Walking on ashes: insect trace fossils from Laetoli indicate poor grass cover associated with early hominin environments

Abstract

More than 4000 insect trace fossils collected in recent years from Pliocene deposits at Laetoli in northern Tanzania provide new insights on early hominin palaeoenvironments. These trace fossils include: Fictovichnus gobiensis, Coprinisphaera murguiai, C. kheprii, Coprinisphaera ispp., Quirogaichnus isp., Teisseirei linguatus isp. nov., Celliforma ritchiei isp. nov., C. spirifer, C. germanica, C. cfr. curvata, Celliforma ispp., Rosellichnus isp., Vondrichnus planoglobus, Laetolichnus kwekai igen. et isp. nov. and Krausichnidae indet. They reveal that at least one species of moth, three dung beetles and five other coleopterans, nine taxa of solitary bees, and an indeterminate number of taxa of termites inhabited the Lower Laetolil environments. The Upper Laetolil environments, which have yielded a rich diversity of vertebrate fossils, including the early hominin Australopithecus afarensis and its putative footprints, supported several taxa of termites, one dung beetle, five other coleopterans, and eleven taxa of bees. The Upper Ndolanya environments, which have yielded the hominin Paranthropus aethiopicus, record four taxa of dung beetles, four other coleopterans, and two taxa of bees. The record of larval mortality and lack of intruder activity, revealed by the absence of emergence and intruder traces, may be associated with the anoxic/hypoxic conditions caused by the instantaneous burial of soils under thick volcanic ashes. The record of the Celliforma Ichnofacies in the Upper Laetolil environments indicates the dominance of shrubland to woodland with limited grass cover. This is supported also by the absence of Coprinisphaera, which suggests a scarcity of fresh grasses and a low abundance of large mammal grazers.

DIFFUSE TERMITINAE NESTS SHED LIGHT ON THE AFFINITIES OF LAETOLICHNUS KWEKAI (KRAUSICHNIDAE)

“…The insect trace fossils included in the ichnofamily Krausichnidae are systems of interconnected chambers occurring in paleosols (Genise 2004). They are represented by 17 ichnogenera, all considered as complete or partial nests constructed by ants or termites (Genise 2016;Genise and Harrison 2018). The newest ichnogenus Laetolichnus, known from fragmentary material, was tentatively included in this ichnofamily (Genise and Harrison 2018).…”

“…They are represented by 17 ichnogenera, all considered as complete or partial nests constructed by ants or termites (Genise 2016;Genise and Harrison 2018). The newest ichnogenus Laetolichnus, known from fragmentary material, was tentatively included in this ichnofamily (Genise and Harrison 2018). Several possibilities were originally considered: pieces of rhizoliths preserving part of a concretion, termite galleries or oothecae surrounding twigs, and chambers of root-sucking insects constructed around roots (Genise and Harrison 2018).…”

“…Laetolichnus kwekai is an insect trace fossil described recently from the Upper Laetolil Beds at Laetoli, Tanzania (Genise and Harrison 2018). This unit, dated to 3.6-3.85 Ma (Deino 2011), also yields fossil plants, invertebrates, vertebrates such as the hominin Australopithecus afarensis, and trace fossils attributed to bees, beetles, and termites (Sands 1987;Darlington 2005Darlington , 2011Harrison 2011aHarrison , 2011bHarrison , 2011cGenise and Harrison 2018). Laetolichnus kwekai, as originally described, is composed of a small empty chamber with a straight, curved, sinuous, V-shaped, single-lobed, bilobate, multilobate, or subtriangular outline.…”

“…8C). On the basis that the specimens would have been originally connected to form a more complex structure, L. kwekai was included in the ichnofamily Krausichnidae and tentatively attributed to termite nests (Genise and Harrison 2018). However, its affinities have been unclear until now.…”

A new terrestrial trace fossil Feoichnus martini n. isp. from the Upper Cretaceous Two Medicine Formation (USA)

“…This process is similar to that observed in soil-dwelling insects, e.g., cicada nymphs, and could be indicative of a lined border composed of multiple stained layers (Krause et al, 2008; Genise, 2016). Traces produced by soil-dwelling organisms, e.g., burrows and chambers used for feeding, nesting, hibernation, or aestivation purposes, typically display a discrete border (Retallack, 1984; Edwards et al, 1998; Downing, 2004; Betadou et al, 2008; Alonso-Zarza et al, 2014; Genise and Harrison, 2018). Pupation and nesting structures, i.e., Pupichnia and Calichnia, resulting from insect activity are one of the most common structures encountered in paleosols, but their walls are generally too complex to be attributed to F. martini n. isp.…”