Terrestrial Tetrapods: Lineages, Respiratory, Circulatory, and Thermoregulation Adaptations

What are the two major lineages of terrestrial tetrapods?

Synapsids (including extant mammals) and Sauropsids (including extant reptiles and birds).

What evolutionary adaptations were made for locomotion in synapsids and sauropsids?

More vertical limb position, lever-like ankle joints, and changes in ventilation.

What type of lung structure do synapsids possess?

Alveolar lung structure.

Describe the airflow in synapsid respiration.

Tidal airflow through the bronchial tree, including trachea, primary bronchi, secondary bronchi, bronchioles, and alveoli.

What is a consequence of tidal airflow in synapsids?

Mixing of oxygenated and deoxygenated air.

What powers tidal flow in synapsids?

The diaphragm.

What type of lung structure do sauropsids have?

Faveolar lung structure.

How does airflow in sauropsids differ from that in synapsids?

Sauropsids have unidirectional airflow through parabronchi.

What are faveoli in sauropsids?

Cuplike chambers lining the walls of parabronchi.

What is the significance of unidirectional airflow in sauropsids?

It allows for separation of oxygenated and deoxygenated air.

What circulatory feature evolved in both synapsids and sauropsids?

Ventricular septa in the heart, allowing for separate pulmonary and systemic circuits.

What is the primary nitrogenous waste excretion method for synapsids?

Ureotelic, primarily secreting urea via urine.

How do non-avian sauropsids excrete nitrogenous wastes?

They can secrete ammonia, urea, or uric acid depending on hydration status.

What is the primary excretory method for birds?

Uricotelic, primarily secreting salts of uric acid.

How do synapsid kidneys concentrate urine?

Through reabsorption of water in the descending limb of the loop of Henle and collecting duct.

What adaptation do many sauropsids have to assist with salt secretion?

Accessory salt glands.

Which sensory system do synapsids rely on more heavily?

Olfaction.

What type of vision do most synapsids have?

Dichromatic vision, with some primates having trichromatic vision.

What is the ancestral vision capability retained by sauropsids?

Tetrachromatic vision.

What is a key difference in the middle ear structure between synapsids and sauropsids?

Synapsids have three bones (stapes, malleus, incus), while sauropsids have one bone (stapes).

How does brain size in mammals and birds compare to other reptiles?

Mammals and birds have larger brains relative to body size.

What complicates the relationship between brain size and intelligence?

Many factors influence the relationship, beyond just relative brain size.

What is thermoregulation?

The process of maintaining an optimal body temperature despite external temperature variations.

How does air temperature compare to water temperature for thermoregulation?

Air temperature is more variable than water temperature, making thermoregulation more difficult for terrestrial tetrapods.

What are the routes of heat gain or loss in ectotherms?

Solar radiation, infrared radiation, convection, conduction, evaporation, and metabolic heat production.

What is ectothermy?

Using external heat sources to raise body temperature; it is the ancestral mode for tetrapods.

What is a benefit of ectothermy?

It is energetically efficient, requiring less food.

What is a cost of ectothermy?

Dependence on external heat sources constrains geographic distributions and seasonal/daily activity periods.

What is endothermy?

Using heat from metabolism to raise body temperature; evolved independently in sauropsids and synapsids.

What are the benefits of endothermy?

Independence from external heat sources, reduced constraints on geographic distributions, and the ability to perform energetically demanding activities.

What are the costs of endothermy?

It is energetically expensive, requiring more food and resulting in higher metabolic rates compared to ectotherms.

What is heterothermy?

The ability of both ectotherms and endotherms to have body temperature that varies over time or among different regions in the body.

What challenges do ectotherms face in dry environments?

Scarcity of liquid water and food, seasonal rainfall, and high daily temperature variation.

What adaptations do ectotherms have for surviving in dry environments?

Burrowing to escape desiccation and extremes of temperature, and hibernation to cope with low rainfall and resource abundance.

What adaptations do ectotherms have for cold environments?

Retreating to burrows that remain above freezing, allowing the body to become supercooled, and hibernation with tolerance to freezing.

How do ectotherms allocate energy differently than endotherms?

Ectotherms allocate less energy to maintaining body temperature, allowing more energy for growth and reproduction.

What is the thermoneutral zone (TNZ) in endothermic vertebrates?

The range of environmental temperatures where the metabolic rate is minimal and body temperature is maintained without extra energy expenditure.

What is facultative hypothermia?

The intentional lowering of body temperature to reduce energetic costs, including seasonal hypothermia, rest-phase hypothermia, and hibernation.

What is hyperthermia as an adaptation in hot environments?

Allowing body temperature to rise to minimize water loss via evaporative cooling, often seen in diurnal rodents and camels.

What is the role of insulation in endotherms in cold environments?

Insulation helps maintain body temperature at low environmental temperatures without increasing metabolic rate.

What is the difference in metabolic rates between ectotherms and endotherms?

Ectotherms have lower metabolic rates and require less food than endotherms of similar body size.

How does body size affect metabolic rates in ectotherms?

Mass-specific metabolic rates increase with decreasing body size, allowing ectotherms to be smaller than endotherms.

How does body shape affect heat loss in ectotherms?

Ectotherms can have elongate or flattened body shapes with high surface area to volume ratios, reducing constraints on heat loss.

What are the two major lineages of lepidosaurs?

Rhynchocephalia (tuatara) and Squamata (lizards and snakes)

What is a defining characteristic of all lepidosaurs?

They have scales and shed the outer layer of epidermis at intervals.

What is the only extant species of Rhynchocephalia?

The tuatara, which is endemic to New Zealand.

How do lizards generally grow?

Most species exhibit determinate growth.

