U4
Palentologists need...
• Correct age of rock • Must be exposed • Must be correct TYPE of rock -Exposed, sedimentary rock of the correct age. What is sedimentary rock? Why not igneous rock?; heat and pressure (lava!)
Where did they decide to go instead?
• Devonian age rocks • Areas that were once river deltas -the arctic
Placozoans
• Discovered in an aquarium in 1880's • ~ 2 mm in diameter • only 4 types of cells specialized some flagellate; other perform digestion • "Primitive (simple)" creatures without a body plan, but specialized cells • Much of the same molecular body building materials in other metazoans already in place within the placozoan lineage! • The same rivets and cell communication as in vertebrates
Porifera (sponges)
• Have no body plan • The body of a sponge consists of... • silica • calcium carbonate • collagen! • More specialization than seen in placozoans
Components of those intercellular spaces in animals tissues:
• Cartilage cells sit in collagen plus proteoglycans which swell up with water to provide cushioning • Bone cells are in collagen with hydroxyapatite • Teeth cells are in mostly hydroxyapatite
So what is the common pattern that connects us all?
"One bone, two bones, lotsa blobs, digits" (fingers/toes).
Aquatic life had numerous challenges. In a fish eat fish world it was necessary to...
-"get big, get armour, or get out of the water."
What is the function of teeth?
-"to make bigger creatures into smaller pieces" -- Shubin
When did mammalian teeth & jaw structure first show up? What characteristic distinguishes mammalian teeth (and jaw) structure from reptilian teeth and jaws?
-225 - 195 million years ago. Varies in different parts of the world. -Occlusion. How our teeth fit together. Shapes. Ours radically different vs uniform. Jaw structure (boomerang shape). Replacement. Replaced once (vs continuously).
When did the first true fingers and toes show up in the fossil record? When did the first full complement of wrist and ankle bones show up?
-365 million years ago. In amphibians. -250 million years ago. In reptiles.
What is the role of ZPA in the development of appendages? (work of Saunders and Zwilling)
-A small piece of tissue at end of limb bud seemed to direct normal growth and development -Called the ZPA - zone of polarizing activity What does mirror image replication mean? -Digits form differently because of a gradient 1990's; Genetics of Drosophila -Discovery of Hox genes, among others, responsible for development and differentiation of different body regions
arches
-Arch 1: jaws (+ ear malleus and incus in humans, trigeminal nerve) -Arch 2: 3 more ear bones—the stapes in humans plus the hyoid bone, facial nerve (swallowing) -Arch 3 & 4: structures used for gill movement in sharks (swallowing and talking in humans) -Arch 1 and Arch 2: bones co-opted from original game plan for a new sense
Johannes Goethe figured out an essential pattern looking at a skeleton of a ram - heads are a continuation of the vertebrae in our backs---linking heads and bodies showing segmentation of the human body.
-As infants plates separated but grow together in adulthood, secondary loss of segmentation -Very evident if you look at early diverging chordates like Amphioxus - animals with a dorsal notochord When does the phylum Chordata first show up in the fossil record? Cambrian Explosion
While most genes evolved alongside bodies - there were some precursors present for natural selection to work with...
-BUT: similar versions DO EXIST in bacteria -often make machinery that causes them to be pathogenic --Streptococcus in our throats has a molecule similar to collagen
What is a body plan? What type do we have?
-Body symmetry: front/back, top/bottom, left/right. -Common to most all animal life forms (save jellies, sponges and such) early days...
Most common protein in animals including the human body?
-Collagen 90% -A structural protein in between our cells
Same developmental pathway for teeth can be co-opted to form a diverse set of complex and structures organs
-Everything from feathers to breasts!
What are the genetic mechanisms underlying the transformation from a fin to hand?
-Extinct taxa can reveal morphological changes -Using extant taxa we can conduct experiments to understand changes in the DNA for producing digits from fins -DNA codes the changes from a generalized singlecelled zygote to a full organism with trillions of specialized cells
What are conodonts and why have they received so much attention by paleontologists?
-For 150 years we didn't know what these things were. -A soft bodied fish with a mouth full of teeth
Tiktaalik has much more of us in it than just the arm bones...
