Science Literature

A group of stick-like grasshoppers known as the Proscopiidae are widely distributed in Central and South America. They are flightless, mostly wingless (although some genera are equipped with rudimentary wings) and are ecological generalists (in that they feed on several different plant families). Although there are many species, their taxonomy is largely based on the details of unusual male genitalia. Their relationship to other grasshopper superfamilies has not been studied systematically.

An extant proscopiid (Credit: Guilherme Ide)

Until now, the fossil record of the Proscopiidae has been a void. One might have infered a recent origin. However, this is no longer an option because the first known fossils of this group have been found in Early Cretaceous strata (so these insects were around with dinosaurs). The fossils show well-developed wings and several other differences from extant forms. The research paper refers to them as stem-group proscopiids, but it should be remembered that these animals are specialised offshoots from their ancestral forms. The "stem-group" designation merely points to a time when they were less derived (notably, they had not yet lost their wings).

"[I]t is clear that Eoproscopia is less specialised than modern forms in this regard. Nonetheless, Eoproscopia does have the remarkable stick-like body typical of crown-group proscopiids, and it would appear that the family adopted their cryptic mode of life as stick mimics very early in their evolution."

The word "evolution" here deserves to be clarified: the loss of wings is analogous to the loss of vision in cave fish. The scenario is not the evolution of something genuinely novel, but the development of a specialised form from a more generalised ancestor. There is no evidence that this needs more than the reorganisation of existing complexity and also it may be combined with a process of genetic impoverishment.

The most significant aspect of this find is that the fossils are Early Cretaceous. This provides yet another pointer to Punctuated Equilibrium - rapid emergence of the new form followed by stasis (albeit with minor changes). Whereas Darwinism puts the emphasis on the origin of species, Punctuated Equilibrium implies that speciation is not really so important. Extant Proscopiidae comprise 215 species (in 30 genera) but they are all clearly proscopiids. The interesting transformation concerns the origin of the Family, and that happened abruptly and early. Darwinism may be the explanation of the post-Cretaceous story, but it has little relevance to what happened earlier.

THE FIRST FOSSIL PROSCOPIIDAE (INSECTA, ORTHOPTERA, EUMASTACOIDEA) WITH COMMENTS ON THE HISTORICAL BIOGEOGRAPHY AND EVOLUTION OF THE FAMILY
SAM W. HEADS
Palaeontology, 51(2), March 2008 , 499-507 | doi:10.1111/j.1475-4983.2008.00756.x

Abstract: Eoproscopia martilli gen. et sp. nov. is described from the Early Cretaceous (Aptian) Crato Formation Lagerstatte of Ceara State, north-east Brazil. The new taxon is assigned to the extant family Proscopiidae and represents the first occurrence of the group in the fossil record. Eoproscopia is similar to crown group proscopiids in its stick-like habitus, elongate prothorax and absence of the cryptopleuron, but differs in the presence of well-developed wings, the short head with a small, simple fastigium, the prothoracic legs being inserted near the posterior margin of the prothorax, and the absence of spines on the metathoracic tibiae. The discovery of Eoproscopia extends the geological range of the family by approximately 110 myr and confirms the presence of stem-group proscopiids in the Atlantic rift zone of South America during the Early Cretaceous.

See also:

Tyler, D. Stasis in the fossil record of leaf insects, ARN Literature Blog, 14 January 2007.