Amphibians and Reptiles: Vertebrate Evolution

• These notes are for the Amphibians and Reptiles section of Vertebrates

Transition to Terrestrial Life

• Chiridium played an important role in the transition to terrestrial life

Class Amphibia

• Amphibia represents the lowest tetrapods

Similarities with Fishes

• Have gills
• Anamniotes
• Pronephros and mesonephros is present
• Contains swim bladders
• Equipped with 10 pairs of cranial nerves
• Features a terminal position of the mouth
• Ectothermic

Similarities with Reptiles

• Exhibit internal nares
• Show adaptations to terrestrial life
• Well-ossified skeletons
• Have a middle ear cavity for vibratory stimuli
• Possess an eardrum

General Characteristics of Amphibians

• Their skin is glandular and lacks dermal scales
• Have an external anatomy that includes limbs, nares, and sometimes a hump
• Their skeleton features 2 occipital condyles
• Vertebral column has 4 regions
• Uses nostrils for respiration, gills as larva, and vocal cords in frogs and roads
• Movable tongue and has villi for digestion

Amphibians Details

• They have a heart with 3 chambers in their circulatory system
• Pronephros and mesonephros present in the excretory system
• Performs oviparous and viviparous for reproductive system
• Can conduct external and internal fertilization

Class Amphibia - Subclasses:

• Labyrinthodontia
• Lepospondyli
• Lissamphibia

Subclass Labyrinthodontia

• Belongs to the most primitive group with a complex tooth structure
• Their teeth have a maze-like pattern of enamel folding
• First to walk on land
• Dermal scales

Subclass Lepospondyli

• Has an hourglass-shaped centrum
• Develops centra of the vertebrae directly as bone
• Features elongated, small bodies, short limbs, and some orders losing limbs completely

Subclass Lissamphibia

• Similar types of glands in their skin tissue
• Masses of fatty tissue associated with their gonads, known as fat bodies
• 3 Orders: Anura, Caudata, Apoda

Order Anura

• Includes the majority of amphibian species, over 4,000 species
• Tails are present only in the larval stage
• Have longer hindlimbs than forelimbs
• Have protruding eyes
• Head and trunk are fused
• Oviparous
• Females are larger and darker while males usually sing

Order Gymnophiona (Apoda)

• Apoda amphibians are limbless
• They have small eyes beneath skull that are covered for protection
• Pointed snout
• Have annuli
• Blind worms
• Secrete mucus to reduce water loss
• Aquatic (oviparous)
• Terrestrial (viviparous)
• Perform internal insemination
• Have phallodeum
• Also known as Caecilians

Order Caudata

• Caudata amphibians possess tails
• Closure of gills at metamorphosis but some are perennibranchiate
• Elongated body with four equally sized limbs
• Have smooth skin with poison glands
• Undergo internal fertilization
• Very little differences between male and female
• Spermatophores are utilized for internal fertilization
• Examples include salamanders

Class Reptilia

• Lowest amniotes
• First to lay eggs on land
• Herpetology is the study of reptiles
• Integument that is dry, cornified, keratinized, epidermal scales (scutes), with claws
• Skeleton with one occipital condyle and single-headed ribs

General Characteristics of Reptiles

• Well-developed teeth and villi are present for the digestive system
• Lungs for respiratory system purposes
• Perform dioecious reproduction, with internal fertilization
• Mesonephros and metanephros in the excretory system
• Uric acid present in the body

Reptilia Subclasses

• Anapsida
• Parapsida
• Lepidosauria
• Archosauria
• Synapsida

Subclass Anapsida

• Dermal bones form a complete roof over the skull, with no temporal fossae
• Extinct: Captorhinida/ Cotylosauria
• Extant: Chelonia

Order Cotylosauria

• Earliest stem
• Oldest, primitive
• Complete roofing of the skull
• Flattened plate-like pelvis

Order Chelonia

• Consists of tortoises and turtles
• No teeth but horny beaks
• Tortoises tend to be herbivorous while sea and fresh water turtles are omnivorous
• Covered with a shell consisting of carapace and plastron
• Ribs and backbone fuse with the carapace

Subclass Parapsida

• Has one temporal fossa, placed high up on the skull
• Includes ichthyosaurs and the plesiosaurs
• Modified for aquatic life
• Ichthyosaurus and the Plesiosaurus became extinct at the end of the Cretaceous

Subclass Lepidosauria

• Has a diapsid skull
• Paired male hemipenes in male
• Possesses fracture planes in the caudal vertebrae that allow the tail to be shed if grabbed by a predator
• Features specialized knee, foot, and ankle joints that improve locomotion
• Teeth are generally fused in position
• Orders: Squamata and Rhynchocephalia

Subclass Lepidosauria Order Squamata

• Largest order of reptiles with snakes and lizards
• Has skin with scales or shield
• Movable quadrate bones which make it possible to move the upper jaw
• Suborders: Sauria (Lacertilia), Serpentes, Amphisbaenia

Subclass Lepidosauria Order Squamata Suborder Sauria (Lacertilia)

• Scaly-skinned
• Has legs, movable eyelids, and external ear openings
• Suction disk
• Autotomy
• Regeneration
• Lizards

Subclass Lepidosauria Order Squamata; Suborder Serpentes

• No eyelids
• Usually have one row of scales on the belly
• Does not have legs
• Have jaw bones that disarticulate allowing them to swallow large objects

Subclass Lepidosauria Order Squamata; Suborder Amphisbaenia

• Worm lizards
• Limbless borrowing squamates
• Has annulated body

Subclass Lepidosauria Order Rhynchocephalia

• Possesses gastralia ie: abdominal ribs
• Has enclosed temporal fossae (depressions) in the skull
• Examples include tuatara
• Endemic to New Zealand

Subclass Archosauria

• Existed during the Mesozoic Era
• Diapsid skull
• Presence of single openings in each side of the skull
• Possess teeth set in sockets (thecodont)
• Modified ankle joint is present
• Orders: Saurichia, Ornithischia, Pterosauria, Crocodilia

Subclass Archosauria Order Saurischia

• Possess reptilian pelvis
• Bipedal and quadrupeds
• Performs Carnivorous and Herbivorous behavior

Subclass Archosauria Order Pterosauria

• Flying reptiles
• Pneumatic bone is present
• Known as the earliest vertebrates to evolve wings

Subclass Archosauria Order Ornithischia

• Bird-like pelvis
• Herbivores

Subclass Archosauria Order Crocodilians

• Equipped with a 4-chambered heart
• They are the sole survivors
• Vary in snout length
• Designed legs and feet to walk on land and strong flattened tails to use when swimming
• Examples include crocodiles and alligators

Subclass Synapsida

• One temporal fossa on the lower side of the temporal region of the skull
• Successful and dominant reptiles during the Permian period
• Replaced by other lines of reptiles such as dinosaurs during the Mesozoic era