Projects due last day of class

Quiz Thursday after Thanksgiving

Notes on North American Pachycephalosaurs

For a general web site on pachycephalosaurs see:

http://www.geocities.com/Athens/Styx/3406/

For a description of the skull of Stygimoloch, and nine referred specimens (mostly skull fragments) from the Hell Creek and Lance formations, see Goodwin et al. 1998. JVP 18(2): 363-375.

For a report a flat-headed homalocephalid (open supratemporal fenesterae) close to the Mongolian Prenocephale, from the late Campanian (Late Cretaceous) of New Mexico, see Williamson and Sealey 1999. JVP 19, 3 supplement, p. 84A.

"Stegoceras" has open supratemporal fenestrae, the taxon formerly known as Stegoceras (including the single fragmentary skeleton) must be renamed, several specimens formerly referred to Stegoceras belong to Prenocephale, see Sullivan 2000. JVP 20, 3 supplement) p. 72A.

There is no evidence of the cranial domes having been altered by trauma, and therefore no histological evidence to support head-butting; see Horner and Goodwin 1998. JVP 18,3 supplement, p. 52A.
 

DINOSAURIAN UNGULATES (ORNITHOPODS)

See Brett-Surman in The Complete Dinosaur (1997, p. 330-346)

For previous literature see: Weishampel and Heinrich 1992, Hist. Biol. 6: 159-184; Coria and Salgado 1996, JVP 16: 445-457. More recent references are cited below.

Following Brett-Surman’s review Heterodontosaurus is considered to be an ornithopod; all other ornithopods are "Euornithopods." Traditionally they are simply unarmored ornithischians. More lately, they are defined by the possession of a "pleurokinetic skull" whereby the closure (and rotation) of the lower jaws force the maxillae apart. As the lower jaws descend, pressure on ligaments within the skull hold the occlusal surfaces together, so that grinding is accomplished on both up and down strokes.

Lesothosaurus is relatively well-placed (morphologically) to be an ancestral ornithopod. The skull, however, does not appear to have been pleurokinetic. Other plesiomorphic features:

• the animal was about 1 m long
• snout is narrow and pointed
• premaxillae with 6 teeth (anteriormost tooth lost)
• antorbital fenestra is large and low
• quadratojugal is small, paraquadratic or quadratojugal foramen absent
• coronoid process very low
• mandibular fenestra present
• angular exposed on lower jaw
• distal end of scapula expanded
• forelimb is small and lightly constructed
• digit I manus well-formed
• five sacral vertebrae
• prepubic process very small
• obturator process incippient only

Small (2-4 m long) bipedal ornithopods, Middle Jurassic- late Cretaceous

Completely known taxa:

Hypsilophodon

Thescelosaurus

Yandusaurus

Hypsilophodonts are traditionally considered as ancestral ornithopods

• subnarial ramus of premaxilla contacts prefrontal or lacrimal
• mx rotates on peg + socket within pmx (pleurokinesis)
• pmx tooth row (when present) below mx tooth row
• crescentric paroccipital processes
• mandibular condyle below level of cheek teeth (long quadrates)
• continuous, if uneven occlusal surface
• scapula shorter than humerus
• prepubis elongate, rod-shaped, wider than deep
• obturator process on ischium (incippient in Lesothosaurus)
• tail with hypaxial (as well as epaxial) tendons

• long forelimbs, grasping (not running) hands
• long, cursorial hind limbs (the tendon sheath functions like the zygapophyseal/chevron tendons of dinosaurian raptors)

• 2.3 m, 15 kg

• fleet, group feeders (chewers to aid digestion)
• plant scavangers; fallen debris of larger herbivores

• 3.5 m long, 300 kg
• short legged "hog" with deer-like head and long tail
• 6 pmx teeth (Hypsilophodon has 5, Lesothosaurus 6)
• primitive cheek teeth
• 2 palpebrals
• uncinate-like cartilagenous plates
• latticework of ossified tendons

Hypsilophodont synapomorphies, according to Winkler et al. 1997 (JVP 17: 330-348):

• tooth ridges connect to denticles
• cingula present on dentary teeth
• small quadratojugal
• long,rod-like prepubic process

2. IGUANODONTIA: Chapter 25

Iguanodontids up to 10 m long

Late Jurassic-early to late Cretaceous

Transition between hypsilophodonts and hadrosaurs

Completely known taxa:

Tentontosaurus

Dryosaurus

Iguanodon

Ouranosaurus

• premaxilla everted, edentulous
• external nares enlarged
• antorbital fossa circular, small
• predentary denticulate, with paired ventral processes
• dentary with parallel dorsal and ventral margins
• femur with deep intercondylar groove

• 12C, 16D, 5S, 60+C (multiplying presacrals)
• 9C, 15-16D, 5-6S, 45-50C (Hypsilophodon)
• no premaxillary teeth
• unossified wrist
• most of tail enclosed in tendon sheath
• prepubic process deep
• intercondylar groove of femur shallow
• mtt V vestigial
• pes 2-3-4-5-0 (still plesiomorphic)
• ossified tendons in long bundles (lattice in advanced iguanodonts)

According to Winkler et al. 1997 (JVP 17: 330-348), Tenontosaurus dossi is the most primitive iguanodontian, and shares many characters with a "weakly supported" Hypsilophodontidae:

Iguanodont synapomorphies, acquired as a result of homoplasy:

• tooth-packing was increasing
• contact between the premaxilla and lacrimal was achieved
• cropping functions were being transferred from the premaxillary teeth to the everted premaxilla
• long post-pubic rods were being shortened
• fifth metatarsal was being reduced

• presence of teeth in the premaxilla
• relatively few large teeth
• relatively small muzzle
• single ventral predentary process
• five manus digits
• four functional digits in pes
• hypaxial tendons in tail

Dryosaurus and Camptosaurus approach iguanodontids in morphology:

• quadratojugal small
• paraquadratic foramen notched into quadrate
• keeled cheek teeth
• two rows teeth per jaw (Camptosaurus)
• fusion of carpals in wrist (Camptosaurus)
• obturator process of ischium proximal in position
• expanded distal end ischium (postpubis long in both genera)
• ischium curved
• pendant 4th trochanter
• mtt I vestigial (Camptosaurus)
• trellis-like ossified tendons

Iguanodontids (mosaic of characters)

From hypsilophodontids:

free palpebrals

small antorbital foramen beneath lacrymal

paraquadrate foramen notched into quadrate

five-fingered manus

Intermediate:

one replacement tooth per position

12-15C, 19D, 10-12S, 50-70C (hadrosaurids)

11C, 17D, 7S, 50+C IGUANODON

12C, 16D, 5S, 60+C (Tenontosaurus)

9C, 15-16D, 5-6S, 45-50C (Hypsilophodon)

carpals heavily ossified (cf. stegosaurs)

thumb spur, hyperextensible digits II-IV with hooves

three functional toes, first digit splint-like mtt

To hadrosaurids:

coronoid process prominant, stands laterally

latticework of tendons across back and tail

sternals from kidney- to hatchet-shaped

prepubic process deep, flat

reduction of postpubic process

straight femur, alate 4th trochanter

According to Forster (1997. JVP 17, 3 supplement, p. 47A), the transformation of iguanodonts into hadrosaurs sequentially involves:

• co-ossification of the carpus and metacarpal I
• rhomboidal arrangement of epaxial tendons
• hatchet-shaped sternal plates
• increase in body size
• loss of digit I, pes
• loss of antorbital fenestra
• loss of surangular foramen
• loss of jugular process on maxilla

• short, flat skull
• well-developed hypapophyses on posterior cervicals
• dorsal centra height 40% of total vertebral height
• unusually massive "thumb" spine
• powerfully constructed forelimb
• hind limb short and powerful

According to Sheetz (1998 JVP 18, 3 supplement p. 75A)an analysis of 20 taxa using 76 cranial and 48 postcranial characters indicates a pandemic distribution of small ornithopods prior to the Upper Jurassic. Most of the major herbivorous adaptations of ornithopods had appeared before the apperance of the angiosperms. The terms hypsilophodont and iguanodont are ambiguous when applied to pre-Cretaceous ornithopods.
 

3. HADROSAURIDS: Chapter 26

Completely known taxa:

Maiasaura

Prosaurolophus

Saurolophus

Edmontosaurus

Lambeosaurus

Corythosaurus

Hypacrosaurus

Parasaurolophus

7 -15 m long, ?Aptian-Albian, Santonian-Maastrichtian

Hadrosaurs are the best known of all dinosaurs. The are large, secondarily simplified ornithopods with expanded snouts (hence, duck-billed dinosaurs).

