Sophisticated CT scanning of the cranium of a Queensland fish fossil has
given new insights to explain how fish first left the water to invade land
about 370 million years ago.
Supported by the Australian Research Council and international experts, the
new research led by Flinders University paleontologists studied
Cladarosymblema narrienense, a 330 million-year-old fish from the
Carboniferous Period found in Queensland, which is an ancestor of the first
land animals or four-limbed vertebrate tetrapods.
Cladarosymblema is a type of 'megalichthyid' fish, a group which existed
from the Devonian-to-Permian periods, typically living in freshwater
environments, and they were large, predatory animals. Through scanning the
fossil, they found evidence this fish had a brain similar to its eventual
terrestrial descendants, compared to the brains of other fishes which
remained living in water.
"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,"
says Professor John Long, Strategic Professor in Paleontology at Flinders
University.
While this fish was first described in 1995, by Professor Long and others
who had earlier explored and excavated the Queensland fossil site, parts of
its anatomy have remained unknown—although using Australia's largest cabinet
CT scanner, located at Flinders University's Tonsley campus, as well as the
Australian Synchrotron in Melbourne, has allowed researchers to unlock new
data from this fossil.
New information obtained from often unseen internal bones has been revealed
in these scans—particularly in 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," says Dr. Alice Clement, lead author of the new paper and
part of the Flinders Paleontology Group.
"Additionally, a cranial endocast (mold 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 (so-called the 'master gland')
is relatively large, suggesting a significant role in regulating various
important endocrine glands."
The study, titled "A fresh look at Cladarosymblema narrienense, a
tetrapodomorph fish (Sarcopterygii: Megalichthyidae) from the Carboniferous
of Australia, illuminated via X-ray tomography," by Alice Clement, Richard
Cloutier, Jing Lu, Egon Perilli, AntonMaksimenko and John Long—has been
published in PeerJ.
The researchers conducted a phylogenetic analysis, which confirms that the
megalichthyid fish form a monophyletic group (a natural clade).
Cladarosymblema is found to be one of the more derived members of the group.
Reference:
Alice M. Clement et al, A fresh look at Cladarosymblema narrienense, a
tetrapodomorph fish (Sarcopterygii: Megalichthyidae) from the Carboniferous
of Australia, illuminated via X-ray tomography, PeerJ (2021).
DOI: 10.7717/peerj.12597
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