p269
動物の大分類最近の補足
Revival of old views?
Philippe et al., Phylogenomics Revives Traditional Views on Deep Animal Relationships
Curr Biol 19 706 (2009)
*128 nuclear concatenated gene data set (30k AA) including newly generated sequence data from ctenophores, cnidarians, and all four main sponge groups. With due cautions for long branch attraction.
R339 says
*The results from Philippe et al. [3] are credible as their experiments were designed to tackle long branch attraction and they successfully demonstrate its effects.
*The idea of the independent evolution of muscles, nerves etc. in ctenophores and other
eumetazoans was particularly hard to explain.
(動物)分類の常識中の訂正
*The resulting phylogeny yields two significant conclusions reviving old views
(1) Sponges (Porifera) are monophyletic and not paraphyletic (100\% bootstrap), thus undermining the idea that ancestral metazoans had a sponge-like body plan;
[C] However, their interpretation of the result is naive.
(2) The most likely position for the ctenophores is together with the cnidarians in a `coelenterate' clade.
*The Porifera and the Placozoa branch basally with respect to a moderately supported `eumetazoan' clade.
*There are just three branches of living animals on the path to the bilaterians (poriferans, placozoans, and coelenterates).
細字で書いてあるところでXenoturbellidaにも言及し，それがDeuterostomiaに属しているとしていたが，形態，分子のどれをとっても， Xenoturbella bocki はAcoelomorphaに属することに疑問の余地がない．下に引用してあるNielsenの論文が明快なレビュー．
HejnolAssessing the root of bilaterian animals with scalable phylogenomic methods
Proc Roy Soc 276 4261 (2009).
New sequence data of Acoela and Nemertodermatida are presented. An automated explicit methods for identifying and selecting common genes across different
species are developed.
Claus Nielsen After all: {¥em Xenoturbella} is an acoelomorph!
Evol Dev 12 241 (2010). (写真あり) Xenoturbella is a centimeter-long, flattened, oval, completely ciliated `worm' with a mid-ventral gut opening; it is rather common on various substrates at 40-100m depths
along the Swedish west coast. It was originally studied by Sixten Bock and subsequently described by Westblad (1950) with incorporation of Bock's material.
Its thick epithelium of cells with numerous cilia and large mucus cells have distinct similarities to those of Acoela and Nemertodermatida. The morphological evidence seems to be overwhelming in
favor of treating Xenoturbellida , Acoela, and Nemertodermatida as one group, the Acoelomorpha.¥¥
¥ind The almost complete Hox cluster of Tricladida indicates that the lack of an anus should
be interpreted as a reduction, and not as an ancestral character like that seen in the acoelomorphs. This is also supported by their embryology.
共通祖先のもつ要素をもっともたくさん保存している分類群に複雑化の可能性がもっとも開かれる
ごく最近(2009年10月)の関係した話題は Ardipithecus ramidus の手である．
9 Lovejoy Careful Climbing in the Miocene: The Forelimbs of Ardipithecus ramidus and Humans Are Primitive
S 326 70, 70e1-70e8.
(BG) Apes must support their large body mass during climbing; this is facilitated by their elongated palms and fingers.They cannot grasp objects and compress them with great dexterity and force: power grip is impossible in contrast to us. Because their thumb has not been elongate, thumb-to-palm and thumb-to-finger oppositions are more awkward for them. We are therefore much more adept at making and using tools.
* The Ardipithecus skeleton reported here has virtually complete intact hand. Ardipithecus
did not knuckle-walk; it lacked virtually all of the specializations that protect great ape hands from injury while they climb and feed in trees.
* Ardipithecus also shows that our ability to use and make tools did not require us to greatly modify our hands. Rather, human grasp and dexterity were long ago inherited almost directly from our last common ancestor with chimpanzees.