• rotation of antorbital foramen beneath lacrimal
• 3-5 replacement teeth per position
• narrower maxillary teeth
• fusion of palpebrals
• loss of paraquadratic and surangular foramen
• 8-10 sacrals
• loss of manal digit I
• presence of large antitrochanter on ilium

• expanded dorsal process of maxilla
• medially displaced antorbital fenestra
• absence of paraquadratic foramen
• medial migration of angular on surangular
• absence of surangular foramen
• three or more dentary teeth per tooth position
• reduction (narrowing) of scapular blade distally

• elevation of dorsal process of maxilla
• absence of paraquadratic foramen
• absence of surangular foramen
• dental battery composed of at least 60 tooth families
• three or more dentary teeth per tooth position
• at least 8 sacrals
• reduced dorsal margin of scapular blade

• 40 or more vertical tooth rows
• loss of fused carupus and manus digit I
• extreme dorsoventral expansion of anterior jugal

hadrosaurs (Hadrosaurinae):

-broad beak

-circumnarial fossa

-grooved sacrum

-slim ischium

lambeosaurs (Lambeosaurinae):

-supraorbital narial system (ACOUSTICS) dimorphic crests

-shallow crown:root angle

-elongate neural spines

-footed ischium
 

More recent lists of hadrosaurine and lambeosaurine synapomorphies:

From Casanovas et al. 1999. Geol. Mag. 136(2): 205-211.

Lambeosaurine characters:

• absence of premaxillary foramina
• external naris surrounded by premaxilla
• hollow supracranial crest in adults
• nasal cavity in supraorbital position
• medial maxillary shelf
• truncated, rounded maxillary-jugal contact
• deltopectoral crest projecting laterally and distally

Hadrosaurine characters:

• reflected premaxillary lip
• enlarged external nares
• circumnarial depression extending onto the nasal
• angle between crown and root of dentary teeth less than 130 degrees
• ventral sacral groove
• reduction of distal ischium
• exclusion of the basioccipital from the foramen magnum
• dentary tooth height/crown ratio less than 3 (teeth broad)

• external nares surrounded by premaxilla
• very tall caudal spines
• robust humerus
• ventral sacral ridge
• participation of the basioccipital in the foramen magnum
• dentary tooth height/crown ratio greater than 3 (teeth narrow)

Notes on hadrosaurs

Eohadros is considered to be a basal hadrosaurid from the Cenomanian of Texas (Head 1998. JVP 18: 718-738).

Eolambia is considered to be a basal, crestless lambeosaurine, the oldest known hadrosaurid; Latest Albian-basal Cenomanian (98.4 myr), upper Cedar Mountain Formation, eastern Utah (Kirkland 1998).

In Maiasaura the nesting period is estimated to be 1-2 months, a late juvenile (3.5 m) phase is attained in 1-2 years, and adulthood is reached in 6-8 years (Horner et al. 2000. JVP 20: 115-129).

On Parasaurolophus in New Mexico:

• Juvenile skull from Fruitland Formation - Bennett and Sullivan 2000 (JVP 20, 3 supplement, p. 29A
• Adult skull, well preserved narial chambers — Kirkland Formation, Sullivan and Williamson 1999. New Mexico Mus. Nat. Hist. Science Bulletin 15

Ornithopod evolutionary trends - 80 myr

• increase in body size

• elongation of head (no gastrolith grinders)
• formation of dental batteries (unique, elephant-like)
• closing of cranial fenestrae
• elongation and "folding" of neck
• increase in number of back, tail vertebrae
• elongation of vertebral spines in proximity to sacrum (stegosaurs elongate the neural arch)
• cantelever extended sacrum plus co-ossified tendons
• reduction of postpubic process
• forelimbs slender "balancing sticks" (not hooks like prosauropods)
• "perissodactylate" hind limb

Yandusaurus Hypsilophodont

-scapula shorter than humerus

-peg-like prepubis, long postpubis

-obturator process distal

-long hind limbs

Thescelosaurus

-6 pmx teeth

-lattice tendons

Dryosaurus

-everted lip

-trochanter pendant

-no hypaxial ossified tendons

-scapula longer than humerus

-pubis expanded

-ischium recurved, distal expansion

-obturator process proximal

Camptosaurus

-elongated muzzle

-two functional rows of teeth

-ossified carpus

-reduced digit one foot

Tenontosaurus

-everted lip

-tall-spined tail

-enlarged digit one foot
 
 

Return to main page