Important developments of the Vertebrates:
brain and sense organs
 The
ancestors of vertebrates switched
from filter feeding to more active feeding,
which required movement and the ability
to sense the environment in detail.
Important developments of the Vertebrates:
brain and sense organs

The need to gather and analyze information led
to the development of multiple sense organs
among the vertebrates.

These include complex eyes, pressure
receptors, taste and smell receptors, lateral line
receptors for detecting water vibrations, and
electroreceptors that detect electrical currents.
Important developments of the Vertebrates:
brain and sense organs
 The
development of sensory structures
and increased mobility generated the need
for a control center to process information.
 The
anterior end of the nerve cord
consequently became enlarged into a
brain.
Important developments of the Vertebrates:
brain and sense organs
 The
vertebrate brain in fact developed into
a tripartite brain (with a forebrain,
midbrain, and hindbrain) that was
enclosed within a protective cranium of
bone or cartilage.
Human Brain
Brain structure
 In
the most primitive forms of brains the
forebrain is associated with the sense of
smell, the midbrain with vision and the
hindbrain with balance and hearing.
 From
this primitive condition the size and
complexity of the brain has greatly
increased.
Hindbrain

The Hindbrain has two portions

Most posterior portion is the Medulla oblongata. It
operates primarily at the reflex level. Reflex centers for
respiration, heartbeat, and intestinal movement are
found in the medulla oblongata.

The medulla oblongata also relays signals from the inner
ear and is a major pathway through which signals pass
to and from higher areas of the brain.

Damage to the medulla, not surprisingly, is lifethreatening.
Hindbrain: cerebellum

The anterior portion of the hindbrain includes the
cerebellum (present only in jawed vertebrates), which is
highly folded and convoluted.

The cerebellum integrates sensory information (touch,
vision, positional, hearing) with motor input to maintain
the organism’s equilibrium (its position and equilibrium in
relation to gravity).

The cerebellum also coordinates motor movements, both
reflex movements and directed movements.
Hindbrain: cerebellum
 If
the cerebellum is removed an
organism’s movements become
uncoordinated and uneven.
 In
humans damage to the cerebellum
causes a condition called dysmetria in
which someone reaching for a target with
their hands (or feet) overshoots or
undershoots it.
Cerebellum

The size of the cerebellum is proportional to its role.

In fish, the cerebellum is proportionally enlarged in part
because it must process lots of input from the lateral line
system, but also because fish must orient themselves in
three dimensions and equilibrium and balance are thus
very important.

In bottom-dwelling fish and those that are not active
swimmers the cerebellum is relatively small.
Midbrain

The midbrain develops in step with the eyes and is the
part of the brain that receives visual information.

The roof of the midbrain (the tectum) is the part that
receives visual information (and also lateral line and
auditory input). The floor of the midbrain (the
tegmentum) initiates motor output based on the input
received.

The midbrain is often the most prominent portion of the
brain in fish and amphibians
Frog brain model
academic.emporia.edu/sievertl/verstruc/fbrain.htm
Forebrain: diencephalon and
telencephalon
 The
forebrain has two major parts the
posterior diencephalon and the anterior
telencephalon.
 The
diencephalon includes the pineal
gland, pituitary gland, thalamus and the
hypothalamus.
Diencephalon: Hypothalamus

The hypothalamus plays a major role in
homeostasis, the regulation of the body’s
internal physiological balance including such
aspects as temperature, water balance, appetite,
blood pressure and sexual behavior.

It achieves this by the release of hormones
either produced in the hypothalamus itself or
stimulating the release of hormones from the
pituitary gland.
Diencephalon: Pituitary Gland
 The
posterior pituitary gland stores and
releases two hormones produced by the
hypothalamus: oxytocin and antidiuretic
hormone (ADH).
 In humans oxytocin stimulates uterine
contractions in childbirth and also milk
production.
 ADH acts on the kidneys to increase water
retention and reduce urine volume.
Diencephalon: Pituitary Gland

The anterior pituitary (AP) produces many
hormones that in turn control the activity and
hormone release from other endocrine glands
including the gonads, adrenal glands, and
thyroid.

Growth hormone is produced in the AP and has
a direct effect on growth. Excess production can
lead to gigantism and deficient production to
dwarfism.
Diencephalon: pineal gland and
thalamus
 The
pineal gland affects skin pigmentation
by affecting melanocytes. It also plays a
role in regulating biological rhythms.
 The
thalamus is the major coordinating
center for incoming sensory impulses from
all over the body and it relays the
information to the cerebral cortex.
Telencephalon

The telencephalon (or cerebrum) includes two
expanded lobes, the cerebral hemispheres
(which in many mammals are greatly folded) and
the olfactory bulbs.

