Transcript Lobe-Fins

Ancestral deuterostome
Notochord
Brain
Head
Vertebral column
Jaws, mineralized skeleton
Lobed fins
Lungs or lung derivatives
Legs
Mammalia
(mammals)
Reptilia
(turtles, snakes,
crocodiles, birds)
Amphibia
(frogs, salamanders)
Dipnoi
(lungfishes)
Actinistia
(coelacanths)
Actinopterygii
(ray-finned fishes)
Chondrichthyes
(sharks, rays, chimaeras)
Cephalaspidomorphi
(lampreys)
Myxini
(hagfishes)
Cephalochordata
(lancelets)
Urochordata
(tunicates)
Echinodermata
(sister group to chordates)
• A hypothetical phylogeny of chordates
Chordates
Craniates
Vertebrates
Gnathostomes
Osteichthyans
Lobe-fins
Tetrapods
Amniotes
Milk
Amniotic egg
Derived Characters of
Chordates
• All chordates share a set of derived
characters
– Although some species possess some of
these traits only during embryonic
Brain
Notochord
Muscle
development
segments
Dorsal,
hollow
nerve cord
Mouth
Anus
Muscular,
post-anal tail
Figure 34.3
Pharyngeal
slits or clefts
• The notochordNotochord
– Is a longitudinal, flexible rod located between
the digestive tube and the nerve cord
– Provides skeletal support throughout most of
the length of a chordate
• In most vertebrates, a more complex, jointed
skeleton develops
– And the adult retains only remnants of the
embryonic notochord
Dorsal, Hollow Nerve Cord
• The nerve cord of a chordate embryo
– Develops from a plate of ectoderm that rolls
into a tube dorsal to the notochord
– Develops into the central nervous system: the
brain and the spinal cord
Pharyngeal
Slits or
Clefts
• In most
chordates, grooves
in the
pharynx
called pharyngeal clefts
– Develop into slits that open to the outside of the
body
• These pharyngeal slits
– Function as suspension-feeding structures in
many invertebrate chordates
– Are modified for gas exchange in aquatic
vertebrates
– Develop into parts of the ear, head, and neck in
terrestrial vertebrates
Muscular,
Post-Anal
Tail to
• Chordates
have a tail
extending posterior
the anus
– Although in many species it is lost during
embryonic development
• The chordate tail contains skeletal elements
and muscles
– And it provides much of the propelling force in
many aquatic species
Tunicates
• Tunicates, subphylum Urochordata
– Belong to the deepest-branching lineage of
chordates
– Are marine suspension feeders commonly
called sea squirts
• Tunicates most resemble chordates during
their larval stage
Notochord
– Which may be as brief as a few minutes
Dorsal, hollow
nerve cord
Tail
Excurrent
siphon
Incurrent
siphon
Muscle
segments
Intestine
Stomach
Atrium
Pharynx with slits
Figure 34.4c
(c) A tunicate larva is a free-swimming but
nonfeeding “tadpole” in which all four
chief characters of chordates are evident.
• As an adult
– A tunicate draws in water through an incurrent
siphon, filtering food particles
Incurrent
siphon
to mouth
Excurrent
siphon
Excurrent
siphon
Atrium
Pharynx
with
numerous
slits
Tunic
Anus
Intestine
Esophagus
Stomach
Figure 34.4a, b
(a) An adult tunicate, or
sea squirt, is a sessile
animal (photo is
approximately life-sized).
(b) In the adult, prominent
pharyngeal slits function
in suspension feeding,
but other chordate
characters are not obvious.
Lancelets
• Lancelets, subphylum Cephalochordata
– Are named forTentacle
their bladelike shape
Mouth
Pharyngeal slits
Atrium
Notochord
Digestive tract
Atriopore
Dorsal, hollow
nerve cord
Segmental
muscles
Anus
Tail
Figure 34.5
2 cm
• Lancelets are marine suspension feeders
– That retain the characteristics of the chordate
body plan as adults
Early Chordate Evolution
• The current life history of tunicates
– Probably does not reflect that of the ancestral
chordate
BF1 in lancelets
• Gene expression
Otx
Hox3
– Holds clues to the evolution
of the vertebrate
form
Nerve cord of lancelet
embryo
BF1
Hox3
Otx
Brain of vertebrate embryo
(shown straightened)
Midbrain
Figure 34.6
Forebrain
Hindbrain
• Concept 34.2: Craniates are chordates that
have a head
• The origin of a head
– Opened up a completely new way of feeding for
chordates: active predation
• Craniates share some common
characteristics
– A skull, brain, eyes, and other sensory organs
Derived Characters of Craniates
• One feature unique to craniates
– Is the neural crest, a collection of cells that
Neural
Neural
Dorsal edges
appears near
the dorsal
margins
tube of the
crest
of neural plate
Ectoderm
closing
neural
tube
in
an
embryo
Ectoderm
Notochord
(a) The neural crest consists of
bilateral bands of cells near
the margins of the embryonic
Figure 34.7a, b
folds that form the neural tube.
Migrating neural
crest cells
(b) Neural crest cells migrate to
distant sites in the embryo.
• Neural crest cells
– Give rise to a variety of structures, including
some of the bones and cartilage of the skull
(c) The cells give rise to some
of the anatomical structures
unique to vertebrates, including
some of the bones and cartilage
of the skull.
Figure 34.7c
The Origin of Craniates
• Craniates evolved at least 530 million
years ago
– During the Cambrian explosion
• The most primitive of the fossils
– Are those of the 3-cm-long Haikouella
(a) Haikouella. Discovered in 1999 in
southern China, Haikouella had eyes
and a brain but lacked a skull, a
derived trait of craniates.
