Osteichthyans and Tetrapod Evolution: Fish Anatomy and Phylogeny

What type of bone structure do osteichthyans have?

Skeleton of endochondral bone

What unique feature do osteichthyans have in their teeth?

Teeth embedded in marginal mouth bones

When did osteichthyans first arise?

In the Late Silurian

What are the two major groups of osteichthyans?

Actinopterygians and sarcopterygians

What is the estimated number of species in actinopterygians and sarcopterygians?

Approximately 33,000 species each

What are the characteristics of actinopterygians?

Fossils date to late Silurian, only dermal fin rays remain, and they have a protrusible upper jaw

What is a defining feature of teleostei?

Extremely protrusible upper jaw and mobile pharyngeal jaws

What is the significance of the Weberian apparatus in ostariophysi?

It connects the gas bladder to the inner ear, amplifying hearing sensitivity

What type of reproductive strategies do most actinopterygians exhibit?

Most are oviparous, with some being viviparous

What is regional heterothermy, and which fish are known for it?

Tuna and billfish maintain heat in muscles and eyes; opah maintains elevated body temperature throughout its body

What are the main characteristics of sarcopterygians?

Most have monobasal fins, two dorsal fins, and a heterocercal caudal fin

What are the two extant groups of sarcopterygians?

Coelacanths and lungfishes

What adaptations do lungfishes have for survival?

Paired lungs, functional lungs, and the ability to estivate

What is the significance of the presence of choanae in tetrapodomorpha?

Choanae are internal nostrils that indicate a transition towards tetrapod vertebrates

What is the evolutionary relationship of Elpistostegalia?

They are the sister group to tetrapod vertebrates, adapted to shallow-water environments

What are the main lineages of extant teleosts?

Osteoglossomorpha, Elopomorpha, Otocephala, and Euteleostei

What is a notable feature of the Chondrostei group?

Their skeleton is secondarily cartilaginous, and they have a gas bladder

What type of feeding adaptations do sturgeons have?

Protrusible jaws for suction feeding

What is the primary habitat of extant Cladistia?

Freshwater environments

What is the significance of the duplication of the genome in teleostei?

It contributed to the diversity of traits in this group

What are the characteristics of the Dipnoi (lungfishes)?

Fused dorsal, caudal, and anal fins; paired lungs; and internal nostrils

What is the primary feeding strategy of Holostei (gars and bowfin)?

They feed on smaller fish and invertebrates

What is the evolutionary significance of the fossil record of Actinistia (coelacanths)?

Fossils date back to the Early Devonian, showing ancient lineage

What are sarcopterygians commonly known as?

Lobe-finned fishes

What type of fins do most sarcopterygians have?

Monobasal fins

What is a characteristic feature of the caudal fin in sarcopterygians?

Heterocercal caudal fin

What is unique about the brain development in sarcopterygians?

Cerebral hemispheres fold inward on themselves

How many extant non-tetrapod species of sarcopterygians exist?

Eight extant non-tetrapod species

What are the two groups of extant sarcopterygians?

Coelacanths and lungfishes

What is a defining feature of Actinistia (coelacanths)?

They lack a maxilla and have a three-lobed tail

Where are extant coelacanths primarily found?

Africa and Indonesia, in deepwater marine environments

What is a notable feature of lungfishes (Dipnoi)?

They possess paired lungs

What type of fins do lungfishes have?

Fused dorsal, caudal, and anal fins

What are the main regions where extant lungfishes are found?

Africa, South America, and Australia

What evolutionary significance do tetrapodomorphs hold?

They gave rise to tetrapod vertebrates in the Late Devonian

What are the characteristics of the Elpistostegalia group?

Sister group to tetrapods, with a flattened body and long-snouted head

What is Tiktaalik known for in terms of evolutionary significance?

It exhibits both fish-like and tetrapod-like characters

What are some fish-like characteristics of Tiktaalik?

Fin rays and lack of contact between pelvic girdle and vertebral column

What are some tetrapod-like characteristics of Tiktaalik?

Mobile head, limb-like fins, and large pelvic girdle

What adaptations did Devonian tetrapods like Acanthostega and Ichthyostega retain?

They retained gills and were primarily aquatic

What skeletal adaptations are necessary for locomotion on land?

Overcoming gravity and resisting torsional forces

How did gas exchange evolve in early tetrapods?

They retained lungs and some also retained gills, with a shift to costal ventilation

What genetic similarity is noted between fish and tetrapods?

The same Hox genes regulate fin and limb development

What are the two major lineages of non-amniote Paleozoic tetrapods?

Batrachomorphs and Reptiliomorphs

During which geological periods were non-amniote Paleozoic tetrapods most diverse?

Late Carboniferous and Early Permian

When did early amniote tetrapods arise?

In the Late Carboniferous

What are the three major lineages of early amniote tetrapods?

Synapsids, Eureptiles, and Parareptiles

What is a derived character of amniote tetrapods?

The amniotic (cleidoic) egg

What are the three additional extraembryonic membranes found in amniotic eggs?

Chorion, Amnion, and Allantois

What is required for the amniotic egg's fertilization?

Internal fertilization and an intromittent organ in males

What are the three types of temporal fenestration in amniote tetrapods?

Anapsid (no openings), Synapsid (one opening), Diapsid (two openings)

What are openings in the skull called in relation to temporal fenestration?

Temporal fenestrae

What are the three eras of the Phanerozoic Eon?

Paleozoic, Mesozoic, and Cenozoic.

What periods make up the Mesozoic Era?

Triassic, Jurassic, and Cretaceous.

How did the climates of the Mesozoic compare to today?

Mesozoic climates were generally warmer and wetter, even in polar regions, which lacked ice caps.

