Reconstructing the wicked skull of Onychodus

Today a GIF animation
provides a great way to put together the skull and palate of the lobe-fin fish with a dental whorl, Onychodus (Fig. 1) that just cannot be matched by the printed page. And there’s no pay wall.  :  )

Onychodus sigmoides (Newberry 1857; Andrews et al. 2006; Late Devonian; 10cm skull, 47 cm length with larger specimens up to 2m in length) is a sister to the much smaller Strunius (Fig. 2). Both are members of the Onychodontida. The large, rotaring tooth whorl at the dentary and long premaxilla extending below the orbit are key traits. The jugal and postorbital are fused. The nasal contacts the orbit. Like Strunius, Onychodus links lobe fin fish to derived ray fin fish.

That tooth whorl
reduced the need for vomer fangs (though still present in Onychodus) and required space in the palate to sheath them.

Interesting note, previously overlooked due to taxon exclusion:
Taxa following onychodontids have a steeply arched palate that continues to the present in extant and extinct teleosts (most bony fish sans those listed below).

Additionally,
several derived taxa, like Strunius, and derived clades among the Teleosti, have an upturned premaxilla. This is where it starts.

Many prior studies
nest onychodontids basal to Osteoleopis (Fig. 3) and similar lobefins with an exit naris (= choana) inside the palate.

By contrast, the LRT tests taxa without bias or tradition. 
Here (Fig. 2) Onychodus and Strunius are derived sarcopterygians that lose the lobe in their fins. The twin narial opening on the side of their rostrum is also a derived trait, going the opposite way that tradition imagined, and giving rise to most of the ray-fin fish.

Earlier we looked at the smaller, more derived sister of Onychodus,
Strunius, and its phylogenetically transitional traits linking lobefins to ray fins in the LRT here.  Phylogenetic miniaturization is once again at play at the base of new major clades.

References
Andrews M, Long J, Ahlberg P, Barwick R, Campbell K 2006. The structure of the sarcopterygian Onychodus jandemarrai n. sp. from Gogo, Western Australia: with a functional interpretation of the skeleton. Transactions of the Royal Society of Edinburgh. 96: 197–307.
Newberry JS 1857. Fossil fishes from the Devonian rocks of Ohio. Geological
Survey of Ohio: Bulletin National Institute: 1–120.

wiki/Onychodontida
wiki/Strunius
wiki/Onychodus