

Small-sized Platyrhacidae, stadium 7 male with head+17 rings, 19.8 mm total length. Head moderately convex, rough, and setose, wider than collum. Antenna clavate, long, copiously covered with setae, antennomeres length relationships: 5>6> (2≈3≈4) > (1≈7), with four long, slender sensory cones. Distinguished by its granulated dorsal sculpture in paranota and metaterguite; paranota on all rings, wide, granulated, with thick, rounded margin, waist laterally striated; metatergite coarsely granulate, mid-dorsally ornamented in a rhomboidal-pattern, all minute tubercles and setae multiple. Intercoxal process between legs in ring 7, irregular with distal, spiniform accessory projection. Gonopods immature, small, in situ on ring 7, gonocoxae bulbous, slightly crooked, with a long distal setae on medial surface; gonopodal telopodite shrunken, bipartite, apical lobes of the tibiotarsus laminate, striated and acute. Monotypic.

Description:.

– General characteristics. Fossil specimen IGM.4544 represents a stadium 7 male, which preserves the entire trunk and head with apical portion of left antenna missing (Fig. 4). Head convex, wider than collum (Fig. 4B). Trunk composed on 17 segments with paranota and telson, ca. 19.8 mm in length, 2.8 in maximum width, W/L ratio of 14.1%. Rings increasing gradually in width from collum to posterior 2/3 of the body and gently narrows over the last rings and telson; epiproct fairly long and spathulate (Fig. 4I). Paranota wide and granulate, metatergites ornamented in a rhomboidal-pattern (diamond-like) in mid-dorsal region (Fig. 4F). Legs long and slender, extended lateroventrally (Fig. 4H). Although relative immature, gonopods are exposed, small, in situ on trunk ring VII, gonocoxae bulbous, crooked, gonopodal telopodite shrunken, bipartite, apical lobes of the tibiotarsus minute, laminate, striated and acute (Fig. 4C and 5C).

Taphonomic features:.

left antenna partially broken, antennomeres 3–6 accidentally missing by polishing amber (Fig. 4B). Empty molds of bubbles are present all over the dorsal portion of the head and trunk; particularly, in the margins of paranota (Fig. 4A–B and 4I). It seems that these bubbles were produced as result of dissolved water vapor from soils during rapid amber hardening (polymerization). Decaying of carcass was drastically interrupted by resin polymerization; because of this the hard/soft tissues and true color morphology have been preserved (Fig. 4). Head and trunk slightly bent ventrolaterally; body randomly surrounded by blackish to brown soils and plant debris. The piece of amber is golden to citrine yellow with translucent glossiness, in a pebble-like shape and roughly polished (Fig. 4A).

Coloration preserved in amber:.

Most of the head and antenna from cream colored to nearly white, 6th antennomere of right antenna colorless, setiferous tubercles blackish-brown, clypeus darker, a conspicuous black patch above the Tömösváry organ, labrum pale yellowish (Fig. 4B–D). Collum gray to white, blackish in midline (Fig. 4B). Paranota generally cream colored with metaterga whitish gray; upper surface of prozona blackish gray and lower sides brownish. Sterna pale yellowish to brown and legs creamy white to pale yellowish (Fig. 4E–H).

Head:.

moderately convex, slightly wider than collum, densely covered with minute setae; surface in the vertex, frons and vertigial sulcus roughened; clypeus sparsely setose. Gnathochilarium with short median expansion, labral surface with several flat papillae, cardo, stipes, and gnathal lobe are appreciably well-defined. The Tömösváry organ is conspicuous below the antenna and between the incisura lateralis (Fig. 4B). Antenna clavate, long, copiously covered with setae, antennal length 2.5 mm. The antennomeres length relationships: 5>6> (2≈3≈4) > (1≈7), with four long, slender sensory cones; 5^th and 6^th antennomeres with long sensitive setae near apex (Fig. 4B–D).

Collum:.

broadly rounded anteriorly, almost semicircular, laterally articulated with the rear of the head capsule, not hiding the head; dorsal surface granulated, with small rounded tubercles and setose, posterior margins irregular and rounded (Fig. 4B).

Trunk:.