What were the two major lineages of amniote tetrapods during the Mesozoic?

Synapsids and Sauropsids.

What event likely caused the End-Permian mass extinction?

Volcanism and related changes in atmospheric composition, climate, and ocean acidification.

What was the supercontinent during the Triassic period?

Pangaea.

Which types of vegetation dominated Triassic terrestrial ecosystems?

Gymnosperms, tree ferns, and horsetails.

What dominant tetrapods arose during the Triassic?

Therapsids and archosaurs (pseudosuchians), along with early mammals, sphenodontids, turtles, and dinosaurs.

What caused the End-Triassic mass extinction?

Volcanism related to the breakup of Pangaea.

What significant geographical change occurred during the Jurassic?

The separation of Pangaea into Laurasia and Gondwana.

What were the dominant plants during the Jurassic period?

Coniferous gymnosperms.

What types of animals were dominant during the Jurassic and Cretaceous periods?

Dinosaurs.

What marine organisms flourished due to nutrient enrichment during the Mesozoic?

Planktonic organisms, which supported the radiation of marine invertebrates and vertebrates.

What caused the End-Jurassic extinctions?

Falling sea levels.

What significant plant group arose during the Early Cretaceous?

Angiosperms.

What modern lineages of mammals arose during the Cretaceous?

Monotremes, Metatherians (marsupials), and Eutherians (placentals).

What caused the End-Cretaceous mass extinction?

Asteroid impact, volcanism, changes in atmospheric conditions, and climate change.

What was the impact of the End-Cretaceous mass extinction on non-avian dinosaurs?

Non-avian dinosaurs were eliminated, allowing mammals to become the dominant land animals during the Cenozoic.

What are the main types of vertebrae found in tetrapods?

Tetrapods have cervical, trunk, sacral, and caudal vertebrae.

How are the trunk vertebrae of mammals categorized?

Mammals' trunk vertebrae are divided into thoracic vertebrae (bearing ribs) and lumbar vertebrae (without ribs).

What structural adaptation helps the axial skeleton of tetrapods resist gravity?

Zygapophyses on the vertebral column help resist gravity.

How is the cranial skeleton of tetrapods connected to the trunk?

The head is connected to the trunk via a mobile neck.

What is the function of axial musculature in tetrapods?

Axial musculature is involved in locomotion, posture, and lung ventilation.

What are the differentiated hypaxial muscles in tetrapods?

They include internal oblique, external oblique, and transversus abdominis.

What are the differentiated epaxial muscles in amniotes?

They include transversospinalis, longissimus dorsi, and iliocostalis.

What are the key features of the appendicular skeleton in tetrapods?

Tetrapods have jointed limbs, wrist and ankle joints, and hands and feet with digits.

How does the pelvic girdle of tetrapods connect to the vertebral column?

The pelvic girdle consists of paired ilia, ischia, and pubis, connecting to sacral vertebrae via modified ribs.

What is the difference in locomotion between salamanders and many amniotes?

Salamanders have a sprawling stance and walking-trot gait, while many amniotes have an upright stance with independent limb movement.

What is the significance of the upright stance in therian mammals?

It is associated with dorsoventral flexion of the vertebral column.

How does body mass relate to bone strength in larger tetrapods?

Body mass increases faster than bone strength, leading to proportionately thicker limb bones in larger-bodied tetrapods.

What type of lung ventilation do non-amniotes rely on?

Non-amniotes rely on positive-pressure buccal pumping for lung ventilation.

What circulatory adaptation allows tetrapods to move blood against gravity?

A thick-walled muscular heart allows for elevated blood pressure.

What prevents backflow of blood in the circulatory system of tetrapods?

Valves within veins prevent backflow.

What is the role of the ventricular septum in certain tetrapods?

It allows for separation of deoxygenated and oxygenated blood in crocodilians, birds, and mammals.

How do terrestrial tetrapods focus light on the retina?

The cornea assists the lens in focusing light, with the lens changing shape rather than moving.

What adaptations do terrestrial tetrapods have for hearing?

They have hair cells in fluid-filled chambers and stapes in the middle ear to amplify sound waves.

How do terrestrial tetrapods conserve water?

They minimize evaporative water loss and have kidneys adapted to excrete metabolic waste with minimal water.

What are the primary nitrogenous waste forms excreted by sauropsids and synapsids?

Sauropsids mainly excrete uric acid, while synapsids primarily excrete urea.

What is the significance of thermoregulation in terrestrial tetrapods?

Air temperature is more variable than water temperature, making thermoregulation more challenging.

What are the two modes of temperature regulation in tetrapods?

Ectothermy (using external heat) and endothermy (using metabolic heat).

What is heterothermy in the context of tetrapods?

Both ectotherms and endotherms may be heterothermic, with body temperature varying over time or by region.

What are the shared derived characters of amphibians?

Moist, permeable, scaleless skin; pedicellate, bicuspid teeth; two auditory ossicles; unique green rod cells for night vision; levator bulbi muscle; carnivorous as adults.

How does the permeable skin of amphibians function?

Water and gases readily pass across the skin, allowing cutaneous respiration to account for a significant portion of gas exchange.

What are the reproductive modes of amphibians?

Most are oviparous, with eggs deposited in water or on land; some are viviparous, and adults may carry eggs in various ways.

What are the three major lineages of amphibians?

Urodela (salamanders), Anura (frogs and toads), Gymnophiona (caecilians).

What is a unique feature of Urodela (salamanders)?

They have a large genome size compared to other vertebrates and many paedomorphic species.

How do plethodontid salamanders adapt their respiration?

They have secondarily lost lungs, allowing for tongue extension.

What is the typical reproductive method in salamanders?

Most have internal fertilization via spermatophore, with courtship involving pheromone transfer.