Chordata Lesson: Skeletal system and characteristics

• The skeletal system consists of bone and cartilage, supporting the body, providing muscle attachment, and storing minerals like calcium and phosphorus.
• The axial skeleton includes the skull, vertebrae, and ribs, positioned along the body's midline.
• The appendicular skeleton comprises fins or limbs and supporting structures like pectoral and pelvic girdles.

Phylum Chordata

• Includes mammals, birds, reptiles, amphibians, and fishes.
• Chordata is named for the notochord, a flexible rod supporting the body and serving as a muscle attachment site.
• In many species, vertebrae replace the notochord during development.
• Synapomorphies include the notochord, pharyngeal gill slits, a muscular post-anal tail, and a dorsal hollow nerve cord.
• Pharyngeal gill slits are involved in gas exchange and feeding.
• The muscular post-anal tail functions in locomotion.
• The dorsal hollow nerve cord is the evolutionary precursor to the central nervous system.

Subphylum Cephalochordata (Lancelets)

• Are the first group to diverge from other chordates.
• They retain all four chordate synapomorphies.
• Lancelets are marine burrowing animals that are suspension feeders.
• Suspension feeders use fleshy cirri around the mouth to capture food particles from the water.

Axial Structures

• Buccal cirri surround the mouth to aid feeding.
• Pharyngeal gill slits trap food particles in mucus.
• A notochord runs the length of the body.
• A dorsal hollow nerve cord runs along the body's length.
• The muscular post-anal tail is used for movement, powered by segmental muscles.

Appendicular Structures

• Lancelets lack an appendicular skeleton.
• They lack paired fins and are poor swimmers.

Subphylum Urochordata (Tunicates)

• Tunicates are named for their tails.
• Larvae possess all four chordate synapomorphies, while adults only have pharyngeal gill slits.
• Larvae are free-swimming, while adults are sessile filter feeders.
• The tunic is a thick tissue coating.

Larval Axial Structures

• The larva has no mouth, but has incurrent and excurrent siphons.
• Pharyngeal gill slits are present.
• A notochord runs the length of the larval body.
• A dorsal hollow nerve cord sits just dorsal to the notochord.
• The muscular post-anal tail allows swimming.

Adult Structures

• Adults lack a mouth, but have incurrent and excurrent siphons for water flow across the pharynx, which is enlarged.
• There is no notochord, dorsal hollow nerve cord, or tail in adults.
• Adults are covered by a tunic.
• They lack paired fins or limbs.

Subphylum Vertebrata (Vertebrates)

• Vertebrates are characterized by a head and a brain protected by a skull.
• They possess vertebral elements that enclose and protect the dorsal hollow nerve cord.
• Vertebrates have a heart with two or more chambers.
• Erythrocytes contain hemoglobin.
• Kidneys filter blood.
• Vertebrates are more active than lancelets and tunicates.

Class Myxini (Hagfishes)

• Hagfishes possess a cartilage skull, but no jaws.
• Have palps and gills.
• They retain a notochord throughout their life.
• Hagfishes feed on small and soft decomposing food due to their fleshy mouths.
• Hagfishes defend themselves by excreting slime when attacked.

Axial Structures

• They possess a small circular mouth lacking a jaw.
• Fleshy palps function like fingers.
• Gill openings numbering up to 12 pairs are located posterior to the mouth.
• A notochord and a dorsal hollow nerve cord are present but not visible.
• Slime glands are located along the body wall.
• They have a muscular post-anal tail and a caudal fin fold.
• Hagfishes lack paired fins or limbs.

Class Petromyzontida (Lampreys)

• The ammocoete is the larval form of lampreys, which is similar to cephalochordates.

Axial Structures

• Lampreys have a suction-cup-like mouth with rasping teeth used to attach to hosts and suck their blood.
• Adults possess seven pairs of gill openings.
• Larvae have pharyngeal gill slits.
• A notochord and dorsal hollow nerve cord are present but not visible.
• The muscular post-anal tail aids in locomotion.

Appendicular Structures

• Lampreys lack paired fins or limbs.

Clade Gnathostomata (Vertebrates with Jaws)

• Gnathostomes possess jaws and a mineralized skeleton.
• Jaws allow for a broader range of food options.
• Some members secondarily lost the mineralized skeleton resulting in cartilage.
• Median fins provide stability.
• Paired fins aid in steering.

