Lepospondyl ontogeny

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com




A new non-dino paper that may be of interest:


Jennifer C. Olori (2013)
Ontogenetic sequence reconstruction and sequence polymorphism in
extinct taxa: an example using early tetrapods (Tetrapoda:
Lepospondyli).
Paleobiology 39(3): 400-428
doi: http://dx.doi.org/10.1666/12031
http://www.bioone.org/doi/abs/10.1666/12031




Ontogenetic sequence reconstruction is challenging particularly for
extinct taxa because of when, where, and how fossils preserve.
Different methods of reconstruction exist, but the effects of
preservational bias, the applicability of size-independent methods,
and the prevalence of sequence polymorphism (intraspecific variation)
remain unexplored for paleontological data. Here I compare five
different methods of ontogenetic sequence reconstruction and their
effects on the detection of sequence polymorphism, using a large
collection of the extinct vertebrates Microbrachis pelikani and
Hyloplesion longicostatum. The postcranial ossification sequences
presented here for those taxa are the first examples known for extinct
lepospondyls. Sequences were reconstructed according to skull length,
trunk length, increasing number of ontogenetic events, majority-rule
consensus, and Ontogenetic Sequence Analysis (OSA). Results generally
were in agreement, demonstrating that paleontological data may be used
to robustly reconstruct developmental patterns. When reconstructing
sequences based on fossils, size-based methods and OSA are more
objective and less dependent on preservational bias than other
techniques. Apart from the other methods, OSA also allows for
statistical analysis of observed and predicted polymorphism. However,
OSA requires a large sample size to yield meaningful results, and
size-based methods are justified in paleontological studies when
sample size is limited by poor preservation. Different methods of
reconstruction detected different patterns of sequence polymorphism,
although across all methods the magnitude of sequence variation for M.
pelikani and H. longicostatum (1.3-3.4%) was within the lower range of
values reported for extant vertebrates. Compared with other extinct
and extant tetrapods, all sequence reconstruction methods consistently
showed that M. pelikani and H. longicostatum exhibit advanced
ossification of the pubis and delayed ossification of the scapula.
However, the postcranial ossification sequences of these two taxa
largely are congruent with those of other tetrapods, suggesting an
underlying conservative ancestral pattern that evolved early in
tetrapod history.