[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Non-Dino articles: Tetrapod vertebrae and temnospondyls
Stephanie E. Pierce, Per E. Ahlberg, John R. Hutchinson, Julia L.
> Molna, Sophie Sanchez, Paul Tafforeau, and Jennifer A. Clack (2013)
> Vertebral architecture in the earliest stem tetrapods.
Julia L. Molnar.
Here we describe the three-dimensional vertebral architecture of the
> Late Devonian stem tetrapod Ichthyostega using propagation
> phase-contrast X-ray synchrotron microtomography.
<Mr. Burns>Excellent!</Mr. Burns>
Our scans reveal [...] a possible posterior-to-anterior vertebral
> ossification sequence
Ah, like in *Eusthenopteron* and unlike any crown tetrapod.
and the first evolutionary appearance of ossified sternal elements.
One of the most intriguing features relates to the positional
> relationships between the vertebral elements, with the pleurocentra
> being unexpectedly sutured or fused to the intercentra that directly
> succeed them, indicating a ‘reverse’ rhachitomous design.
Whoa. The longer people look at *Ichthyostega*, the more bizarre it becomes!
Comparison of Ichthyostega with two other stem tetrapods,
> Acanthostega and Pederpes, shows that reverse rhachitomous vertebrae
> may be the ancestral condition for limbed vertebrates.
That, actually, is not surprising (though it hadn't reached
textbook-wisdom status yet); some temnospondyls have hinted in that
direction. What's surprising is the suturing or fusion in *Ichthyostega*.
Rainer R. Schoch (2013) The evolution of major temnospondyl clades:
> an inclusive phylogenetic analysis. Journal of Systematic
> Palaeontology (advance online publication)
Huh. I had no idea he was working on this. It'll be interesting to find
out why the tree he gets is so different from that which Julia McHugh is
getting (PhD thesis, presented at last year's SVP meeting). And I really
hope there are enough outgroups; the single one J. McHugh uses doesn't
Phylogenetic analysis of a large dataset (72 taxa, 212 characters)
Almost 3 times as many characters as taxa. Sadly, that's progress in
a potential clade (or grade) of small terrestrial taxa containing
> Balanerpeton and Dendrerpeton (‘Dendrerpetontidae’).
Heh. Ever since *B.* was described in 1994, people (myself included)
have been unable to figure out if it's the sister-group of *D.* or one
node away. :-)
The remainder of Temnospondyli fall into four robust and undisputed
> clades: (1) Dvinosauria; (2) Zatracheidae plus Dissorophoidea; (3)
> Eryopidae; and (4) Stereospondyli. These taxa are together referred
> to as Rhachitomi (node).
That wasn't a good name to reanimate. It was nicely dead, rotting in the
old literature as a term for non-stereospondyl temnospondyls and
occasional other limbed vertebrates with rhachitomous vertebrae (as
described above by Pierce et al.).
Florian Witzmann & Rainer R. Schoch (2012) Reconstruction of cranial
> and hyobranchial muscles in the Triassic temnospondyl Gerrothorax
> provides evidence for akinetic suction feeding. Journal of Morphology
> (advance online publication) DOI: 10.1002/jmor.20113
> The cranial and hyobranchial muscles of the Triassic temnospondyl
> Gerrothorax have been reconstructed based on direct evidence
> (spatial limitations, ossified muscle insertion sites on skull,
> mandible, and hyobranchium) and on phylogenetic reasoning (with
> extant basal actinopterygians and caudates as bracketing taxa). The
> skeletal and soft-anatomical data allow the reconstruction of the
> feeding strike of this bottom-dwelling, aquatic temnospondyl. The
> orientation of the muscle scars on the postglenoid area of the
> mandible indicates that the depressor mandibulae was indeed used for
> lowering the mandible and not to raise the skull as supposed
> previously and implies that the skull including the mandible must
> have been lifted off the ground during prey capture. It can thus be
> assumed that Gerrothorax raised the head toward the prey with the
> jaws still closed.
So it wasn't a toilet-lid animal. :-(