[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
RE: Platypuses may be older than we think...
David Marjanovic wrote:
>> The divergence between the platypus and echidna lineages undoubtedly
>> pre-dates the divergence between any two crown-group placental orders.
You don't think so? What if Rowe &c are correct? As it says in the SVP
abstract, which you kindly posted (http://dml.cmnh.org/2007Oct/msg00309.html)...
"New evidence from high-resolution X-ray computed tomography indicates that
*Teinolophos*, an Early Cretaceous fossil from Australia's Flat Rocks locality
(121-112.5 Ma), lies within the crown clade Monotremata, as a basal platypus.
Divergence of the two monotreme clades therefore had occurred in or before the
I know this contradicts Bininda-Emonds et al. (2007; Nature 446: 507-512), who
provide a molecular-clock-based divergence at around the end-K extinction for
the echidna and platypus lineages. They also favor a eutherian diversification
("hotspot") around 100 Ma, when "all four placental superorders (Afrotheria,
Euarchontoglires, Laurasiatheria and Xenarthra)" emerged. Thus, if
Bininda-Emonds &c are correct on the divergence times of the major placental
groups (and way off on the intra-monotreme divergence times), then no
crown-group placental "order" could have appeared prior to the platypus-echidna
split. Rowe &c place the latter "in or before the Early Cretaceous." So the
first monotreme had taken the plunge way back when placentals were just a
twinkle in the eye.
>> Given just how distinct the two modern monotreme lineages are,
> Surely the same must hold for cows and dolphins...?
I meant temporally. Though I'm not denying they're highly morphological
distinct - although this is obviously difficult to quantify.
>> the names Platypoda and Tachyglossa might turn out to be useful for future
>> phylogenetic usage.
Yep, Rowe &c refer to _Teinolophos_ as a "basal platypus", so perhaps we could
substitute "platypodan". _Teinolophos_, _Steropodon_, and _Kollikodon_ would
all be "basal platypodans". Tachyglossans, AFAIK, are known only from the
Peek-a-boo FREE Tricks & Treats for You!