Figure 5.Extrascapular bones of the posterior skull roof in †Chondrosteusand representatives of all genera of Acipenseridae: The
median extrascapular (excm; Character 5 ) is a midline bone that bears the commissure of the occipital canal (ocll; Character 24) in all
acipenserids. The lateral extrascapulars (excl) carry the occipital canal from the posttemporal (pt) to the median extrascapular in all
acipenserids except Pseudoscaphirhynchus,where the lateral extrascapular series includes the origin of the occipital canal (Character
56).Lateral extrascapulars typically form a series of canal bones or are variable in position, but are clustered inScaphirhynchus(Charac-
ter 60). †Chondrosteus(a-redrawn from Traquair, 1887) possesses a series of extrascapulars (exc), but no distinct median and lateral
extrascapulars.pa= parietal,st= supratemporal,op= opercle,stll= supratemporal canal,trll= trunk canal,dsl= first dorsal scute.
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(Martin Jones)
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