Title: Neurocranial anatomy of Seymouria from Richards Spur, Oklahoma Authors: K.D. Bazzana, B.M. Gee, J.J. Bevitt, R.R. Reisz Journal: Journal of Vertebrate Paleontology vol. 39(5), article e1694535 DOI to paper: 10.1080/02724634.2019.1694535 (email Kayla at kayla[dot]bazzana[at]mail[dot]utoronto[dot]ca if you don't have access or have questions, concerns, compliments, etc.) General summary: The first (first-authored) paper by my labmate / fellow PhD student Kayla Bazzana and more data coming out of our collaboration with Joseph Bevitt and ANSTO! Slowly crawling back down the tetrapod phylogeny after my second-author paper on the latest Richards Spur varanopid with Sigi last year, this time to a stem amniote, the seymouriamorph Seymouria. With an increasing interest among early tetrapod workers on the inner anatomy, mostly the braincase region, of various groups, one of the groups that remains undersampled are stem amniotes like seymouriamorphs that are phylogenetic intermediates between non-amniotes like temnospondyls and crown amniotes like synapsids (realistically every group to stand to be sampled more). Among the specimens that we've had scanned at ANSTO are the most complete cranial specimens of Seymouria from Richards Spur. Like the recently described varanopid, previous material described from the site was isolated vertebrae and limb bones, which are generally not very useful for species-level identification among tetrapods (three species of Seymouria in this instance). This would have been the first CT analysis of Seymouria if not for a broader comparative paper published by Jozef Klembara, arguably the leading expert in seymouriamorphs, a week after ours had been formally accepted for publication that included some data on a Texas specimen. That paper mostly focused on the endosseous labyrinth, basically what the soft tissue contained within the bones would have looked like, and ours is a much more detailed analysis with more information on the hard tissue anatomy. Is there some famous guy named Seymour who the taxon was named after? The taxon is actually named after the town of Seymour in north-central Texas. It was originally called Oregon City since many of the early settlers came from Oregon, but apparently that name was already taken, so it got switched; the city homepage suggests it came from a local cowboy named Seymour Munday.
Controversies on the synotic tectum The synotic tectum bridges the otic capsules and may not always ossify depending on the clade. However, it is more of a region than a defined osteological structure. For example, in some stem tetrapods, the paired opisthotics, part of the otic capsules, extend far medially to meet at the midline. In others, the synotic tectum is open, without any ossification filling it. The most frequent feature is a distinct unpaired ossification called the supraoccipital, which is supposed to be a crown amniote feature, although it's also found in diadectomorphs (e.g., Berman et al., 1992; Berman, 2000) whose position as either very derived stem amniotes has recently been questioned in favour of a placement at the base of Synapsida (Klembara et al., 2019). As you can imagine, the presence or absence of an ossification of the synotic tectum warrants at least one phylogenetic character in many analyses, and often many more. However, determining the homology of synotic tectum ossifications is tricky for extinct taxa because various precursors could be responsible for an ossification that fills the same space, so they may not necessarily be homologous. We identified a novel structure in the synotic tectum of Seymouria that appears to be an unpaired element at the time of death, although there is some suggestion that it might have been two paired elements that fused together. Regardless, it looks very different from the supraoccipital that we see in Paleozoic amniotes like recumbirostrans and captorhinids, which is more distinct from the overlying postparietals and with more developed topology. As such, we refrained from calling it a 'supraoccipital,' and we'll need more sampling to fill in the gaps to get a better handle on the variety and distribution of synotic tectum ossifications in Paleozoic tetrapods. Refs
David Marjanović
1/27/2020 04:55:48 pm
The pressure relief window is amazing, because even turtles don't have it today. They have tympanic ears, but the pressure in the inner ear just goes in a circle. At some frequencies & amplitudes it probably interferes with the movements of the stapes. Comments are closed.
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About the blogA blog on all things temnospondyl written by someone who spends too much time thinking about them. Covers all aspects of temnospondyl paleobiology and ongoing research (not just mine). Categories
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