Tikémi
lambeosaure
Nombre de messages : 193
Age : 41
Localisation : Bruxelles
Emploi : doctorante
Loisirs : lecture, puzzles
Date d'inscription : 07/06/2006
 | | Sujet: Yanoconodon allini Jeu 15 Mar - 11:40 | |
| Un nouveau mammifère décrit dans Nature : Zhe-Xi Luo, Peiji Chen, Gang Li and Meng Chen (2007). A new eutriconodont mammal and evolutionary development in early mammals. Nature 446: 288-293Abstract: Detachment of the three tiny middle ear bones from the reptilian mandible is an important innovation of modern mammals. Here we describe a Mesozoic eutriconodont nested within crown mammals that clearly illustrates this transition: the middle ear bones are connected to the mandible via an ossified Meckel's cartilage. The connected ear and jaw structure is similar to the embryonic pattern in modern monotremes (egg-laying mammals) and placental mammals, but is a paedomorphic feature retained in the adult, unlike in monotreme and placental adults. This suggests that reversal to (or retention of) this premammalian ancestral condition is correlated with different developmental timing (heterochrony) in eutriconodonts. This new eutriconodont adds to the evidence of homoplasy of vertebral characters in the thoraco-lumbar transition and unfused lumbar ribs among early mammals. This is similar to the effect of homeobox gene patterning of vertebrae in modern mammals, making it plausible to extrapolate the effects of Hox gene patterning to account for homoplastic evolution of vertebral characters in early mammals. Introduces Yanoconodon allini (gen. et sp. nov.), family Jeholodentidae (nov.) PS : comme d'habitude, le pdf et les infos supplémentaires sont chez bibi  | |
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Tikémi
lambeosaure
Nombre de messages : 193
Age : 41
Localisation : Bruxelles
Emploi : doctorante
Loisirs : lecture, puzzles
Date d'inscription : 07/06/2006
| | Sujet: Re: Yanoconodon allini Ven 16 Mar - 12:45 | |
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