Palaeos Vertebrates: Ornithischia 320.200 Eurypoda

*Palæos:*		Unit 320: Ornithischia
*The* *Vertebrates*		200: Eurypoda

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Ornithischia: Eurypoda

Descriptions

Characters: skull width very broad with intraorbital width at the supraorbitals widest portion of the skull; $ reduced or absent antorbital fenestra and fossa; $ three palpebrals ("supraorbitals") form dorsal rim of orbit [G90]; $ supraorbital horns; $ quadrate with shaft and pterygoid ramus in same plane (??) and no distinct lateral ramus [G90]; $ quadrate with articular surface directed ventrolaterally [G90]; $ no ("otic") notch between paroccipital process and quadrate [G90]; $ exoccipital ventral portion around foramen magnum recessed and overhung by dorsal part and supraoccipital [G90]; $ deep median keel on hard palate (may have supported soft secondary palate) from vomers & pterygoids [G90]; $ ossified epipterygoid; $ atlas neural arches fused to atlas intercentrum [G90]; parascapular spines present; $ scapular blade of roughly constant width [G90]; robust ulna with convex external margin and huge olecranal expanse; $ short metacarpals with hoof-like unguals (also on pes) [G90]; $ laterally tilted, dorsoventrally compressed preacetabular blade (of ilium, presumably); $ ilium anterior process diverges at least 35° laterally from midline [G90]; ilia broad and overhang entire pelvic area; $ ilium posterior process very short, with antitrochanter (sensu Romer) [G90]; $ partially closed acetabulum (plesiomorphic?); femur neckless, with head almost terminal [G90]; $ enlarged greater trochanter confluent with femoral head; femur with reduction of the fourth trochanter; $ pendent fourth trochanter (?!); mediolaterally expanded tibia with width about equal to craniocaudal length of proximal end; $ proximal tarsals tend to fuse with epipodials in adults [G90]; mediolaterally expanded calcaneum; metapodials short & robust; $ metatarsals short and arranged for spreading, elephantine stance (vs. compact) [G90] [S99]; $ cervical dermal rings (not sure what this means); $ cranial dermal ossicles; parasagittal arrangement of armor.

Characters: Medium to large (to 9m) [G90]; skull: skull relatively small, low and wedge-shaped with long facial region [R56]; premaxilla & mandible covered with rhamphothecae[G97]; premaxilla dorsal process does not reach lacrimal [G90]; nares elongate ovals [R56]; nasals & maxillae elongate [R56]; nasals longest bone in skull [G90]; fleshy cheeks likely present with supporting ridges on maxilla & dentary for musculature [G90] [G97]; flat parietal plate separates small upper temporal fenestrae [R56]; orbit large for small skull, with 3 supraorbital (modified palpebrals) on dorsal rim [R56]; palpebrals exclude prefrontal & frontal from orbit [G90]; postorbital triradiate [G90]; jugal overlaps quadratojugal which overlaps quadrate [G90]; lateral temporal fenestra large [R56]; squamosal triangular & roofs posterolateral section of lateral temporal fenestra [G90]; quadrate probably immovable, with simple orthal chomping [G97]; quadrate nearly vertical ventrally [R56]; $ quadrate pterygoid ramus with large oval fossa [SD92]; jaw articulation well below toothrow [R56]; $ quadrate articular ramus ("head") large, rectangular & plate-like [SD92]; occipital condyle large & mostly from basioccipital [G90]; deep median keel on hard palate (may have supported soft secondary palate) from vomers, palatines & pterygoids [G90] [G97]; rounded, ventrally directed pterygoid flanges [G90] [R56]; pterygoid quadrate ramus slants sharply back (?) [R56]; pterygoid quadrate ramus forms large fossa or fenestra [G90]; pterygoid vacuities very small [G90]; pterygoid body overlaps basisphenoid [G90]; remarkably small brain; predentary present (single?) [G90] [G97]; predentary does not extend to as far as premaxilla [G90]; jaw, particularly dentary, elongate [R56]; coronoid eminence formed into long vertical ridge [G90]; coronoid emminence largely from surangular [G90]; ridge rises and hides posterior teeth in lateral view [G90]; articular broad & thick [G90]; teeth smaller than mot ornithischians [G90]; cheek teeth with simple crowns, bulbous cingulum & few wear facets; teeth with enamel on both surfaces [R56]; significant species differences in form & arrangement of teeth, although all generally foliate [G90]; axial: $ no ossified tendons [G90] [SD92] [G97]; centra amphiplatyan anteriorly & strongly amphicoelous posteriorly [G90] [R56]; atlas arches fused to intercentrum [G90]; odontoid process present and ankylosed to axis centrum [G90]; short cervical ribs [R56]; anterior dorsal vertebrae with neural canal >50% diameter of centrum [SD92]; $ dorsal vertebrae tall due to long neural arch pedicels > 150% centrum height [SD92]; upward-slanting articulations with ribs (increased size of body cavity) [G97]; neural canal enlarged in

