Advanced Early Jurassic termite (Insecta: Isoptera) nests: Evidence from the Clarens Formation in the Tuli Basin, southern Africa (discussion)

F GENISE, JORGE; SERGIO BELLOSI, EDUARDO; RICARDO NESTOR MELCHOR; MARCELA COSARINSKY,

PALAIOS

SEPM Society for Sedimentary Geology

Lugar: Lawrence, Kansas, USA; Año: 2005 vol. 20 p. 302 - 311

0883-1351

Insect paleoichnology, being a young discipline, needs to gain acceptance and recognition as a sister counterpart of paleoentomology and entomology. Accordingly, the analyses and discussions to ascertain the attribution of continental trace fossils to insects should be carried out very carefully. Such analysis (e.g., Machado, 1983; Sands, 1987) for fossil termite nests, which is lacking in the recent contribution by Bordy et al. (2004) on supposed Jurassic termite nests, is critical, because their results are at odds with our previous knowledge of the evolutionary history of termites and their relationship with coevolving groups of plants and fungi. Many invertebrate trace fossils are more preservable than their constructors are. For example, fossil bee nests predate the oldest known bees by about 25 My (Elliot and Nations, 1998; Genise, 2000; Engel, 2000), which is an expected gap. In contrast, the gap between the oldest termites, which come from the Lower Cretaceous (Jarzembowski, 1981; Martý´nez-Delclo`s and Martinell, 1995), and the supposed termite nests described by Bordy et al. (2004) would be about 60 My. However, it is neither the time involved nor the difficulties of imagining fungusgrowing termites in an early Jurassic environment deprived of Basidiomycotina and grasses that promoted this comment. Instead, it is the understanding that the description and affinities of the Tuli structures are not treated with the necessary detail and their termitic origin was not demonstrated. Termite nests comprise closed and dynamic systems, largely isolated from the external environment, within which the microclimate can be controlled, food can be stored, and protection from enemies achieved (Lee and Wood, 1971). Some termite nests are considered the most complex constructions of the animal kingdom (Noirot, 1970). Such morpho-functional complexity is accomplished by the spatial arrangement of different morphological parts, following distinct basic bauplans, according to the biology of the species and the environment. The internal morphology of the Tuli structures does not exhibit any of these basic termitic bauplans. The important evolutionary conclusions to which the paper seems to arrive are based on controversial and weak evidence—as is the case with other records of supposed Triassic and Jurassic termite nests mentioned in the bibliography (see Genise, 2004 for discussion). At present, the body and ichnofossil record shows that the appearance of eusocial insects and flowering plants occurred during the early Cretaceous (Jarzembowski, 1981, 2003; Labandeira, 1998; Grimaldi, 1999; Engel, 2000, 2001; Genise, 2004). Insect paleoichnology is a fortunate branch of ichnology because frequently, insect trace fossils can be attributed to modern taxa, contributing to knowledge of the evolutionary history of producers. However, the degree of reliability of such attributions has been uneven. Several fossil termite nests are undisputable, such as those described by Coaton (1981), Schuster et al. (2000), or Krausichnus trompitus (Genise and Bown, 1994), whereas other claims need further analysis and confirmation; and still others are unlikely (Genise, 2004). The reliability of attributions depends on the complexity of the described trace fossils, the methodology applied for their study, the existence of a sound ichnotaxonomy, and particularly, the control by the body-fossil record (Genise, 2004). Even evolutionary hypotheses based on objective evidence, such as molecular clocks, are calibrated or contrasted with the body-fossil record (Brochu et al., 2004). The contribution by Bordy et al. (2004) lacks the pertinent macro- and micromorphological analyses and comparisons of the structures that would allow their attribution to termites. In exhaustive analyses (e.g., Machado, 1983; Sands, 1987), the external and internal (macro- and micro-) morphologies of the structures are extensively compared with modern termite nests—a first hand comparison that is lacking in the paper by Bordy et al. (2004). The micromorphology of the Tuli structures was not studied at all, even when these data would be a primary tool to determine their termitic origin (Stoops, 1964; Machado, 1983; Mermut et al., 1984; Sands, 1987; Cosarinsky et al., 2004). In addition, Sands (1987) had to appeal to the complex distribution of the possible termite nests in the deposits to demonstrate that they were as old as the host rocks—a possibility completely absent in Bordy et al.’s (2004) discussion. In contrast, Bordy et al. (2004, p. 71) stated ‘‘The complex external and internal architecture of the structures described above is strikingly consistent with the nest architecture of some recent termite mounds found in the savanna close to the study area.’’ This statement is followed by a short paragraph in which only two paleoichnological references are mentioned as comparison with modern examples. The whole paper should have been focused on demonstrating the termitic origin of the structures, however, this origin is claimed from the very beginning.