INTRODUCTION

The announcement of a new Recent insect order has stirred renewed excitement among entomologists (Klass et al., 2002, 2003; Berenbaum, 2002; Devetak, 2002; Hansen, 2002; Hall, 2002; Chen et al., 2002; Adis et al., 2002; Anonymous, 2003). The order Mantophasmatodea, or African rock crawlers, consists of 14 previously described species in 11 genera (Klass et al., 2002, 2003; Zompro et al., 2002, in press). Ten of these genera occur in sub-Saharan Africa, while the 11th, Raptophasma, is known only from mid-Eocene Baltic amber (table 1). Rightly so, the proposal of this new order has stirred debate among entomologists (e.g., Tilgner, 2002; Hamilton, 2003). Indeed, the cohort Polyneoptera includes insects differing dramatically in their morphology and biology, perhaps more so than any other superordinal clade, and this ancient group is today represented by numerous autapomophic orders with little apparent affinity with one another, like Dermaptera (earwigs) and Grylloblattodea (rock or ice crawlers). The Mantophasmatodea have already been contended to belong within the Orthoptera (Tilgner, 2002), rather than forming a sister group to one of the other lineages. Arillo et al. (1997) recorded the first individual of the order in Baltic amber, but relationships were obscure and it was not until the discovery of Recent species that the phylogenetic affinities of the fossils were clarified (Klass et al., 2002). The order is characterized most notably by the apomorphic absence (loss) of ocelli (although see description of new fossil, below), epistomal sulcus (with the subgenal sulcus looping from the posterior mandibular articulation to the anterior tentorial pit and back to the anterior mandibular articulation), and wings; and by the hypognathous head capsule, enlarged pretarsal arolium with a ventral series of elongate setae (in modern species), presence of a vomer-like process articulating on the apical margin of the tenth sternum (termed “vomeroid” by Klass et al., 2003), and unsegmented cerci (clasping in males; see also Klass et al., 2003).

Herein we present the description of a second species of this order from Lutetian-aged Baltic amber (ca. 45 Ma) and provide some general commentary on the order Mantophasmatodea as a whole. Measurements were made using an ocular micrometer and photomicrographs were prepared using a Microptics ML-1000 digital imaging system.

SYSTEMATIC PALEONTOLOGY

DISCUSSION

The first individual of Mantophasmatodea was recorded and described by Arillo et al. (1997) but left unnamed and unassigned as to order. Zompro (2001) subsequently described a series of specimens and named the fossils R. kerneggeri, considering them as Orthoptera incertae sedis, although he simultaneously provided the first “ordinal” name for the group, Raptophasmatodea. Based on the description, photograph, and drawing of Arillo et al. (1997), their fossil could be a species of Raptophasma, perhaps R. kerneggeri.3 However, Arillo (personal commun.) indicates that the forelegs do indeed have spines similar to Adicophasma and that it may represent a second species of this genus (the pronotal and abdominal structure differing from A. spinosa). Certainly the Arillo et al. (1997) specimen is deserving of further study. The fossil described herein was attributed to and even designated as a paratype4 of R. kerneggeri (Zompro, 2001), despite its considerable differences. It may eventually prove that additional species of Raptophasma and Adicophasma also occur in Baltic amber.

The genus Adicophasma appears to be more closely related to the living genera Mantophasma and Praedatophasma (among others) than to Raptophasma owing to the spination on the forelegs, as well as elsewhere on the body. The absence of the row of elongate setae on the arolium would appear to exclude Adicophasma (and likely Raptophasma) from a clade of the living species. The enlarged compound eyes and transverse head are presumably plesiomorphic features shared with Raptophasma (and in the case of the eyes, with Praedatophasma as well).

It is not surprising to discover Baltic amber relatives of taxa today restricted to sub- Saharan Africa, as is the case with Adicophasma and Raptophasma. Indeed, this is a common biogeographic connection, with numerous lineages in Baltic amber surviving in southern Africa or Asia (e.g., Larsson, 1978, for summaries). Mantophasmatodea may have been relatively widespread, albeit not common, during the Paleogene, having perhaps experienced significant declines in diversity following the Eocene to arrive at the modern, isolated distributions of the known extant members. Although unlikely, Mantophasmatodea may eventually be discovered outside of Africa and species will almost certainly be recovered from other fossiliferous deposits elsewhere in the world.

