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In analogy to molecular dating, the following SVP meeting abstract presents
the idea of using morphological data for deriving divergence date estimates.
My thesis supervisor had the same idea; we'll put it into my thesis, but we
won't be able to sell it as new anymore.
And in case anyone wonders, I'm a touch-typist :o)
Thomas DeCecchi & Hans Larsson: Tempos and modes of theropod evolution, p.
Genomic clocks, a method [sic] for dating lineage divergences through the
steady regular accumulations of sequence mutations, has become a standard
tool in evolutionary biology[,] yet is of limited use in paleontology.
Genomic information is generally absent in fossils but a large amount of
data is preserved in skeletal morphology. We present a novel method that
estimate[s] a "morphological clock" to examine divergence times within
Theropoda. Origination times for major clades of theropods are calculated
using a recent large and broad-ranging data set from [the book] "The
Dinosauria" and grounded with known geological times for specimens. This
method has also been extended to predict the origin of theropods and can,
when combined with traditional "relative" rate measurements, allow for
comparisons between different evolutionary trajectories within Theropoda.
The results presented give the first insight into absolute evolutionary
rates within theropod evolution. They provide data for the evaluation of
modular evolutionary rates across the skeleton and transformational
evolutionary modes across the lineage. Using this method we have determined
the origin of Theropoda at during the Late [sic] Anisian, 5 -- 7 million
years before the [Carnian] Ischigualasto fauna, a date consistent with other
estimates of theropod origins. Our data shows that at Eumaniraptora
(Deinonychosaurians + Aves) there is a noted increase in the rate of
character evolution coincident with the origin of flight, especially in the
pectoral region. Beginning at the node Eumaniraptora a separate
morphological clock using a different calibration points [sic] is proposed
to estimate early avian divergence times, since this increase in character
rate evolution during this transition is not adequately modeled by the
general theropod trend.