SPECIALIZATIONS

Nails, Claws, Hooves
Nails- plates of tight cornified epithelial cells on the surface of fingers and toes

Claws or talons- curved, laterally compressed keratinized projections from the tips of digits

Hooves- enlarged keratinized plates on the tips of ungulate digits

Horns and Antlers
Horns- a cornified sheath, produced by the integument, that overlies a bony core

Antlers- living skin, called velvet, that overlies and shapes growing bone

Baleen
Baleen- integument within the mouths of some whales that act as strainers

Scales
Scales- folds in the integument

Dermal Armor
Carapace- the dorsal half of turtle shells

Plastron- fused dermal bones along the belly of turtles

Color
Melanophore- a chromatophore that contains the pigment melanin

Melanosomes- cellular organells that house melanin granules that stop harmful radiation

Dermal melanophore- a broad flat cell that changes color rapidly, found in ectotherms

Epidermal melanophore- a thin elongated cell in vertebrates, mostly in endotherms

Iridophore- a chromatophore that contains light-reflecting, crystalline platelets

Erythrophore- a chromatophore that contains red pigments
INTRODUCTION
The vertebrate cranium (skull) is a structure formed of three distinct parts:
1.Splanchnocranium (visceral cranium)-
arose to support pharyngeal slits in protochordates
2. Chondrocranium- underlies and supports
the brain, formed of bone or cartilage
3. Dermatocranium- forms most of the outer casing of the skull of later vertebrates

Braincase- the fused cranial components surrounding and encasing the brain (dermato, chondro, and splanchnocrania)

Neurocranium- the chondrocranium along with fused or attached sensory capsules

CHONDROCRANIUM
Elements of it appear to lie in series with the bases of the vertebrae.

Embryology
Cartilage grows and fuses together to produce the:
1.Ethmoid plate- the region between the
nasal capsule- sensory capsules associated
with the nose
2. Basal plate- between the otic capsules-
sensory capsules associated with ears
3. Occipital arch- cartilage around the nerve cord that later ossify and form basic bones and optic capsules- sensory capsules
associated with eyes
SPLANCHNOCRANIUM
In amphioxus it, or at least its forerunner, is associated with the filter-feeding surfaces.

Among vertebrates, it supports the gills and offers attachment for respiratory muscles. Its elements contribute to jaws and hyoid apparatus of the gnathostomes.

Embryology
It arises from neural crest cells.

In protochordates, neural crest cells are absent. Pharyngeal bars form the branchial basket, the predecessor of the vertebrate splanchnocranium.

In vertebrates, cells of the neural crest depart from the sides of the neural tube and move into the walls of the pharynx between pharyngeal slits to form pharyngeal arches-
branchial/gill arches of aquatic vertebrates

Each arch has 5 elements, dorsal to ventral:
1.the pharyngobranchial element
2.the epibranchial element
3.the ceratobranchial element
4.the hypobranchial element
5.the basibranchial element

One or more anterior branchial arches may: 1. Border the mouth
2. Support soft tissue
3. Bear teeth

Jaws- branchial arches that support the mouth.

Mandibular arch- the largest and most anterior of the modified arches.

This arch is composed of, dorsal to ventral:
1.the palatoquadrate
2.Meckel’s cartilage (mandibular cartilage)

Posterior to the mandibular arch but anterior to the branchial arches is the hyoid arch.
The hyoid arch is composed of the hyomandibula.
Origin of Jaws
Jaws arose from one of the anterior pair of gill arches. Evidence is from these sources:
1.Embryology of sharks suggests that jaws
and branchial arches develop similarly in series and both arise from neural crest
2. Nerves and blood vessels are
Distributed in a pattern similar to branchial arches and jaws
3. The musculature of the jaws appears to be
transformed and modified from branchial arch musculature
The specifics of the above are controversial.

Types of Jaw Attachments
Suspensorium- how the mandible is attached to the skull.

Paleostylic- none of the arches attach themselves directly to the skull (agnathans).

Euautostylic- the mandibular arch is suspended from the skull by itself without help from the hydroid arch (placoderms).

Amphistylic- jaws are attached to the braincase through two articulations:
1.by a ligament connecting the
palatoquadrate to the skull (anteriorly)
2. by the hyomandibula (posteriorly)
[early sharks (most modern ones have a
variation of this), some early bony fish]

Hyostylic- the mandibular arch is attached to the braincase primarily through the hyomandibula. Often a new dermal element, the symplectic bone, aids in jaw suspension (most modern bony fish)

Metautostylic- jaws are attached to the braincase directly through the quadrate- a bone formed in the posterior part of the palatoquadrate (most amphibians, reptiles, and birds).

Craniostylic- the entire upper jaw is incorporated into the braincase but the lower jaw is suspended from the dermal squamosal bone of the braincase (mammals).