-For the first time here is an animal that has: —A neck that rotates —Ribs —Ears —Wrists
Why did Randy implant mouse sonic hedgehog into a skate embryo?
-Giving sharks a hand: All the rods in skates look alike -But if you implant a bead with a tetrapod version of Sonic Hedgehog you get differentiation of digits—in a skate! -Bottom line: "The connections among living creatures run deep."
Scientific prediction time
-If differentiation of the vertebrate limb is under similar genetic control, and this similarity is due to common ancestry between Drosophilia and said vertebrates, what would we expect to find in genome of a vertebrate like a chicken? -A Sonic hedgehog gene homologue in chickens!
Is this little guy a reptile or a mammal or something in between?
-It's teeth worked like scissors with upper teeth moving against outer surface of lower teeth.
Where has the notochord gone in postembryonic humans?
-Late in development it breaks apart to form your intervertebral discs! -If you are even unfortunate enough to slip a disk you have our early chordate ancestors to thank!
Microbes develop new ways of interacting with their environments (forming sheets or biofilms) and in doing this they evolve new molecular tools...
-Microbes begin to eat each other so formation of a larger body-plan adaptively beneficial -By about 1 billion years ago finally (thanks to photosynthesis) the earth's atmosphere became oxygen rich -As earth's oxygen increased bodies appeared everywhere...the "perfect storm"!; Animal bodies, Plant bodies, Fungal bodies
What was the significance of Hans Spemann's studies with embryos?
-Microsurgical manipulation of embryos -- had unexpected results -split into identical twins
What was von Baer's epiphany?
-Nearly all animal organs can be traced back to an exact layer of cells - one of 3 germ layers
On molecular side: Do single celled animals have the genes for cell adhesion, communication, etc???
-No—most don't; genes evolved with bodies
planning
-Only access via small aircraft so weight critical. -They planned everything down to the number of candybars -After 4 summers with no luck they found a fossil fish with a flat head
Gill arch genes:
-Otx genes associated with 1st gill arch -Hox genes associated with 2nd- 4th gill archs. -each gill arch has a different set of active Hox genes -change the "address" of these active genes and you can get a mutant with more parts than they should have -Just as in Drosophila Hox genes control segmental development
Where did Shubin and colleagues try looking first? What age rock are they targeting?
-Pennsylvania -Devonian era
When do the earliest bodies appear in the fossil record?
-Pre-cambrian >600 million years
The eight Hox genes (all have the homeobox sequence) discovered in the 1980's:
-Proteins made from these genes specify characteristics controlling position during development so that structures form in correct place. -The coolest part is that they are collinear! They are positioned in the same order of their expression along the front to back of the developing animal.
Sonic hedgehog controls fin development in these animals in the same way it worked in chickens (Cliff Tabin's et al.'s research)...
-Randy Dahl's work with Sonic hedgehog in skates and sharks (cartilaginous fish).
What is significance of Wilson's experiments with sponges early 20th century?
-Show specialization and can reassemble after being sieved! -While all the molecular body building components are all present they are in simpler form and smaller numbers
Who pointed out this pattern and how all tetrapods share these traits?
-Sir Richard Owen, Mid-1800's, On the Nature of Limbs -Darwin used Owen's book a few years later to bolster his argument for common descent
So what came first? Jaws Teeth Bones or did All evolve simultaneously
-TEETH EVOLVE FIRST!
So what exactly did Spemann's student Hilde Mangold discover?
-The "organizer" region -- a group of cells with the ability to instruct adjacent cells into to doing specific things. -Worthy of a Nobel Prize! But not for her..... -The award cites "his discovery of the Organizer and its effect in embryonic development."
But then there are Choanoflagellates. First thought to be degenerate sponges but phylogenetic analysis places them as sister to metazoans so they are not sponges.
-They are true single-celled organisms. -However, They DO HAVE genes for glue, rivets, communication
So no bodies for 3.5 billion years and then suddenly over a span of 40 million years --- bodies everywhere. WHY? Timing is everything.... What are some of the reasons postulated for origin of bodies?
