Magnicapitixyela dilettae, Montagna & Magoga & Stockar & Magnani, 2024

Montagna, Matteo, Magoga, Giulia, Stockar, Rudolf & Magnani, Fabio, 2024, The contribution of the Middle Triassic fossil assemblage of Monte San Giorgio to insect evolution., Communications biology 7 (1), No. 1023, pp. 1-10 : 4-5

Magnicapitixyela dilettae sp. n. Montagna M. & Magoga G.

Code Zoobank: LSID urn:lsid:zoobank.org:act:0C78D2B1-A392- 49A6-8C92-FE606E044476.

Etymology: Specific epithet dilettae is derived from the prosoponym of the first author daughter Diletta, to whom the species is dedicated.

Material: M. dilettae , holotype MCSN 8678 , an almost complete male specimen ( Figs. 3A, S 7) ; and paratype MCSN 8683 , a partially preserved phosphatized female specimen (Fig. S8); both fossils in dorsal view.

Type horizon: Upper Kalkschieferzone member of Meride Limestone Formation (transition interval to Archelaus and Regoledanus Ammonoid Zones; upper Ladinian).

Type locality: VM12 site (45°53’26” N, 8°56’49” E), Val Mara near Meride (Monte San Giorgio, Switzerland).

Repository: Museo cantonale di storia naturale, Lugano, Switzerland.

Diagnosis: As for the genus, being the only species.

Description ( Figs. 3A, S 7, S8). Small sawfly with a body length of 7.8 mm (♂) and of 8.1 mm (♀), including the ovipositor. Abdomen width (at III urite level) = 2.6 mm. Head capsule (frons apex–post occipital sulcus) = 1.3 mm (♂) and 1 mm (♀), gena–gena margins = 2 mm (♂) and 1.7 mm (♀), eyes very large and three ocelli visible on the holotype (diameter of 0.26 mm) (Fig. S8B). Antennae poorly preserved, visible only the scape. Head capsule almost of the same width as the thorax, mesoscutum well-developed. Forewing almost totally preserved in the holotype (only partially visible on the paratype), with a length of ~ 5.3 mm and a width (at distal upper apex of pterostigma and 2cua distal lower apex) of 1.74 mm, wing length/width ratio = 3.05, tegula visible on the left forewing (Fig. S7). Pterostigma completely sclerotized, SC developed over the entire length, joining C approximately at RS base (Fig. S7). R sinuous, slightly dilated at RS base. 1-RS and RS + M are slightly longer than 1-M (~ 1.4 times) and 1-RS (~ 1.3 times), respectively. Angle between 1-RS and RS-M of forewings of 146°. M+CuA slightly concave until the split between M and CuA.1 A straight.Presence of cells 3r and 4r; cell 1 mcu ~ 3 times as long as high, distally dilatated; cell 2 rm wide, ~ 3 times as long as width.Hind wing only partially preserved. Legs partially preserved, mostly only femur and tibia are preserved; tarsus and tarsal claws visible on the paratype (Fig. S8). Abdomen almost completely preserved, with ten visible segments. The paratype preserves the ovipositor with the 3 rd valvulae of 1.3 mm in length and a maximum width of 0.35 mm, transversal ornamentations are visible (Fig. S8C).

Neuropterida . Seven almost complete fossils (length ranging from ~ 2.4 mm to ~ 6.5 mm) were assigned to Neuropterida based on shape and venation pattern of wings; some specimens possess nygmata. Six specimens resemble Raphidioptera, while one almost complete specimen was assigned to the extinct family † Permithonidae Tillyard, 1922 (MCSN 8679; Fig. 3B ) and recently described as a new genus and species, Merithone laetitiae Montagna and Magoga, 2024 19.

Coleoptera . Thirty-seven specimens were found in the MSG assemblage, most of them completely preserved, and assigned to Coleoptera based on highly sclerotized exoskeleton and forewings transformed into sclerotized elytra. The assemblage includes representatives of three out of the four beetle suborders, namely Archostemata ( Cupedidae incertae sedis MCSN 8691, 8692; Fig. 3C, D ), Adephaga (MCSN 8681; Fig. 3E ) and Polyphaga (MCSN 8693; Fig.3F ). The fossils consist of small to medium size specimens (~ 1.3 mm to ~ 6.9 mm in length) characterized by terrestrial and aquatic habitus. Natatorial hind legs are visible in the specimen MCSN 8681 ( Fig. 3E ).

Amphiesmenoptera. A ~ 3.6 mm almost complete insect preserved in dorsal view (MCSN 8701; Fig. S9A). Head with hair on the front, rather complete filiform antennae and eyes partially visible. Both fore and hind wings are visible (left wings superposed), presenting hairs along the margins, nygmata not visible. Forewings with 3-branched M vein, as in Lepidoptera; the separation between M1 and M2 veins forms an angle greater than 45°, which precludes its assignment to Trichoptera, but in the meantime not greater than 60° as in Lepidoptera.Legs are partially visible on the right side. A second almost complete fossil in ventral view (MCSN 8702, a male; Fig. S9B) may belong to the same morphospecies because of the similar habitus and size (~ 2.8 mm).However,in this case,the 3-branched M vein in the forewing is not visible due to the poor preservation of the area. On the head, compound eyes and filiform antennae are visible, as well as, elongate structures compatible with laciniae departing from the mouthpart region. Abdomen terminal appendages visible.

