Clade | |
Subclade |
Taxon | |
Taxon |
Ornithischia
|
Nominal Author | Seeley 1888 |
2nd Nominal Author | |
Taxon Status | ACTIVE |
Comments | Ornithischia was first defined by Padian and May (1993) using Triceratops and “birds” as specifiers. Sereno (1998) subsequently replaced “birds” with Neornithes, linking Ornithischia with Saurischia and Dinosauria as a node-stem triplet. Benton (2004) cited Sereno’s definition of Ornithischia in The Dinosauria, whereas Weishampel (2004) and Norman (2004) presented first-order alternatives in the same volume without explanation, the former using Tyrannosaurus in place of Neornithes and the latter using Iguanodon and Cetiosaurus as internal and external specifiers, respectively. Presumably Norman’s choice of specifiers was based on their antiquity, although Megalosaurus, not Cetiosaurus, was the first named basal saurischian. Regardless, neither Megalosaurus nor Cetiosaurus are well understood, and both have functioned historically as repositories for disparate taxa. Megalosaurus, Cetiosaurus and Iguanodon, in addition, are less nested within Dinosauria than alternative specifiers. The practice of selecting first-named or historically significant taxa for specifiers can decrease stability and clarity in definitions. For these reasons, the active definition is a first-order revision of the original definition (Padian and May 1993). It employs species as specifiers and, should sauropodomorphs prove to be more closely related to ornithischians than to theropods, maintains the taxonomic content of Ornithischia by adding Saltasaurus loricatus as a second external specifier. |
Potential Synonomy | Predentata |
Active Phylogenetic Definition | |
Active Definition |
The most inclusive clade containing Triceratops horridus Marsh 1889 but not Passer domesticus (Linnaeus 1758) or Saltasaurus loricatus Bonaparte and Powell 1980.
|
Shorthand |
> Triceratops horridus but not Passer domesticus or Saltasaurus loricatus. |
Definitional Author |
Sereno 2005 |
Definition Status | checked |
Definition Type | STEM |
Node-Stem Triplet | STEM |
Other Triplet Taxa |
Dinosauria, Saurischia |
Specifiers | |
Specifier(s) A |
Triceratops horridus |
Specifier(s) B | |
Specifier(s) C |
Passer domesticus, Saltasaurus loricatus
|
Qualifiers | |
+Taxon | |
-Taxon | |
Datum | |
Taxonomic Content | |
Publication Year |
Unknown Unknown Unknown 1993 |
Inactive Taxon Status | |
Rejection Criteria | |
Critique | |
Definitional History #1 | |
Earliest Record | Those dinosaurs closer to Triceratops than to birds. |
Latest Record | Padian and May 1993:379 |
Range (My) | |
Range (My) |
Triceratops, birds |
Range (My) |
Definitional History #2 | |
Earliest Record | All dinosaurs closer to Triceratops than to Neornithes. |
Latest Record | Sereno 1998:61 |
Range (My) | |
Range (My) |
Triceratops, Neornithes |
Range (My) |
Definitional History #3 | |
Earliest Record | All dinosaurs more closely related to Triceratops than to Tyrannosaurus. |
Latest Record | Weishampel 2004:323 |
Range (My) | |
Range (My) |
Triceratops, Tyrannosaurus |
Range (My) |
Definitional History #4 | |
Earliest Record | All dinosaurs closer to Iguanodon than to Cetiosaurus. |
Latest Record | Norman et al. 2004:325 |
Range (My) | |
Range (My) |
Iguanodon, Cetiosaurus |
Range (My) |
Definitional History #5 | |
Earliest Record | |
Latest Record | |
Range (My) | |
Range (My) | |
Range (My) |
Definitional History #6 | |
Earliest Record | |
Latest Record | |
Range (My) | |
Range (My) | |
Range (My) |
Definitional History #7 | |
Earliest Record | |
Latest Record | |
Range (My) | |
Range (My) | |
Range (My) |
Definitional History #8 | |
Earliest Record | |
Latest Record | |
Range (My) | |
Range (My) | |
Range (My) |
Definitional History #9 | |
Earliest Record | |
Latest Record | |
Range (My) | |
Range (My) | |
Range (My) |
Definitional History #10 | |
Earliest Record | |
Latest Record | |
Range (My) | |
Range (My) | |
Range (My) |