posterior cervicals (brachial plexus) and posterior dorsals (but cut here by septum) [G97]; diapophyses angled upward 50-60° in mid-dorsals ($ per [SD92]), decreasing to 25-40° anteriorly & posteriorly [G97]; length of transverse processes increases posteriorly [G90]; plates supported by angled diapophyses and by ribs; mid-dorsal ribs with T-shaped crossection, flat dorsally [G97]; zygapophyses meet anteromedially to form V-shaped anterior slot [G90]; centra massive [G90]; sexual dimorphism(?) with additional 1^st sacral rib (of 4-6) in some species; sacral enlargement of neural canal for sacral plexus, motor nerves for caudofemoralis and other leg muscles, and possibly glycogen body as in birds (unknown function) [G97]; caudo-sacral transition marked by assymetric vertebrae permitting lateral, but not vertical movement of tail [G97]; caudal vertebrae vary considerably with species [G90]; caudal neural canals small [G90]; anterior caudal centra laterally expanded expanded & posterior caudal centra almost square [G97]; $ posterior caudal centra almost square [SD92 & G97]; appendicular: $ parascapular spine with expanded base projecting posterolaterally from shoulder [G90] [SD92]; scapular blade becomes wider distally [G90]; $ lower scapula (acromion process) broad & plate-like (except Huayangosaurus?) [G90] [SD92] [G97]; clavicles, interclavicles & (probably) sternum absent [G90]; forelimbs short & massive [G90]; humerus short, massive, with expanded ends [G97]; humerus with large deltopectoral crest & lateral epicondyle [G90]; $ humerus with prominent triceps tubercle (see figure) and descending ridge [SD92]; manus elephantine & inflexible [G97]; $ (1? or) 2 blocklike compound carpals in adults [G90] [SD92]; $ intermedium & ulnare fused & no distal carpals [SD92][G97]; 5 short metacarpals with short digits, at least two with hoof-like unguals [G90] [G97]; long anterior process of ilium & short posterior process [R56]; short ischium with prominent emminence on dorsal midshaft [G90]; ischia in contact only distally [G90]; $ long anterior pubic process (>50% length of posterior pubic process) [SD92] [G97]; pubic anterior process distally expanded [G90]; $ acetabulum oval & laterally directed [SD92] [G97]; strong supraacetabular shelf [R56]; femur columnar, (very) long, flattened anteroposteriorly & wide [G90] [G97]; femur lacks proximal constriction ("neck") [G90]; femur lesser trochanter small or absent [G90]; femur 4th trochanter as low ridge [G90]; tibia short, massive & may be fused with fibula distally [G90]; astragalus massive & articulates proximally only with tibia [G90]; calcaneum small and variable [G90]; metatarsals short, straight & divergent [G90]; pes with I absent & V reduced, II & IV symmetrical [G97]; pedal phalanges much larger than manual [G90]; pes II-IV with hoof-like unguals [G90] [G97]; integument: 2 parasagittal rows of anterior plates & posterior spikes; $ "prominent osteoderms that angle slightly away from the sagittal plane and grade in form from ... plates to ... spikes ... ." [SD92]; plates are paired in all except Stegosaurus [G97]; plates supported richly vascularized tissue (thermoregulatory?); quadrupedal [G90], graviportal; low-level browsers.