Mecoptera. A small (~ 4.2 mm in length), almost complete, insect preserved in lateral view was attributed to Mecoptera due to the presence of the genital bulb folded underneath the distal part of the abdomen, likely a postmortem position acquired in the depositional environment (MCSN 8699; Figs. 4A, S 10). The head with well-developed compound eyes, ocellus, and an elongate rostrum with maxillary palps; bristles are present on the vertex (Fig. S10A). Antennae are filiform and composed of at least by 26 segments. Legs are partially visible. Two pairs of subequal wings with pterostigma and setae on the venations are present. CUA of forewings is not visible due to the poor preservation of the area and to the partial overlap of fore- and hindwings.

Diptera. A total of 56 fossils (54 adults and two pupae), with different degrees of preservation,were attributed to Diptera (MCSN 8686, 8673-8676, 8694-8698; Figs.4B–D, 5A, S 11). Adults (length from ~ 1.5 mm to 4.9 mm) possess hind wings reduced to halteres and one Cu vein on the forewings. Moreover, the presence of filiform antennae with more than ten segments and CuA veins not coalesced with 1 A (when visible) prompted their ascription to the Nematocera clade. The almost complete exarate pupae (MCSN 8698, ~ 4.1 mm in length, ~ 1.5 mm width, Fig. 4D; MCSN 8686, ~ 5.7 mm in length, ~ 1.4 mm width, Fig. S11A) can be assigned to Nematocera incertae sedis as well. These specimens preserve three pairs of legs, antennae, and respiratory horns on the head capsule. On the distal part of the specimen MCSN 8686, the abdomen preserves ovoidal structures attributable to seminal capsules ( Fig. 5A ).

Among these dipteran fossils, six out of 56 are phosphatized but no soft tissues or inner organs are recognizable (Fig. S11B–E). Some adults are complete and well preserved; setae are visible on legs, wings, and at the margin of compound eyes; in some cases, the outlines of the hexagonal facets within compound eyes are visible ( Fig. 5A, B ). The specimen MCSN 8680 presents a prolonged labium and maxillary palps ( Fig. S6 ). Interestingly, twelve Pleciofungivoridae-like fossils possess round-shaped bodies adhering to the distal part of their abdomens ( Fig. 5A ). These bodies appear to be external to the abdomen, which appears intact and their texture differs from the thin cuticula of the urites. On each insect are present two to four round-shaped units (each with a diameter of ~100–130 µm) with visible ornamentation ( Fig. 5C, D ). The shape of these enigmatic bodies is compatible with the one of seminal capsules as well as lycophyte spores of the genus Reticulatisporites (Lycopodiopsida) , even if based on literature the size of the latter is ~ 65 µm (19). The association of these enigmatic round-shaped bodies with the insect abdomen (mean = 2.83 for the round-shaped units) is not random, indeed their abundance on insect bodies significantly differs from the one of those dispersed into the fossil matrices (mean = 0.09 round-shaped units) (Wilcoxon rank sum test results: W = 0, p -value <0.001).

Figures

Fig. 3 | Representatives of holometabolous insects. A Magnicapitixyela dilettae (Hymenoptera, Xyelidae), MCSN 8678. B Merithone laetitiae (Neuropterida, †Permithonidae), MCSN 8679 (19). Coleoptera: MCSN 8691, Archostemata (C); MCSN 8692, Archostemata (D); MCSN 8681, Adephaga (E); MCSN 8693, Polyphaga (F). Scale bars: A–D, 1 mm; E, F 200 µm.

Fig. 5 | Diptera preserving peculiar features. A MCSN 8696, adult preserving the hexagonal facets of compound eyes and three round-shaped bodies at the end of the abdomen. B MCSN 8696, enlargement of the hexagonal facets of compound eyes. C MCSN 8696, enlargement of the three round-shaped bodies present externally on the abdomen, with visible ornamentations. D MCSN 8697, three round-shaped bodies present externally on the abdomen, with visible ornamentations. Scale bars: A, 500 µm; B, C, 200 µm; D, 100 µm.

Fig. 6 | Abundance of fossils per insect lineage found at VM12 site and location of the main Middle Triassic insect deposits. A Time-calibrated phylogenetic tree of insect evolutionary relationships from Montagna et al. (5) where the abundance of insects collected at VM12 per lineage, expressed as the natural logarithm of the number of individuals,is reported;(B). Location of main Middle Triassic fossil insect deposits as in Zheng et al. (11) with the addition of Monte San Giorgio. (1) Tongchuan, China (Ladinian); (2) Karamay, China (Carnian); (3) Madygen, Kyrgyzstan (Ladinian-Carnian); (4) Vosges,France (early Anisian); (5) Solite, USA (late Carnian); (6) Ipswich, Australia (Carnian); (7) Brookvale, Australia (Anisian); (8) Molteno, South Africa (Carnian); (MSG) Monte San Giorgio, Switzerland (Ladinian). Giulia Magoga drew insect silhouettes.