Paleontologists Take Fresh Look at Carboniferous Tetrapodomorph Fish

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Paleontologists have used high-resolution micro-CT and synchrotron tomography to scan two well-preserved 3D specimens of the tetrapodomorph fish Cladarosymblema narrienense, an ancestor of the first land animals. They’ve updated the original description of the species and revealed never-before-seen details of its anatomy.

Cladarosymblema narrienense: (A) lateral head reconstruction of Cladarosymblema narrienense; color-coded as follows: dermal skull roof (dark blue), cheek (light blue), lower jaw (pale green), opercular series (purple), and pectoral (dark green); bones marked with ‘?’ remain unknown in this species; (B-E) micro-CT 3D rendering of all segmented bones in the holotype. Image credit: Clement et al., doi: 10.7717/peerj.12597.

Cladarosymblema narrienense lived in what is now Australia during the Carboniferous period, some 330 million years ago.

This fish was first described in 1995 from the Early Carboniferous Raymond Formation in Queensland on the basis of several well-preserved specimens.

Cladarosymblema narrienense was a member of Megalichthyidae, a group of tetrapodomorph fish that existed from the Devonian period to the Permian period, typically living in freshwater environments, and they were large, predatory animals.

“This fish from Queensland is one of the best preserved of its kind in the entire world, in perfect 3D shape, which is why we chose to work on it,” said Professor John Long, a paleontologist at Flinders University.

In the new study, Professor Long and colleagues studied two well-preserved specimens of Cladarosymblema narrienense.

They found evidence that this fish had a brain similar to its eventual terrestrial descendants, compared to the brains of other fishes which remained living in water.

They revealed and described never before seen morphological details of the gill arch skeleton, the shoulder girdle and the palate bones (the upper mouth roof area).

“This helps us to understand the functional morphology and relationships of Cladarosymblema,” said Dr. Alice Clement, a paleontologist at Flinders University.

“Additionally, a cranial endocast — mould of the internal cavity of this fish’s unusually large skull — gives clues as to the shape of the brain of this animal.”

“The area for the pituitary gland — the so-called the ‘master gland’ — is relatively large, suggesting a significant role in regulating various important endocrine glands.”

The results were published in the journal PeerJ.

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A.M. Clement et al. 2021. A fresh look at Cladarosymblema narrienense, a tetrapodomorph fish (Sarcopterygii: Megalichthyidae) from the Carboniferous of Australia, illuminated via X-ray tomography. PeerJ 9: e12597; doi: 10.7717/peerj.12597

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