dorsal sail造句

• A third dorsal sail extends from the spine down the back and tail.
• In " Dimetrodon ", the neural spines develop into long, narrow, cylindrical projections that support a tall vertical dorsal sail that ends near the base of the tail.
• However, " Sphenacodon " had a low crest along its back, formed from blade-like bones on its vertebrae ( neural spines ) instead of the tall dorsal sail found in " Dimetrodon ".
• The deep-skulled but low-crested " Sphenacodon " would be outside the " Secodontosaurus "-" Dimetrodon " clade and would retain characteristics of an earlier stage of sphenacodontid evolution before a tall, thin-spined dorsal sail evolved.
• Alternative scenarios in which " Dimetrodon ", " Sphenacodon ", and " Ctenospondylus " are united in a deep-skulled clade ( Sphenacodontinae ) that excludes " Secodontosaurus " require that either ( 1 ) tall, rod-like neural spines are plesiomorphic in the Sphenacodontidae so that the common ancestor of all four genera had a tall dorsal sail that was retained in " Secodontosaurus " and in " Dimetrodon ", but was lost by character reversal in " Sphenacodon ", or ( 2 ) the common ancestor of all four genera lacked a tall dorsal sail ( and so more closely resembled " Sphenacodon " ), in which case both " Secodontosaurus " and " Dimetrodon " would have evolved their very similar-looking tall sails completely independently as an apomorphy.
• Alternative scenarios in which " Dimetrodon ", " Sphenacodon ", and " Ctenospondylus " are united in a deep-skulled clade ( Sphenacodontinae ) that excludes " Secodontosaurus " require that either ( 1 ) tall, rod-like neural spines are plesiomorphic in the Sphenacodontidae so that the common ancestor of all four genera had a tall dorsal sail that was retained in " Secodontosaurus " and in " Dimetrodon ", but was lost by character reversal in " Sphenacodon ", or ( 2 ) the common ancestor of all four genera lacked a tall dorsal sail ( and so more closely resembled " Sphenacodon " ), in which case both " Secodontosaurus " and " Dimetrodon " would have evolved their very similar-looking tall sails completely independently as an apomorphy.