. Bulletin. Natural history. RUSSELL: AMERICAN MOSASAURS 19 median dorsal axis of tlie parietal. The frontal is narrow anteriorly and forms die posteriormost portion of the internarial bar, enclosing the premaxillary shaft in a tight "V"-shaped notch (Clidastes, Plotosaunts, Platccarpus, Ectenosaurus and Plesiotylosaurus). In Tylosaurus the internarial bar is formed almost en- tirely of the premaxilla which penetrates deeply into the anterior end of the frontal. The frontal dilates behind the external narial opening, in some instances forming a rounded posterior boundary for the nari
. Bulletin. Natural history. RUSSELL: AMERICAN MOSASAURS 19 median dorsal axis of tlie parietal. The frontal is narrow anteriorly and forms die posteriormost portion of the internarial bar, enclosing the premaxillary shaft in a tight "V"-shaped notch (Clidastes, Plotosaunts, Platccarpus, Ectenosaurus and Plesiotylosaurus). In Tylosaurus the internarial bar is formed almost en- tirely of the premaxilla which penetrates deeply into the anterior end of the frontal. The frontal dilates behind the external narial opening, in some instances forming a rounded posterior boundary for the narial fenestrae (Plotosaurus, Platccarpus and Tylosaurus), in others the anterolateral margins diverge poste- riorly in a more regular manner (Clidastes, Plesiotylosaurus). In Mosasaiirus the anterior edges of the frontal parallel the cranial midline behind the pointed. Text-fig. 3. Frontal of Mosasaurus maximus (NJSM 11052, X %). posterior ends of the external nares, then in front of the antorbital wall diverge at a nearly 180° angle for a short distance, and finally turn posteriorly and a little laterally to continue in a straight line back to the posterior base of the bone. In Platccarpus and Ectenosaurus the lateral margins of the frontal curve out- wardly back to a point above the antorbital wall. Here they turn gently medially and then diverge again, forming a shallow sulcus over the orbits. The frontal is similar in Clidastes but is relatively narrower and has straighter margins. In Prognathodon the frontal is shorter and broader than in Platecarpus. Its anterior margins diverge in straight lines back to the prominence above the antorbital wall and from here posteriorly parallel the longitudinal axis of the skull, show- ing no signs of a supraorbital emargination. In Tylosaurus, Plesiotylosajirus and Plotosaurus the frontal margins are more regular than in the foregoing genera and not so strongly divergent posteriorly. In the former two genera the margins are slightly conv
Size: 1764px × 1417px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookc, bookcentury1900, bookdecade1920, booksubjectnaturalhistory
