Evidence of arthropod‐plant interactions in the Upper Triassic of the southwestern United States

Abstract

Leaves from the Upper Triassic Chinle Formation in the southwestern United States show evi dence of having provided nourishment and shelter for several different types of arthropods. This evidence consists of three or four morphotypes of feeding traces and a well-defined type of gall. The feeding traces occur on the pinnules of the filicalean fern Cynepteris lasiophora (Daugherty) Ash and the pinnae of the bennettitalean leaf Zamites sp. and Marcouia neuropter-oides Ash, a gymnosperm leaf of uncertain relationships. Typically, the feeding traces are only a few mm in length and have smooth, continuous margins which are often bordered by a nar-row dark band that represents reaction tissue formed in response to feeding. Presence of this tissue indicates that the leaves continued to function after the damage occurred and while they were still attached to the parent plant. The relatively small size and shape of the feeding traces shows that they were most likely produced by grazing insects. Gall-like swellings are found on the leaves of Dechellyia gormanii Ash, another gymnosperm fossil of uncertain relationships. The swellings are well defined, round to deltoid in outline, and bulbous. Typically, only one such swelling occurs on a leaf. Leaves that have these swellings are often distorted or terminate abruptly at the disturbance, particularly if the structure extends over the edge of the leaf. The swellings resemble galls induced on leaves of certain modern plants by eriophyid mites and apparently are either prosoplasmatic histioid pit galls or pouch galls.