Reptiles: Evolution and Characteristics

• This study guide focuses on tetrapods, specifically amniotes, and more specifically, reptiles.

Introduction

• Amniotes are tetrapod vertebrates adapted to survive on land and lay eggs on land.
• Amniotic eggs refer to eggs that have facilitated terrestrial survival.
• Amniotes include reptiles, birds, and mammals.
• Reptiles are considered the most primitive amniotes and feature embryonic membranes and an amnion

Reptilian Evolution

• Reptilian tetrapods include turtles, lizards, snakes, amphisbaenians, and birds.
• The ancestors of modern reptiles and mammals emerged in the Carboniferous period during the late Paleozoic era.
• Reptiles can reproduce on land without water and have a skin barrier that reduces water loss.
• Reptile evolution, especially of extinct lineages, occurred through small bursts of morphological changes, like armor or gliding wings, over about 50 million years.

Reptilian Evolution: Clades

• Living reptiles are represented by Archosauria (crocodylians and birds), Testudines (turtles), and Lepidosauria (tuataras and squamates).
• Turtles were once considered an outgroup because they lack fenestrae (openings) in their skulls, classifying them as anapsids.
• Recent DNA evidence suggests turtles have a diapsid skull origin and are related to crocodylians and birds.

Reptile Characteristics: Skin and Eggs

• Reptiles possess tough, dry, scaly skin for protection and to prevent water loss.
• Reptile skin has a thin epidermis that is shed periodically.
• Reptile skin has a much thicker, well-developed dermis containing chromatophores responsible for the diverse coloration of lizards and snakes.
• Reptile scales are mainly made of keratin.
• Shelled amniotic eggs contain food and protective membranes to support embryonic development on land.
• Shelled eggs are laid in sheltered locations on land.
• Young reptiles hatch as lung-breathing juveniles, not aquatic larvae.

Reptile Characteristics: Jaws and Reproduction

• Reptilian jaws are designed for crushing or gripping prey.
• Reptilian jaws: Muscles became larger and longer for better mechanical advantage.
• Reptiles have copulatory organs for internal fertilization.
• Reptiles must reach the egg with sperm before the egg is enclosed.
• Sperm travel from the testes via the vasa deferentia to a copulatory organ that is part of the cloacal wall.
• The female reproductive system includes glandular oviducts, which secrete albumin, amino acids, minerals, and water for the embryo.

Reptile Characteristics: Circulation

• Reptiles possess an efficient circulatory system with higher blood pressure relative to amphibians.
• The right atrium receives unoxygenated blood from the body.
• The left atrium receives oxygenated blood from the lungs.
• Crocodilians have completely separated ventricles.
• Other reptiles have incompletely separated ventricles, but specific flow patterns in the heart prevent most mixing of pulmonary oxygenated and systemic unoxygenated blood.

Reptile Characteristics: Respiration

• Reptiles depend almost exclusively on lungs for gas exchange, but aquatic turtles also use pharyngeal membranes.
• Reptiles draw air into their lungs by enlarging the thoracic cavity, either through expanding the rib cage (snakes and lizards) or moving internal organs (turtles and crocodilians).
• Reptiles lack a muscular diaphragm.
• Reptiles exhibit no cutaneous respiration.

Reptile Characteristics: Water Conservation and Limbs

• Reptiles evolved efficient strategies for water conservation.
• All amniotes have a metanephric kidney drained by the ureter.
• Reptilian nephrons lack the loop of Henle.
• The loop of Henle enables the kidney to concentrate solutes in urine.
• Reptiles excrete nitrogenous wastes as uric acid, allowing water conservation.
• Most reptiles, except limbless ones, have better body support with more efficiently designed limbs for land travel.
• Modern reptiles walk with legs splayed outward and their belly close to the ground.

Reptile Characteristics: Nervous System

• Reptilian nervous systems are more complex than amphibian systems.
• The cerebrum in a reptile's small brain is larger relative to the rest of the brain, initiating, coordinating movement, and regulating temperature.
• Advanced connections to the central nervous system enable complex behaviors.
• Well-developed sensory organs are present, except for hearing.
• Reptiles have Jacobson's organ/vomeronasal organ, which is a specialized olfactory chamber detecting moisture-borne odor particles that is highly developed in lizards and snakes.

