Ichnogenus Phymatoderma Brongniart, 1849

Phymatoderma (Lower Jurassic-Pliocene) appears to be similar in some aspects to Cladichnus since it represents an actively filled burrow system consisting of numerous branches, which deviate at a few levels from a common stem, diverging distally (e.g. Fu 1991; Izumi 2012). However, the producers tended to operate in a plane or only a few levels, less than in Cladichnus . In most cases, the branches are filled with pellets that are darker than the surrounding material (e.g. Uchman 1999), suggesting a higher content of organic matter that could foster enhanced microbial activity (e.g. Izumi et al. 2015). In black shales, in contrast, the pellets are lighter than the host sediment but document incorporation of surface detritus (Seilacher 1978; Izumi 2012).