Minimal insect herbivory for the Lower Permian Coprolite Bone Bed site of north-central Texas, USA, and comparison to other Late Paleozoic floras

摘要

An examination of 598 leaves from the Lower Permian (late Sakmarian) Coprolite Bone Bed (CBB) site in north-central Texas, USA, reveals low herbivory levels based on analyses of foliar surface-area removed (0.25%) and frequency of herbivorized leaves (15.6%). These values contrast with a similar study from a somewhat younger (mid-Artinskian) nearby site where analogous values are 2.55% and 31.8%, respectively. As at the younger site, when compared to all other co-occurring plant taxa, CBB pteridosperms were overwhelmingly herbivorized, particularly the peltasperm Autunia cf. conferta and the medullosan Odontopteris cf. lingulata, the latter preserving an exceptionally high herbivory level of 3.31%. These two host-plant taxa accounted for 96.8% of all herbivorized leaves and 96.4% of all leaf surface area removed by insects. For the bulk flora, four subgroups of feeding were documented: margin feeding (70.1% of all occurrences), hole feeding (24.1%), and minor skeletonization (earliest occurrence), and galling. Distinctive gall types, one on the midveinal region of A. cf. conferta and the other on a branchlet of Walchia piniformis (also occurring in the European Early Permian) add to an existing but depauperate insect gall record for the Pennsylvanian and Permian. Emerging evidence indicates that herbivory intensity was spatiotemporally heterogeneous across fluvially-associated landscapes during the Early Permian in both western Euramerica (Texas, USA) and western Gondwana (Paraná Basin, Brazil), differing by an order of magnitude within each of these areas. Localities with the highest percentages of bulk leaf surface-area removed by herbivores in both realms ranged from 2.39 to 2.97%. This range approximates about a third of modern surface-area removal values by insect herbivores in both subtropical to tropical floras.