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| Subject: | | Re: Close Relations? For us evos to help me answer this |
| From: | |
Ozraptor4
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posted
Wed, Jun 15 2005, 11:23pm
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>Pikaia seems to be the earliest fossil chordate, which appears to be something
>like the wee, filterfeeding lancet still found today. It has all the basic parts that
> define a chordate, a hollow nerve cord, a dorsal notochord, pharyngeal slits,
> and a muscular extending >beyond the bunghole. Every cordate has these
> features at least briefly in their ealy life.
fossil-otaku nitpick time!
Well, while Pikaia certainly is a very nice archetypal chordate, its trophy for oldest chordate has been rescinded - theres another Early Cambrian Lagerstätten besides the Burgess Shale, the Chengjiang Fauna of Yunnan Province, Peoples Republic of China which is between 10-15 million years older than the Burgess. While the 2 Lagerstätten share many genera, the Chinese site has vastly superior soft-body preservation - While the Burgess has only produced a handful of fossil chordates, all representing a single taxon (Pikaia gracilens) - the Chengjiang has produced hundreds (possibly over 1000) of complete basal chordates representing at least 8 species:
* Cathaymyrus diadexus Shu, Zhang & Morris, 1996
* Cathaymyrus haikouensis Luo & Hu, 2001.
* Haikouella lanceolata Chen, Huang & Li, 1999.
* Haikouichthys ercaicunensis Luo, Hu & Shu, 1999.
* Myllokunmingia fengjiaoa Shu, Zhang & Han, 1999.
* Shankouclava shankouense Chen, Huang, Peng, Chi, Wang & Feng (and a partridge in a pear tree...), 2003
* Yunnanozoon lividum Hou, Ramsköld & Bergström, 1991.
* Zhongxiniscus intermedius Luo & Hu, 2001.
Cathaymyrus and Zhongxiniscus are generalised basal chordates similar to Pikaia (Z. seems to be a tad more advanced). Shankouclava is the world's oldest tunicate/seasquirt. Haikouella (300+ specimens) seems to lie just outside the Craniata. Myllokunmingia and Haikouichthys (250+ specimens) are early jawless vertebrates, decked out with such decadant extravagances as paired-eyes, nostrils (in H.), ray-supported dorsal fins and vertebral arcualia. I'm sure their neighbours thought they would never amount to anything.
Yunnanozoon is a weirdo that could either represent an extinct group of early chordates, an early hemichordate or something teetering on the chordate/hemichordate borderline.
A form known as Cheungkongella was also thought to be a seasquirt but has since turned out to be a syonym of Phlogites, a weird lophophorate (ie. not a chordate).
(my rendition of the Chengjiang)
http://www.geocities.com/ozraptor4/chengjiang.html
http://www.sc
iencenews.org/pages/sn_arc99/11_6_99/fob1.htm
http://palaeo.gly.bris.ac.uk/Palaeofiles/Lagerstatten/chngjang/exordium.html
http://www.gs-rc.org/repo/repoe.htm
Thereis a remote possibility that even the Chengjiang chordates may soon be supplanted as the oldest fossil chordates - a purported early chordate has turned up in the 560 million year old Ediacaran fauna in South Australia. The specimen has yet to be scientifically described and many experts are doubtful of it's chordate affinity (looks like a Kimberella to me...) but I'll wait and see...
http://www.abc.net.au/science/news/ancient/AncientRepublish_984724.htm
Cheers
O4 |
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| Subject: | | Re: Close Relations? For us evos to help me answer this |
| From: | |
jellyroll
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posted
Thu, Jun 16 2005, 2:14am
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I enjoyed that nitpicking, thank you! |
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| Subject: | | Re: Close Relations? For us evos to help me answer this |
| From: | |
Ozraptor4
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posted
Thu, Jun 16 2005, 5:38am
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>Myllokunmingia and Haikouichthys (250+ specimens)
Oops! Make that 500+ specimens. Typical, I turn my head for 5 minutes and Haikouichthys start pouring out of the woodwork.
D.-G. Shu, S. Conway Morris, J. Han, Z.-F. Zhang, K. Yasui, P. Janvier, L. Chen, X.-L. Zhang, J.-N. Liu,Y.Li & H.-Q. Liu (2003) "Head and backbone of the Early Cambrian vertebrate Haikouichthys", NATURE VOL 421:526-529 |
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| Subject: | | Re: Close Relations? For us evos to help me answer this |
| From: | |
Rainbow Medicine Man
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posted
Thu, Jun 16 2005, 3:53pm
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Awsome, Ozraptor, thank you very much, teacher. I enjoyed this. |
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