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A primitive sarcopterygian fish with an eyestalk
M Zhu1, X Yu, P E Ahlberg
1Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing.
Nature
|March 10, 2001
Summary
New fossil fish, Achoania, reveals early bony fish evolution and challenges ideas about the divergence of actinopterygians and sarcopterygians. This discovery highlights parallel evolution in early osteichthyans.
Area of Science:
- Paleontology
- Evolutionary Biology
- Vertebrate Zoology
Background:
- Early Devonian osteichthyans (bony fish) fossils like Psarolepis and an Australian braincase challenge existing theories on osteichthyan origins and divergence.
- These fossils exhibit a mix of derived sarcopterygian and actinopterygian traits alongside primitive features, suggesting significant parallelism in early osteichthyan evolution.
- Previous interpretations were limited by poor phylogenetic resolution.
Purpose of the Study:
- To describe a new basal sarcopterygian fish, Achoania gen. et sp. nov.
- To clarify the morphological gap between Psarolepis and more derived sarcopterygians.
- To investigate the presence of eyestalk attachments in early osteichthyans.
Main Methods:
- Fossil description and comparative morphology of Achoania gen. et sp. nov.
- Phylogenetic analysis incorporating new fossil data.
- Examination of fossil specimens for specific anatomical features, such as eyestalk attachments.
Main Results:
- Achoania gen. et sp. nov. is described, representing a basal sarcopterygian that bridges the morphological gap between Psarolepis and higher sarcopterygians.
- Eyestalk attachments were identified in both Achoania and Psarolepis.
- This finding indicates that eyestalk attachments, previously thought to be exclusive to non-osteichthyans, are present in basal sarcopterygians.
Conclusions:
- The discovery of Achoania refines our understanding of sarcopterygian evolution and the early diversification of bony fishes.
- The presence of eyestalk attachments in basal sarcopterygians and actinopterygian-like fossils suggests this feature evolved earlier than previously understood.
- Early osteichthyan evolution likely involved substantial parallelism between the major lineages of bony fishes.
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