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Questions and Answers
What is the significance of the appearance of Neoselachii in the Late Triassic?
What is the significance of the appearance of Neoselachii in the Late Triassic?
It marks the first appearance of the modern elasmobranch radiation.
Describe the feeding mechanism of the holocephalan Cladoselache.
Describe the feeding mechanism of the holocephalan Cladoselache.
Cladoselache fed by trapping, piercing, and cutting its prey with a circular saw-like tooth whorl.
What distinguished the Paleozoic group known as menaspoids?
What distinguished the Paleozoic group known as menaspoids?
Menaspoids were heavily armored fishes with plates of dermal bone on their heads and paired spines projecting from the side of their mouths.
What is the fate of the stem members of extant chondrichthyan lineages mentioned in the text?
What is the fate of the stem members of extant chondrichthyan lineages mentioned in the text?
What characterized Xenacanths in terms of their anatomy and timeframe of existence?
What characterized Xenacanths in terms of their anatomy and timeframe of existence?
What does the term 'Elasmobranchii' refer to?
What does the term 'Elasmobranchii' refer to?
How do Neoselachii differ from Holocephali in terms of gill openings?
How do Neoselachii differ from Holocephali in terms of gill openings?
What is the characteristic feature of Neoselachii's upper jaw?
What is the characteristic feature of Neoselachii's upper jaw?
Describe the appearance of Holocephali's head.
Describe the appearance of Holocephali's head.
What are some common names of extant holocephalans?
What are some common names of extant holocephalans?
What do the terms 'Elasmobranchii' and 'Holocephali' refer to in Greek?
What do the terms 'Elasmobranchii' and 'Holocephali' refer to in Greek?
What are the body forms of fishes mentioned in the text?
What are the body forms of fishes mentioned in the text?
When are definitive forms of chondrichthyans known to appear?
When are definitive forms of chondrichthyans known to appear?
What distinguishes iniopterygians from holocephalans?
What distinguishes iniopterygians from holocephalans?
What is a conspicuous difference between stem elasmobranchs and modern sharks?
What is a conspicuous difference between stem elasmobranchs and modern sharks?
What is the representative example of a stem elasmobranch mentioned in the text?
What is the representative example of a stem elasmobranch mentioned in the text?
When did the first elasmobranchs appear?
When did the first elasmobranchs appear?
What is a distinctive feature of the upper jaw in chimaeras and their fossil relatives?
What is a distinctive feature of the upper jaw in chimaeras and their fossil relatives?
What unique skeletal characteristic defines chondrichthyans?
What unique skeletal characteristic defines chondrichthyans?
Which element of the hyoid arch in chondrichthyans is separate and not fused into a hyomandibula?
Which element of the hyoid arch in chondrichthyans is separate and not fused into a hyomandibula?
What is the purpose of pelvic claspers present in male chondrichthyans?
What is the purpose of pelvic claspers present in male chondrichthyans?
Which group demonstrates the ancestral condition of a cartilaginous endoskeleton in vertebrates?
Which group demonstrates the ancestral condition of a cartilaginous endoskeleton in vertebrates?
What is the microstructural feature of the small calcium-containing units in chondrichthyans' skeletons?
What is the microstructural feature of the small calcium-containing units in chondrichthyans' skeletons?
What is a distinguishing characteristic of stethacanthid stem elasmobranchs from the Early Carboniferous?
What is a distinguishing characteristic of stethacanthid stem elasmobranchs from the Early Carboniferous?
What is the unique sexual dimorphism feature observed in some stethacanthid males?
What is the unique sexual dimorphism feature observed in some stethacanthid males?
How did Xenacanthans differ from other stem elasmobranchs in terms of habitat?
How did Xenacanthans differ from other stem elasmobranchs in terms of habitat?
What was the probable function of the structure known as the spine-brush complex in stethacanthids?
What was the probable function of the structure known as the spine-brush complex in stethacanthids?
