Intracranial anatomy of Romundina stellina Ørvig 1975 (Vertebrata, Placodermi, Acanthothoraci) revealed by phase contrast synchrotron imaging

• Acanthothoracid placoderms are considered amongst the most basal of primitive gnathostomes. However, their endocranial morphology is poorly understood, and only one genus (Brindabellaspis) has been described in detail. Here we present a synchrotrongenerated 3D reconstruction of a nearly complete skull of Romundina stellina, a taxon established in 1975 by the Norwegian-born Swedish palaeontologist Tor Ørvig based on remains from the Lochkovian (Lower Devonian) of Prince of Wales Island, Canadian Arctic Archipelago. The specimen was imaged with propagation phase contrast microtomography on the ID19 beamline of the ESRF, using a 7.45 µm isotropic voxel size. Most structural features of the fossil are very well preserved, allowing missing elements to be virtually rebuilt by symmetry. This permitted reconnection of the external foramina and blood vessel/nerve canals, and alignment of the central/internal structures. Expanding on Ørvig’s original interpretations, our virtual models show the vasculature of the skull bones, and indicate establishment of successive dermal over perichondral bone layers. The perichondral bone wrapping the endocranial cavity, in between the trigeminal and vagus nerve (and the inner ears), shows a “lace” pattern, which is otherwise unknown in vertebrates (presumably because of the lack of data). The significance of this trait is unclear but it is not an artifact of taphonomy or scanning.

Subject headings

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

NATURVETENSKAP  -- Biologi -- Evolutionsbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Evolutionary Biology (hsv//eng)

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vet (subject category)

kon (subject category)