Classification of Reptiles

• Kingdom: Animalia
• Phylum: Chordata
• Subphylum: Vertebrata
• Superclass: Tetrapoda
• Clade: Amniota
• Clade: Sauropsida (Lizard faces); broadly equivalent to class Reptilia
• Class: Reptilia
• Subclass: Parareptilia
  • Order: ?Testudines (Turtles)
• Subclass: Eureptilia
  • Clade: Lepidosauromorpha
    • Superorder: Lepidosauria
      • Order: Rhynchocephalia (Tuatara)
      • Order: Squamata (Lizard and Snakes)
  • Clade: Archosauromorpha
    • Order: Crocodilia (Crocodilians)
    • Superorder: Dinosauria (Dinosaurs)
• Class: Aves (Birds)

Subclass Parareptilia

• Reptilia is a class, Parareptilia is a subclass, ?Testudines (Turtles) is an order
• Parareptilia: skull typically without temporal openings.

Order ?Testudines (Turtles): Characteristics

• Skull without pineal opening
• Jaws are toothless.
• Armored with a shell encasing the body (carapace) and below (plastron).
• Exhibit varied sizes and diets.

Turtle vs Tortoise

• Turtles are water-dwelling reptiles, tortoises are land-dwelling.
• Turtles are omnivores, tortoises are herbivores.
• Turtles generally have lighter shells, tortoises have heavier, robust shells.
• All tortoises are turtles, belonging to the order Testudines.
• Turtles usually have a shorter lifespan from 20-40 years and tortoises usually have a long life from 80-150 years
• The difference between tortoise and turtle is apparent when habitat is considered.
• All tortoises are terrestrial, while most turtles are aquatic or semi-aquatic.

Order ?Testudines: Suborders

• Suborder Cryptodira: Includes most living tortoises and turtles.
  • They lower their necks and pull their heads straight back into their shells.
  • This suborder includes freshwater turtles, snapping turtles, tortoises, softshell turtles, and sea turtles.
• Suborder Pleurodira
  • Known as side-necked turtles; Pleurodira translates to "side neck".
  • Restricted to freshwater habitats in the Southern Hemisphere.
  • Families include Chelidae (Austro-South American side-necked turtles), Pelomedusidae (African mud terrapins), and Podocnemididae (American side-neck river turtles).

Subclass Eureptilia

• The subclass Eureptilia has skulls typically with temporal openings.
• All taxa except for captorhinids (t) have diapsid skulls.
• Diapsid skulls are characterized by upper and lower temporal fenestrae.
• The subclass contains the clades Lepidosauromorpha and Archosauromorpha

Superorder Lepidosauria

• Lepidosauria is a subclass or superorder of reptiles consisting of the Squamata and Rhynchocephalia orders.
• Lepidosaurs are distinguished by several traits, one being keratinous scales that overlap.
• Scales are attached superficially to the upper and lower jaws and include a parietal eye and a transverse cloacal opening

Order Rhynchocephalia

• An order of lizard-like reptiles that includes only the tuatara species, found in New Zealand.
• The order contains 3 families, about 20 genera, but only one genus, Sphenodon, that is surviving, with two living species in New Zealand
• Primitive diapsid skull.

Order Squamata

• Squamata consists of lizards, snakes, and amphisbaenians which are collectively known as squamates or scaled reptiles.
• Squamates are distinguished by their skins, possessing horny scales and shields and must periodically engage in molting.
• They possess movable quadrate bones, making movement of the upper jaw relative to the neurocranium.
• Snakes can open oral cavities very wide to accommodate large prey.

Order Squamata : Dibamidae

• Dibamidae is a family of lizards characterized by elongated cylindrical body and a lack of limbs.
• Female dibamids are entirely limbless
• Males retain small flap-like hind limbs, which they use to grip their partner during mating

Order Squamata: Gekkota

• Geckos are small, carnivorous lizards with a wide distribution, found on every continent except Antarctica.
• They are found in warm climates throughout the world.
• Geckos are unique among lizards for their vocalizations, which differ from species to species.
• Almost all species lack eyelids.
• Species without eyelids lick their own corneas to clear them of dust and dirt.

