Vertebrates evolution Flashcards
What are the roots of the Chordata phylum?
530 MYA
- Chordate-like fossils in Canada & China are ancestral “missing links” between invertebrates & vertebrates
- Similar to lancelets but appeared to have a
larger brain and eyes, no cranium
- Present but rare in Burgess Shale
- Segmented body & tentacles 1.5 inches long
What are the four main features of chordates anatomy?
- Notochord
- Dorsal, hollow nerve cord
- Pharyngeal slits
- Muscular, post-anal tail
What is a notochord?
The notochord is a longitudinal, flexible rod between the digestive tube and nerve cord
- It provides skeletal support throughout most of
the length of a chordate
- In most vertebrates, a more complex, joined
skeleton develops, and the adult retains only
remnants of the embryonic notochord
What are dorsal hollow nerve cords?
The nerve cord of a chordate embryo develops from a plate of ectoderm that rolls into a tube dorsal to the notochord
- The nerve cord develops into the central
nervous system: the brain and the spinal cord
What is the muscular post-anal tail?
In many species, the tail is greatly reduced during embryonic development
- Chordates have a tail posterior to the anus
- The tail contains skeletal elements and muscle
blocks
- It provides propelling force in many aquatic
species
What are the pharyngeal clefts/slits?
In most chordates, grooves in the pharynx called pharyngeal clefts develop into slits that open to the outside of the body
- Functions of the pharyngeal slits:
- Suspension-feeding structures in many
invertebrate chordates
- Gas exchange in aquatic vertebrates
- Tetrapods have pharyngeal pouches that develop into parts of the ear, head, and neck (eustachian tube, middle ear, tonsils, parathyroid, and thymus)
What do Hox genes control?
They control morphology
How did Lewis discover hox genes?
- Found a cluster of homeotic (Hox) genes in the
chromosome - Saw colinearity in time and space
What did the gene order in the cluster Lewis found mimic?
The order of expression of genes and their function along the anterior-posterior (A-P) body axis
What does exhibiting temporal colinearity look like?
Having the anterior genes expressed first during development and posterior later
What are Hox genes?
Transcription factors
- Proteins that bind to specific sequences of DNA
(the Cis-regulatory elements) to control the
transcription of genetic information from DNA to
RNA
How do HOX genes orchestrate the construction of body parts?
- DNA is wound up like a spool of yarn. As the
spool is unwound the emerging genes become
active - A new gene comes out of the spool every ninety
minutes, which corresponds to the time needed
for a new layer of the embryo to be built - It takes two days for the strand to completely
unwind, the same time that’s needed for all the
layers of the embryo to be completed
What organisms make up the subphylum Urochordata?
Also known as Tunicata, tunicates or sea squirts
- Two siphons
- Filter-feeding
What are tunicates?
Adult animals without backbones, a Chordate-like larva
What does appearance of self-recognization affect?
Whether tissue transplants graft or are rejected
- Fusion/rejection based on sharing same allele
for FuHC gene (Fusion Histocompatibility
Complex)
What makes the vertebrates phylum special?
- A skeletal system and complex nervous system
that allows vertebrates efficiency at two essential
tasks- Capturing food
- Evading predators
- Vertebrae enclosed the spinal chord and
replaced notochord
How many sets of Hox genes do vertebrates have?
2 sets
What do vertebrates possess that is involved in the formation of the cranium?
A neural crest
What is the neural crest and what does it form?
- The neural crest is a group of embryonic cells
that form near the dorsal margins of the closing
neural tube - They form certain craniofacial structures
What are craniates?
Chordates that have a head
- A distinct skull contains a brain at the anterior
end of the dorsal nerve cord, eyes and other
sensory organs
- Enables chordates to coordinate more complex
movement and feeding behaviors
What are the main differences between chordates and craniates?
Chordates
- One hox gene cluster
- Less active
- No muscles lining the digestive tract
- Tubular heart
- No kidneys
Craniates
- Two hox gene clusters
- More active + higher metabolic rate
- Muscular lining of digestive tract
- 2-chambered heart
- Kidneys
- Hemoglobin & Red blood cells
What organism belongs to the myxini family?
Hagfish (~30 species)
- Marine scavengers
- Cartilaginous skeleton & notochord
- No jaws and very reduced vertebrae
- Fossil evidence date them at ~300 MYA
- Glands along body produce copious amounts of
slime
What organism belongs to the Petromyzontida family?
Lampreys
- Represent the oldest living lineage of vertebrates
- Cartilaginous skeleton
- The notochord has cartilaginous projections that
enclose the nerve cord
- Jawless mouth
- External parasites
What are conodonts?
Extinct jawless vertebrates with mineralized elements
What are ostracoderms?
Extinct jawless vertebrate with mineralized teeth and armor from ~450-375 MYA
- Used muscular pharynx to suck in food
What hypothesis about mineralization was formed after the discovery of the ostracoderms?
Mineralization was initiated in teeth, then spread to armor, and later still to the endoskeleton
What are gnathostomes?
Vertebrates that have jaws and paired fins
What is the advantage of having jaws & paired fins?
Jaws & paired fins enabled many fish species to be active predators, allowing for diversification of lifestyles & nutrient sources
What is the current hypothesis about how vertebrates jaws evolved?
Vertebrate jaws evolved by modification of skeletal rods that previously supported anterior pharyngeal slits
- Remaining gill slits remain as sites of respiration
What characteristic are common to gnathostomes?
- Genome duplication, including duplication of
Hox genes - An enlarged forebrain associated with enhanced
senses of smell and vision - The lateral line system, rows of organs sensitive
to vibrations that are located along each side of
the body of aquatic gnathostomes
What did the Silurian and early Devonian periods see a dramatic increase in?
