||Olivia P. Judson, The energy expansions of evolution, Nature ecology & evolution, 28 April 2017 | Volume: 1 | Article number: 0138 p.4 right column bottom paragraph
|| Carbone, C. & Narbonne, G. M. When life got smart: the evolution of behavioral complexity through the Ediacaran and early Cambrian of NW Canada. J. Paleontol. 88, 309–330 (2014). link
||P.4 right column bottom paragraph: "A third geological impact of animals is caused by their ability to burrow. Simple, horizontal burrows appear in the fossil record around 555 Ma (primary source), by the early Cambrian, the abundance, size, depth and complexity of burrows had increased considerably (primary source). Widespread burrowing creates a mixing of sediments known as bioturbation. As Darwin (ref 111) observed with respect to earthworms, burrowing is analogous to ploughing: it redistributes nutrients as well as sifting, irrigating, and aerating sediments and soils."