-To escape predation, to eat bigger things, to move faster, all possibilities but.. -Definitely required the manufacture of collagen because collagen is metabolically expensive and requires oxygen it was impossible until oxygen levels in the atmosphere reached about todays levels; roughly 1 billion years before present
In humans, the facial nerve co-opted for control over muscles used for facial expression, facial expression important in primates. What adaptive importance does expression have for sharks?
-Trigeminal nerve retains a similar role in sharks and humans - muscle control and sensory information
This hypothetical column does not exist—not even in the Grand Canyon
-Uplift of the Colorado Plateau was a key step in the eventual formation of Grand Canyon -The action of plate tectonics lifted the rocks high and flat, creating a plateau through which the Colorado River could cut down.
1950's -1960's Research on limb development
• A lot of microsurgery • Depending upon when the apical limb bud tissue was removed affected how much of the limb developed
What do the teeth (incisors, premolars, molars) of humans tell us about human lifestyle or, at least, their eating habits?
-We are generalist feeders. Not terribly specialized.
filling the gap
-Zebrafish have many bones at base of webbing -Lungfish are an enigma with a single digit at the base of a linear array -Eusthenopteron has the beginnings of upper bones -Acanthostega has all bones with fully formed digits
All chordates and arthropods share...
-a body plan with a front and back end -as well as bilateral symmetry
What was the first animal group/phylum on land?
-arthropods
This book is all about why we are a mess—
-because we carry with us the history of all of our vertebrate ancestors -Natural Selection couldn't start over and fix things so we are an amalgamation of our past -Imperfect design as a result of evolution through natural selection
Tree thinking time: If Sonic hedgehog gene homologues are found in both arthropods like fruit flies and vertebrates like chickens, where did this gene first evolve (at a minimum) based on the tree shown?
-bilateria
1990's; What is the role of the Sonic hedgehog gene?
-bristle formation; differentiation on thorax
Haeckel
-developmental stages recapitulate adult evolutionary stages Does this mean that "ontogeny recapitulates phylogeny"?
Why does the exposure of a hand on a cadaver bring about such an emotional response in Shubin?
-hand is what makes us human -"The most remarkable is the hand. It's a physical manifestation of our ability to go to the bottom of the ocean and into outer space."
What does Neil mean when he says "Finding fossils is something we can often do with surprising precision and predictability"? What is Neil looking for in the fossil record?
-looking for transition from fish to amphibian -composition of rocks; law of superposition
Von Baer
-no recapitulation: embryo's development increasingly diverse
How is Neil Shubin uniquely qualified to teach human anatomy at a medical school?
-paleontology
"It took us six years to find it, but this fossil confirmed a prediction of...
-paleontology: not only was the new fish an intermediate between two different kinds of animal, but we had found it also in the right time period in earth's history and in the right ancient environment"
Scientific prediction time: If chickens (birds) and cartilaginous fishes, like skates, share a more recent common ancestor do than fruit flies and chickens, what too should they possess and why?
-sonic the hedgehog; common ancestor
If you imagine the human body as a wiring diagram...
-that's where you'd say, "No way does that work" -Neil Shubin
how genes in humans and flies
-this shared DNA machinery holds true for things with bilateral symmetry -members of Bilateria
Hilde Mangold (grad student of Spemann's) remarkable work with embryos and the discovery of the Organizer region of cells.
-twin production
Embryos of chordates all share:
1. Notochords 2. Gill arches
How does this relate to the zoo?
• Just like the zoo there is an organization to fossil appearances • Synapomorphies
1930's -1940's Research on limb development required:
• Large embryos (chickens) • Readily available • Easy to manipulate--Microsurgery • Contained in a protected environment
Properties common to all bodies:
• Structural molecules (collagens, proteoglycans) • Rivets to hold cells together (many types of rivets) • Ability to communicate
What do Osteostraci (formerly Ostracoderms) represent?
• The sister group to all jawed vertebrates • 425-450 mya Ordovician • Slow, bottom-dwelling with thick bony plates and scales, poorly developed fins no jaws • First vertebrates with a bony head case • The bony plates are formed from millions of tiny teeth under the microscope
Von Baer named the three layers:
• ectoderm (skin/brain cells, hair, tooth enamel, nails) • mesoderm (organs, muscle) • endoderm (lungs, gut track) -Then he started comparing embryos of MANY DIFFERENT SPECIES