What is inferred about the feeding behavior of Cladoselache based on the text?
What is inferred about the feeding behavior of Cladoselache based on the text?
When did Xenacanthans cease to exist?
When did Xenacanthans cease to exist?
What is the purpose of the tooth whorl in Helicoprion?
What is the purpose of the tooth whorl in Helicoprion?
How did paraselachians differ from extant chimaeras?
How did paraselachians differ from extant chimaeras?
What was a notable characteristic of Helicoprion among paraselachians?
What was a notable characteristic of Helicoprion among paraselachians?
When did paraselachians first appear?
When did paraselachians first appear?
What differentiated holocephalans from paraselachians?
What differentiated holocephalans from paraselachians?
Which group of organisms did not appear until the Late Carboniferous according to the text?
Which group of organisms did not appear until the Late Carboniferous according to the text?
What unique type of scales do chondrichthyans possess?
What unique type of scales do chondrichthyans possess?
How do the teeth of chondrichthyans differ from those of bony fishes?
How do the teeth of chondrichthyans differ from those of bony fishes?
Why are fossil teeth the main remnants of extinct chondrichthyans?
Why are fossil teeth the main remnants of extinct chondrichthyans?
How do chondrichthyans differ from other jawed fishes in terms of their exoskeleton?
How do chondrichthyans differ from other jawed fishes in terms of their exoskeleton?
What complex structures do some chondrichthyans, especially chimaeras, have associated with their jaws?
What complex structures do some chondrichthyans, especially chimaeras, have associated with their jaws?
How do placoid scales develop in chondrichthyans?
How do placoid scales develop in chondrichthyans?
What was a characteristic feeding behavior of the holocephalan Cladoselache?
What was a characteristic feeding behavior of the holocephalan Cladoselache?
Which group of Paleozoic fishes resembled placoderms due to heavy armor on their heads and paired spines projecting from their mouths?
Which group of Paleozoic fishes resembled placoderms due to heavy armor on their heads and paired spines projecting from their mouths?
Which group of fishes survived until the end of the Triassic period, showing characteristics similar to stem elasmobranchs?
Which group of fishes survived until the end of the Triassic period, showing characteristics similar to stem elasmobranchs?
When did the modern elasmobranch radiation, Neoselachii, first appear?
When did the modern elasmobranch radiation, Neoselachii, first appear?
What characteristic feature distinguishes basal Xenacanths from modern elasmobranchs?
What characteristic feature distinguishes basal Xenacanths from modern elasmobranchs?
Which term refers to the radiation of stem members of extant chondrichthyan lineages that did not survive into the Cenozoic era?
Which term refers to the radiation of stem members of extant chondrichthyan lineages that did not survive into the Cenozoic era?
What structure in chondrichthyans is responsible for attaching developing teeth behind the functional teeth?
What structure in chondrichthyans is responsible for attaching developing teeth behind the functional teeth?
How frequently do young sharks replace their upper-jaw teeth on average based on the text?
How frequently do young sharks replace their upper-jaw teeth on average based on the text?
Which group of organisms is now considered to be the sister group to chondrichthyans?
Which group of organisms is now considered to be the sister group to chondrichthyans?
Tooth replacement in extant sharks varies significantly due to all of the following EXCEPT:
Tooth replacement in extant sharks varies significantly due to all of the following EXCEPT:
What is a secondary modification from the original tooth condition in chimaeras according to the text?
What is a secondary modification from the original tooth condition in chimaeras according to the text?
Which extinct group mentioned in the text also exhibited tooth whorls similar to chondrichthyans?
Which extinct group mentioned in the text also exhibited tooth whorls similar to chondrichthyans?
What is a distinguishing feature between stem chondrichthyians and modern sharks mentioned in the text?
What is a distinguishing feature between stem chondrichthyians and modern sharks mentioned in the text?
Which era saw the appearance of the first elasmobranchs?
