01.2 Appearances

01. Appearance & Anatomy

Saurischian Dinosaurs

Share an evolutionary ancestor w a pubis that extended downwards & forwards, towards ribcage

“lizard hipped“

Two Major Groups of Saurischian Dinos

1) Sauropodomorphs (sauropods)

2) Theropods

Sauropomorphs

Large herbivores w elongated necks & relatively small heads

(Saurischian → sauropod)

Prosauropods

(4)

Were an early group of sauropodomorphs → first group of large-bodied herbivorous dinos to evolve

• Small heads & long necks

• Some could walk on back feet

• Had gripping claws

Sauropods

(5)

Were a later group of sauropodomorphs → many attained truly giant size

• Long necks & tails

• Stood on four legs

• Vertebrae (particularly cervical) are filled w complex air sacks → help reduce weight

• Simple peg-like teeth

Theropods

(6)

Were bipedal carnivorous dinos that share a carnivorous ancestor

• Many were carnivores → serrated blade-like teeth & sharp hook claws

• Some were herbivores

• A few lacked teeth entirely

• Birds → kind of theropod

• Walked on hindlegs → bipedal

• Originally had three clawed fingers

Ornithischian Dinosaurs

Share an evolutionary ancestor that had a pubis that extends downwards & backwards (towards tail) & a special beak-forming bone in the upper jaw (the predentary)

“bird hipped“

What were the adaptations in the ornithischians thought to be for?

(3)

Their adaptations were to aid in a herbivorous lifestyle

• Backwards pubis → created more space in the ribcage probably filled w extra large digestive organs (to digest plant matter)

• Beaks were also a herbivorous adaptation

Five Major Groups of Ornithischians

1) Ornithopods

2) Pachycephalosaurs

3) Ceratopsians

4) Stegosaurs

5) Ankylosaurs

Ornithopods

(4)

Wide range of dinos that lack armor & walk bipedally either all the time or assumed bipedal when running

Includes → iguanodonts & hadrosaurs

Iguanodonts

(2)

Large ornithopods → w spike-shaped claw on each hand

Hadrosaurs

(4)

Group of large ornithopods → the “duckbilled dinos“

• Evolved late but were highly successful

• Some had elaborate boney crests

• Had dental batteries → large beaks in the front of their mouths & dense, tightly packed rows of small teeth in the rear

Pachycephalosaurs

(6)

Were bipedal, short arms, unusually stout & strong tails, & armored skulls

• Some have thick, domed skull roofs & backwards pointing horns

• Heads may have been used as battering rams

• Have conical teeth in front of mouths behind beak & leaf-shaped teeth in the rear → suggested may have been omnivores

Ceratopsians

(5)

Had large parrot-like beaks & skulls that are greatly expanded in the rear

• In most, rear skull expansion → large boney frill or a neck shield

• Many have large horns & dental batteries

• Most were quadrupedal w short tails

• Evolved late in dino history

Stegosaurs

(4)

Were quadrupedal dinos w rows of projecting osteoderm plates down their backs & long individual osteoderm spines on their tails

• Front limbs were much shorter than hindlimbs

• Small heads relative to body

• Narrow snouts

Ankylosaurs

(5)

Most heavily armored dinos → quadrupedal w short legs & wide ribcages

• Backs & skulls covered w spikey protective osteoderms

• Some have large osteoderms on the ends of their tails → forming a club

• Most have short snouts & broader, rounded beaks

Integument

Body covering

Why is it difficult to know what a dino’s integument was like?

B/c soft tissues decay more rapidly than bone

Conditions under which soft tissues can be fossilized

(2)

Fossil footprints → foot molds make in soft, fine-grained sediments → may include impressions of foot scales

Skin impressions → if a dino was covered by mud shortly after it died (before flesh rotted away)

Dinos found w a lot of skin are often called —A—.

The first was a —B— in 1910, which showed that —C—.

A → “mummies“

B → hadrosaur

C→ they were covered in scales that differed in shape in diff regions of the body

Why does the scaly skin of dinos have a better change of being fossilized compared to humans?

B/c scales are covered in keratin → tough, flexible material

• Also composes hair, feathers, fingernails, & the outside of claws, beaks, & horns

Sinosaurooteryx

(2)

Small theropod was found in 1996 w feathers → feathers preserved b/c body was suddenly buried by fine ash from a volcano

Now know that lots of small theropods had a cover of simple hair-like feathers

Yutyrannus

Found in 2012 → feathers found from this large tyrannosauroid

Largest known feathered dino

Theropod dinos are thought to have ___________ integument

Have feathers & filamentous integument

Few specimens suggest that some ornithischians might have _________ integument

Feather-like

Specimen of the early ceratopsian Psittacosaurus was found to have preserved _____________

Unusual long, stiff, bristle-like structures on its tail

Primitive ornithischian called Tianyulong was found to be cover in ____________

Long filament over most of its body

Osteoderms

(2)

Bones that develop within the skin & are common component of animal armor

Are considered integumentary structures

Four Possible Functions of Osteoderms

1) Storing calcium

2) Gathering heat from the sun

3) Protection from predators

4) To look good → attract mates or intimidate rivals

Melanosomes

Pigment cells within a feather

If observed in fossil feathers → clue to the dino’s colour based on studies of modern birds

What is feather colour influenced by?

(2)

The shape & arrangement of melanosomes

What three colours of feathers have not been found?

No feathers of green, red, or blue

What colour is associated w long & narrow melanosomes?

Black & grey

What colour is associated w short & wide melanosomes?

Brown & reddish

What colour is associated w no melanosomes?

White

What colour is associated w narrow melanosomes aligned in the same direction?

Iridescence/glossiness

Based on melanosome arrangements, what colours are the microraptor and anchiornis thought to be?

Microraptor → was glossy black

Anchiornis → was black & white w some reddish-brown on its head

How do we analyze muscles to understand how the dinos may have moved?

(3)

Shape of bones often corresponds to particular muscle shapes

Muscles often leave behind scars on the surface of bones where they attached

Pattern of muscle arrangement is very similar across tetrapods