New Perspective on Cambrian Explosion: Construction of the First Animal Consumer-Driven Marine Ecosystem on Earth

The Cambrian Explosion represents one of the most profound phases in the history of life, with the near-simultaneous emergence of most modern animal phyla, including all of the Bilateria. Since this time, the proliferation of animals across all ecospace, including terrestrial environments, suggests that the Earth has become increasingly habitable for animal life. Along with the sudden appearance of essentially all the readily fossilized major animal groups, the Cambrian Explosion (540-510 Ma) also results in the first appearance of macro-consumers, complex trophic interactions and establishes patterns of emergence and diversification that define the modern animal tree of life. Following the Cambrian, despite numerous major geological events and the migration of both plants and animals into the terrestrial realm, no new animal phyla appear. The Cambrian Explosion can therefore be considered a unique event in the history of life, representing both a key transition in global habitability and the starting point for animal consumer-driven marine ecosystems. Past work by multiple research teams, has explored the Cambrian Explosion from many different perspectives, and have markedly increased our understanding of this major evolutionary event. This abstract proposes three macroevolutionary phases in the evolution of early life, with each phase defined by both organismal “hierarchical level” and geological settings and the Cambrian Explosion representing the culmination of the three phases. These three phases are: molecular-level evolution during origin of early continents, cellular-level evolution along with the supercontinent evolution of Nuna (Colombia) and Rodinia and tissue-level evolution coupled with the early assembly and breakup of Pangea. At the earliest stages of Earth history, macro-level prokaryotes first formed, derived from protocell-forming molecules (Molecular Phase). The first appearance of eukaryotic cells, derived from prokaryotes, represents the next milestone in biological evolution (Cellular Phase). The subsequent emergence of multicellular eukaryotes (metazoans) represents the third and final phase (Tissues Phase). Combined with the advent of multicellularity comes a revolution in body-plan organization, facilitated by the innovative capacity to develop specialized tissues. This included the spontaneous development of mineralized epithelial exoskeletons and connective tissue endoskeletons. Based on these developments, a ‘Lego Blocks’ hypothesis for the Cambrian Explosion is proposed, driven by the initiation of the modern plate tectonic regime characterized by full-plate deep subduction and the associated changes in Earth multi-sphere interactions and bio-litho-atmospheric cycles during Rodinia breakup and Gondwana assembly. During this period of geological disruption, the diversity of marine niches expanded, resulting in both accelerated phylogenetic diversity and ecological expansion, as organisms developed both a wide range of specialized biological tissues and tissue arrangements to exploit the newly available vacant niche space. The failure of new animal phyla to emerge following the Cambrian Explosion can thus possibly be explained by both a maximization of potential organismal complexity and the relative stabilization of ecospace, with major palaeogeographic changes in the Phanerozoic following the breakup of the Neoproterozoic supercontinent Rodinia, limited to the opening and closing of the Neo-Paleo-Tethys Ocean during the Phanerozoic, neither of which created novel ecological niches not previously in existence.