Taxonomy

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).