I don't have immediate access to the text of this new article and I am unsure if it names a new species of Dimetrodon.
Kirstin S. Brink, Mark J. MacDougall & Robert R. Reisz (2019)
Dimetrodon (Synapsida: Sphenacodontidae) from the cave system at Richards Spur, OK, USA, and a comparison of Early Permianâaged vertebrate paleoassemblages.
The Science of Nature 106:2Â (advance online publication)
The Early Permian Richards Spur locality is unique in preserving a highly diverse faunal assemblage in a cave system, composed of synapsids, reptiles, and anamniotes. However, the presence of Dimetrodon, the most common synapsid of Early Permian localities of the southwestern USA, has never been recorded from the site. Here, we describe for the first time the morphology and histology of a small neural spine with the distinctive figure-8 shape attributable to Dimetrodon. Additionally, histological analysis of previously described sphenacodontid teeth suggests the presence of a derived species of Dimetrodon at the Richards Spur locality. The presence of this derived synapsid, typical of the later occurring Kungurian localities of Texas and Oklahoma, is unexpected at the stratigraphically older Richards Spur locality. The cave system at Richards Spur preserves mainly basal synapsid taxa, including small caseid, varanopid, and sphenacodontid skeletal remains. The presence of a derived species of Dimetrodon suggests not only that this animal was more widespread than previously thought, but that there are different patterns of Early Permian synapsid evolution in different ecological settings.
David MarjanoviÄ &Â Michel Laurin (2019)
Phylogeny of Paleozoic limbed vertebrates reassessed through revision and expansion of the largest published relevant data matrix
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The largest published phylogenetic analysis of early limbed vertebrates (Ruta M, Coates MI. 2007. Journal of Systematic Palaeontology 5:69â122) recovered, for example, Seymouriamorpha, Diadectomorpha and (in some trees) Caudata as paraphyletic and found the "temnospondyl hypothesis" on the origin of Lissamphibia (TH) to be more parsimonious than the "lepospondyl hypothesis" (LH)--though only, as we show, by one step. We report 4,200 misscored cells, over half of them due to typographic and similar accidental errors. Further, some characters were duplicated; some had only one described state; for one, most taxa were scored after presumed relatives. Even potentially continuous characters were unordered, the effects of ontogeny were not sufficiently taken into account, and data published after 2001 were mostly excluded. After these issues are improved--we document and justify all changes to the matrix--but no characters are added, we find (Analysis R1) much longer trees with, for example, monophyletic Caudata, Diadectomorpha and (in some trees) Seymouriamorpha; Ichthyostega either crownward or rootward of Acanthostega; and Anthracosauria either crownward or rootward of Temnospondyli. The LH is nine steps shorter than the TH (R2; constrained) and 12 steps shorter than the âpolyphyly hypothesisâ (PH--R3; constrained). Brachydectes (Lysorophia) is not found next to Lissamphibia; instead, a large clade that includes the adelogyrinids, urocordylid "nectrideans" and aÃstopods occupies that position. As expected from the taxon/character ratio, most bootstrap values are low. Adding 56 terminal taxa to the original 102 increases the resolution (and decreases most bootstrap values). The added taxa range in completeness from complete articulated skeletons to an incomplete lower jaw. Even though the lissamphibian-like temnospondyls Gerobatrachus, Micropholis and Tungussogyrinus and the extremely peramorphic salamander Chelotriton are added, the difference between LH (R4; unconstrained) and TH (R5) rises to 10 steps, that between LH and PH (R6) to 15; the TH also requires several more regains of lost bones than the LH. Casineria, in which we tentatively identify a postbranchial lamina, emerges rather far from amniote origins in a gephyrostegid-chroniosuchian grade. Bayesian inference (Analysis EB, settings as in R4) mostly agrees with R4. High posterior probabilities are found for Lissamphibia (1.00) and the LH (0.92); however, many branches remain weakly supported, and most are short, as expected from the small character sample. We discuss phylogeny, approaches to coding, methods of phylogenetics (Bayesian inference vs. equally weighted vs. reweighted parsimony), some character complexes (e.g. preaxial/postaxial polarity in limb development), and prospects for further improvement of this matrix. Even in its revised state, the matrix cannot provide a robust assessment of the phylogeny of early limbed vertebrates. Sufficient improvement will be laborious--but not difficult.