Note: [1] Romer's concept of the Stegosauria is a little different from current ideas. He did not have Huayangosaurus, and considered Scelidosaurus to be a stegosaurian. Therefore, his description (1956: 632-33) has been selectively incorporated and should be taken with some caution. [2] The fusion of the odontode process and axis centrum is strange. Something similar occurs in ceratopsians and is believed to be an adaptation for holding up the massive head. That makes good sense -- but why here? ATW040729

Comments: It is still controversial whether or not Tatisaurus is a proper stegosaurian, but it is the earliest known (but not the most primitive) member of the dinosaurian clade Thyreophora, a group that included various types of armoured dinosaurs. It is still not very far removed from its "fabrosaur" ancestors, but within a few million years Tatisaurus, or a form like it, evolved into large armoured quadrepeds. This poorly-known ornithischian has been related to Scelidosaurus, but seems to be more closely related to the Stegosauria. Possibly it represents a form transitional between or ancestral to the two groups.

Characters: smaller than stegosaurids; skull: skull shorter, broader and taller than stegosaurids [SD92] [G97]; premaxillary attachment for beak present [SD92]; dorsal process of premaxilla short & broad [G90]; nares small [G90]; $ small oval depression between maxilla & premaxilla on lateral snout [SD92]; retain antorbital fenestra [SD92]; antorbital fenestra set in deep, triangular antorbital fossa [SD92]; antorbital fossa rimmed by maxilla & lacrimal, with small contribution from jugal [SD92]; orbits located relatively far forward above posterior cheek teeth; prefrontal overlaps frontal and nasal [SD92]; $ (possibly sexually dimorphic) little "horns" on postorbital [SD92]; posterior and median processes of postorbital overlap squamosal & jugal (respectively) [SD92]; parietal short (~50% frontal length) [SD92]; vomers short [G90]; braincase poorly known [G90]; stapes slender [G90]; external mandibular fenestra smaller than in stegosaurids [G90]; premaxilla with 7 teeth [G97]; $ maxilla (and dentary [G90]) with 25-30 teeth [SD92]; no diastema on lower jaw [G97]; axial: vertebral count 8, 17-18, 4, 35-42 [G90]; $ anterior dorsal ribs with intercostal flanges ("hamular processes" [G90]) and flared distal ends [SD92]; flared distal rib ends; postzygapohyses separated by notch [G90]; sacrum with 3 large foramina between transverse processes [G90]; appendicular: scapula without well-defined acromion process [G90]; coracoid wider than long & only slightly wider than scapular blade [G90]; forelimbs relatively long, with humerus 90% of femur length [SD92]; $ intermedium, ulnare, pisiform and radiale fused to carpal block [SD92]; ilium anterior process broad, angles laterally ~35° [G90]; antitrochanter small [G90]; ischial peduncle pronounced [G90]; integument: spiked-shaped armor along the body midline; keeled armor scutes in a row down its sides [SD92].

Note: this group tends to be discussed in terms of its shared primitive characters -- a dangerous sign. ATW020208.

This animal has been compared to a miniature version of Huayangosaurus, the skull of which is very similiar. MAK990724.

Huayangosaurus taibii Dong, Tang, and Zhou, 1982
Age: Bathonian-Callovian
Place: north-east Pangea
Remains: complete skeleton, skull, fragmentary postcrania
Length: 4.3 meters
Weight: 400 kg

Comments: Huayangosaurus is one of the best-known stegosaurians, with remains belonging to over a half dozen individuals. The skull (left) is deep with a relatively short snout, and has what may be little "horns," which may be a gender-related character. It is also unique for having armor scutes, something like those of scelidosaurs and ankylosaurs, in a row down its sides. This is one of the characters which indicate that these three groups are descended from a common ancestor and may be combined in a single clade, the Thyreophora. Huayangosaurus is protected by two pairs of tail spikes and a pair of spines on the shoulders

Ornithischia: Eurypoda

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