Hemichordates are known as fossils from at least the earliest mid-Cambrian Period (ca. 510 Ma) and are well represented in the fossil record by the graptolithinid pterobranchs ("graptolites"), which include the most abundantly preserved component of Paleozoic macroplankton. However, records of the soft tissues of fossil hemichordates are exceedingly rare and lack clear anatomical details. Galea...

Sponge remains have been identified in the Early Vendian Doushantuo phosphate deposit in central Guizhou (South China), which has an age of approximately 580 million years ago. Their skeletons consist of siliceous, monaxonal spicules. All are referred to as the Porifera, class Demospongiae. Preserved soft tissues include the epidermis, porocytes, amoebocytes, sclerocytes, and spongocoel. Among ...

In the annals of Earth history, few associations have proven more iconic or durable than that between animals and oxygen. As early as 1919, the experimental physiologist August Krogh (1) explored the relationship between O2 and animal anatomy, and 40 y later J. R. Nursall (2) posited explicitly that metazoans appear as fossils only in uppermost Proterozoic rocks because pO2 was insufficient to ...

A synthesis of the knowledge Schist-Greywacke Domain (SGD) in Portugal is here presented. Until recently, this sequence assumed designation Dúrico-Beirão Supergroup composed by Douro Group (DG) and Beiras (BG). The DG considered Neoproterozoic – Cambrian age BG age. identification mapping an unconformity as Cadomian identified Spain, which splits “lower Alcudian” “upper Alcudian”, a turning poi...

This paper presents a phylogenetic analysis of the ‘‘Fallotaspidoidea,’’ a determination of the biogeographic origins of the eutrilobites, and an evaluation of the timing of the Cambrian radiation based on biogeographic evidence. Phylogenetic analysis incorporated 29 exoskeletal characters and 16 ingroup taxa. In the single most parsimonious tree the genus Fallotaspidella Repina, 1961, is the s...

A well-preserved Cambrian section in the Zanskar Valley of northern India has previously been interpreted to record the transition from a passive to an active tectonic margin related to Cambrian–Ordovician orogenesis. This interpretation has been used to support the tectonostratigraphic interpretation of other successions across the Tethyan Himalaya. Our detailed paleoenvironmental analysis sig...

ECOS III The slender, spine-shaped, apatitic protoconodonts appear in the fossil record near the Precambrian-Cambrian boundary and persist through the Cambrian . Recent work (Szaniawski 1 982, J. Paleont. 56) suggests that protoconodont elements were homologous to the grasping spines of modern chaetognaths . Paraconodonts are similar to protoconodonts in their mode of growth by basal accretion ...