Greg Laden's Blog

... has been found. Inside the fish's skull, in fact. This is from a chimaeroid fish, which today are fairly rare but during the Carboniferoius were quite common and diverse. There are really two aspects of this find that are especially interesting. One is the 3D imagery that was obtained of the ancient fossilized brain, and the other is the analysis of the fish's ear canals. The brain is cool just because it is cool (and shows some interesting morphology). The ear canal study is interesting because it shows a pattern different than expected for a fish: This creature was probably really good at keeping track of it's position in the horizontal plane, but not the vertical plane. That is odd for a fish.

From the abstract:

...During Carboniferous times, 358-300 million years (Myr) ago, [the chimaeroids] underwent a remarkable evolutionary radiation, with some odd and poorly understood forms, including the enigmatic iniopterygians that were known until now from poorly informative flattened impressions. Here, we report iniopterygian skulls found preserved in 3 dimensions in ≈300-Myr-old concretions from Oklahoma and Kansas. The study was performed by using [ a mixture of traditional and novel technologies, fancy software, and analytical techniques] which revealed their peculiar anatomy. Iniopterygians also share unique characters with living chimaeroids, suggesting that the key chimaeroid skull features were already established 300 Myr ago. Moreover [visualization] of an articulated skull revealed a strikingly brain-shaped structure inside the endocranial cavity, which seems to be an exceptional case of soft-tissue mineralization of the brain, presumably as a result of microbially induced postmortem phosphatization. This was imaged with exceptional accuracy by using holotomography, which demonstrates its great potential to image preserved soft parts in dense fossils.

The anatomy of iniopterygians. (A) Reconstruction of Sibyrhynchus denisoni (based on ref. 5, not to scale). (B and C) Part (B) and counterpart (C) of a phosphatic nodule from the Pennsylvanian of Oklahoma (AMNH OKM38) containing the braincase and shoulder girdle of Sibyrhynchus sp. (D-F) Threedimensional reconstruction of the same specimen, obtained from conventional X-ray CT images, showing the braincase in dorsal (D), ventral (E), and lateral (F) view, with associated teeth. (G-I) Three-dimensional reconstruction of the braincase, shoulder girdle, and pectoral fin elements of a sibyrhynchid iniopterygian from the Pennsylvanian of Kansas (KUNHM 21894), based on SR- CT images. Braincase in dorsal (G), posterior (H), and ventral views, with articulated shoulder girdles and pectoral fin radials (I). (Scale bar, 5 mm; f.IX and f.X, foramina for glossopharyngeus and vagus nerves).

I quickly add that previous finds of soft tissue preserved have turned out to be something else. (See: The seductive siren of soft tissue preservation: Ancient dinosaur flesh wasn't ancient. Or dinosaur flesh.)

Braincase anatomy and exceptional brain preservation in a sibyrhynchid iniopterygian from the Pennsylvanian of Kansas. (A and B) Articulated skull preserved in a nodule (KUNHM 22060) (see also Fig. S1) in dorsal (A) and anterior (B) view (arrow points forward). (C-Q), Three-dimensional reconstructions and putative preserved brain structures of the same specimen, obtained from SR- CT images (and holotomography for brain details). (C-H), Braincase, teeth, and lower jaw in lateral (C), anterior (D), ventral (E), posterior (F), and dorsal (G) view, showing by transparency the outline of the endocranial cavity and labyrinth (H). (I-K), Selected transverse (I and J), and horizontal (K) SR- CT (holotomography) slices through the calcite-filled endocranial cavity, showing the probably phosphatized brain at the level of the rhombencephalon (I), hypophysis (J), and roof of the optic tectum and cerebellum (K). (L-N) Reconstruction of the endocranial cavity and otic capsule in dorsal (L and M) and lateral (N) view, showing the putative brain by transparency (M and N). (O-Q), reconstruction of the putative phosphatized brain in dorsal (O), ventral (P), and lateral (Q) view. (Scale bar, 5 mm for A-N and 1 mm for I--K and O-Q. Asc, anterior semicircular canal; Cer, cerebellum; Ed, endolymphatic duct; Hsc, horizontal semicircular canal; Hyp, hypophysis; Olftr, canals for olfactory tracts; Opch, optic chiasm; Optec, optic tectum; Psc, posterior semicircular canal; II, optic nerve; III?, oculomotorius nerve?; IV?, trochlear nerve?; X?, roots of vagus nerve?).

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