Which era saw the appearance of the first elasmobranchs?
What differentiated iniopterygians from crown chondrichthyians?
What differentiated iniopterygians from crown chondrichthyians?
Which Paleozoic group had a feeding mechanism described as sharklike but lacked some characteristics of modern sharks?
Which Paleozoic group had a feeding mechanism described as sharklike but lacked some characteristics of modern sharks?
What characteristic shape were iniopterygians compared to in the text?
What characteristic shape were iniopterygians compared to in the text?
Which feature of Cladoselache distinguishes it as a representative example of a stem elasmobranch?
Which feature of Cladoselache distinguishes it as a representative example of a stem elasmobranch?
What was a unique characteristic of the Paleozoic group known as menaspoids?
What was a unique characteristic of the Paleozoic group known as menaspoids?
Which group of fishes survived until the end of the Triassic period, showing characteristics similar to stem elasmobranchs?
Which group of fishes survived until the end of the Triassic period, showing characteristics similar to stem elasmobranchs?
When did the modern elasmobranch radiation, Neoselachii, first appear?
When did the modern elasmobranch radiation, Neoselachii, first appear?
What is the significance of Xenacanths in the context of elasmobranch evolution?
What is the significance of Xenacanths in the context of elasmobranch evolution?
What differentiated the Mesozoic elasmobranch radiations from Xenacanths?
What differentiated the Mesozoic elasmobranch radiations from Xenacanths?
What was a key feature of the Late Cretaceous elasmobranch Hybodus?
What was a key feature of the Late Cretaceous elasmobranch Hybodus?
What type of prey were the stout, blunt teeth of hybodonts primarily suited for?
What type of prey were the stout, blunt teeth of hybodonts primarily suited for?
What morphological changes were observed in the posterior teeth of hybodonts compared to their anterior teeth?
What morphological changes were observed in the posterior teeth of hybodonts compared to their anterior teeth?
What advancement in the structure of fins made hybodonts more mobile compared to earlier elasmobranchs?
What advancement in the structure of fins made hybodonts more mobile compared to earlier elasmobranchs?
What function is suggested by the ridges and barbs on the posterior surface of hybodont dorsal-fin spines?
What function is suggested by the ridges and barbs on the posterior surface of hybodont dorsal-fin spines?
How did the narrow base of the hybodont fin contribute to their locomotion?
How did the narrow base of the hybodont fin contribute to their locomotion?
What was the significance of the disappearance of hybodonts at the end of the Mesozoic era?
What was the significance of the disappearance of hybodonts at the end of the Mesozoic era?
What is a distinguishing characteristic of Hybodonts based on their dentition?
What is a distinguishing characteristic of Hybodonts based on their dentition?
In what period did Hybodonts first appear according to the text?
In what period did Hybodonts first appear according to the text?
What is the significance of the euselachian heterocercal tail mentioned in the text?
What is the significance of the euselachian heterocercal tail mentioned in the text?
What characteristic feature distinguishes Hybodonts' teeth from those of other fish?
What characteristic feature distinguishes Hybodonts' teeth from those of other fish?
How does the hybodont tail's distribution of force aid in swimming?
How does the hybodont tail's distribution of force aid in swimming?
What distinguished Hybodus, a well-known genus of hybodonts, among other fish?
What distinguished Hybodus, a well-known genus of hybodonts, among other fish?
What geologic era saw the appearance of the first elasmobranchs?
What geologic era saw the appearance of the first elasmobranchs?
What is the significance of Neoselachii in the Late Triassic?
What is the significance of Neoselachii in the Late Triassic?
What distinguishes holocephalans from other chondrichthyans?
What distinguishes holocephalans from other chondrichthyans?
During which era did paraselachians first appear?
During which era did paraselachians first appear?
What was a characteristic feeding behavior of Cladoselache?
What was a characteristic feeding behavior of Cladoselache?
What is the defining characteristic of Elasmobranchii mentioned in the text?