The receipt of olfactory information is a major
role of the telencephalon and in species in which
olfactory information is important the olfactory
bulbs are greatly enlarged.
Cerebral hemispheres
 The
cerebral hemispheres in reptiles and
especially in birds and mammals are
enlarged 5 to 20-fold over those of nonamniotes of comparable size.
 The
enlarged size of the cerebral
hemispheres allows more and faster
processing of sensory information and
thus greater intelligence.
Cranial nerves

Not all nervous inputs and outputs to and from
the brain travel via the spinal cord.

A series of cranial nerves connect directly into
the brain.

Most have Roman numerals for names and
many of them directly connect to sensory
structures and other structures in the head.
Cranial nerves

The cranial nerves are:





Cranial nerve 0: Nervus terminalis runs to blood
vessels of the olfactory epithelium.
Cranial nerve I: Olfactory nerve: connects with
olfactory cells in the mucous membranes of the
olfactory sac.
Cranial nerve II: Optic nerve: connects to the eyes.
Cranial nerves III and IV and VI: connect to extrinsic
eye muscles.
Cranial nerve V: Trigeminal nerve: branches into three
nerves that connect to the eye, jaws and the skin of
the head. Cranial nerve VII also innervates the face
as well as the taste buds.
Cranial nerves






Cranial nerve VIII Auditory nerve connects to the inner
ear.
Cranial nerve IX: Glossopharyngeal nerve connects to
taste buds and parts of the throat.
Cranial nerve X: Vagus nerve: serves areas of the
mouth, pharynx and most of the viscera.
Cranial nerve XI: supplies some jaw muscles and the
trapezius.
Cranial nerve XII: Hypoglossal nerve innervates tongue
muscles
Cranial nerves arise from both neural crest cells and
from ectodermal placodes in the embryo
Neural crest cells

Neural crest cells are groups of special cells
derived from the embryonic dorsal tubular nerve
cord.
 Early in development these cells separate from
the neural tube before it closes.
 They assemble into cords above the neural tube
and migrate along distinct pathways to various
permanent locations where they differentiate into
a variety of structures.
Image Source: http://www.niaaa.nih.gov/publications/arh25-3/175-184.htm
Neural crest cells

Neural crest cells give rise to among other
structures:








Schwann cells
Some components of the peripheral nervous system
Odontoblasts (give rise to dentin)
Dermis of facial region (from which many skull bones
are produced)
Beak of birds
Some chromatophore cells
Connective tissue of the heart
Parts of the meninges
Ectodermal Placodes
 Ectodermal
placodes (with some
exceptions in fish) are thickenings of the
surface ectoderm that sink inwards and
develop into various sensory structures.
 Paired olfactory placodes that form at the
tip of the head develop into odor
receptors that connect to the brain.
 Paired optic placodes produce the lens of
the eye.
Ectodermal Placodes: Vestibular
apparatus
 Some
dorsolateral placodes (in fish) give
rise to the lateral line system.
 The otic placode (one of the dorsolateral
placodes) forms the vestibular apparatus
in the inner ear.
 The vestibular apparatus plays a major
role in both balance and hearing.
Ectodermal Placodes: Vestibular
apparatus

There are three semicircular canals (arranged at
roughly 90 degree angles to each other) and two
connecting structures (the sacculus and
utriculus) in the vestibular apparatus

The canals are fluid filled and respond to
rotation when the head is tilted. The information
about orientation and motion is then delivered to
the brain for interpretation.
http://goodrich.med.harvard.edu/pictures/BRODEL34smaller.bmp
Ectodermal Placodes: Vestibular
apparatus
 In
some fishes and in reptiles, birds and
mammals a section of the vestibular
apparatus (the lagena) is specialized for
sound reception.
 In
terrestrial vertebrates the lagena is
usually elongated and in most mammals it
becomes coiled forming the cochlea.
Ectodermal Placodes: Vestibular
apparatus

In mammals sound vibrations are transferred
from the eardrum via the inner ear bones
(malleus, incus and stapes) to the cochlea.

