Tiny Middle Devonian Millerosteus provides another Bauplan for the bits and pieces of Late Silurian Psarolepis

More complete taxa,
like Milerosteus, can provide insight into less complete taxa, like Psarolepis (Fig 1). In this case, the latter does not preserve the posterior parietal (skull cap), which is restored here (in purple).

Restoring that cranial bone helps one compare and contrast Psarolepis with Millerosteus, which is otherwise a good match (Fig 1). IMHO, without Millerosteus, Psarolepis remains enigmatic.

Yet another reason to keep adding taxa.

Long 2021 considered Psarolepis
close to the onychodontiformes, like Onychodus.

Zhu et al 2002 considered Psarolepis
“A primitive fish close to the common ancestor of tetrapods and lungfish.”

The LRT does not confirm either hypothesis of interrelationships.

Instead, Psarolepis turns out to be a derived placoderm, with marginal teeth.

Psarolepis romeri
(Yu 1998; Zhu et al. 2014; Long 2001; Late Silurian; mandible 3.3cm) is known from parts of its face and a complete mandible perhaps lacking a medial spiral tooth whorl at its tip. Other elements include a dorsal spike, plus cheek and mandible elements with tooth rows. Here Psarolepis nests with the placoderm, Millerosteus and the shark, Maghriboselache. The upturned and short rostrum includes large incurrent and excurrent nares. Nearly all the pebbled bones of the cranium are fused together, except for a straight suture between the prefrontals and parietals. An internal premaxilla separates toothed lacrimals, as in sharks, with teeth directed medially.. The toothy mandible is well preserved. Spikes lead the pectoral fins.

Millerosteus minor
(Stensiö 1959, Middle Devonian, 8.5cm long) was twice the size of Bianchengichthys and half the length of Coccosteus with a relatively larger orbit. Pelvic fins and a tail were preserved. This tiny arthrodire placoderm was close to Psarolepis, and a clade of traditional sharks, including Maghriboselache and Ferromirum.

Readers may remember
prior efforts at nesting Psarolepis elsewhere. That was prior to the restoration of the posterior parietal and postparietal. Those earlier errors are updated here.

References
Long JA 2001. On the relationships of Psarolepis and the onychodontiform fishes. Journal of Vertebrate Paleontology. 21 (4): 815–820.
Yu X 1998. A new porolepiform-like fish, Psarolepis romeri, gen. et sp. nov. (Sarcopterygii, Osteichthyes) from the Lower Devonian of Yunnan, China. Journal of Vertebrate Paleontology. 18 (2): 261–274.
Zhu M and Yu X 2002. A primitive fish close to the common ancestor of tetrapods and lungfish. Nature 418: 767–770.

wiki/Psarolepis
wiki/Millerosteus