Development and Evolution of the
Vertebrate Head
(Skull & Jaws)
Neural Crest Cell Fate Specification
Expression of Developmental Genes
Dorsky & Raible, 2000
Neural Crest Formation in Chick Embryos
BMP
?
Colas & Schoenwolf,
Schoenwolf, 2003
Regions of the Neural Crest
Allometric Growth in Whale Heads
Fate Map of the Cranial Placodes in the
Chick Embryo
How We Got a Head
The Evolution of the Vertebrate Head
Outline
• Chordate phylogeny: who are the players?
• What’s special about the vertebrate head
- the big brain
- the skull
- Gans and Northcutt: “The New Head”
• Evolution of the vertebrate brain: a foundation in the non-vert. chordates?
- gene expression patterns in non-vert. chordates and lower verts
- neuroanatomy
• Evolution of the neural crest: a foundation in the non-vert. chordates???
- gene expression patterns in chordates and lower verts.
- cross-species cis-regulation: Manzanares et al. (2000). (Surprises)
• What is the motor for evolutionary change/increased complexity? (Speculation)
- whole genome duplications/acquisition of new cis-regulatory modules
From Schilling and Knight, Phil. Trans. R. Soc. Lond. (2001) 356:1599
Cephalochordates (Amphioxus) Extant
Pikaia (earliest known chordate)
Lower Cambrian, Burgess Shale
Figure 13.8(1) Cranial Neural Crest Cell Migration in the
Mammalian Head
An Early Cambrian Vertebrate, Haikouichthys: The first fish?
From the Chengjiang Lagerstatte
From Shu et al., (2003) Nature 421:526
Chordate synapomorphies
Vertebrate synapomorphies
• Notochord
• segmented muscle
• dorsal nerve cord
• pharyngeal slits
• bone
• vertebral column
• neural crest/placodes
• skull
• “segmented” brain
Gnathostome synapomorphies
• occipital skull
• jaws
• paired appendages
Evolution of the Vertebrate brain
From Holland and Holland (1999) Curr. Opin. Neurobiol. 9:596
From Tomsa and Langeland, Developmental Biology 207, 26–37 (1999)
Origins of Neural Crest: Dlx expression in lamprey
Origins of Neural Crest: Amphioxus
Vertebrate Synapomorphies (Gans and Northcutt (1983) Science 220: 268)
Character
Nervous system
Cranial nerves with sensory ganglia
Trunk nerves with sensory ganglia
Forebrain
Paired Special Sense Organs
Nose
Eyes
Ears
Lateral line
Pharyngeal modifications
Cartilage Bars
Branchiomeric Muscle
Circulatory System
Gill capillaries
Muscular Heart
Skeletal
Anterior neurocranium
Cephalic Armor (Skull) and derivatives
Embryonic Origin
N.C., P
N.C.
CNS
P
CNS/P
P
P
N.C.
Mesoderm
Mesoderm
Mesoderm
N.C.
N.C., Mesoderm
Chordate synapomorphies
Vertebrate synapomorphies
• Notochord
• segmented muscle
• dorsal nerve cord
• pharyngeal slits
• bone
• vertebral column
• neural crest/placodes
• skull
• “segmented” brain
Gnathostome synapomorphies
• occipital skull
• jaws
• paired appendages
The Giant Placoderm Dinichthys: an early Gnathostome (jawed) fish
2.5-3 m (8-10 feet)
Cranio-Facial Skeleton (Evolution of
Jaws)
Figure 13.8(2) Cranial Neural Crest Cell
Migration in the Mammalian Head
Figure 13.8(3) Cranial Neural Crest Cell
Migration in the Mammalian Head
Evolution of the Vertebrate Skull
Figure 23.10 Representation of Skeletal
Elements
Figure 13.9(2) Intramembranous Ossification
Figure 13.9(1) Intramembranous
Ossification