Building upon the hypothesis of polyneopteran relationships outlined by Engel and Grimaldi (2000; fig. 5), the placement of Mantophasmatodea would indicate a relationship with the Orthopterida (i.e., Phasmatodea and Orthoptera; also the extinct †Titanoptera and †Caloneurodea, not discussed further herein) within the Anartioptera (= Plecopterida + Orthopterida: fig. 5). The gonoplac is short in Mantophasmatodea but is sclerotized and more developed than the second valvulae. Thus, as in Orthopterida, the gonoplac may act as the functional ovipositor, suggesting a placement near that superordinal complex. Mantophasmatodea possess a vomer-like process on the apex of the tenth sternum and therefore resemble Phasmatodea among Orthopterida. Dismissed as being nonhomologous with the vomer of Phasmatodea by Klass et al. (2002, 2003), owing to the articulation of this sclerite along its posterior margin to the tenth sternum (versus the anterior margin in Phasmatodea, and hence the reason it was termed a “vomeroid”), it is possible that there was an inversion and this rearrangement is merely autapomorphic for Mantophasmatodea. Such placement is intuitively pleasing owing to the superficial similarity of African rock crawlers to plesiomorphic Phasmatodea (i.e., Timema) and to possession of a “vomer” (sensu lato) in these orders. Unlike the stick insects, however, African rock crawlers lack a true operculum or micropylar plate in oö cytes but do possess a circular ridge reminiscent of an operculum (Klass et al., 2002). Tilgner (2002) indicated a possible placement of Mantophasmatidae near Proscopiidae in the Orthoptera (Caelifera); however, as noted by Klass (2002), the absence of striking orthopteran synapomorphies (e.g., cryptopleuron, jumping hind legs) and the synsclerotic conditions of the tarsi are not homologous (basal three tarsomeres completely fused to form a single subsegment of the podite in Orthoptera, united but still pentamerous and differentiated by distinct, dorsal grooves in Mantophasmatodea) would seem, for now, to exclude African rock crawlers from Caelifera. The assertion of a relationship between Mantophasmatodea and Mantodea based on sperm ultrastructure (Dallai et al., 2003) is not supported by any other characters, is based on an exceedingly small sampling of derived members of some polyneopteran orders, and includes characters which may be rampantly labile even within some of the lineages under consideration. The African rock crawlers are certainly not dictyopterans, despite the unfortunate similarity in the names of the two taxa considered.

Perhaps more striking is the similarity between Mantophasmatodea and the ice crawlers (i.e., Grylloblattodea). Both lineages share a similar configuration of sclerites in the proventriculus and the structure of the midgut caeca (Klass et al., 2002). In such a case, the African rock crawlers would be in tantalizing Gondwanan juxtaposition to the Laurasian Grylloblattodea, analogous to the biogeographic split between the suborders of Plecoptera ; i.e., Arctoperlaria and Antarctoperlaria (Zwick, 2000). At present there is little justification for a definitive placement of the Mantophasmatodea within Orthopterida near Phasmatodea or, more drastically, within Orthoptera.

Certainly new material of Mantophasmatodea, particularly more ancient fossils and molecular data, will provide improved insight into the phylogenetic placement of these insects. Already our knowledge of the distribution of these insects is expanding with new species and new records from South Africa (e.g., Pennisi, 2002; Picker et al., 2002; Klass et al., 2003), and the further description and study of these taxa will hopefully clarify the validity of the order and its placement in the greater context of polyneopteran insects. It would be very interesting to explore similar plants in Chile to see if mantophasmatodeans are lurking there. Should a Grylloblattodea + Mantophasmatodea clade exist, the two groups could be considered suborders of a single order (Grylloblattaria s.l. or Notoptera). Such a relationship would reflect an apparent Jurassic split between Gondwanan and Laurasian suborders of a single lineage, again analogous to that seen in Plecoptera.