Questions and Answers
What are the characteristics of Sarcopterygii?
- Skeleton with bone of endochondral origin; caudal fin diphycercal in living representatives, heterocercal in ancestral forms, skin with embedded dermal scales with layer of cosine and a thin layer of enamel of fossil species; 2. Paired and median fins present; paired fins with a single basal skeletal element and short dermal rays; muscles that move paired fins located on appendage; 3. Jaws present; teeth covered with true enamel and typically are crushing plates restricted to palate; olfactory sacs paired, may or may not open into mouth, intestine with spiral valve; 4. Gills supported by bony arches and covered with an operculum; 5. Swim bladder vascularized and used for respiration and buoyancy (fat-filled coelacanths); 6. Circulation consisting of heart with a sinus venosus, two atria, a partly divided ventricle, and a conus arteriosus; double circulation with pulmonary and systemic circuits; characteristically five aortic arches; 7. Nervous system of a relatively small brain; 10 pairs of cranial nerves; three pairs of semicircular canals; 8. Separate sexes; fertilization external or internal.
What is Class Sarcopterygii?
Lobe-finned fishes.
Who is considered the ancestor of modern Sarcopterygii?
Class Sarcopterygii; probable ancestor of all tetrapods.
What is the sequence of fossils of Class Sarcopterygii?
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What is Eusthenopteron?
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What is Acanthostega?
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What is Tiktaalik rosae?
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What were two challenges of terrestrial life?
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What adaptations to aquatic life didn't work on land?
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What primitive features from aquatic life were retained during the transition to land?
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What were the solutions for the adaptations from water to land for fish-type limb structure?
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What was the solution for the transition from water to land regarding water-permeable skin that leads to moisture loss?
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What are the limitations to adaptations of water-permeable skin?
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What does permeable skin allow?
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What are amphibians similar to regarding their permeable skin?
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What is the solution to gas exchange through gills causing moisture loss during the transition to land?
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What are the limitations of the solution to gas exchange?
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What is cutaneous respiration?
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What is the solution to external fertilization and water-permeable eggs that don't work on land?
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What is the limitation to the solution of external fertilization?
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What are additional adaptations to the problem of external fertilization?
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In salamanders, what does indirect insemination refer to?
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Study Notes
Characteristics of Sarcopterygii
- Skeleton comprised of endochondral bone; living representatives have diphycercal caudal fins, while ancestral forms possess heterocercal fins.
- Presence of paired and median fins; paired fins feature a single basal skeletal element and short dermal rays; muscles for movement are located directly on the appendage.
- Jaws are present, with teeth covered in true enamel, often forming crushing plates; olfactory sacs are paired and may not connect to the mouth; intestines exhibit a spiral valve.
- Gills are supported by bony arches and protected by an operculum.
- Swim bladder serves both respiratory and buoyancy functions, particularly noted in fat-filled coelacanths.
- Heart structure consists of a sinus venosus, two atria, a partly divided ventricle, and a conus arteriosus; possesses a double circulation including pulmonary and systemic circuits along with five aortic arches.
- Nervous system is characterized by a relatively small brain, ten pairs of cranial nerves, and three pairs of semicircular canals.
- Reproduction involves separate sexes with either internal or external fertilization.
Class Sarcopterygii Overview
- Known as lobe-finned fishes.
Ancestry
- Considered the probable ancestor of all tetrapods.
Fossil Sequence
- Evolutionary sequence includes fish, fishapod, and then tetrapod.
Eusthenopteron
- Fossil lobe-finned fish known for having many fin rays.
Acanthostega
- Primitive tetrapod identified by its eight toes.
Tiktaalik Roseae
- Recognized as the latest "missing link" fossil in the evolutionary transition.
Challenges of Terrestrial Life
- Risks of desiccation and the need for structural support present major challenges for terrestrial life.
Non-Working Aquatic Adaptations
- Features not suitable for land include fins, undulatory locomotion, disarticulated appendicular skeleton, gills, external fertilization, filter feeding, and "inhalation" feeding.
Retained Primitive Aquatic Features
- Transitioning to land retained certain characteristics like water-permeable skin, splayed gait, horizontal undulation, and dependence on water for reproduction and larval stages.
Solutions for Water to Land Adaptations
- Limb structures redirected ventrally, strengthened appendicular skeleton articulations, developed rib cages for belly-crawling support, and underwent significant skeletal modifications driven by selective pressure (illustrated in frogs).
Addressing Moisture Loss from Skin
- Adaptations to combat water loss include secreting mucus and staying in or near moist habitats.
Limitations of Permeable Skin Adaptations
- Energy and water costs associated with mucus production, while skin remains somewhat permeable.
Implications of Permeable Skin
- Permeable skin can facilitate toxin penetration.
Amphibian Skin Comparison
- The permeable skin of amphibians is likened to a "canary in a coal mine," indicating environmental health.
Gas Exchange Solutions
- Transitioning to land required lungs due to moisture loss associated with gills.
Limitations of Lung Adaptation
- Absence of a diaphragm necessitates buccal breathing to facilitate gas exchange.
Cutaneous Respiration
- This form of respiration, which supplements lung-breathing, also increases moisture loss; skin secretes mucus to mitigate this loss.
Reproductive Adaptations to Terrestrial Challenges
- To address external fertilization and the limitations of water-permeable eggs, many species return to aquatic environments for reproduction.
Limitations of External Fertilization Solutions
- The requirement for metamorphosis into adult forms presents a significant limitation.
Additional Reproductive Adaptations
- Some species have developed marsupia for offspring protection and utilize spermatophore deposition to facilitate terrestrial sperm transfer.
Salamander Reproductive System
- Indirect insemination in salamanders equates to internal fertilization.
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Test your knowledge on the characteristics of Sarcopterygii with this flashcard quiz. Explore the unique features of these ancient lobe-finned fishes and their evolutionary significance. Perfect for biology students and enthusiasts alike!
