Taxonomy
Macropoma lewesiensis an extinct coelacanth fish.
Classification of the coelacanths
Coelacanths (Infraclass Actinistia) are assigned to the Subclass Sarcopterygii (‘lobe-finned’ fishes), and include several families. Macropoma lewesiensis belongs to the Family Latimeriidae, which also includes the two species of the living coelacanth, Latimeria.
Morphological features
Fossils of Macropoma are well-preserved in the English chalk, allowing morphological features to be readily described. It is medium-sized coelacanth with the following morphological features
- body relatively deep and rounded
- premaxilla of the upper jaw and rostral bones of the skull form a solid snout, covered in large denticles
- cheek bones are well-developed
- typical features of the coelacanth lower jaw are present, including having the main coronoid bone of the jaw modified into a rounded process
- teeth are small, although some are larger and pointed - most teeth show fine ridges converging to the tip
- sensory canals open on the skull via many small pores, although some larger pores are present on the skull
- pectoral girdle is narrow
- ossified air bladder (shown in main photo) large and extends back to anal fin
- lateral line scales with enlarged and branched sensory tubes with dorsal and ventral openings (modified from Forey, 1998).