Types of fins

• Dorsal fins are located on the top of the body.
• Anal fins are located on the bottom rear.
• Caudal fins are located on the tail.
• Pectoral fins are located at the booby.
• Pelvic fins are located on the bottom front.

Class Chondrichthyes (Cartilaginous Fishes)

• Includes sharks, rays, chimeras, and related species.
• The skeleton is primarily cartilage, a derived trait.

Axial Structures

• A chondrocranium protects the brain.
• Cartilaginous gill arches support gill filaments.
• Jaws are derived from anterior gill arches, including the palatoquadrate (upper jaw) and Meckel's cartilage (lower jaw).
• Vertebrae replace the notochord as the primary dorsal support.
• Remnants of the notochord persist as intervertebral discs.
• A dorsal fin provides stability.

Appendicular Structures

• Pectoral fins are paired, anterior fins supported by the pectoral girdle.
• Pelvic fins are paired, posterior fins supported by the pelvic girdle.

Class Actinopterygii (Ray-Finned Fishes)

• Contains over 27,000 species with diverse feeding and reproductive strategies.
• Sizes range from 1cm to 17m.

Axial Structures

• Jaw movement allows fish to push their jaws outward to create suction for feeding.
• The upper jaw consists of the maxilla and premaxilla.
• The dentary forms the lower jaw.
• The operculum covers and protects the gills.
• Gill arches support gill filaments.
• Water flows in through the mouth, over the gills, and exits behind the operculum.
• Centrum sections are round
• Dorsal area includes the neural arch and the neural spine to surround and protect the spinal cord.
• Ventral area includes the hemal arch and hempal spine surrounding and protecting major blood vessels
• Pleural ribs and dorsal/anal fins articulate the vertebrae protecting body cavity
• In Actinopterygii, the vertebrae does not extend to find the caudal fin.
• The caudal peduncle is a muscular area between the anal and caudal fins.

Appendicular Structures

• Pectoral fins are supported by the pectoral girdle.
• Pelvic fins are supported by the pelvic girdle.

Class Lissamphibia (Salamanders, Frogs, Caecilians)

• Contains approximately 6,150 species.
• Possess four digits on forelimbs if present.
• Skin glands secrete mucous (for gas exchange) or poison.
• Fat bodies store energy.

Axial Structures

• The upper jaw is fused, with sutures visible.
• The mandible consists of fused dentaries.
• The foramen magnum allows the spinal cord to attach to the brain.
• Occipital condyles allow articulation with the first vertebra.
• The atlas is the first cervical vertebra, articulating with the occipital condyles.
• Trunk vertebrae support the majority of the body.
• The sacral vertebra articulates with the pelvic girdle.
• They lack ribs.

Appendicular Structures

• The Pectoral Girdle supports forelimbs consisting of the suprascapula, scapula, clavicle and coracoid.
• Forelimbs are made of the humerus, radioulna, carpals, metacarpals, and phalanges.
• The Pelvic Girdle supports hindlimbs consisting of the ilium, ischium, and pubis.
• Hindlimbs are made of the femur, tibiofibula, astragalus, calcaneum, tarsals, metatarsals, and phalanges.

Clade Testudines (Turtles)

• Upper jaw is tightly fused.
• The mandible lacks teeth.
• Jaws are covered by a keratin ridge.

Axial Structures

• The foramen magnum allows the spinal cord to attach to the brain.
• Occipital condyle (just one) single bump immediately adjacent to foramen magnum. allows skull to articulate with the first vertebra
• Cervical vertebrae allow a greater range of motion in the neck.
• Dorsal vertebrae are fused to the carapace.
• The sacral vertebra articulates with the pelvic girdle.
• The shell is composed of bone and keratin, consisting of the carapace and plastron.

Appendicular Structures

• The Pectoral girdle consists of the scapula and coracoid.
• Forelimbs are made of the humerus, radius, ulna, carpals, metacarpals, and phalanges.
• The Pelvic girdle consists of the ilium, ischium, and pubis.
• Hindlimbs are made of the femur, tibia, fibula, tarsals, metatarsals, and phalanges.

