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evolution and development of the skull
modules and networks
modular development and evolution
when and how during development and evolution? • increase in brain size • decrease in facial size
human “candidate genes”
• FOXP2 [forkhead box P2] (Lai et al. 01) – some alleles associated with speech and language disorder – humans have specific allele, different from great apes – “human” allele also in Neanderthals (Krause et al. 07)
• MYH [myosin heavy chain expression] (Stedman et al. 04) – less expressed in humans (MYH16 inactivation) compared to great
apes
• ASPM [abnormal spindle-like microcephaly-assoc.] (Mekel Bobrov et al. 05) MCPH1 [microcephalin] (Evans et al. 05) – some alleles involved in primary microcephaly – some alleles show signs of recent selective sweeps in humans,
but they are not related to brain size
skull: development, evolution, function
human neonate skull (CT reconstruction)
neurocranium desmocranium: intramembranous (desmal)
splanchnocranium chondrocranium: enchondral (cartilaginous)
Meckel’s cartilage
ear ossicles
developmental modules or developmental network?
skull development and evolution branchial (pharyngeal) arch transformation
Reichert's theory
eye
stapes
incus
malleus
proc. styl.
hyoid
mandibula
maxilla
squa- mosum
MC: Meckel's cartilage PQ: palatoquadratum TR: trabeculae
nasal bones
larynx
synapsid (mammal-like reptile)
mammal
Liem et al. 04
angular
Reichert's theory
branchial arches and circulation
Liem et al. 04
branchial arches and circulation Li
em e
t al.
04
frog human
external (ventral) carotid
internal (dorsal) carotid
carotid pathways
most lemuriforms
cheirogaleids loriforms
tarsiers anthropoids
Geissmann, 03 Gray’s Anatomy
ce/ci: carotis ext./int. s: a. stapedia p: a. promontorii pa: a. pharyngea ascendens
branchial arches and human anatomy
arch" skeletal elements" muscles" arteries" cranial nerves"
1" maxilla, mandible, incus, malleus"
mastication" -" V trigeminus"
2" stapes, styloid process, "body and lesser horns of hyoid"
facial expression" -" VII facialis"
3" body and greater horns of hyoid "
stylopharyngeus" int. carotis"
IX glossopharyngeus"
4-6" laryngeal cartilages" palatine, pharyngeal, laryngeal, trapezius, sternomastoid"
4: aorta, "subclavia"5,6: -"
X vagus + acc.cran."XI acc.spin."
gene expression patterns during early head development
Kuratani 04
genetics of craniofacial development
San
taga
ti &
Rijl
i, 03
congenital malformations
Franceschetti (Treacher-Collins) syndrome Apert/Crouzon (1st branchial arch) syndrome
skull evo-devo and human craniofacial malformations
FGFR-2 gene mutations lead to congenital malformations of head and limbs: „1st+2nd branchial arch disorders“
• e.g. Apert syndrome (acrocephalo-syndactyly) – craniosynostoses – underdevelopment of maxilla – low position of ears – syndactyly
• e.g. Franceschetti (Treacher Collins) syndrome – underdevelopment of mandible, zygomatic bones and
external/middle ears
developmental reorganization during evolution
• heterotopy: spatial reorganization – deposition vs. resorption – size, shape, arrangement of dep. and res. fields
• heterochrony: temporal reorganization – sequence of growth events (onset - duration - offset) – local rates of growth and development
speciation and development
heterochrony, heterotopy, allometry
definitions
• ontogeny: structural (form) change from conception to death
• form: size and shape • growth: change in size • development: change in shape • allometry: size-related change (or variation) in shape
speciation through ontogenetic reorganization
• heterotopy: spatial reorganization of ontogeny, change in directions of growth and development
– e.g. migration patterns of NCC – e.g. nr. and arrangement of dental cusps – e.g. spatial arrangement of depository and resorptive bone growth fields
• heterochrony: temporal reorganization of ontogeny, change in rates of growth and development
– e.g. proliferation rates of NCC – e.g. onset, duration, and offset of dental cusp formation – e.g. local rates of bone resorption and deposition
heterochrony example: humans and chimps
cranial size
dental age
birth adult
neurocranial size
dental age
human
chimp
birth adult
splanchnocranial size
dental age
heterochrony example: humans and chimps
cranial shape: splanchno/neuro size
dental age birth adult
log (cranial size)
human
chimp
log (cranial shape)
ontogenetic allometry
birth
adult
heterochrony: paedomorphosis
phenotype
developmental time
adult descendant similar in shape to juvenile ancestor
adult descendant juvenile ancestor
heterochrony: peramorphosis
phenotype
juvenile descendant adult ancestor
juvenile descendant similar in shape to adult ancestor
developmental time
heterochrony: pattern and process
• different heterochronic processes can result in similar heterochronic patterns
• example: paedomorphy of the human head can result from – delayed facial growth – decelerated facial growth – early cessation of facial growth – advanced brain growth – accelerated brain growth – long duration of brain growth – … or a combination of these processes è all result in small-faced, large-brained heads
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