Ancient baby penis worm hits the news

China is proving to be the repository of a vast wealth of well-preserved ancient faunas, thanks to several lagerstãtten, the most famous being that which hosts early ancestral birds that show links with dinosaurs.  But Chinese strata with exceptional preservation also occur in Cambrian sediments, close enough to the first appearance of preservable life forms to make any out-of-the-ordinary finds especially revealing.  Ten years ago many palaeontologists scoffed at reports of trilobite embryos being unearthed in southern China, yet there has been a steady flow of material that opens up what might be called “palaeoembryology”.  Being able to describe and analyse an entire life cycle of an organism is vital in studies of the inter-relatedness of living metazoans.  The lack of data on fossil life histories to some extent thwarts attempts to place extinct animals accurately within an evolutionary scheme.  Palaeontologists from the University of Bristol and Peking University have therefore put such studies on the map through finding exquisitely preserved Cambrian embryos of what is now a rare and bizarre animal group, but one thought to lie at the root of the explosive radiation of the arthropods, which includes insects (Dong, X. et al.  2004.  Fossil embryos from the Middle and Late Cambrian period of Hunan, south China.  Nature, v. 427, p. 237-240).  They are in eggs, and therefore had yet to hatch and develop further; true embryos, from their initial development to the last stage before emerging.  They are Scalidophores, which include today the individual phylla of Priapulida, Kynorhyncha and Loricefera, all marine worm-like animals (the priapulids are the notorious, and fortunately rare, penis worms from their evocative contours).  Interestingly. the embryonic stages clearly indicate direct development from egg to adult, rather than going through the intermediary larval stage that characterises most insects and other invertebrates.  Such direct development seems to be a primitive evolutionary stage from which more complex life-histories developed later.  Penis worms are well known to grow hugely once hatched, so the search is on for a fully grown adult from the Cambrian of southern China, as well as early developmental stages of other animal groups..

See also: Budd, G.E. 2004.  Lost children of the Cambrian.  Nature, v. 427, p. 205-206.

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