The controversy about a Cambrian “explosion” of morphological disparity (followed by decimation), cladogenesis and fossilization is of central importance for the history of life. This paper revisits the controversy (with emphasis in onychophorans, which include emblematic organisms such as Hallucigenia), presents new data about the Chengjiang (Cambrian of China) faunal community and compares ii...

According to the conventional evolutionary-uniformitarian time scale of Earth history, multicellular organisms first appeared in abundance about 550 million years ago, in the "Big Bang of Evolution," the Cambrian explosion. But (again, according to the conventional time scale) a handful of odd multicellular organisms existed before the astonishing explosion of new forms in the Cambrian. These o...

Late Precambrian to early Cambrian sediments of the Amadeus Basin, Central Australia, contain two stable directions of magnetization. Lithologies are diverse and include red beds, green beds, and carbonates, all of which respond to thermal cleaning. Positive fold and unconformity tests, and a well-defined polarity zonation reveal the primary component and direction of magnetization. This direct...

We generalize the brick polytope of V. Pilaud and F. Santos to spherical subword complexes for finite Coxeter groups. This construction provides polytopal realizations for a certain class of subword complexes containing all cluster complexes of finite types. For the latter, the brick polytopes turn out to coincide with the known realizations of generalized associahedra, thus opening new perspec...

For an arbitrary Coxeter group W , Reading and Speyer defined Cambrian semilattices Cγ as sub-semilattices of the weak order onW induced by so-called γ-sortable elements. In this article, we define an edge-labeling of Cγ , and show that this is an EL-labeling for every closed interval of Cγ . In addition, we use our labeling to show that every finite open interval in a Cambrian semilattice is e...

Despite the protracted history of life on earth spanning well over 3.8 Ga, fossil record of the Precambrian (>543 Ma) largely documents only microscopic life. The mostly simple Precambrian life forms were followed by a sudden explosive radiation of multicellular animals at the turn of the Cambrian period (543-490 Ma) between 530 and 520 Ma ago, when almost two-thirds of the animal phyla make th...

We describe many different realizations with integer coordinates for the associahedron (i.e. the Stasheff polytope) and for the cyclohedron (i.e. the Bott-Taubes polytope) and compare them to the permutahedron of type A and B respectively. The coordinates are obtained by an algorithm which uses an oriented Coxeter graph of type An or Bn respectively as only input and which specialises to a proc...

The Ordovician System, cropping out in southern and west-central Jordan, consists entirely of a 750 m thick clastic sequence that can be subdivided into six formations. The lower Disi Formation starts conformably above the Late Cambrian Umm Ishrin Formation. According to Cruziana furcifera occurring in the upper third of the Disi Formation, an Early Ordovician age is con®rmed. The Disi Formatio...

Fossils of the sponge Angulosuspongia sinensis from calcareous mudstones of the middle and upper part of the Kaili Formation (Cambrian Stage 5) in the Jianhe area of Guizhou province, South China, exhibit an apparently reticulate pattern, characteristic of the Vauxiidae. Energy Dispersive X-Ray Spectrometry (EDS) and Raman spectroscopy analysis indicate the presence of silica in the skeletal el...