Abstract:
Fishes of the order Tetraodontiformes previously have been known with assurance from as early as the Lower Eocene, about 55 MYA. Two Upper Cretaceous taxa, Protriacanthus d'Erasmo (1946) from Comen, Slovenia, about 90 MYA, and Plectocretacicus Sorbini (1979) from Hakel, Lebanon, about 95 MYA, were referred by their authors to the tetraodontiforms, respectively in the vicinity of triacanthoids and ostracioids. Both of these taxa were originally based on single specimens in which insufficient details of critical osteological features were exposed, and their familial and ordinal placement were open to question. Based on additional specimens now available, including acid preparations of several specimens of both species, we believe that they represent two new families (Protriacanthidae and Plectocretacicidae) of tetraodontiforms with numerous features that are more primitive than previously reported for the order. We describe a third taxon, the new genus Cretatriacanthus (and new family Cretatriacanthidae), based on a single specimen from the Upper Cretaceous of Nardò, Italy, about 70 MYA. It shares most of the numerous primitive features of Protriacanthus and Plectocretacicus.
Although many of their features are primitive, all three of these Upper Cretaceous taxa possess the most salient derived features of tetraodontiforms (e.g., reduced number of vertebrae, no anal-fin spines, reduced number of pelvic-fin rays, absence of certain skull bones, and, when present, long posterior process of pelvis with its halves in close contact or fused). The three Upper Cretaceous taxa share four derived features (absence of teeth, modified scales around base of pelvic spine, presence of subocular shelf, and diminutive size) that unite them in a clade herein recognized as the superfamily Plectocretacicoidea, whereas all other tetraodontiforms (those from the Lower Eocene to present) are united by seven derived features. Within the Plectocretacicoidea, five derived features support the sister-group relationship of Protriacanthus and Plectocretacicus.
Each of the three Upper Cretaceous taxa has a mosaic of primitive and specialized features, with some of the latter being independently derived relative to similar features of triacanthoids, balistoids, and ostracioids. The evidence indicates that the Plectocretacicoidea (presently known from 70 to 95 MYA) are the morphologically primitive sister group of all other tetraodontiforms (presently known from 55 MYA to Recent).
