Fossil juvenile coelacanths from the D evonian of S outh A frica shed light on the order of character acquisition in actinistians

A new coelacanth genus from the F amennian ( U pper D evonian) of S outh A frica is described, principally from presumed juveniles. Serenichthys kowiensis gen. et sp. nov. uniquely shares with D iplocercides a ventral expansion of the elbow‐like lachrymojugal, as well as a symmetrical diphycercal tail supported by expanded neural and haemal spines and radials. S erenichthys is distinguished from D iplocercides by a number of derived characters, including possession of longer anterior parietals, a more crescent‐shaped postorbital with a more anteriorly positioned infraorbital canal, and a far smaller squamosal, which is well separated from the skull roof. By contrast, S erenichthys appears to lacks a second dorsal fin lobe, a derived feature present in D iplocercides . Most specimens of S erenichthys are between 3 and 6 cm in length. They have large eyes, and dermal bones of the skull ornamented with long wavy ridges, similar to the dermal ornament of other D evonian coelacanths such as G avinia . Larger isolated operculae also collected from the W aterloo F arm locality and attributed to S erenichthys indicate that with growth the ridges on the dermal bones transformed into elongate tubercles, reminiscent of those of D iplocercides and C arboniferous taxa. Phylogenetic analysis resolves S erenichthys as the sister group of H olopterygius and all known post‐ D evonian coelacanths. The clade including the unusual leaf‐shaped coelacanths, the D evonian H olopterygius and C arboniferous Allenypterus , branches from the coelacanth lineage immediately crownward of S erenichthys . The presence of abundant juveniles within an estuarine setting strongly parallels the discovery of similarly sized juveniles of R habdoderma exiguus together with eggs and yolk‐sack larvae in the U pper C arboniferous M azon C reek biota. It is therefore argued that S erenichthys , like R habdoderma , was using the sheltered estuarine environment as a nursery. © 2015 The Linnean Society of London