Diadectids and Diadectomorpha are basal lepidosauromorph reptiles once thought to be the closest anamniotes (amphibians) to amniotes. Wikipedia still promotes this antiquated hypothesis. Here (Fig. 1) you’ll see that Diadectes and Procolophon both evolved from a sister to Romeria primus as recovered by the large reptile tree.
Today we’ll look at a humpback diadectid, Diadectes (formerly Diasparactus) zenos (UC679). You’ll note the neural spines are much larger than in sister taxa.
The high neural spines of D. zenos were robust, more like those of a bison, than a Dimetrodon. That’s why they may have supported fatty or meaty tissues, rather than a sail.
The skull of D. zenos is poorly known, but the palate is well exposed. The dorsal ribs are short, as is the tail. Note that the axis bone (cervical #2) grows from D. zenos to D. sammiguelensis (Fig. 2).
Earlier we looked at a putative diadectid, Stephanospondylus, which is actually a diadectid mimic that was ancestral to turtles. It had no neural spines, and neither do turtles, because they don’t need back muscles when they have a shell.
The anterior dorsal ribs of D. zenos were the widest among diadectids. These helped support that large pectoral girdle.
Please contact the writer(s) of the Wikipedia article and encourage them to update their account of Diadectes. You can’t be derived from reptiles and still be a ‘reptile-like amphibian.’
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