. Bulletin of the British Museum (Natural History), Geology. EVOLUTION OF THE SNOUT IN ACTINOPTERYGIANS 3H (Text-fig. 18D), Nematoptychius greenocki (Text-fig. 18F)). This pattern is still retained in much later forms such as Lawnia taylorensis (Text-fig. 18H) from the Permian and Pteronisculus arambourgi (Text-fig. 18A) and Birgeria groenlandica (Text-fig. 18B) from the Lower Triassic. The rostro-premaxillary in all these examples bears teeth and contains the ethmoid commissure, while the antorbital which lies posterior to it still retains the characteristic " Y " shaped division of
. Bulletin of the British Museum (Natural History), Geology. EVOLUTION OF THE SNOUT IN ACTINOPTERYGIANS 3H (Text-fig. 18D), Nematoptychius greenocki (Text-fig. 18F)). This pattern is still retained in much later forms such as Lawnia taylorensis (Text-fig. 18H) from the Permian and Pteronisculus arambourgi (Text-fig. 18A) and Birgeria groenlandica (Text-fig. 18B) from the Lower Triassic. The rostro-premaxillary in all these examples bears teeth and contains the ethmoid commissure, while the antorbital which lies posterior to it still retains the characteristic " Y " shaped division of the infraorbital sensory canal system. In the antorbital the anteriorly directed branch of the infraorbital canal extends forwards passing through the rostral process and then into the rostro-premaxillary as the ethmoid commissure (see p. 280). The antorbital may or may not bear teeth ventrally, depending upon where the fragmen- tation occurred. Thus the antorbital bears teeth in such forms as Cosmoptychius striatus (Text-fig. 18C), Watsonichthys pectinatus (Text-fig. 18D) and Mesonichthys aitkeni (Text-fig. 18E), while teeth are not present on the antorbital of Pteronisculus arambourgi (Text-fig. 18A), Birgeria groenlandica (Text-fig. 18B), Nematoptychius greenocki (Text-fig. 18F), Moythomasia nitida (Text-fig. 18G) and Lawnia taylorensis (Text-fig. 18H). na1 na1. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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