Morphology, Fill and Size: Chondrites is one of the most common and widely distributed trace fossils; due to its rootlike appearance it was originally interpreted as a plant fossil. It consists of tunnel systems possessing a single or a small number of master shafts, presumably open to the surface, which ramifies with depth under acute angle to form a dendritic or root-like system (Osgood1970; Fu1991). Most of the burrows show an active fill,sometimes with portions preserving a meniscate structure.The burrows are unlined. The tunnel diameter remains constant in different parts of the burrow and typically is in the range of less than 1 mm to a few millimeters.
Remarks. Chondrites is ethologically classified as a feeding trace (fodinichnia). It is generally assigned to depositivorous and/or suspensivorous annelids or sipunculids.
Recent work suggests that Chondrites may represent specialized feeding behavior that involves chemosymbiosis, being interpreted as a sulfide pump (Fu, 1990, Seilacher, 1990; Bromley, 1996). It has been regarded that the Chondrites animal developed adaptations to cope with oxygen-depleted conditions (Bromley & Ekdale, 1984; Savdra, 1992).
Diagnosis: Dendritic, smooth walled, regularly but asymmetrically branched small burrow systems that ordinarily do not interpenetrate or interconnect. Diameter of components within a given system remains more or less constant.