Composed of 17 rings with paranota and telson (Fig. 4A). Trunk rings generally similar on structure, prozonite and metazonite separated by a well-defined striated waist (Fig. 4E–F). Metatergite mid-dorsally surface rough, granulated, with polygonal furrows in a rhomboid pattern, all setiferous tubercles multiple (Fig. 4F and 5B). Rings 16 and 17 with posterior margin of metatergite coarsely granulate. Pleural tubercles on all rings are conspicuous, variable in size. Prozonite surface polished, lightly smooth (4E–F). Paranota on all rings wide, arising low on body and slightly declined, with posterior margin rounded. Paranota dorsal surface roughened, in middle paranotal process with copious granules on anterior angle nearly rectangular; paranota lateral margins distinctly but irregularly toothed; anterior margin lightly convex, posterior lightly concave (Fig. 4F); paranota in rings 11 and 12 with posterior angle acute and not lateral marginal thickening. The posterior edge of the paranota and metatergite dorsally striated (Fig. 4F). Ozopore open dorsally in rings11 and 12, hard to distinguish in other rings. Sternites surface moderately setose, as wide as long. Spiracles small and pyriform as seen on ring 6. Legs extended lateroventrally on all rings, slender with elongated femora and tarsi, ending in a long claw; relative lengths of podomere are as a follows: femur >tarsus >prefemur > (postfemur, tibia) (Fig. 4H). Intercoxal process between legs in ring 7, irregular with distal, spiniform accessory projection (Fig. 4G).

Telson:.

Preanal ring with several large setae, epiproct spathulate in outline, fairly long, extending beyond the paraprocts, with caudal edged rounded-triangular and slightly acute; paraproct semicircular, each with setae; hypoproct sharply truncated (Fig. 4I).

Gonopods:.

relatively immature, small, in situ on ring 7; gonocoxae bulbous, slightly crooked, with a conspicuous setae on medial surface, posterior margin in plate greater almost the height of the sternites, gonopod telopodite thin, short, shrunken, bipartite, apical lobes of the tibiotarsus minute, laminate, striated and acute; gonopore inconspicuous due to body position (Fig. 4G and 5C).

Remarks:.

– Anbarrhacus adamantis gen. et sp. nov. is a stadium 7 male, consequently, the putative apomorphic characters from the male gonopods cannot be assessed unequivocally. The living species are typically diagnosed using male/female genitalia [26]–[27], [30], [34]–[35]. Other living species of the Platyrhacidae described upon female specimens have been considered species inquirenda [34]. At the present, there is no satisfactory treatment of platyrhacidan species that includes fossils in the available literature. Probabilities of finding adult male specimens with preserved, exposed genitalia in the fossil record are extremely low. In this context, A. adamantis shares somatic characters with several extant species of the family Platyrhacidae as seen in the genera Nyssodesmus, Psammodesmus, Exallostethus, Platyrhacus and Hoffmanorhacus [27], [34]–[36]. Taxonomical affinities include the shape of collum, paranota, metatergites, epyproct, others, as described above. Thus, the specific relationships at the genus and species level of A. adamantis with living platyrhacidan millipedes are indicated by somatic characters; but distinguished from them by four long, slender sensory cones in antenna and the conspicuous, granulated dorsal sculpture in paranota and metaterguite. Also differs from them by the intercoxal process among legs in ring 7.

The extant representatives of Platyrhacidae comprise a greater diversity of about 37 genera and 180 species. Those are distributed in the Indo-Australian region from Myanmar to the Solomon Islands [37]; whereas the New World members of Platyrhacidae are found in the Neotropics from the southernmost Mexico to northern Brazil [30], [33]–[36]. Here nine genera were proposed by Cook, 1895 [38], platyrhacids from South America have been reviewed by Chamberlin, 1941 [39] and platyrhacids from southern México, West Indies and Central America have been studied in significant works [34]–[36].

There are few living species of the Platyrhacidae recorded in México, i.e. Exallostethus trinax Hoffman, 1975 collected in the Chiapas Highlands [26]. Other species such as the first-described living forms of Platyrhacus, i.e. P. bilineatus and P. mexicanus Lucas, 1840 have been considered species inquirenda [34]. Thus, A. adamantis represents the first fossil species of the Platyrhacidae in the southernmost part of North America.