Allodelphinidae

Kimura and Barnes (2016, pp. 3–4) diagnose the family as follows:

A family of the odontocete superfamily Platanistoidea including relatively large dolphinlike odontocetes having estimated adult total body lengths of approximately three to five meters, cranial lengths of approximately one meter, having cranium with elongate and narrow rostrum, rostral length approximately four times braincase length, premaxillae and maxillae both reaching anterior rostral extremity, premaxillae and maxillae fused together distally, mesorostral canal open dorsally only in posterior part of rostrum, anteroposteriorly elongated groove present on lateral side of rostrum approximately following maxilla-premaxilla suture, posterior maxillary foramen located posterolateral to dorsal naris and not close to posterior end of premaxilla, posterolateral sulcus and posteromedial sulcus on premaxilla shallow or absent, posterior ends of premaxillae separating from lateral sides of corresponding nasal bones, posterior ends of premaxillae relatively thin dorsoventrally and narrow (not expanded transversely), nasal bones small and narrow transversely, nuchal crest thick anteroposteriorly, lateral lamina of pterygoid forming bony plate extending posteriorly from palate and contacting anterior falciform process of squamosal, palatine bone extending posteriorly from palate dorsal to lateral lamina of pterygoid, forming part of bony plate within orbit, and also contacting anterior falciform process of squamosal, preorbital lobe of pterygoid sinus absent, postorbital lobe of pterygoid sinus absent, posterior sinus not present in anterior surface of paroccipital process; internal acoustic meatus of the petrosal opening anteromedially, superior process of the petrosal wide, smooth and almost flattened, posterior process of the petrosal atrophied; tympanic bulla with elongated and pointed anterior process, outer lip inflated and with smooth ventral surface; mandible with transversely narrow symphyseal portion, anteroposteriorly elongated and somewhat compressed dorsoventrally, mandibular symphysis very long and firmly ankylosed, elongate sulcus present on lateral surface of symphyseal part of dentary; all teeth single rooted, crowns tall and slender; neck relatively long with cervical vertebrae proportionally large and with anteroposteriorly elongated centra, atlas vertebra bearing separate dorsal and ventral transverse processes, axis vertebra with relatively large odontoid process; caudal vertebrae enlarged; humerus with diaphysis proximodistally elongated and oval in cross section, humeral head proportionally large; propensity for distal trochlea of humerus to fuse to olecranon process of ulna; radius and ulna equal to or less than length of humerus.[3]

Allodelphis and Zarhinocetus were formerly classified as members of Delphinidae and Squalodontidae in the original descriptions.[4][5] In his overview of eastern North Pacific marine mammal assemblages, Lawrence Barnes noted that these two genera did not belong in those families and reassigned Allodelphis to Platanistidae, while removing Squalodon errabundus from Squalodon.[6] Barnes later realized that Allodelphis was more primitive than extinct members of Platanistidae and Squalodelphinidae and placed it and "S." errabundus in a separate family, Allodelphinidae.[7]