Clade Lepidosauria (Snakes, Lizards, Tuataras)

Axial Structures

• The upper jaw is fused to varying degrees.
• Foramen magnum allows the spinal cord to attach to the brain
• Occipital condyle allows skull to articulate with first vertebra
• Multiple cervical allows a better range of motion

Appendicular Structures

• Pectoral girdle consists of the scapula and coracoid
• Forelimbs are made of the humerus, radius, ulna if animal has an "elbow", it is formed by this, carpals, metacarpals and phalanges
• Pelvic girdle consists of the ilium, ischium, and pubis
• Hindlimbs are made of the femur, tibia, fibula, tarsals, metatarsals and phalanges

Clade Crocodylidae (Crocodiles, Alligators, Caimans, Gharials)

• Thick skulls

Axial Structures

• Thick skull that is less mobile. Upper jaw and mandible is tightly fused
• Foramen magnum allows the spinal cord to attach to the brain
• Occipital condyle allows skull to articulate with first vertebra
• Multiple cervical allows a better range of motion
• Thoracic vertebrae and lumbar vertebrae is long
• Sacral vertebrae and sternum are also included
• Tail is chungus supported by vertebrae

Appendicular Structures

• Pectoral girdle consists of the scapula and coracoid
• Forelimbs are made of the humerus, radius, ulna if animal has an "elbow", it is formed by this, carpals, metacarpals, and phalanges
• Pelvic girdle consists of the ilium, ischium, and pubis
• Hindlimbs are made of the femur, tibia, fibula, tarsals, metatarsals, and phalanges

Clade Aves (Birds)

Axial Structures

• Upper jaw and mandible are tightly fused and known as a bill
• Foramen magnum allows the spinal cord to attach to the brain
• Occipital condyle allows skull to articulate with first vertebra
• Multiple cervical with at least two vertabrae for greater motion
• Thoracic with ribs and unique uncinate processes
• Fused lumbar and sacral vertebrae
• Keel to allow surface for attachment of bird's pectoral muscles
• Caudal and pygostyle vertebrae

Appendicular Structures

• Furcula is the fused clavicles

• Scapula is long

• Procoracoid is sturdy

• Wings are modified from front limbs

• Pectoral girdle does not exist

• Pelvic Girdle:

  • Ilium
  • Ischium
  • Pubis

• Hindlimbs rear limbs, consists of 6 types, ordered from proximal to distal:

  • Femur
  • Tibia faces anteriorly. tibia is usually larger than fibula (if there is a size difference)
  • Fibula
  • Tibiotarsus bone fused to distal end of tibia
  • Tarsometatarsus fused ankle and foot bone
  • Phalanges toe bones. birds stand entirely on their "toes"

Class Mammalia

Axial Structures

• Upper jaw and mandible are fused
• Foramen magnum allows the spinal cord to attach to the brain
• Occipital condyle allows skull to articulate with first vertebra
• Multiple cervical allows a better range of motion
• Thoracic vertebrae with ribs
• Lumbar vertebrae without ribs
• Coccyx for caudal vertebrae

Appendicular Structures (for cat)

• Pectoral girdle consists of scapula and clavicle
• Forelimbs are made of the humerus, radius, ulna if animal has an "elbow", it is formed by this, carpals, metacarpals, and phalanges
• Pelvic girdle consists of the ilium, ischium, and pubis
• Hindlimbs are made of the femur, tibia, fibula, patella (the kneecap), tarsals, metatarsals, and phalanges

Modifications for locomotion in mammals

• Cursorial (running):
  • Have all for limbs directly under their bodies
  • Tend to have reductive or absent clavicle
  • Digitigrade:
    • Walks on it's toes.
    • Limbs are lengthened
    • Reduces size of foot to minimize contact with ground
  • Unguligrade:
    • Walks on it's tippy toes
    • Stands on top of one digit
    • Fusion of metacarpals
    • Fusion of metatarsals
• Plantigrade (walking):
  • Walks using posterior limbs
  • Feet are modified to have a large area of stability
• Arboreal (climbing):
  • Modified with a very large prominent clavicle, long limbs, long digits, and prehensile tail
• Saltatorial (jumping):
  • Hindlimbs tend to be significantly longer that forelimbs to help balance
• Fossorial (burrowing):
  • Strong short forelimbs with wide bones and long claws
• Volant (flying):
  • Metacarpals and phalanges are elongated to support the skin that makes up the wing