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Science 16 June 2006:
Vol. 312. no. 5780, p. 1569
DOI: 10.1126/science.312.5780.1569a
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This Week in Science

Figure 1
CREDIT: YOU ET AL.
Because many of the earliest well-described birds are from extinct lineages, it has been difficult to resolve the early evolution of the lineage that led to modern birds. An early ornithuran bird, Gansus yumenensis, has been known only from fragmentary fossils. You et al. (p. 1640) now describe several fossils which show that this Early Cretaceous bird has many derived features. It was also well adapted for an aquatic-amphibian lifestyle--the fossils even show what appears to be webbing in the feet. The early embryos of some animals, such as mollusks, develop through the formation and cleavage of polar lobes to form functionally specific cells. Chen et al. (p. 1644 please see the news story by Unger) describe fossils of what appear to be polar-lobed embryos in rocks dated to the Late Precambrian in China. This developmental strategy originated near the time that the first animals appeared.

Figure 2
CREDIT: CHEN ET AL.




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