Fig 1.
Fossil evidence of different springtails behaviors, and the geological range of the body fossil record.
From top to bottom: Sminthurus longicornis depositing eggs (Baltic amber) [1]; S. longicornis with stalked spermatophores (Baltic amber) [12]; courtship behavior of Pseudosminthurides stoechus (herein described; Spanish amber); aggregation of Proisotoma communis (herein described; Spanish amber) and unidentified entomobryomorphans (Dominican amber) [13]; phoresy: S. longicornis over a harvestman, Dicranopalpus ramiger (Arachnida: Opiliones) (Baltic amber) [1], and unidentified sminthuridid on an oedemerid beetle [14], and a Sphyrotheca? sp. over a mayfly, Borinquena parva (Ephemeroptera) (Dominican amber) [15] (see also S1 Fig for a review of the general fossil record of Collembola).
Fig 2.
Fossil and extant Sminthurididae showing mating behavior and/or its underlying anatomy.
(A) Dorsal habitus of the male of Pseudosminthurides stoechus (holotype; accession number MCNA 12788) as preserved in Early Cretaceous Spanish amber. Left arrow indicates the left modified clasping antenna. Right arrow indicates the wing-like enlarged mucrones, an adaptation to the epineustic way of life. (B and C) Reproduction biology of Recent Sminthurides aquaticus in a pond (coordinates: 52°16'11.9"N 8°06'46.4"E; Osnabrück, Germany) (images credit K. Beck, with permission). Pair formation on the water surface (B). The female carries the smaller male raised in the air as part of the courtship behavior (C). Body size of S. aquaticus is up to 1.0 mm in females, and 0.3–0.4 mm in males. Scale bar, 200 μm (A).
Fig 3.
Assemblage evidencing gregariousness of Proisotoma communis in Early Cretaceous Spanish amber.
(A) Overview of the amber piece MCNA 11231. (B) Camera lucida drawing showing the general configuration of the syninclusions. (C) Close up of box in (A), showing some individuals from the main group of the association. (D and E) Close up of boxes in (C), showing the intraspecific character variability described and mainly concerning the size of the specimens (see also S1 Table). (F and G) Cycadopites-type pollen grains from the assemblage (box in (F) indicate the magnified cluster in (G)), and possibly attributable to falling pollen being concentrated in the viscous resin. Scale bars, 2000 μm (A, B), 300 μm (C), 100 μm (D–F), 50 μm (G).
Fig 4.
Reconstruction of an aggregation of P. communis.
Leaves constituting the litter are of Eretmophyllum (Ginkgoales), a common plant macroremain as cuticles in the Spanish amber-bearing strata. Body color of the collembolans is conjectural but based on the coloration seen in the close extant relatives (artist J. A. Peñas, with scientific supervision).