Palaeomacropis eocenicus, Michez & Nel & Menier & Rasmont, 2007

Michez, Denis, Nel, Andre, Menier, Jean-Jacques & Rasmont, Pierre, 2007, The oldest fossil of a melittid bee (Hymenoptera: Apiformes) from the early Eocene of Oise (France), Zoological Journal of the Linnean Society 150 (4), pp. 701-709 : 706-707

POSITION OF PALAEOMACROPIS EOCENICUS GEN.

NOV. SP. NOV. IN MELITTIDAE

Engel (2001) distinguishes four subfamilies within Melittidae : Dasypodainae, Macropidinae , Meganomiinae, and Melittinae. Engel (2001) notably resurrects the subfamily Macropidinae Robertson 1904 for the contemporary genus Macropis Panzer 1809 and the Baltic amber genus Eomacropis Engel, 2001 , both with two submarginal cells. He excludes Macropidinae from the Dasypodainae on the basis of the hairy paraglossa and the second abscissa of Rs that is slanting and widely separated from 1m-cu. He excludes them from the Melittinae on the basis of the presence of only two submarginal cells, the presence of yellow maculations on the face of the male, and the presence of a pygidial plate in the male. Macropidinae differs from the Meganomiinae due to its two submarginal cells, the pointed apex of its marginal cell, and its mandible with a very large preapical tooth on the upper margin.

In relation to this diagnosis, it appears that P. eocenicus must be considered as a Macropidinae . However, P. eocenicus shares some apomorphic characters with other melittid genera: no basitibial plate (like Dasypoda ), a propodeal structure like that of Meganomia and mid-basitarsal setae like those of Rediviva . Thus, cladistic analysis helps us find the most parsimonious solution for classification.

The cladistic analysis yielded one shortest tree length (23 steps, CI = 0.78, RI = 0.76) ( Fig. 5 ). This confirms the position of P. eocenicus in Macropidinae sensu Engel (2001) . The subfamily is characterized by the venation of the forewing (character 8 a). Palaeomacropis eocenicus differs from Eomacropis in the long, erect setae on its metasomal sterna (character 17) and dense plumose setae on its mesotarsus (character 12). It differs from Macropis by lacking dense plumose setae on each side of its protarsus (character 11). Palaeomacropis eocenicus differs from other Macropidinae genera ( Macropis and Eomacropis ) in the curved setae on its trochanter (character 13), and the absence of a basitibial plate (character 14). The originality of P. eocenicus is such that it can fall within a new monobasic genus included in Macropidinae .

FOSSILS OF MELITTIDAE

In common with other bee families, fossils of Melittidae are very rare. Dasypoda basaltica Zhang 1989 is a compression fossil only recognizable by its forewing. It strongly resembles the Macropidinae and differs from the Dasypodainae on the basis of its second abscissa of Rs widely separated from 1m-cu ( Zhang, 1989). Therefore, we include it in the Macropidinae and in the genus Macropis s.l., under the name Macropis basaltica comb. nov. Melitta willardi Cockerell 1909 is also a compression fossil. It is characterized by the scopa of the hind tibia and basitarsus, three submarginal cells and their diagnostic shape ( Cockerell, 1909). Without any other indications, it appears that M. willardi is indeed a Melittidae : Melittinae. Eomacropis glaesaria Engel 2001 is from Baltic amber of the late Eocene. It is characterized by two submarginal cells subequal in length and its slanting second abscissa of Rs widely separated from 1m-cu. This bee is indeed a Melittidae : Macropidinae . The Baltic amber genera Glyptapis Cockerell 1909 and Ctenoplectrella Cockerell 1909 were previously included in the Melittidae together with the contemporary genus Ctenoplectra Kirby 1826 ( Zeuner & Manning, 1976; Burnham, 1978). These two fossil genera are now included in Megachilidae : Osmiini ( Engel, 2001). Likewise, Gerlach (1989) described an unnamed Dasypoda species from Baltic amber (Dasypodainae) that Engel (2001) designated as a Glyptapis (Megachilidae) .

Therefore, all the fossils attributed to Melittidae are from the middle Eocene or later, and P. eocenicus is thus the oldest record of a melittid bee.

FOSSIL RECORDS AND PHYLOGENY OF APOIDEA

Palaeomacropis eocenicus highlights the gap between fossil data and the traditional phylogenetic tree of bees ( Fig. 1A ). Presently, the three oldest described bee fossils are an Apidae ( C. prisca ), a Megachilidae ( P. hirsutus ) and a Melittidae ( P. eocenicus ). We can add the corbiculate Apini Eckfeldapis electrapoides Lutz, 1993 discovered in Eocene shales from Germany ( Lutz, 1993). All of these taxa are included in the monophyletic clade of ‘ Melittidae + LT bees’. The first nonmelittid ST bee fossil is Electrolictus antiquus Engel 2001 from more recent Baltic amber ( Engel, 2001). These fossil data support one of the hypotheses put forth by Alexander & Michener (1995) and Danforth et al. (2006a, b): Melittidae could be the most basal group of the Apoidea ( Fig. 1B ). They also support the Perkins–McGinley hypothesis, namely that obtuse or bilobed glossa of Colletidae could be apomorphic ( Michener, 2000).

PALAEOMACROPIS EOCENICUS GEN. NOV. SP. NOV.:

Figures

Figure 1. Alternative phylogenetic trees of bee. A, traditional phylogenetic tree with Colletidae as basal branch. B, alternative suggestion with Melittidae as basal branch (Michener, 2000).

Figure 5. Best tree of cladistic analysis (length = 23 steps, CI = 0.78, RI = 0.76). Black square, apomorphy; double line, possible convergency; grey square, possible reversion. The state of character 8 is indicated by a (state 1) and b (state 2).