What are the primary diets of most lizard species?

Most are either insectivores or herbivores, with a few being carnivores.

What adaptations do chameleons have for climbing?

Zygodactyl feet and a prehensile tail.

How many times has the secondary loss of legs evolved in lizards?

At least 60 times.

What distinguishes snakes from legless lizards?

Snakes have long trunks and short tails.

What are the four types of locomotion used by snakes?

Lateral undulations, concertina locomotion, rectilinear locomotion, and sidewinding.

What are the characteristics of sit-and-wait predators?

They ambush prey, rely on vision, have stout bodies, and often exhibit territorial behavior.

What distinguishes active foragers from sit-and-wait predators?

Active foragers search for prey, rely on chemoreception, and usually have slim bodies.

What type of skull does the tuatara have?

An akinetic, diapsid skull with two temporal arches.

How do snakes use their kinetic skull for feeding?

They can swallow prey whole using a wide gape and alternating movements of their jaws.

What are the three categories of venomous snakes based on fang anatomy?

Opisthoglyphous, proteroglyphous, and solenoglyphous.

What are some defense mechanisms used by squamates?

Cryptic coloration, spines, blood or sticky secretions, autotomy, and venom.

How do squamates communicate?

They use visual, auditory, chemical, and tactile signals.

What is the common method of sex determination in squamates?

Genetic sex determination (GSD) is common, with some taxa exhibiting male or female heterogamy.

What is the main benefit of viviparity in squamates?

It allows the mother to regulate the temperature of the embryos.

What is parthenogenesis and where is it commonly found?

Parthenogenesis is widespread among lizards and rare in snakes.

What parental care behaviors are observed in some squamates?

Mothers may guard eggs or hatchlings and brood eggs to maintain temperature.

What mechanisms do squamates use for thermoregulation?

Behavioral responses, changing color, and altering peripheral blood flow.

What are the shared characteristics of turtles?

Bony external shell, absence of skull fenestrae, limbs positioned inside ribs, and species found in marine, freshwater, and terrestrial environments.

What are the two major lineages of turtles?

Cryptodires, which retract their head vertically, and Pleurodires, which retract their head laterally.

Where are Cryptodires primarily found?

Mainly in the northern hemisphere.

Where are Pleurodires primarily found?

Mainly in the southern hemisphere.

What is the composition of a turtle's shell?

The shell is formed of bony plates covered by horny scutes made of beta-keratin.

What is the carapace of a turtle?

The upper portion of the shell, formed mainly through the expansion of ribs (endochondral bone).

What is the plastron of a turtle?

The lower portion of the shell, formed mainly of dermal bone.

How does the carapace differ between terrestrial and aquatic turtles?

Terrestrial species usually have a domed carapace, while aquatic species usually have a flattened carapace.

How do turtles ventilate their lungs?

They cannot expand and contract their rib cage; instead, they ventilate lungs by moving viscera.

What is unique about the turtle's heart?

It is anatomically three-chambered but functionally five-chambered, allowing blood to be shunted to systemic or pulmonary circuits.

What thermoregulation behaviors do small aquatic turtles exhibit?

They leave the water to bask in the sun.

What is the reproductive strategy of turtles?

All turtles are oviparous, laying eggs typically on land.

What is temperature-dependent sex determination (TSD) in turtles?

The sex of the embryo is determined by the temperature to which it is exposed during the middle third of its development.

What are the types of temperature-dependent sex determination (TSD) in turtles?

Type Ia TSD produces males at low temperatures, Type Ib TSD produces males at high temperatures, and Type II TSD produces males at intermediate temperatures.

What parental care behaviors are exhibited by turtles?

Most species provide no parental care, but some tortoises may guard nests, and one aquatic turtle species is known to guard young after hatching.

How do sea turtles navigate during migration?

They use light, wave direction, olfaction, and a magnetic compass.

What are some life history characteristics of turtles?

They have slow developmental rates, long life spans, high juvenile mortality, and low replacement rates for populations.

What are the two main groups of ancient crocodilian relatives?

Notosuchians and Neosuchians

Where were Notosuchians primarily found?

Mainly in the Southern Hemisphere

What type of predators were Sebecid notosuchians during the Cretaceous?

Dominant land predators in South America

What is the time range during which some Notosuchians survived?

Into the Miocene (5-23 million years ago)

Where were Neosuchians mainly found?

Mainly in the Northern Hemisphere

What is a characteristic of Neosuchians?

They were semi-aquatic predators and many were very large

How many extant species of crocodilians are recognized?

26 species

What is the habitat distribution of extant crocodilians?

Almost all are tropical or subtropical in distribution

Name the three major lineages of extant crocodilians.

Alligatoridae, Crocodylidae, Gavialidae

What is a unique feature of Alligatoridae?

Teeth of lower jaws fit into grooves in upper jaws and are not visible when the mouth is closed

What distinguishes Crocodylidae from Alligatoridae?

Teeth of lower jaws are visible when the mouth is closed

What is a characteristic feature of Gavialidae?

They have a slender snout with a long mandibular symphysis

How do crocodilians swim?

They swim with lateral undulations of the tail and steer with hindfeet

What are the three gaits of crocodilians on land?

Belly crawl, high walk, and gallop

What adaptation allows crocodilians to breathe while submerged?

The secondary palate allows them to breathe with only nostrils and eyes above water

What prevents water from entering the trachea of crocodilians?

The gular valve

How do crocodilians typically handle terrestrial prey?

They drag it into water to drown it

What is the primary form of communication among crocodilians?

Vocalizations, especially for territoriality, courtship, and dominance hierarchies

What type of reproduction do all crocodilian species exhibit?

Oviparous reproduction