What is the defining characteristic of Elasmobranchii mentioned in the text?
What feature distinguishes Holocephali from other groups mentioned in the text?
What feature distinguishes Holocephali from other groups mentioned in the text?
What is the distinguishing factor between sharks and rays (including skates) in Neoselachii?
What is the distinguishing factor between sharks and rays (including skates) in Neoselachii?
What is the significance of the operculum in Holocephali anatomy?
What is the significance of the operculum in Holocephali anatomy?
Which characteristic is common among extant holocephalans mentioned in the text?
Which characteristic is common among extant holocephalans mentioned in the text?
What does Neoselachii's independently mobile upper jaw refer to?
What does Neoselachii's independently mobile upper jaw refer to?
What was unique about Helicoprion among the paraselachians?
What was unique about Helicoprion among the paraselachians?
Why did paraselachians look like sharks according to the text?
Why did paraselachians look like sharks according to the text?
What did Helicoprion use its tooth whorl for?
What did Helicoprion use its tooth whorl for?
How did Helicoprion's tooth whorl differ from typical shark teeth?
How did Helicoprion's tooth whorl differ from typical shark teeth?
What feature of Helicoprion's tooth whorl allowed its lifelong production of teeth?
What feature of Helicoprion's tooth whorl allowed its lifelong production of teeth?
How did the tooth whorl of Helicoprion differ from typical shark teeth structures?
How did the tooth whorl of Helicoprion differ from typical shark teeth structures?
What Paleozoic group of fishes had heavily armored plates of dermal bone on their heads and paired spines projecting from the side of their mouths?
What Paleozoic group of fishes had heavily armored plates of dermal bone on their heads and paired spines projecting from the side of their mouths?
Which group of fishes, known for a circular saw-like tooth whorl, probably fed on soft-bodied prey by trapping, piercing, and cutting them?
Which group of fishes, known for a circular saw-like tooth whorl, probably fed on soft-bodied prey by trapping, piercing, and cutting them?
Which modern chondrichthyan radiation first appeared in the Late Triassic according to the text?
Which modern chondrichthyan radiation first appeared in the Late Triassic according to the text?
Which freshwater fish, similar to stem elasmobranchs, survived until the end of the Triassic period and possibly into the Jurassic?
Which freshwater fish, similar to stem elasmobranchs, survived until the end of the Triassic period and possibly into the Jurassic?
Which Paleozoic group will be considered in Chapter 7 as part of modern radiations, despite none of its members surviving into the Cenozoic era?
Which Paleozoic group will be considered in Chapter 7 as part of modern radiations, despite none of its members surviving into the Cenozoic era?
Which Late Cretaceous elasmobranch is depicted in Figure 6.6 and mentioned in the text?
Which Late Cretaceous elasmobranch is depicted in Figure 6.6 and mentioned in the text?
What is the primary metabolic substrate of skeletal and cardiac muscles in extant chondrichthyans?
What is the primary metabolic substrate of skeletal and cardiac muscles in extant chondrichthyans?
What feature renders extant chondrichthyans neutrally buoyant in water?
What feature renders extant chondrichthyans neutrally buoyant in water?
Which division of extant chondrichthyans reflects a classification dating back almost to the start of chondrichthyan history?
Which division of extant chondrichthyans reflects a classification dating back almost to the start of chondrichthyan history?
Which group is evolutionary related to the extinct sharklike paraselachians but is distinct from holocephalans?
Which group is evolutionary related to the extinct sharklike paraselachians but is distinct from holocephalans?
In which era did chondrichthyans likely exhibit their greatest diversity?
In which era did chondrichthyans likely exhibit their greatest diversity?
Which group besides Holocephali can be seen to be part of a larger group known as Euchondrocephali?
Which group besides Holocephali can be seen to be part of a larger group known as Euchondrocephali?
