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Mammalia - Ungulata - Platanistidae
If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
|A. T. Boersma et al. 2017||Dilophodelphis is a small- to medium-sized odontocete (approx. 2.27 m in total length), which belongs to Platanistoidea (sensu ) based on two synapomorphies: emargination of the posterior edge of the zygomatic process by the sternomastoid muscle fossa with the skull in lateral view (character 52) andventral surface of the posterior process of the periotic, concave along a straight path perpendicular to its long axis (character 66). Character 52 shows state reversals among the platanistoids. The remaining four platanistoid synapomorphies recovered in our phylogenetic analysis are either not preserved or obscured by matrix in the holotype of Dilophodelphis.
Dilophodelphis differs from all known Waipatiidae, Squalodelphinidae and Allodelphinidae in having a distinct dorsal crest in the antorbital–supraorbital region (character 8). Dilophodelphis differs from waipatiids and squalodelphinids in having a deeply grooved lateral rostral suture between the premaxilla and the maxilla (character 3); in having a small tooth diameter as a percentage of postorbital skull width (character 45); in having the robust and globose/rectilinear antorbital processes of the maxilla in dorsal view (character 46) and in having the ventral edge of the zygomatic process almost straight in lateral view (character 53). Dilophodelphis further differs from waipatiids and allodelphinids by having an elevated antorbital region distinctly higher than the dorsal margin of the rostrum base in lateral view (character 7); having a deep fossa in the frontal on the orbit roof at the level of the frontal groove (character 12) and having a circle-shaped dorsal outline of the zygomatic process of the squamosal in lateral view (character 18). Dilophodelphis differs from waipatiids and other platanistids in having a square-shaped pars cochlearis of the periotic (character 20).
Dilophodelphis also differs from the Waipatiidae in having a deep, ‘V’-shaped antorbital notch in relation to an anteriorly pointed antorbital process (character 6); having a cranium distinctly shorter than wide with a ratio <0.90 (character 10); wide hamular fossa of the pterygoid sinus, extending anteriorly onto the palatal surface of the rostrum (character 16); transverse thickening of the anterior process of the periotic (character 23) and in having a lateral lamina of the palatine (character 54).
Dilophodelphis differs from the Allodelphinidae in lacking an elongated rostrum (character 1), having wide premaxillae at the rostrum base (character 4), having the dorsal opening of the mesorostral groove anterior to the rostrum base narrower than the premaxilla (character 5), having a concave lateral margin of the rostrum anterior to the maxillary flange (character 41), having a deep posterolateral sulcus (character 47), having a shallow premaxillary cleft (character 50) and having the ventral surface of the posterior process of the periotic concave along a straight path perpendicular to its long axis (character 66).
Dilophodelphis belongs to the Platanistidae based on the following: medial margin of the antorbital notch made of a thin plate (character 38), and dorsal surface of the vertex markedly transversely and longitudinally convex (character 39). Dilophodelphis also shares the following characteristics with all the platanistids, excluding Araeodelphis: lateral rostral suture between premaxilla and maxilla deeply grooved (character 3), distinct dorsal crest in the antorbital–supraorbital region (character 8), antorbital process of maxilla robust and globose or rectilinear in dorsal view (character 46), and the presence of a shallow premaxillary cleft (character 50).
Dilophodelphis differs from all other known platanistids in having an enlarged tympanosquamosal recess forming a large triangular fossa medial and anteromedial to the postglenoid process (character 55). Dilophodelphis demonstrates one clear apomorphy: a deep emargination of the posterior edge of the zygomatic process by the sternomastoid fossa, in lateral view (character 52). Further features that distinguish Dilophodelphis from other platanistids are discussed in the ‘Morphological comparisons’ section of the discussion. Finally, Dilophodelphis demonstrates the following possibly plesiomorphic character states (shared with at least some squalodelphinids): deep, ‘V’-shaped antorbital notch in relation to an anteriorly pointed antorbital process (character 6); semicircular dorsal outline of the zygomatic process of the squamosal in lateral view (character 18); pars cochlearis of the periotic square-shaped in ventral view (character 20).