Ecological innovations in the Cambrian and the origins of the crown group phyla

Research output: Contribution to journalArticle


Simulation studies of the early origins of the modern phyla in the fossil record, and the rapid diversification that led to them, show that these are inevitable outcomes of rapid and long-lasting radiations. Recent advances in Cambrian stratigraphy have revealed a more precise picture of the early bilaterian radiation taking place during the earliest Terreneuvian Series, although several ambiguities remain. The early period is dominated by various tubes and a moderately diverse trace fossil record, with the classical ‘Tommotian’ small shelly biota beginning to appear some millions of years after the base of the Cambrian at ca 541 Ma. The body fossil record of the earliest period contains a few representatives of known groups, but most of the record is of uncertain affinity. Early trace fossils can be assigned to ecdysozoans, but deuterostome and even spiralian trace and body fossils are less clearly represented. One way of explaining the relative lack of clear spiralian fossils until about 536 Ma is to assign the various lowest Cambrian tubes to various stem-group lophotrochozoans, with the implication that the groundplan of the lophotrochozoans included a U-shaped gut and a sessile habit. The implication of this view would be that the vagrant lifestyle of annelids, nemerteans and molluscs would be independently derived from such a sessile ancestor, with potentially important implications for the homology of their sensory and nervous systems.


  • Graham Budd
  • Illiam Jackson
External organisations
  • Uppsala University
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Ecology
  • Evolutionary Biology
  • Geology
Original languageEnglish
Article number371 20150287
Number of pages12
JournalPhilosophical Transactions of the Royal Society B: Biological Sciences
Issue number1685
Publication statusPublished - 2015 Nov 23
Publication categoryResearch
Externally publishedYes