Study Notes
Chondrichthyan Evolution
- Chondrichthyans are a group of fishes characterized by a cartilaginous endoskeleton and the presence of dermal denticles.
- The earliest known chondrichthyans date back to the Early Ordovician period.
Late Triassic Neoselachii
- The appearance of Neoselachii in the Late Triassic marks a significant milestone in the evolution of chondrichthyans.
- Neoselachii is characterized by a modern elasmobranch radiation and is distinct from earlier stem elasmobranchs.
Holocephali and Cladoselache
- Holocephali are a group of chondrichthyans characterized by a unique head shape and a distinctive feeding mechanism.
- Cladoselache is a representative example of a stem elasmobranch and exhibits a shark-like feeding mechanism.
- The feeding mechanism of Cladoselache involves a tooth whorl used for grasping and piercing prey.
Menaspoids and Iniopterygians
- Menaspoids are a Paleozoic group of fishes characterized by heavily armored plates of dermal bone on their heads and paired spines projecting from their mouths.
- Iniopterygians are a group of fishes that resemble sharks but lack some characteristics of modern sharks.
- Iniopterygians are characterized by a unique tooth shape, with their teeth being compared to razors.
Xenacanthans and Stem Elasmobranchs
- Xenacanthans are a group of stem elasmobranchs that differed from other stem elasmobranchs in terms of their habitat and anatomy.
- Xenacanthans are characterized by a unique upper jaw and a distinctive spine-brush complex.
- The probable function of the spine-brush complex in Xenacanthans was for grasping and piercing prey.
Elasmobranchii and Holocephali
- Elasmobranchii refers to a group of chondrichthyans that includes modern sharks and rays.
- Holocephali are a group of chondrichthyans that are distinct from Elasmobranchii and are characterized by a unique head shape and a distinctive feeding mechanism.
- The term 'Elasmobranchii' refers to the Greek words "elasma" meaning thin plate and "branch" meaning gill.
Chondrichthyan Anatomy
- Chondrichthyans are characterized by a cartilaginous endoskeleton and the presence of dermal denticles.
- The unique skeletal characteristic of chondrichthyans is the presence of small calcium-containing units called tesserae.
- The hyoid arch in chondrichthyans is separate and not fused into a hyomandibula.
Chondrichthyan Radiation
- The modern elasmobranch radiation, Neoselachii, first appeared in the Late Triassic.
- The term 'Neoselachii' refers to the Greek words "neos" meaning new and "selachii" meaning shark.
- Neoselachii is characterized by a modern elasmobranch radiation and is distinct from earlier stem elasmobranchs.
Extant Holocephalans
- Extant holocephalans are characterized by a unique head shape and a distinctive feeding mechanism.
- Common names of extant holocephalans include ratfish, spookfish, and elephant fish.
Fossil Record
- The fossil record of chondrichthyans is primarily composed of teeth, which are the main remnants of extinct chondrichthyans.
- The unique characteristic of chondrichthyan teeth is that they are constantly replaced throughout their lifetime.
- The tooth replacement process in extant sharks varies significantly due to factors such as diet, habitat, and growth rate.
Hybodonts
- Hybodonts are a group of extinct elasmobranchs that appeared in the Early Cretaceous period.
- Hybodonts are characterized by a unique dentition, with their teeth being stout and blunt.
- The function of the ridges and barbs on the posterior surface of hybodont dorsal-fin spines is suggested to be for grasping and piercing prey.
Paraselachians and Helicoprion
- Paraselachians are a group of extinct chondrichthyans that resembled sharks but lacked some characteristics of modern sharks.
- Helicoprion is a well-known genus of paraselachians characterized by a unique tooth whorl.
- The tooth whorl of Helicoprion was used for grasping and piercing prey and was constantly replaced throughout its lifetime.
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Description
Learn about Elasmobranchii, a group of cartilaginous fish that includes sharks and rays. They are known for their unique anatomy with multiple gill openings on each side of the head. Discover more about these fascinating creatures!