The vibrations cause hair cells in the fluid filled
cochlea to move and this movement is
converted into nerve signals that are then
transmitted to the brain where they are
interpreted as sounds.
http://www.tchain.com/otoneurology/images/master-ear.jpg
Significance of neural crest cells
and ectodermal placodes
 The
vertebrate head is mostly a collection
of parts that are derived from neural crest
or ectodermal placode tissue.
 These
unique tissues and their mode of
embryonic production distinguish
vertebrates from all other chordates.
The role of hox genes in the
evolution of the Vertebrates
 A factor
that may have played a role in the
evolution of the vertebrates is the
duplication of the Hox gene complex.
 Hox
(short for hemeobox) genes are
master control genes that regulate the
expression of a hierarchy of other genes
during development.
Hox genes
 Because
a single hox gene influences the
expression of many other structural genes
a change in when and where a hox gene
is turned on may lead to major
morphological changes in the phenotype
such as the addition or loss of legs, arms,
antennae and other structures.
http://evolution.berkeley.edu/evolibrary/images/mutantfly.jpg
Induced ectopic eyes
In Drosopila (arrowed)
From Induction of Ectopic Eyes by
Targeted Expression of
the eyeless Gene in Drosophila
Georg Halder,* Patrick Callaerts,*
Walter J. Gehring.
Science. Vol. 267 24 March 1995
Hox genes
 Invertebrates
and amphioxus have only
one set of hox genes, the living jawless
vertebrates have two sets, but all jawed
vertebrates have four sets.
Hox genes
 The
duplication of the Hox genes appears
to have occurred around the time
vertebrates originated and it may be that
this gene duplication freed up copies of
these genes, which control development,
to generate more complex animals.
Hox genes
 One
group of animals in whose evolution
hox genes are hypothesized to have
played a major role is snakes.
 It’s
suggested that the how genes
controlling the expression of the chest
region in lizard ancestors of snakes
expanded their zone of control in the
developing embryo.
Hox genes
 As
the hox genes for thoracic development
increased their influence, limb
development was suppressed at the same
time giving the limbless condition we wee
in snakes today.
Geological Time Scale
 Precambrian
4,500-542mya
 Paleozoic: 542-200 mya
 Mesozoic: 200-65 mya: Age of Dinosaurs
 Cenozoic: 65mya to present: Age of
Mammals
Paleozoic
 Cambrian:
542-488 mya. first appearance
of chordates
 Ordovician: 488-444 mya:
 Silurian: 444-416 mya
 Devonian: 416-359 mya
 Carboniferous: 359-299 mya
 Permian: 299-251 mya
 Triassic: 251-200 mya
Mesozoic
 Jurassic:
200-146 mya
 Cretaceous: 146-65 mya
 “Camels
Often Sit Down Carefully,
Perhaps Their Joints Creak”
Early vertebrate ancestors

Fossils of early chordates are scarce, but a few
are known including Pikaia from the Burgess
Shale (approx 505 mya) that appears to be an
early cephalochordate and has a notochord and
segmented muscles.

Unlike living cephalochordates it has a pair of
sensory tentacles. It was small, about 5cm long.
Figure 23.10
15.8
Pikaia
Pikaia
http://proto5.thinkquest.nl/~jre0294/pikaia%20plaatje.jpg
Early vertebrate ancestors

Another fossil from China is Haikouella lanceolata
about 525mya, which places it in time at the base
of the vertebrate radiation and a likely vertebrate
ancestor. It was about an inch long (<3cm).

Haikouella possesses all the chordate characters
and also a suite of vertebrate characters:





Dorsal nerve cord with a relatively large brain
Gills
Head with possible eyes
Pharyngeal muscles and gills
Myomeres
Haikouella lanceolata
Haikouella
Haikouichthys and Myllokunmingia
 Two
other Chinese fossils from the early
Cambrian are clearly early vertebrates.
These are Haikouichthys and the very
similar (perhaps identical) Myllokunmingia.
 As
in the case of Haikouella, both of these
animals were also small (<3cm).
Haikouichthys and Myllokunmingia

Both Haikouichthys and Myllokunmingia lacked
bone and cranial elements, but both possessed







Gill bars and gills,
V-shaped myomeres,
A head
A heart
Large eyes
An ear
Possible vertebrae
Myellokunmingia
Conodonts
 For
almost 150 years tiny, tooth-like
microfossils have been important index
fossils in geological studies.
 These
conodont elements are extremely
common in rocks from the late Cambrian
through the end of the Triassic. It was
unclear what organism they belonged to
until the early 1980’s.
Conodont
elements
http://content.answers.com/main/content/img/McGrawHill/Encyclopedia
/images/CE157400FG0010.gif
http://www.toyen.uio.no/palmus/galleri/montre/mic01.jpg
Conodont (Manticolepis subrecta) elements composed of
calcium-phosphate, and are tiny (0.1-0.2mm), toothlike
structures from the Devonian
Conodonts
 In
the 1980’s the discovery of
Carboniferous era conodont fossils in
Scotland and later in South Africa solved
the mystery.
 These
fossils were of a soft-bodied,
slender, laterally compressed animal with
a complete set of conodont elements in its
pharynx.
http://www.le.ac.uk/gl/map2/abstractsetc/conanimals.jpg
Conodonts

The fossils showed clear evidence that
conodonts were vertebrates. There were Vshaped myomeres, a notochord, caudal fin rays,
and what appeared to be a postanal tail and a
dorsal nerve cord.

