Unit 1: Early verts, cranial skeleton, axial skeleton, embryology, etc. Flashcards
Study for Exam 1
Polyphyletic
Includes two different organisms without a common ancestor.
Paraphyletic
Includes a group of SOME organisms and their common ancestor.
5 Chordate Synapomorphies
Endostyle (creates mucus traps food), pharyngeal arches (create one-way flow of water), post-anal tail (facilitates locomotion), dorsal hollow/nerve tube, notochord.
When was the Cambrian Explosion?
600-500 million years ago.
Earliest Cells
RNA, lipid bilayer, likely used geological energy sources.
Prokaryotic Cells
DNA, ribosomes, specialized proteins.
Eukaryotic Cells
Cell membrane, mitochondria.
Choanoflagellates (And what makes them different from the earliest cells).
Flagella, cytoskeletal structures, extracellular matrices, adhesion proteins.
What kind of specialized tissue layers came to be?
Tissue: Inside (digestion + nutrient intake), Outside (protection).
Also, gained neurons and muscles.
Bilateral Symmetry
Show symmetry if you cut them in half (left + right).
Stage set for vertebrates!
Through gut, 3 tissue layers, specialized tissues, cells adhere + work together, planet can sustain life, cells can pass on info.
Protostome
Blastopore becomes mouth.
Deuterostomes
Blastopore becomes anus.
Gastrulation
Formation of the gut.
How do vertebrates form the coelom (body cavity)?
Enterocoely; formed by the presumptive mesoderm.
Chordates from echinoderms?
Paedomorphosis: Retain larval characteristics as an adult.
Ostracoderms
Armored, jawless fish.
Gnathostomes
Fish with jaws.
Chondrichthyans
Early jawed cartilaginous fish (lose bone, extensive braincases, dental tissues).
Osteichthyes
Bony fishes.
Placoderms
Extinct early jawed fishes.
Actinopterygians
Ray finned fish, a class of bony fish, make up a shit ton of vertebrates, broad body shape and mouth diversity.
Sarcopterygians
Lobe-finned fishes, bones and muscles extend to the fins.
What makes up the cranial skeleton?
Dermatocranium, splanchnocranium, Chondrocranium.
What makes up the postcranial skeleton?
Axial skeleton, appendicular skeleton.
Splanchnocranium
Originates as pharyngeal slits, became structures including the jaws, gill supports, parts of shoulder girdle + inner ear bone.
Evidence for Arches turning to Jaws
Both develop from neural crest cells, spiracle is hyoid bone (reduced gill opening), nerve and blood supply patterns are similar, jaw musculature appears to be modified arch musculature.
Chondrocranium
A cartilaginous structure that supports the brain and sensory organs, articulates with the jaws, ossified in some verts.
Dermatocranium
Comprised of dermal bone (bone that develops from interaction of ectodermal and mesodermal tissues), initially external tissues, but migrates inward with Osteichthyes. (intramembranous ossification).
The Composite Skull
Made up of splanchno, dermato, chondro-cranial components. In most mammals, these bones have fused.
How do the jaws articulate with the cranium?
Suspension: 2 connections to the skull via a joint with the mandible.
Axial Skeleton
Vertabrae + ribs + notochord.
Appendicular Skeleton
Appendages paired limbs and their girdles (etc. forelimbs, pec. fin + girdle, clavicle, arms scapula; hindlimbs: pelv. fin + girdle, legs, hips).
Fin Fold Theory
Vertebral ancestor had two long lateral fins that persisted in the pelvic and pectoral reigns, forming two separate appendages.
Gill Arch Theory
Final gill arches move posteriorly becoming the pelvic and pectoral girdles, brachial ray become the fins.
Evidence and Problems of two theories
Fin fold: paired fins have similar developmental + genetic similarities as the median fins, suggesting whole genome makes lateral fin fold, but no solid fossil evidence and pec comes before pelvic.
Gill Arch: Developmental origin shows pharynx as origin of pectoral girdle, but no evidence that radials become fins and it is unlikely that the arches would move that far back.
Current Hypothesis of Appendicular Skeleton Development
Pec. girdle from final pharyngeal arch, pec. + pelv. fins from fin fold, pelv. girdle unknown origins.