Order Squamata: Scinomorpha

• The infraorder includes skinks, wall lizards, and their relatives
• Characteristics include an elongated body and limbs to be reduced
• Many also have developed armoured scales that cover the head and trunk
• Primarily ground dwelling or burrowing, some arboreal, some semiaquatic

Order Squamata: Toxicofera

• Toxicofera is a proposed clade of scaled reptiles that includes the Serpentes, Anguimorpha and Iguania.
• It encompasses all venomous reptile species, as well as numerous related non-venomous species.

Order Squamata: Serpentes

• Serpentes are elongated, limbless, carnivorous reptiles
• Snakes are ectothermic, amniote vertebrates covered in overlapping scales.
• Many species of snakes have skulls with several more joints enabling them to swallow prey larger than their heads (cranial kinesis).
• Around thirty families are recognized, comprising about 520 genera and about 3,900 species.
• Most snake species are nonvenomous, those that are venomous primarily kill and subdue prey.
• Nonvenomous snakes either swallow prey alive or kill by constriction.

Order Squamata: Anguimorpha

• Anguimorpha includes monitor lizards, gila monsters, and alligator lizards.
• Sexual reproduction
• Rely on running for mobility.

Order Squamata: Iguania

• Iguania includes iguanas, agamas, and chameleons.
• The group comprises nearly 11,000 named species, roughly 2000 of which are iguanians
• Most species are arboreal but there are multiple terrestrial groups.
• They usually display primitive fleshy, non-prehensile tongues. Although the tongue is highly modified in chameleons.

Clade Archosauromorpha

• Archosauromorpha is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs, such as crocodilians, dinosaurs, and including birds.
• They originated in the late Middle or Late Permian, becoming more prevalent and diverse during the Triassic period.
• Archosauromorpha display great variation in size, ranging from small to giant reptiles with diverse body plans.

Order Crocodilia

• Consists predominantly of sizable, predatory, semiaquatic reptiles commonly referred to as crocodilians.
• The closest existing relatives of birds.
• Are large, solidly built, lizard-like reptiles
• Have long flattened snouts, laterally compressed tails, and eyes, ears, and nostrils at the top of the head.
• Highly adapted for swimming and can move on land.
• Their skin is thick and covered in scales.

Order Crocodilia: Subfamilies

• Alligatoridae: lower jaw teeth fit inside upper jaw. Includes alligators and caimans
• Crocodylidae is a classification of the existing crocodilians which includes true crocodiles. Teeth of upper and lower jaw are interdigitated.
• Gavialidae: Family under crocodiles consisting of gharials. They display extremely long and thin snouts -and contain more than 22 teeth in each jaw.

Distribution of Reptiles

• Reptile activity is dependent on the temperature of their environment.
• Reptiles are ectothermic, requiring an external heat source.
• Many species, particularly lizards, have preferred body temperatures above 28 °C (82 °F).
• To maintain optimal body temperature, some species undergo periods of shuttling in and out of sunlight.
• Reptiles are ubiquitous, found in all habitats from open seas to high elevations.
• Many Snakes, crocodiles, and lizards are all aquatic
• On land, turtles, snakes, and lizards also occur widely in forests, grasslands, and deserts.

Integument

• The epidermis is thicker consisting of keratinous layers.
• Cells die as they progress to the surface.
• Skin is modified into scales.
• Scales are called plates, scutes, shields, laminae, lamellae, scansors, or tubercles based on their features.
• Scales overlap in squamates, unlike crocodylians and turtles.

Integument (Multicellular skin glands)

• Reptiles have multicellular glands for a variety of functions, including waterproofing, promoting surface tension, communication and defense.
• Specialized Glandular Aggregations in turtles called Musk or Rathke’s Glands are used as exocrine scent glands serve as a defensive mechanism.
• Mental gland is a special integumentary organ located on the chin and is used as a chemical signal.

