Early Cretaceous origin of pollen‐feeding beetles (Insecta: Coleoptera: Oedemeridae)

Abstract

The taxonomic position of a new pollen‐feeding fossil beetle from Spanish amber (late Albian, 105 Ma) is analysed. A phylogenetic analysis allows me to accommodate Darwinylus marcosi gen. et sp. nov. in the Polyphaga: Oedemeridae within current limits for the family, which clearly belongs in the subfamily Oedemerinae. It corresponds to the oldest definitive record for the family. Some autapomorphies, mainly in antennae, are observable in the fossil compared with extant members of the family. A discussion about these problematic characters and the evolution of the family is proposed.

False Blister Beetles and the Expansion of Gymnosperm-Insect Pollination Modes before Angiosperm Dominance

“…The holotype of Darwinylus marcosi from Spanish amber in the Basque-Cantabrian Basin of northern Spain recently was reexamined (Figures 1, 2, and S1). This specimen represents the oldest definitive fossil so far described for the beetle family Oedemeridae (false blister beetles) and is phylogenetically basal within the subfamily Oedemerinae [9]. The amber piece containing the beetle revealed 126 associated pollen grains, some of which formed distinct clumps (Figures 1A, 1C, 1D, and 1E-1G).…”

“…Darwinylus marcosi bore mandibulate-ectognathate mouthparts, a common type of mostly prognathous mouthparts that employ a chewing feeding style [35]. A related feature was a body surface laden with cycad-attributed Monosulcites pollen [9] (Figures 2 and S2). These features constitute the first direct evidence of pollination in the fossil record of beetles and the fourth major gymnosperm-insect pollination mode documented in the fossil record during the mid-Mesozoic (Table 1).…”

“…Insect pollinator response to the mid-Cretaceous angiosperm radiation provides an additional refinement that relates cohort persistence through time to host association (gymnosperm or angiosperm) and evolutionary pattern (extinction, continuation, or origination) (Figure 3A). During the 35-million-year-long interval, these four cohorts of insect families were those with (1) gymnosperm host associations that became extinct earlier in the interval, such as zhangsolvid flies [11]; (2) gymnosperm host associations that survived the interval and continued largely to the present, exemplified by merothripid thrips [5]; (3) gymnosperm host associations that transitioned laterally onto new angiosperm hosts, which included false blister beetles [9]; and (4) new angiosperm host associations later in the interval, of which bees are an example [21] (Figure 3A). For pollinators, the Aptian-Albian gap is explained as a consequence of older insect lineages with gymnosperm hosts undergoing extinction (cohort 1) that generally occurred before younger insect lineages originated on angiosperm hosts (cohort 4).…”

“…However, most evidence supports gymnosperm-insect pollinator associations, buttressed by direct evidence of pollen on insect bodies, currently established for four groups: Thysanoptera (thrips), Neuroptera (lacewings), Diptera (flies), and now Coleoptera (beetles). Each group represents a distinctive pollination mode linked to a unique mouthpart type and feeding guild [4][5][6][7][8][9]. Extensive indirect evidence, based on specialized head and mouthpart morphology, is present for one of these pollinator types, the long-proboscid pollination mode [10], representing minimally ten family-level lineages of Neuroptera, Mecoptera (scorpionflies), and Diptera [8,10,11].…”

The case of Darwinylus marcosi (Insecta: Coleoptera: Oedemeridae): A Cretaceous shift from a gymnosperm to an angiosperm pollinator mutualism

“…This new species corresponds to the oldest, definitive fossil described for this family, and was accommodated in a basal position within Oedemeridae after a phylogenetic analysis. 10 Darwinylus marcosi exhibits autapomorphies and many characters identified as primitive among extant oedemerid species, which were interpreted as uniquely optimized ecological features or an indication of ancestral habits. After the amber piece was exhaustively studied, it revealed that the beetle possessed 126 associated and occasionally clumped pollen grains, 5 of which were still adherent to various parts of the insect's body.…”