Unser Haushund: Eine Spitzmaus im Wolfspelz? - Wolf-Ekkehard ...

366Zusammenfassung in der Wikipedia zu Eomaia (last modified on 27 April 2013):“In 2013, a much larger study of mammal relationships (including fossil species) was published byMaureen O'Leary and colleagues. The study, which examined 4541 anatomical characters of 86 mammalspecies (including Eomaia scansoria), found "100% jackknife support that Eomaia falls outside of Eutheriaas a stem taxon to Theria", and so could not be considered a placental or a eutherian as previouslybelieved.” 749Aber zurück zu Juramaia sinensis: In der Wikipedia (last modified on 31 May2013) werden wir zu diesem Fund zurzeit unmissverständlich wie folgt informiert:"The oldest known eutherian species is Juramaia sinensis, dated at 160 millionyears ago from the Jurassic in China.” 750Warum aber wurde J. sinensis nicht in die Arbeit von O’Leary et al. (2013)miteinbezogen? Die Antwort finden wir in den Supplementary Materials for ThePlacental Mammal Ancestor and the Post-K-Pg Radiation of Placentals (2013, p. 2):“Juramaia, a new Mesozoic specimen (19) was not available for study by our team.” 751Diese Aussage darf man wohl als überraschend bezeichnen, sind doch dieAutoren Zhe-Xi Luo (Erstautor) und Qing-Jin Meng (Koautor) der insgesamt nur 4Autoren des Nature-Papers von 2011 zu Juramaia zugleich Koautoren desScience-Papers von 2013. Luo et al. betonen – wie im Prinzip schon im Jahre 2002in ihrer Arbeit zu Eomaia – 2011, pp. 442 und 443/444 die Annäherung derpaläontologischen Befunde an die molekularen Datierung wie folgt:“Here we report the discovery of a new eutherian of 160 Myr from the Jurassic of China, which extends thefirst appearance of the eutherian–placental clade by about 35 Myr from the previous record, reducing andresolving a discrepancy between the previous fossil record and the molecular estimate for the placental–marsupial divergence.”[…] “Timing of the divergence of marsupials and placentals is critical for calibrating the rates of evolution intherian mammals, especially for molecular evolutionary studies and comparative genomic. Previously, somemolecular time estimates for marsupial and placental divergence postulated significantly older windowsfor this divergence than the then-oldest fossil records. However, these and other previous molecular estimatesdiffered widely. Several were compatible with relatively young placental intraordinal divergences (for example,ref. 10), and just about all showed wide error margins (reviewed by ref. 13). Regarding the marsupial–placental split, recent molecular rate studies provided estimates of 147.7 +/- 5.5 Myr (ref. 11), or 160 Myr(median) with a 95% highest posterior distribution of 143–178 Myr (ref. 12), or a window of 193–186 Myr (ref.9). This new eutherian fossil age is now similar to the age of placentals at 160 Myr with 95% posteriordistribution from 143 to 178 Myr by the latest molecular estimate. The age of Juramaia has now set theminimal divergence time by the fossil to coincide with the range of molecular time estimates, serving as acorroboration of the newest fossil record with the molecularclock of evolution.”Wie oben nach O’Leary at al. (2013) zitiert, ist das Zeitfenster jedoch drastischzu korrigieren (“crown clade Placentalia and placental orders originated afterthe K-Pg boundary”). Und ob es sich mit Juramaia sinensis tatsächlich um "Theoldest known eutherian species“ handelt – das sollte, so vermute ich, nochgründlich weiter untersucht werden (should really be meticulously further tested).Es werden also zurzeit zwei diametral entgegengesetzte Auffassungen zumpostulierten Stammbau der plazentalen Säugetiere vertreten: Ein Langzeitmodellund ein Kurzzeitmodell (“explosive model“) – Ironie der Situation: Zum Teil vondenselben Autoren. Erinnert mich an “Six impossible things before breakfast“ 752 .749 http://en.wikipedia.org/wiki/Eomaia (Zugriff 24. Juni 2013).750 https://en.wikipedia.org/wiki/Eutheria751 http://www.sciencemag.org/content/suppl/2013/02/07/339.6120.662.DC1/1229237OLeary.SM.pdf752 http://en.wikiquote.org/wiki/Through_the_Looking-Glass