Integument (Specialized Glandular Aggregations)

• Mandibular and Cloacal Glands are utilized in communication and defense.
• Cloacal glands are located in the tail base, opening into the cloaca.
• Reptiles use scent glands for various forms of communication.
• Salt glands are organs used to excrete excess salt, located in various places like the tongue, orbits, or nasal passages.

Integument: Structures

• The dry skin of reptiles allows them to move around for periods of time without water.
• Specialized keratinous structures are common in reptiles.
• claws are structures that encase the tips with functional digits.
• Jaw sheaths occur in turtles that replace teeth.
• Egg tooth supports hatching.

Integument: Cell Types

• Colouration - Reptiles generally have two types of colour-producing cells.
• Melanophores- scattered throughout the basal layers of the epidermis
• Chromatophore - different types of chromatophores are stacked in the outer portion of the dermis:
  • xanthophores
  • iridophores
  • melanophores
• Stacked chromatophores may represent the general pattern for all reptiles that change color.

Nervous System

• Reptiles contain a basic vertebrate plan with two regions, the forebrain and hindbrain.
• One forebrain region of of adult reptiles contains cerebral hemispheres comprised of olfactory and thalamic lobes.
• One hindbrain region of reptiles contains cerebellum and medulla oblongata.

Sensory System

• Sensory System: Cutaneous sense organs are located throughout the skin.
• Pit organs are specialized infrared heat receptors typically found on the head.
• Sense of Hearing: Structurally serve two functions:
  • Hearing - reception of sound waves.
  • Balance - detection of the position and movement of the animals head.
• The receptors for both functions are neuromasts located in the inner ear.
• Paired ears are located on each side of the head just above the lower jaw.

Sensory System: Sight and Smell

• The coranea is a ring of bony plates on the eyes.
• Pupils range from round to elliptical.
• Eyes consist of an eyeball and lens that are usually spherical.
• Each nasal organ of reptiles consists of an external naris, a vestibule, a nasal cavity proper, a nasopharyngeal duct, and an internal naris
• Air passages are lined with non-sensory epithelium
• Vomeronasal organ: An olfactory structure used primarily to detect nonaerial, particulate odors

Digestive System

• Mouth opens directory
• Some species have lips whereas other do not.
• Tooth structure varies whereas other species do not have teeth.
• Teeth function by grasping, piercing, or fragmenting food items

Digestive System: Tongue and Glands

• Tongue - Tongue morphology varies in association with a variety of feeding behaviors
• Glands - Various variety is situated near head region
  • Small, multicellular mucous glands
  • Salivary glands: produce saliva which are crucial for chewing, and protecting the mouth and teeth
  • Venom glands support envenomation.

Respiratory System

• Reptiles have an identical respiratory pathway.
• Air exits and enters the trachea through the glottis at the rear of the pharynx.
• Larynx: a simple tubular structure in most reptiles
• Trachea extends down the neck beneath the esophagus and forks into a pair of bronchi, each of which enters a lung.
• Breathing occurs by expansion and contraction of the body cavity.

Urogenital System

• Reproductive and urinary systems are related in location on the dorsal body-wall
• Urinary System:
  • Kidneys lie on the dorsal wall in front of the cloaca
  • Ureter drains each kidney
  • Urinary bladder: Stores urine
• The bladder joins the cloaca through a median duct.

Urogenital System: (Reproductive System)

• Ovaries aid occupy location near abdomen
• Oviduct is not continuous with the ovary
• Testis aid located by seminiferous tubules.
• All reptiles support copulatory organs such as snakes.

Reproduction

• Reproduction is mediated by hormones and is affected by environmental cues.
• Fertilization takes place internally.
• Copulation requires storing sperm inside females.
• This aids flexible reproduction and delays pregnancy leading to offspring survival.

Reproduction and Development : Oviparity vs Vivparity

• Reptiles display three main reproductive strategies:
  • oviparity
  • viviparity
  • ovoviviparity
• Oviparous species is egg-laying which includes mostly turtles and crocodilians.
• Viviparous is a live birth that include most snakes and lizards.
• Ovoviviparity is in-between that hatch eggs internally.