In addition, histological examination of conodont
elements showed they contained a variety of
mineralized vertebrate dental tissues: cellular
bone, calcium phosphate crystals, calcified
cartilage, enamel and dentin.
Conodonts
 Because
dentin is laid down by
odontoblasts, the presence of dentin in
conodont elements is indirect evidence of
neural crest tissue, which is a uniquely
vertebrate characteristic.
 Condonts
animals were mostly 3-10cm
long although some may have been as big
as 30cm.
Conodont
Conodonts

There is evidence of wear on conodont elements
which suggests they were used to crush and slice
food.

Recent fossil evidence also shows the conodont
elements were attached to tongue-like or
cartilaginous plates that could be moved in and out
of the mouth presumably to impale and catch food
items.

This and the animal’s large eyes suggests that
conodonts actively selected larger food items and
likely were predators.
Ostracoderms: Jawless early
vertebrates
 A wide
variety of armored jawless fishes
collectively referred to as ostracoderms
(from the Greek ostrac a shell and derm
skin) are known from the very late
Cambrian and early Ordovician (488-444
mya) up to near the end of the Devonian
period (359 mya).
Ostracoderms

First vertebrates to possess bone and also the first to
possess an intricate lateral line system and an inner ear
with two semicircular canals.

Ostracoderms were encased in bony plates (with skin in
between the plates so they could flex). The bony plates
of the head in many cases were large and often fused
into a head shield

They did not have a well developed endoskeleton and it
was usually of cartilage. Given the lack of bony
vertebrae in fossils, presumably the body was stiffened
by a notochord.
Silurian marine fish fauna. Mostly agnathans, but also (#10) a gnathostome;
an acanthodian called Nostolepis . www.palaeos.com .
Ostracoderms
 Most
ostracoderms were small (10-35 cm
in length) and most lacked paired fins so
they probably were not precision
swimmers.
 The
ostracoderms were jawless with
narrow, fixed mouths. They appear to
have been mainly filter feeders that used
their pharyngeal muscles to pump water.
Ostracoderms
 Because
most ostracoderms were small,
filter feeders, many were dorsoventrally
flattened and most lacked fins it is likely
that they were poor swimmers and almost
certainly were bottom dwellers that
extracted food from sediments.
Ostracoderms
 The
phylogenetic relationships of the
various ostracoderm groups are still being
figured out.
 Major
groups include the
Pteraspidomorphs, Osteostracans and
Anaspids.
Pteraspidomorphs

Most Pteraspidomorphs had head shields formed by the
fusion of large bony plates. The rest of the body behind
the head is covered with small plates and scales.

None possessed paired fins, but some had spines that
projected from the head shield.

Pteraspidomorphs occur from the Ordovician to the late
Devonian.

They possessed paired nasal openings and a vestibular
apparatus with two semicircular canals.
(A Pteraspidomorph)
(An Anaspid)
Anaspids
 Appear
late in the Silurian and possess
much more flexible body armour made up
of small plates and a hypocercal tail (with
an extended ventral lobe) which suggest a
trend towards more open-water swimming.
Figure 23.14
A Pteraspidomorph
15.10
Ostracoderms (it should read anaspid not anapsid in the caption on the right).
Osteostracans
 Osteostracans
were also heavily armoured
and possessed a large head shield.
 Unlike
pteraspidomorphs, there were in
some species anterior lobes that projected
from the head shield (and are now
believed to be homologous to the pectoral
fins of gnathostomes). These would have
enhanced stability in swimming.
Osteostracans
 The
Osteostracans are considered to be
the closest known relatives of the
gnathostomes.
 Shared
derived characters linking them to
the gnathostomes include cellular dermal
bone, pectoral fins with a narrow base,
large orbits and calcified cartilage.
Figure 23.14
A Pteraspidomorph
15.10
Ostracoderms (it should read anaspid not anapsid in the caption on the right).
http://www.nature.com/nature/journal/v443/n7114/images/443921a-f1.0.jpg
Silurian marine fish fauna. Mostly agnathans, but also (#10) a gnathostome;
an acanthodian called Nostolepis . www.palaeos.com .
Ostracoderms
 Ultimately,
the ostracoderms were
outcompeted by fish that possessed the
next big evolutionary development: jaws.
 By
the end of the Devonian the
ostracoderms had become extinct. The
conodonts survived into the Jurassic and a
few other agnathans have survived to
today.