Chondrites intricatus (Brongniart, 1823)

Chondrites intricatus (Brongniart, 1828) has downward radiating straight branches; branching angle less than 45° (Uchman, 1998). Fu (1991) and Uchman (1999) placed Chondrites furcatus Sternberg, 1833 in synonymy with Chondrites intricatus, but Blissett and Pickerill (2004) have retained C. furcatus as a distinct ichnospecies;

Description. Three morphotypes A (the most common), B and C, are recognized. Morphotype A (Figs. 2C, 3B, 6A-B) is a system of tree-like branching, downward penetrating, markedly flattened tunnels. The width of the tunnels is constant in each specimen, but ranges from 0.2 to 0.6 mm overall. Branches form sharp angles. In most specimens, only second order branches occur; third-order branches are much rarer. Width of the burrow system ranges from 20 to 35 mm. The tunnels are filled with clayey material that is darker than the host rock and derives from the background sediments. Morphotype A penetrates up to 10 cm below the top of the marlstones. Morphotype B (Figs.4F,6C) occurs exclusively in fillings of Planolites beverleyensis as short, branched and unbranched, straight or slightly curved dark bars about 0.5 mm wide and up to 3 mm long. Morphotype C (Fig. 2D) is represented by branched tunnels of general geometry as in morphotype A, but tunnels are subdivided into segments that are less than 1 mm long (specimen no. 5081).

Remarks. Chondrites is a deep-tier trace fossil produced probably by surface ingestors (Kotake, 1991) that probably live in dysaerobic conditions as chemosymbiotic organisms (Seilacher, 1990; Fu, 1991).