Article

A Lower Cambrian vertebrates from South China

Nature (Impact Factor: 41.46). 11/1999; 402(6757):42-46. DOI: 10.1038/46965

ABSTRACT

The first fossil chordates are found in deposits from the Cambrian
period (545-490 million years ago), but their earliest record is
exceptionally sporadic and is often controversial. Accordingly, it has
been difficult to construct a coherent phylogenetic synthesis for the
basal chordates. Until now, the available soft-bodied remains have
consisted almost entirely of cephalochordate-like animals from Burgess
Shale-type faunas. Definite examples of agnathan fish do not occur until
the Lower Ordovician (~475Myr BP), with a more questionable record
extending into the Cambrian. The discovery of two distinct types of
agnathan from the Lower Cambrian Chengjiang fossil-Lagerstätte is,
therefore, a very significant extension of their range. One form is
lamprey-like, whereas the other is closer to the more primitive hagfish.
These finds imply that the first agnathans may have evolved in the
earliest Cambrian, with the chordates arising from more primitive
deuterostomes in Ediacaran times (latest Neoproterozoic, ~555Myr BP), if
not earlier.

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    • "In addition to molecular systematics, growing research on the evolution of developmental mechanisms, or evo-devo, and availability of new fossils from Greenland (Sirius Passet) and China (Doushantuo and Chengjiang) started to impact our understanding of animal evolution. For example, ConwayMorris and Peel (1995)had hypothesized that fossils halkieriids were a stem group Eutrochozoan animals close to mollusks and brachiopods, fossil embryos provided a glimpse into early embryology (Bengston and Zhao 1997), and early fossils refined understanding of chordate origins (Shu et al. 1999). Importantly China had become more open to Western scientists starting a steady stream of discoveries of Ediacarian and early Cambrian fossils that were informative in terms of morphology, but did little to resolve relationships among animal phyla. "
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    • "Living fossil lineages are particularly well represented among among non-tetrapod vertebrates, or ''fishes'' (Nelson, 2006), a fact that is not terribly surprising when viewed in the context of their deep-time evolutionary history and current species diversity. Fossils identifiable as ''fishes'' date to the Cambrian (Shu et al., 1999, 2003) and extant species diversity of ray-finned fishes represent approximately half of the planet's current vertebrate species diversity (Stiassny et al., 2004). With such a long time span in which to diversify and the great extent to which they have done so, chance alone would dictate that many present day fish species should represent the remnants of formerly species-rich radiations (Stanley, 1979). "

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    • "The latter has 20–30 pairs of gonads that can yield 30,000 low-yolky eggs ca 90–150 μm per year (Song and Xu, 1989; Yasui and Kubokawa, 2005). Both Haikouella and Yunnanozoon, as well as the earliest putative vertebrate Haikouichthys ercaicunensis Luo, Hu & Shu (Shu et al., 1999a), similarly have two strings of glands comparable in size and number with those of Amphioxus , and thus they possibly shed a large amount of small eggs per unit time; this case could then account for the fossil concentrations of numerous individuals of Haikouella/Yunnanozoon on the same bedding plane – the result of rapid burial in the Chengjiang deposits (Han et al., 2006). The apparent great fecundity of these animals would inevitably have triggered more intense competition among the members of the Chengjiang fauna, and this is consistent with the unfolding of the three discussed main extreme directions of animal development during "
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