Jawed fish in the fossil record
What kind of skeletal structure do cartilaginous fish have?
They have a flexible endoskeleton of cartilage rather than bone
What is the cartilaginous skeleton?
A derived condition
What is the evolution of the cartilaginous skeleton in chondrichthyes?
- Primitive gnathostomes that pre-date the
Chondrichthyes had bony skeletons and teeth,
ie. contained mineral mineral calcium phosphate - Bonelike tissues are found in some early shark
fossils - Traces of bone found in scales, based of teeth,
and on vertebrae surface - Loss of bone is modern Chondrichthyes
emerged after they diverged from gnathostomes
What are osteichthyes (bony fish)
- The most numerous vertebrates, both in
individuals & species (~30,000) - Bony endoskeleton containing calcium
phosphate - Scales also derived from bone
What are the three extant classes?
- Actinopterygii: ray-finned fishes
- Actinistia: lobe-finned fishes (coelocanths)
- Dipnoi: lungfish
What kind of organisms belongs to the Actinopterygii class?
The ray-finned fishes - named for the bony rays that support fins
- Includes bass, trout, perch, tuna and herring
- Fins may be modified for maneuvering, defense,
and other functions
What kind of organisms belongs to the Actinistia class?
Lobe-finned fishes with muscular pectoral & pelvic fins supported by extensions of bony skeleton
What did Marjorie Courtenay-Latimer do?
- Rediscovered Coelacanths, which were thought
to have gone extinct 65 mya, in 1938 - Genus Latimeria is named for her
- Now present in S. Africa and S. Pacific
What organism belongs to the dipnoi class?
Lungfish
- Generally inhabit stagnant ponds & swamps
- Can gulp air into lungs connected to the pharynx
- Australian lungfish still have gills
- During dry season, some lungfishes can burrow
into mud & aestivate
Where would we find transitional species?
- Shallow estuary or tidal flat
- Warm, equatorial climate
- Late Devonian era, around 370 mya
- Presently exposed for exploration
What did Ted Daeschler & Neil Shubin discover in 2006?
10 specimens of Tiktaalik found in a Canadian rock bed estimated to be 375 million years old
What fish like characteristics did the Tiktaalik specimens have?
- Gills and a lung, gills had a reduced bony covering
- Had scales covering its body like a fish
- Had fins that could be used for swimming
What tetrapod characteristics did the Tiktaalik specimens have?
-Had a flat skull
- Had eyes on top of its skull
- Had ear notches that were larger than those
seen in other Devonian fish (notches later
became ears)
- Had a full set of ribs that were needed for
breathing and support out of water
- Had a neck that could move its head around
What was known about the fin skeleton that Tiktaalik specimen had?
- It is a transition between a fin and foot
- Probably wasn’t used for walking but could
support animal’s weight - Fossil record shows fins increasingly evolved an
internal structure similar to limbed animals
What did Neil Subin dub the Tiktaalik and why?
He dubbed it a “FIshapod” because it possessed multiple intermediate characteristics of fish and tetrapods
Why was the date of the first tetrapod revised to 395 mya?
- Tracks were found on what would have been the
Polish coast - Spacing indicates animals from 0.5 to 2.5 cm
long - No fossil skeleton found yet
What are the five main characteristics of tetrapods?
- Four “feet”
- Digits - feet have digits to transmit muscle force
to ground - Neck - head is separated from body by 1 or
more vertebrae - Pelvic girdle - bones fused to vertebrae so that
force from hind legs on ground is transferred to
rest of body - Pharyngeal clefts - give rise to facial structures
and glands, loss of gills
What did amphibians benefit from as the earliest terrestrial tetrapods?
They benefited from moist climate, abundant food & relatively little competition
What amphibians live two lives?
Aquatic tadpole larva metamorphoses to a terrestrial adult frog
- Tadpoles usually aquatic herbivores with gills, a
lateral line system, and swim by undulating tail
- During metamorphosis, the tadpole develops
legs, the lateral line disappears, and gills are
replaced by lungs
- Adult frogs are carnivorous hunters
What amphibians live one life?
- Amphibians such as salamandres do not live 2
lives - larvae and adults look alike - Aquatic salamander species often show
paedomorphosis - retention of larval features in
a sexually mature adult
Where are amphibians generally found?
- Generally found near water or in very humid
environments - Many species rely on moist skin for gas
exchange - Eggs lack shell & dehydrate quickly in dry air
What kind of egg enables all-terrestrial life cycles?
An amniotic egg
- Extraembryonic membranes function in gas
exchange, waste storage, and transfer of stored
nutrients to embryo
What reptilian adaptations for terrestrial life are not generally found in amphibians?
- Reptiles obtain oxygen with lungs (increasing use
of ribcage), not through their skin - Scales, containing keratin, waterproof skin,
preventing dehydration - Internal fertilization, has to occur before shell is secreted
What is an ectotherm?
- Organisms that regulate their body temperature
through behavior adaptations like basking or
panting - Most reptiles are ectothermic, absorbing
external heat as the main source of body heat
What did scientists discover about dinosaurs when they were able to measure their body temperature?
That some dinosaurs were as warm as most modern mammals
- They did this by measuring the concentrations of
isotopes carbon-13 and oxygen-18 in bioapatite,
a mineral found in teeth and bone
What did the sequences of T. rex collagen proteins indicate?
That the closest living relative to them is an ostrich
What are archaeopteryx?
Mesozoic birds known from Bavarian fossils, fist found in 1860
- Lived ~150 MYA, during late Jurassic
- Had clawed forelimbs, teeth, and a long tail
containing vertebrae
- Probably glided or flew short distances
What were extinct by the end of the Cretaceous period?
Dinosaurs went extinct
- Dinosaurs may have been in decline before the
asteroid impact near Yucatan Peninsula
