Chapter 5 – Dinosaur Bones: Their Formation, Names and Features
Refined Definition of
“Dinosaur”
Additional Characteristics
Three or more sacral vertebrae
Shoulder girdle with backward-facing
glenoid
Asymmetrical manus with less than or
equal to three phalanges on digit IV
Acetabulum with open medial wall
Tibia with cnemial crest
Astragalus with a long ascending
process that fits into the anterior part of the tibia
Sigmoidally shaped third metatarsal
Postfrontal absent
Humerus with long deltopectoral crest
Femur with ball-like head on proximal
end
Based on hard parts, not soft parts
Biomineralization and Biochemistry of
Bones
Bones, teeth and ossified tendons
Made of a combination of mineral and
organic matter
Dahllite
Mineral that makes bone in chordates
Made of calcium, phosphate
and variable amounts of fluoride, carbonate
and hydroxide
Fossil bone is usually altered
Biomolecules
Involved in biomineralization
Only proteins have been undisputedly found preserved in dinosaur bones
Bone Structure
Ossification occurs in cartilage
Cancellous bone has a “spongy” texture
Compact bone is denser
Long bones have compact bone along the shaft (diaphyses), while the
ends (epiphyses) are mostly cancellous bone
Bone Growth Patterns
Generally stops with adulthood in endotherms
Continues throughout life of ectotherms
Dinosaur Anatomical Vocabulary
See Handout and Figures 5.3 and 5.5
Terms to learn:
Positional terms
Anterior – Posterior; Medial
- Lateral; Dorsal -
Ventral; Proximal –
Distal
Pre sometimes substitutes for Anterior
Vertebral column
terms
Cervical; Dorsal; Sacral; Caudal; Chevrons; Ribs; Gastralia; Centrum; Neural arch; Processes
Shoulder and
forelimb terms
Scapula; Coracoid; Humerus; Ulna; Radius; Carpal; Metacarpal; Phalanx; Manus; Clavicles; Sternum; Deltopectoral crest; Glenoid; Unguals; Phalangeal formula
Hip and hindlimb
terms
Ilium; Pubis; Ischium; Femur; Tibia; Fibula; Tarsals; Metatarsals; Phalanges; Astragalus; Calcaneum; Cnemial crest; Acetabulum; Pes; Digitigrade; Plantigrade
Skull terms
Dentary; Jugal; Maxilla; Premaxilla; Foramen; Fenestra; Orbit; Antorbital fenestra; Mandibular fenestra; Occipital condyle
Dinosaur Skin, Other Integuments (Yes,
Feathers too), and Organs
Skin and its Derivatives (Nails,
Feathers, Hooves, Hair)
Composed of Keratin,
a structural protein
Lower preservation
potential than skeletal material
Some dinosaurs had dermal armor or osteoderms set in the skin, including ankylosaurs, titanosaurs and stegosaurs
Skin may be
preserved as impressions (see Figure 5.8)
Typically show patterns of scales, sometimes of equal size, sometimes of different sizes
Patterns of different sizes have been interpreted as evidence for coloration in dinosaurs
Feathers have been
preserved as impressions (Archaeopteryx) and in carbonized form (Sinosauropteryx, Caudipteryx)
Patterns on feathers probably reflect colors
Location of some
muscles can be inferred from muscle attachment sites on bones and from toe-pad
impressions in some tracks
Other soft parts
have been preserved or can be inferred quite confidently
Crops and gizzards based on position of gastroliths
Stomachs or intestines based on position of animal remains
Oviduct can be inferred from egg-like structures in Sinosauropteryx
Specimen of Scipionyx polydon preserves some muscles, intestines, trachea and liver
Brain endocasts from well-preserved skulls
Dinosaur Anatomy Related to
Classification
Some Terms
Genotype vs Phenotype
Genotype – genetic expression of
an organism
Phenotype – outward physical
expression of an organism, caused by a combination of environmentally caused
traits and the genotype
Phylogeny – evolutionary history
of a group of organisms
Main Dinosaur Clades
See Table 5.1 and Figure 5.11
Naming a New Dinosaur Species
Pitfalls
Synonomy – assigning a different
species name to a dinosaur already given another name
Assigning a species name to a dinosaur
that is already being used for another organism, maybe not even a dinosaur
Naming a dinosaur on the basis of so
little material that the definition of its characters is too vague
Giving a mostly interpretive name
Sexual dimorphism and Juveniles
– not recognizing that two specimens are the same species because of
differences arising from one individual being male and the other female or one
individual being adult and the other juvenile; different names may be assigned
to each specimen
International code of zoological
nomenclature
Rules for naming a new animal species
Publication
Good description
Good illustration
Type specimen
The material used to describe a new
species if a new name is accepted after peer review
Archived in a safe place where future
workers can use it for comparison