Reproduction and Development : Eggs and Membrane

• Reptilian eggs consists of reptile eggs and composed of:
  • amnion which protects embryo
  • yolk sac which facilitates nutrients
  • allantois store for metabolic waste
  • chorion creates gas exchange

Birth

• Birth in reptiles appears to be triggered by maternal hormonal activity.
• Hatching in reptiles requires a unique penetration and projection on the snout.

Growth

• Growth depends on temperature as temperature declines.
• If temperature does not decline it does alter growth due to energy requirement.
• Quality over food can influence quality
• They have and advantage of endotherms depending on food requirement.

Nesting

• Survival is dependent on high oviposition.
• The survival is covered within the reproductive behavior called nesting.
• Reproduction is supported through water intake.
• Mortality is higher during embryos phase.

Other Body Movements

• Communication: Visual cues.
• Body movement and flashing a signal
• Limb movements:
  • Rapid shuttling
  • Head bobs

Other Behaviours : Sounds

• Communication: Acoustic cues.
• Crocodilians is used on both lizard and sound cues.
• Cues involve rubbing cues to create pressure.

Other Behaviours (Monogamy)

• In general, mating systems are categorized according to the levels of polygamy within a species.
• Monogamy - when neither males nor females gain by mating with additional individuals of the opposite sex and also expected in mating systems requiring both parents
• Polyphenism - in most reptiles; males increase their fecundity by mating with a large number of females but females have no gains by mating with more than one male
• Polyandry - females producing clutches or litters indicating multiple paternity.

Other behaviours (Movement)

• Most Reptiles will go breeding during their life.
• Movement is critical of:
  • locate food.
  • Locate mates.
  • Avoid extreme.
    • Diurnal - active
    • Cathemeral
      • Nocturnal

Other Behaviours: Territoriality and Defense

• A territory is an area defended against intruders that has defendable resources.
• Territories or home ranges of females are contained within the territory of the male.
• Male territorial boundaries include low male home range overlap.
• Defense include physical contact
• Threats of chemical signals can be considered.

Other Behaviours: Aggregations

• Aggregations are the use of space centered:
  • breeding
  • brumation
    • estviation for weather conservation.

Parental Care

• Egg attendance
  • Nest guarding
    • Hatch tiling
      • Egg brooding
        • Guarding the offspring's

Sampling Methods

• Reptiles need a challenging behavior depending on their habitats
• Time constrained.

1. Area
2. Quadrat
3. Patch 4. Transect

Reptilian (and Amphibian) Sampling Methods : Active

• Visual
  • Egg
    • Basking

Reptilian (and Amphibian) Sampling Methods : Passive

• Reptiles and covered areas and funnel areas
  • reptile and amphibians has some advantages:
    • Useful for capturing species.
    • Suitable for standards. -Sensitive for overtimes.
      • Useful for monitoring.

Capturing and Handling Animals (Snakes)

• Most snakes must considered potential
• Experienced needed to to handle

Capturing and Handling Animals (Lizards)

• Most on average a hard to care for.
• Must be skilled and wear gloves.

Capturing and Handling Animals (Crocodiles)

• Most need an expert to watch crocodiles
• Animals that can be graved from head need to be handled by multiple.
• Crocodiles mouths should be measured through tape, animals need shade.

Importance of Reptiles: Gene Transporters

• Reptiles are gene transporters:
  • Epiosis transfer seeds .
  • Tendency is the best way to transfer and provide to create more food for seed damage.

Importance of Reptiles: Transporters

• Reptiles can take function.
• They are aquatic egg-layers.
  • Predators also help assist to provide transportation.

Importance of Reptiles Trophic

• To reduce the importance of the community.
• They prey on the species
• They act like top predators in aquatic and terrestrial mammals
• They act as a way of transport like nile predators
• Reptiles provide nutrients and source of food.

Importance of Reptiles : Ecosystem

• The use of the following to make life better
• Profound effect on ecosystems.
• Reptiles are recognized burrows.
• Mounds of rotting vegetation

Importance

• Serve as research to expand on physiology
• To humans they provide food and leather They also can be used for bags.