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Structurally the amphibian heart closely resembles the dipnoan, though the increased size of the left auricle is an advance.

For instance Holmgren's numerous figures of embryonic limbs of salamanders show patterns of cartilage elements that he would trace to the Dipnoan type of fin, yet it is difficult to see that the weight of evidence requires this, when the pattern does not differ in any fundamental manner from those seen in other embryonic tetrapods, and the differences that do appear may well be taken to have ontogenetic rather than phylogenetic meaning.

Further, the Dipnoan specialization of dental plates and autostylic jaw suspension, already accomplished early in the Devonian, would seem to exclude Dipnoi from possible ancestry of the Urodela, an order unknown prior to the Mesozoic, in which the teeth are essentially similar to those of late Paleozoic Amphibia, and the jaw suspension is not yet in all members autostylic.