Diodon the pufferfish
(Fig. 1) offers a vexing problem for phylogenetic scoring. Are those facial spines transformed from circumorbital bones? Ore are they novel dermal ossifications?
The two cheek spines
are placed like the lacrimal and jugal in the bowfin Amia (Fig. 2).
On the other hand,
a traditional sister taxon, Mola mola (Fig. 4), does not have circumorbital bones. As a hatchling Mola has pufferfish proportions and spines. So in the large reptile tree (LRT, 1514 taxa, Fig. 5) the spines of the pufferfish were not scored as circumorbital bones. And the ocean sunfish is an overgrown puffer!
Pufferfish are traditional members of the Tetraodontiformes
which traditionally nest with Perciformes using genomic scores. That nesting is confirmed by the LRT. Hughes et al. 2018 nested highly derived Tetraodontiformes with highly derived Lophiformes (angler fish). In the LRT, these clades are also related, though other taxa are closer.
Diodon sp. (Linneaus 1758) is the extant porcupinefish. The teeth are extremely tiny, lining or (perhaps due to tooth fusion), creating beak-like jaws. The spines are distributed all over the body and skull. Pelvic fins are absent. The tail is reduced. The pectoral fins provide thrust distinct from Mola. I do not see dorsal ribs inside the spines (Fig. 1). If present, they would presumably restrict the pufferfish’s ability to expand to a balloon like shape as it fills with water or air when threatened.
Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.