In mammals, the splanchnocranium does not contribute to the adult jaws or their suspension.

DERMATOCRANIUM
It consists of dermal bones that form:
1.the sides and roof of the skull to complete the protective bony case around the brain
2.most of the bony lining of the roof of the
mouth
3. much of the splanochnocranium
These bones arise from the bony armor of the integument of early fishes.

Parts of the Dermatocranium
Facial Series
The facial series encircles the external naris and collectively forms the snout

Maxilla and premaxilla- the margin of the snout that has the teeth

Nasal- lies medial to the naris

Septomaxilla- sunken below the surface bones and aids in forming the nasal cavity

Orbital Series
The dermal bones that encircle the eye to define the orbit.

Lacrimal- the ring of bones in front of the orbit where tear ducts are located

Prefrontal, postfrontal, and postorbital- the ring of bones above and behind the orbit

Jugal- the lower rim of the orbit

Temporal Series
Lies behind the orbit and completes the posterior wall of the braincase.

Intertemporal, supratemporal, and tabular- a row of bones that make up the medial part

Squamosal and quadratojugal- bones that form the cheek

Vault Series
The vault (roofing bones) that run across the top of the skull and cover the brain beneath.
Frontal- anterior roof bone

Postparietal (interparietal)- posterior roof bone
Parietal- center roof bone between the frontal and postparietal bones

Palatal Series
Primary palate- bones that cover much of the roof of the mouth

Pterygoid- the largest and most medial bone

Vomer, palatine, and ectopterygoid- bones lateral to the pterygoid that may have teeth

Parasphenoid- an unpaired medial bone present in fishes and lower tetrapods

Mandibular Series
Meckel’s cartilage is usually encased in dermal bone.

Dentary- the lateral wall that has teeth

Angular- the posterior corner of the mandible
Surangular- above the angular

Prearticular and coronoids- make up the mandibular wall

Mandibular symphysis- the midline where left and right mandibles meet anteriorly
PHYLOGENY OF THE SKULL
Agnathans
Ostracoderms
Eyes: two, close-set, dorsally placed
Pineal opening: single, between eyes
Nostril: in front of the pineal opening

They had a single bony shield covering the head

Sequential branchial arches stretched like beams across the roof of the pharynx
Ostracoderms-Anaspids
Eyes: lateral,
Pineal opening: between eyes
Nostril: single, in front of pineal opening

Many small bony scales covered the head

Ostracoderms-Heterostracans
Eyes: small, laterally placed
Pineal opening: median
Nostril: not median, not present

Head was made of several fused bony plates

Cyclostomes
They lack bone entirely

Cyclostomes-Lampreys
Pineal opening: single
Nostril: single, median

Branchial arches form an unjointed branchial basket
Cyclostomes-Hagfishes
Pineal opening: not external
Nostril: median
Gnathostomes
Fishes
Fishes-Placoderms
Had a cranial shield- dermal plates of the head that were thick and tightly joined.

The braincase was heavily ossified and the upper jaws were attached to it.

Fishes-Acathodians
Some had an operculum- a bony flap that covered the exit gill slits

The mandibular arch was much like that of sharks and bony fishes. A hyoid arch and 5 successive branchial arches were present.

Fishes-Chondrichthyans
They have almost no bone
A dematocranium is absent
In primitive chondrichthyans, six gill arches trailed the mandibles. The upper jaw (palatoquadrate) of primitive sharks was supported by the braincase and probably by the hyomandibula.

In modern sharks, there is not a strong, direct attachment between hyomandibula and palatoquadrate. Instead, the jaws are suspended at two other sites.

Fishes-Actinopterygians
Early ones had long jaws that extended to the front of the head. The jaws carried numerous teeth and an operculum covered the gill arches. The hyoid arch increased its support of the mandibles.

In primitive ones the suspensorium is formed from the fusion of various bones that includes the hyomandibula, the palatine, and the quadrate. The suspensorium is shaped like an inverted triangle.

In advanced ones (like the teleosts) the neurocranium is raised and the mandible is lowered during jaw opening. The hyoid apparatus aids in suction.

Fishes-Sarcopterygians
In early lungfishes the upper jaw (palatoquadrate) was fused to the braincase.

Amphibians
In the early ones the hyomandibula ceases to be involved in jaw suspension and instead becomes dedicated to hearing as the columella (or stapes) within the middle ear. The opercular series of bones are lost.

They had a dermatocranium

In modern ones the jaw suspension is by the articular and quadrate bones through which the mandible articulates with the skull. The branchial arches are in the larvae are reduced to the hyoid apparatus in adults.
The splanocranium which is prominent in fish is reduced

Primitive Reptiles
The palatoquadrate of the mandibular arch was reduced to the small epipterygoid and separate quadrate. The hyoid arch produced the columella (stapes).

