Lecture 10

1. Lecture 10

2. Phylogenetic trees are hypotheses - a phylogenetic tree is nothing more than an hypothesis. - the tree may have very strong support, or it may have very little support. - the former arises when there are a large number of characters supporting a specific topology. - the latter arises when there are many possible trees that are difficult to exclude as possible alternatives. - considerable caution must be exercised in the generation and testing of phylogenies, a point not appreciated by many researchers.

3. Gene trees are not the same as species trees - species trees illustrate the evolutionary histories of a group of related species. - in other words, species trees record the details of speciation for the group. - gene trees show the evolutionary relationships among DNA sequences for a locus. - gene trees may not be the same as species trees for one main reason – the existence of ancestral polymorphism. - if this ancestral polymorphism is lost in some taxa but not in others, then one sequence isolated in species A may be more closely related to one in species B than to any other conspecific sequence. - the gene tree will thus be different from the true species tree. - the best way to guarantee that this will no occur is to use information provided by multiple independent loci!

4. Types of data - any type of data can be used to reconstruct phylogenetic trees. - until recently, trees were constructed solely from morphological characters. - now, the vast majority of researchers use molecular data. - this molecular data can be in various forms: 1. Immunological distance. 2. DNA-DNA hybridization. 3. Allozyme data. 4. Restriction site data. 5. Amino acid sequences. 6. DNA sequences.

5. Skulls • Skull is defining characteristic of "vertebrates" • modern term for phylum of animals to which humans belong is Craniates • Divisions of skull 1) functional • a) neurocranium - houses the brain • b) facial skeleton (viscerocranium) - surrounds oral and nasal cavities • 2) developmental - skull divided into components by embryological / phylogenetic origin • a) chondrocranium - forms base of skull; as name suggests endochondral ossifications • b) splachnocranium - derived from pharyngeal arches; also endochondral ossifications • c) dermatocranium - remnant of ancestral exoskeleton; as name suggests dermal ossifications

6. Skull Anatomy • Comprised of 22 separate bones divided into two groups: • Cranial bones – 8 • Facial bones – 14 • Cranial bones further subdivided into • Calvaria • Floor

7. Calvaria Frontal Occipital R. parietal L. parietal Floor Ethmoid Sphenoid R. temporal L. temporal Cranial Bones

8. Skull Anatomy • Sutures = fibrous joints that connect the bones of the skull • Coronal = between frontal and parietal bones • Sagittal = on top of head between two parietal bones • Squamosal = between temporal bone and the parietal bones • Lambdoidal = between occipital and the parietal bones

9. Sutures joint (G, arthroses) = articulation between two or more bones • joint classifications • 1) relative mobility: syn-, amphi- and vs di-arthroses • 2) structural: • a) fibrous (solid or non-cavitated joints) - collagenous fibers link articulating bones; sub-types distinguished by location and slight differences in histology • i) sutures - limited to skull • ii) syndesmoses (interosseous ligament) - post-cranial • iii) gomphoses (periodontal ligament) - bind teeth to alveolar bone • b) cartilaginous (solid or non-cavitated joints) - pad of cartilage interposed between bony elements • i) synchondroses (primary cartilaginous joint) - hyaline pad between • e.g., metaphyses, costal cartilage • ii) symphyses (secondary cartilaginous joint) - pad of fibrocartilage between hyaline covered bony elements • limited to median sagittal plane • c) synovial (cavitated joints) • actual gap (synovial cavity) between bony elements which are covered with thin layer of articular (hyaline cartilage) • encased within fibrous articular capsule line by synovial membrane

10. Splanchnocranium • Splanchnocraniumphylogentically oldest part of skull, derived from pharyngeal arches • pharyngeal arches present in chordates (sister group of craniates (vertebrates)) • pharynx ancestral respiratory and feeding organ • series of U-shaped bars separated by slits (incomplete in tetrapods), each bar containing a cartilaginous skeleton with associated muscles and nerves • these cartilaginous rods give rise to the bones and cartilages of the splanchnocranium • small but important part of cranial skeleton • derivatives of splanchnocranium • first or mandibular arch: cartilage splits into cranial (palatoquadrate) and caudal (mandibular) arches around which the dermal bones of the upper and lower form • palatoquadrate: incus (quadrate) and alisphenoid (greater wing of sphenoid) • mandibular cartilage: malleus (articular) • second or hyoid arch: stapes, styloid process, body and lesser horn of hyoid • third arch: greater horn of hyoid • fourth and fifth (sixth) arches: laryngeal cartilages

11. Chondrocranium • Chondrocraniumphylogenetically second oldest part of skull • as name suggests, series of cartilages which form base of cranial cavity • derives from • 1) series of paraxial mesodermal condensations (names not important), and • 2) sensory capsules which form which form around the nasal, eyes and the inner ear organs • capsule and condensations turn to cartilage, expand and then ossify to form bones of the skull base • bones include: portions of occipital, temporal, and sphenoid and all of ethmoid and inferior nasal concha

12. Evolution of mammalian ear ossicles in earliest mammals (pelycosaurs), lower jaw reptilian like (see iguana) • 1) lower jaw formed by multiple bones • tooth bearing dentary • multiple post-dentary bones • 2) jaw joint (primary) formed by quadrate and articular • unique to mammals, however, is that tympanum carried not by quadrate (upper jaw) but by post-dentary angular bone • thus lower jaw functioned in both feeding and hearing • during evolution (and development) note two trends: • 1) expansion of dentary • ultimately contacts squamosal and forms new (secondary) jaw joint (TMJ or sq/d) • 2) reduction of post-dentary bones with eventual transferal from "jaw" to temporal bone • basically separates original dual functions of jaws (hearing and feeding) to increase acuity of hearing

13. Dermatocranium • Dermatocraniumphylogenetically, remnant of ancestral exoskeleton • primitive condition for all vertebrates is to be encased in a bony exoskeleton of dermal origin • secondarily evolved exoskeletons common in many terrestrial vertebrates • as name suggests, dermatocranium represents intramembranous ossifications within the dermis of the skin • gives rise to the vast majority of bones covering the cranial cavity and face • dermal bones: frontal, parietal, zygomatic, nasal, vomer, lacrimal, palantine, maxilla, dentary (mandible) and portions of occipital, temporal and sphenoid

14. Composite bones result from fusion between separate centres of ossification • found in mammals and birds (endotherms) • phenomenon accounts for apparent complex morphology of many cranial "bones" • temporal • fusion of elements from all three developmental components • dermatocranium > squamosal and tympanic annulus (angular) • chondrocranium > petrous (prootic and opisthotic) and mastoid • splanchnocranium > styloid process • sphenoid • also fusion of elements from all three developmental components • dermatocranium > pterygoid process (pterygoid, ectopterygoid and parasphenoid) • chondrocranium > oriboto-, pre- and basi-sphenoid • splanchnocranium > alisphenoid (greater wing) • occipital • fusion of chondocranial and dermatocranial elements • chondrocranium > basi-, paired exo-and supra-occiptal bones • dermatocranium > interparietal (post-parietal)

15. Why skulls? • two important assumptions about the characters used to build trees: 1. the characters are independent 2. the characters are homologous - a homologous character is one shared by two species because it was inherited from a common ancestor. - if a similar character or trait is possessed by two species but was not possessed by all the ancestors intervening between them, it is said to exhibit “homoplasy”. - homoplasy can result from convergent or parallel evolution, or from evolutionary reversals.