Bony fish vs. Vertebrates (Appendicular Skeleton)
Ancestral State of Both: Propterygium, Mesopterygium, Metapterygium.
Fish lose the metapterygium while sarcopterygians keep it but lose the other two.
Limbs form from what bone?
Endochondral bone; cartilaginous is replaced by this bone.
Specializations to Limbs
Running: Elongation of the limbs.
Fossorial Specializations: Digging = shorter limbs.
Cursorial Specializations: Articulation of the clavicle + sternum to allow swinging in apes + monkeys, stabilizes and strengthens the shoulders.
Also specializations for flight.
Physical Restrictions to Biological Design
Size, Shape, Forces (Gravity or fluid + torque), Material Properties (stiffness and loading).
Size changes require…
Changes in design to perform the same functions (i.e. oxygenation, heat loss, metabolism often slower in bigger endothermic organisms).
Allometry
What effect size has on certain processes, like bone cross-section width.
Torque
Rotational forces around a point.
Principles of lever system
Parts: Fulcrum, inner lever + input force, output lever + output force, mechanical advantage, velocity ratio.
Maximization: can be for speed or force.
Embryology
The study of development of an embryo from fertilization into the fetal phase.
Ontology
The study of the development of an organism from fertilization to adulthood.
Major stages of vertebral development
Cleavage: Newly fertilized zygote splits into multiple cells.
Gastrulation: The formation of the gut (Endoderm, mesoderm, and ectoderm are defined).
Organogenesis: Internal organs form and differentiate (neurulation: Formation of the dorsal hollow nerve tube).
Why is studying ontology important?
Development timing -> changes during embryology can lead to vastly different adult organisms.
Patterns give evolutionary insight.
Conservatism
Presentation of ancestral traits in embryo which reflect shared evolutionary history.
Why is the notochord important even if it doesn’t exist in the human adult?
Notochordal cells produce chemical signs that establish left/right and dorsal/ventral axes, also induce formation of nerve tube + helps with vetrebral formation.
Radical Cleavage in Deuterostomes and Protostomes
D: Cell division occurs in parallel.
P: Cell division occurs at oblique angles.
Endoderm
Alimentary tract, lungs.
Mesoderm
Muscles, limb bones.
Ectoderm
Skin, brain.
Yolk Sac
Nutrients for developing embryo.
Amnion
Surrounds embryo + keeps it hydrated.
Allantois
Stores waste, facilitates gas diffusion.
Chorion
Surrounds the membranes.
Shell
Calcified, hard but air permeable.
Monotremes
Mammals lay eggs.
Marsupials
Have pouch, undeveloped embryo finishes development here.
Mammalian difference from other verts (birthing process)
Stays in mother longer with modified membranes connected to the mother, lose yolk sac but still present in umbilical cord, gastrulation is highly derived as a process.
Placenta in mammals is…
Allantois + chorion.
Yolk sac in mammals vs. others
Others: asymmetry in eggs cells formed by yolk, daughter cells have unequal amounts of yolk, cells determined (and polarity) early development .
Mammals: no yolk, lose early patterning, more cell fate flexibility.
Gastrulation before amniotes
Blastula forms from morula, cells from blastula migrate inwards and start gastrulation, blastopore forms as cells become endoderm, mesoderm buds from endoderm.
Gastrulation in mammals
Blastula from morula, turns into hypoblast (yolk sac) and epiblast (tissue layers), Primitive streak forms as cells migrate and have a primitive node from epiblast migrating down to become the endoderm, second wave of migration moves between endo and ectoderm becoming the mesoderm.
What does the endoderm become?
Foregut -> mouth/pharynx, esophagus/lungs.
Midgut -> stomach, liver, intestines, pancreas.
Hindgut -> bladder and cloaca.
What does the mesoderm become?
Somites -> limb muscles and dermis, vertebral column.
Mesomere -> kidneys.
Hypomere -> vascular system, gonads, and appendages.
What does the ectoderm become?
Epidural ectoderm -> epidermis, placodes, mouth/anus.
Neural plate -> spinal column, brain.
Neural crest -> PNS, teeth, craniid muscles.