Modern Reptiles
There is no significant mobility in the in the dermatocranium so the mandible slides back and forth on the fixed quadrate from which it is suspended.

Birds
The palatal bones are reduced and lightened.
Vomers and ectopterygoids are small, pterygoids are short struts articulating with the quadrate, and epipterygoids are usually lost. The jaws are drawn out into a beak.

The upper temporal bar is absent, and the lower temporal bar is a slender rod called the jugal bar (quadratojugal-jugal bar), which extends from the beak posteriorly to the side of the movable (streptostylic) quadrate.

Synapsids
Primitive Synapsids
In the early ones, the temporal region developed an opening under which was the jugal and the squamosal bones.

In advanced ones and primitive mammals, the connection between the jugal and squamosal bones forms the cheek region

Mammals
Various dermal elements are lost in therian mammals including the septomaxilla, prefrontal, postorbital, postfrontal, quadratojugal, and supratemporal bones.

Monotremes retain several reptilian skull features, including prefrontal, and postfrontal bones

Placental Mammals
On the side of the brain case behind the orbit, a large temporal bone is formed by the fusion of contributions from all three parts of the skull

THE APPENDICULAR SKELETON
BASIC COMPONENTS
Appendicular skeleton- the fins or limbs and the girdles- the braces within the body that support the fins or limbs

Anterior girdle- the shoulder or pectoral girdle that support the pectoral fin or limb

Posterior girdle- the hip or pelvic girdle that support the pelvic fin or limb

Fins
Fins- membranous or webbed processes internally strengthened by radiating and thin dermal fin rays

Ceratotrichia- dermal fin rays in elasmobranchs

Lepidotrichia- dermal fin rays in bony fishes

Actinotrichia- keratinized rods that stiffen the fin tips of some bony fishes

Pterygiophores- supports the proximal part of the fin close to the body. There are two types:
1.Basals- in the proximal part of the fin
2.Radials- in the middle part of the fin
(Basals and radials are connected)

Fins occur singly, except for the pectoral fins (near the head) and the pelvic fins (posterior to pectoral fins).

These paired fins, pectoral and pelvic fins, receive attention because they are the phylogenetic source of the tetrapod limbs.

Limbs
The forelimbs and hindlimbs of tetrapods are composed of three regions:
1.Autopodium- the distal end of the limb
2. Zeugopodium- the middle region
3. Stylopodium- the region near the body

PHYLOGENY
Fishes
Agnathans
Ostracoderms had unpaired medial fins, a caudal fin on the tail, and often unpaired anal and dorsal fins. Most lacked paired pectoral fins. All lacked pelvic fins.

Some anaspids had long lateral fin folds running the length of their bodies.

Heterostraci and Galeaspida fossils lacked traces of paired fins

Living cyclostomes clearly lack paired fins

Only among some osteostracans were paired fins present and only in the pectoral region

Placoderms
Both pectoral and pelvic girdles were present.

Chondrichthyans
Primitive ones had pectoral and pelvic fins. They consisted of basal elements and tightly packed radials supporting the fin.

In later ones, the paired basal components of the pectoral and pelvic girdles became extended across the midline of the body to fuse into U-shaped:
Scapulocoracoid bars- fused basal components of pectoral girdles
Pubioischiac bars- fused basal components of pelvic girdles

Acanthodians
They had large spines that formed the leading edge of dorsal, anal, and paired fins. In some, the pectoral spine articulated with a girdle but the pelvic spine did not.

Bony Fishes
In actinopterygians the dermal shoulder girdle forms a U-shaped collar of bone around the posterior border of the gill chamber.

The sarcopterygians have muscles that project from the body to form the fleshy base of the fin.

The primitive ones had fin features that gave rise to the limb features of early tetrapods.

Surviving sarcopterygians such as the lungfish have reduced fins that are unsuited for land.

Surviving crossopterygians such as the coelacanth have fins that are unsuited for land as well

The pectoral and pelvic appendages of fossil rhipidistians had bones homologous to bones of early tetrapod limbs. The pectoral and pelvic fins articulated with girdle bone.

Tetrapods
In early amphibians, such as Ichthyostega, the girdles and limbs became stronger. The pectoral girdle lost its attachment to the skull. The fins were replaced by digits.

Aerial Locomotion
“Flying” fish spread especially wide pectoral fins during short flights above water

A species of tropical frog spreads its long, webbed toes to slow its airborne fall

Lizards with special flaps of skin and squirrels with loose skin between fore- and hindlimbs spread these membranes to slow their drop through the air or to extend the distance of their horizontal travel

All of these tentative fliers are not really fliers at all. They are gliders and parachutists.

True power flight occurs in just three groups:
1.bats
2.pterosaurs
3.most birds

In each group above, the forelimbs are modified into wings that both generate the force driving them forward through the air and provide lift against gravity.