Figure 34.8a
• In other Cambrian rocks
– Paleontologists have found fossils of even
5 mm
more advanced chordates, such as
Haikouichthys
(b) Haikouichthys. Haikouichthys had a
skull and thus is considered a true craniate.
Figure 34.8b
Hagfishes
• The least derived craniate lineage that still
survives
Slime glands
– Is class Myxini, the hagfishes
Figure 34.9
• Hagfishes are jawless marine craniates
– That have a cartilaginous skull and axial rod
of cartilage derived from the notochord
– That lack vertebrae
• Concept 34.3: Vertebrates are craniates
that have a backbone
• During the Cambrian period
– A lineage of craniates evolved into vertebrates
Derived Characters of
Vertebrates
• Vertebrates have
– Vertebrae enclosing a spinal cord
– An elaborate skull
– Fin rays, in aquatic forms
Lampreys
• Lampreys, class Cephalaspidomorphi
– Represent the oldest living lineage of
vertebrates
– Have cartilaginous segments surrounding the
notochord and arching partly over the nerve
cord
• Lampreys are jawless vertebrates
– Inhabiting various marine and freshwater
habitats
Figure 34.10
Fossils of Early Vertebrates
• Conodonts were the first vertebrates
– With mineralized skeletal elements in their
mouth and pharynx
Dorsal view
of head
Figure 34.11
Dental
elements
• Armored, jawless vertebrates called
ostracoderms
– Had defensive plates of bone on their skin
Pteraspis
Pharyngolepis
Figure 34.12
Origins of Bone and Teeth
• Mineralization
– Appears to have originated with vertebrate
mouthparts
• The vertebrate endoskeleton
– Became fully mineralized much later
• Concept 34.4: Gnathostomes are
vertebrates that have jaws
• Today, jawless vertebrates
– Are far outnumbered by those with jaws
Derived Characters of
Gnathostomes
• Gnathostomes haveGill jaws
slits
Cranium
– That evolved from skeletal supports of the
pharyngeal slits
Mouth
Skeletal rods
Figure 34.13
• Other characters common to gnathostomes
include
– Enhanced sensory systems, including the
lateral line system
– An extensively mineralized endoskeleton
– Paired appendages
Fossil Gnathostomes
• The earliest gnathostomes in the fossil
record
– Are an extinct lineage of armored vertebrates
called placoderms
(a) Coccosteus, a placoderm
Figure 34.14a
• Another group of jawed vertebrates called
acanthodians
– Radiated during the Devonian period
– Were closely related to the ancestors of
osteichthyans
(b) Climatius, an acanthodian
Figure 34.14b
•
Chondrichthyans (Sharks, Rays,
Membersand
of class
Chondrichthyes
Their Relatives)
– Have a skeleton that is composed primarily of
cartilage
• The cartilaginous skeleton
– Evolved secondarily from an ancestral
mineralized skeleton
• The largest and most diverse subclass of
Chondrichthyes
– Includes the sharks and rays
(a) Blacktip reef shark (Carcharhinus melanopterus).
Fast swimmers with acute senses, sharks have
paired pectoral and pelvic fins.
(b) Southern stingray (Dasyatis americana).
Most rays are flattened bottom-dwellers that
crush molluscs and crustaceans for food. Some
rays cruise in open water and scoop food into
Figure 34.15a, b their gaping mouth.
Pectoral fins
Pelvic fins
• A second subclass
– Is composed of a few dozen species of
ratfishes
(c) Spotted ratfish (Hydrolagus colliei). Ratfishes,
or chimaeras, typically live at depths greater
than 80 m and feed on shrimps, molluscs,
and sea urchins. Some species have a poisonous
spine at the front of their dorsal fin.
Figure 34.15c
• Most sharks
– Have a streamlined body and are swift
swimmers
– Have acute senses
Ray-Finned Fishes and LobeFins
• The vast majority of vertebrates
– Belong to a clade of gnathostomes called
Osteichthyes
• Nearly all living osteichthyans
– Have a bony endoskeleton
• Aquatic osteichthyans
– Are the vertebrates we informally call fishes
– Control their buoyancy with an air sac known as
a swim bladder
• Fishes breathe by drawing water over four
or five pairs of gills
Caudal
– Located in chambers
covered
by
a
protective
fin
Swim bladder
Spinal cord
bony flap
called the operculum
Brain
Dorsal fin
Adipose fin
(characteristic of
trout)
Nostril
Cut edge of
operculum Gills
Heart
Figure 34.16
Gonad
Urinary
Anus bladder
Liver
Kidney
Intestine
Stomach Pelvic fin
Anal fin
Lateral
line
Ray-Finned Fishes
• Class Actinopterygii, the ray-finned fishes
– Includes nearly all the familiar aquatic
osteichthyans
(a) Yellowfin tuna (Thunnus
albacares), a fast-swimming,
schooling fish that is an important
commercial fish worldwide
(b) Clownfish (Amphiprion
ocellaris), a mutualistic
symbiont of sea anemones
Figure 34.17a–d
(c) Sea horse (Hippocampus
ramulosus), unusual in
the animal kingdom in that
the male carries the young
during their embryonic
development
(d) Fine-spotted moray eel
(Gymnothorax dovii), a
predator that ambushes
prey from crevices in its
coral reef habitat
• The fins, supported mainly by long, flexible
rays
– Are modified for maneuvering, defense, and
other functions
Lobe-Fins
• The lobe-fins, class Sarcopterygii
– Have muscular and pectoral fins
– Include coelacanths, lungfishes, and
tetrapods
Figure 34.18
• Concept 34.5: Tetrapods are gnathostomes
that have limbs and feet
• One of the most significant events in
vertebrate history
– Was when the fins of some lobe-fins evolved
into the limbs and feet of tetrapods