Parayunnanolepis xitunensis bears a pair of nasal capsules underlying the rostral plate between the eyes, resembling Romundina but differing from most euantiarchs, whose nasal capsules are encased in the preorbital recess in front of the eyes. The study provides new anatomical details of the headshield including the sclerotic capsules, the visceral side of the rostral and pineal plates, and the dorsal profile of the endocranium. Here we re-describe the headshield of Parayunnanolepis xitunensis, a yunnanolepidoid antiarch from the Lower Devonian of China, using X-ray computed tomography scanning. However, the condition in primitive antiarchs (i.e., the Yunnanolepidoidei) remains unclear, and the positional shift of nasal capsules in the Antiarcha has never been mentioned.

The diversity in positions of nasal capsules has been well documented in various subgroups of placoderms or jawed stem gnathostomes. The braincase morphology appears less extreme than that of Brindabellaspis, and is in some respects more reminiscent of a basal arthrodire such as Kujdanowiaspis. The high level of detail enables description of the main arterial, venous and nerve canals of the skull, and other perichondrally ossified endocranial structures such as the palatoquadrate articulations, the endocranial cavity and the inner ear cavities.

This virtual approach offers the possibility to connect with certainty all the external foramina to the blood and nerve canals and the central structures, and thus identify accurate homologies without destroying the specimen. Despite some loss of material along an oblique crack, most of the internal structures are remarkably preserved, and most of the missing structures can be reconstructed by symmetry. This is the first model of an early gnathostome skull produced using this technique, and as such represents a major advance in objectivity compared to past descriptions of placoderm neurocrania on the basis of grinding series.

Here we present a near-complete three-dimensional skull of Romundina stellina, a small Early Devonian acanthothoracid from the Canadian Arctic Archipelago, scanned with propagation phase contrast microtomography at a 7.46 μm isotropic voxel size at the European Synchrotron Radiation Facility, Grenoble, France. The acanthothoracid placoderms are among the phylogenetically most basal and morphologically primitive gnathostomes, but their neurocranial anatomy is poorly understood. Placoderms are considered as the first jawed vertebrates and constitute a paraphyletic group in the stem-gnathostome grade.

Knut Miller Atlas Of Anatomy