Ornithischia Seeley, 1887

Nesbitt, Sterling J., 2011, The Early Evolution Of Archosaurs: Relationships And The Origin Of Major Clades, Bulletin of the American Museum of Natural History 2011 (352), pp. 1-292 : 210-211

Ornithischia Seeley, 1887

ORIGINAL DEFINITION: Those dinosaurs closer to Triceratops than to birds ( Padian and May, 1993).

REVISED DEFINITION: Stem: The most inclusive clade containing Triceratops horridus Marsh, 1889 , but not Passer domesticus Linnaeus, 1758 , or Saltasaurus loricatus Bonaparte and Powell, 1980 (sensu Sereno, 2005).

TEMPORAL RANGE: Late Triassic (?Carnian–early Norian Pisanosaurus mertii Casamiquela, 1967 ) to Late Cretaceous (Maastrichtian, Triceratops horridus Marsh, 1889 ).

SUPPORT: (1) Buccal emargination separated from the ventral margin of the antorbital fossa of the maxilla (23-1)*. (2) Predentary present (151-1)*. (3) Dorsally expanded coronoid process of the mandible (161-1)*. (4) Mandibular fenestra reduced, anteroposterior length less than maximum depth of dentary ramus (162-2)*. (5) Extensive planar wear facets across multiple maxillary/dentary teeth (168-2)*. (6) Medial or lateral overlap of adjacent crowns in maxillary and dentary teeth (170-1). (7) Maxillary and dentary crowns apicobasally short and subtriangular (173-1). (8) Anterior (5 preacetabular, 5 cranial) process of the ilium long and extends anterior to the acetabulum but shorter than the posterior process of the ilium (269-1). (9) Pubis rotated posteroventrally to lie alongside the ischium (opisthopubic) (279-1). (10) Prepubic process present (280-1). (11) Anterior trochanter (5 M. iliofemoralis cranialis insertion) forms a steep margin with the shaft and separated from the shaft by a marked cleft (308-2). Unknown in Pisanosaurus . (12) Anterior trochanter shelf proximal to the fourth trochanter absent (311-0). Unknown in Pisanosaurus . (13) Posterolateral flange of the distal portion of the tibia present and extends well posterior to the fibula (334-2). (14) Transversely compressed calcaneum (379-1).

Other possible synapomorphies: AC- CTRAN: Facial portion of the maxilla equal in length or longer than portion posterior to anterior edge of fenestra (14-1); palpebral(s) present (147-1); dorsal margin of the neural spine of the axis expanded posterodorsally (179-0); third cervical vertebra subequal in length to the axis centrum (183-0); primordial trunk vertebrae incorporated into the sacrum (205-1); insertion of a sacral vertebra between the first primordial sacral vertebra (207-1); primordial caudal vertebrae incorporated into the sacrum (206-1); proximal portion of the pubis, articular surfaces with the ilium and the ischium continuous (286-0). Unknown in Pisanosaurus ; posterolateral flange of the distal portion of the tibia extends well posterior to the fibula (334-2); gastralia absent or few (412-2).