[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: The Return of More New Papers - Dinosaur monophyly
I see what Tony Thulborn's saying, but I didn't think Dinosauria could
be polyphyletic by accepted definitions (/Passer/+/Triceratops/ or
/Megalosurus/+/Iguanodon/+/Cetiosaurus/, etc.), even it turned out to
include crocs. Which wouldn't be disastrous in my opinion.
Jerry D. Harris wrote:
Thulborn, T. 2006. On the tracks of the earliest dinosaurs: implications
for the hypothesis of dinosaurian monophyly. Alcheringa 30:273-311.
ABSTRACT: From the record of dinosaurian skeletal remains it has been
inferred that the. origin and initial diversification of dinosaurs were
rapid events, occupying an interval of about 5 million years in the Late
Triassic. By contrast numerous reports of dinosauroid tracks imply that
the emergence of dinosaurs was a more protracted affair extending
through much of the Early and Middle Triassic. This study finds no
convincing evidence of dinosaur tracks before the late Ladinian. Each of
the three dinosaurian clades - Theropoda, Sauropodomorpha, Ornithischia
- produced a unique track morphotype that appears to be an independent
modification of the chirotherioid pattern attributed to stern-group
archosaurs (thecodontian reptiles). The existence of three divergent
track rnorphotypes is consistent with the concept of dinosaurian
polyphyly but can be reconciled with the hypothesis of dinosaurian
monophyly only by invoking many and rapid reversals in the locomotor
anatomy of early dinosaurs. The origin of dinosaurs was not the
correlate or consequence of any single event or process, be it global
change, competitive replacement, or opportunism in the wake of mass
extinction. Instead the origin of dinosaurs is envisaged as a series of
three cladogenetic events over an interval of at least 10 million years
and possibly as much as 25 million years. This scenario of dinosaurian
polyphyly is as well-supported by fossil evidence as is the currently
favoured view of dinosaurian monophyly.
--
Palaeontography: http://palaeo.jconway.co.uk