Elasmobranch Palaeontology
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Questions and Answers

How long have elasmobranchs been part of the paleontological record?

  • 150 million years
  • 300 million years
  • 250 million years
  • 400 million years (correct)

    • Batoids, which include skates and rays, emerged earlier than sharks.

    False

    What is a significant fossil left behind by sharks that aids in paleontological studies?

    large teeth

    The Batoids first appeared during the _____ period.

    <p>lower Jurassic</p> Signup and view all the answers

    Match the following elasmobranchs with their characteristics:

    <p>Sharks = Leave behind large teeth Skates = Leave fewer traces Batoids = Emerged 150 million years ago Elasmobranchs = Exist for over 400 million years</p> Signup and view all the answers

    Sharks/Elasmobranchs have been around since the ___ period.

    <p>Ordovician</p> Signup and view all the answers

    What role do large sharks play in marine ecosystems?

    <p>They have a strong top-down impact that can shape marine communities</p> Signup and view all the answers

    Sharks, skates, and rays contribute to the stability of food webs in ocean ecosystems.

    <p>True</p> Signup and view all the answers

    What is one way that sharks help prevent the spread of disease in marine ecosystems?

    <p>By removing weak and diseased specimens.</p> Signup and view all the answers

    The presence of sharks impacts the habitat use and behavior of their prey through ________ effects.

    <p>risk</p> Signup and view all the answers

    Match the following ecological roles with their descriptions:

    <p>Scavenging = Cleaning up dead organisms in the ocean Bioturbation = Disturbing the sediment and enhancing nutrient movement Predator release = Change in prey population dynamics when predators are removed Foraging facilitation = Creating conditions for other organisms to find food</p> Signup and view all the answers

    Squalimorphs ___ anal fins.

    Signup and view all the answers

    Galeomorphs ___ anal fins.

    Signup and view all the answers

    How many species of elasmobranchs are found in the Canadian Arctic and Atlantic waters?

    <p>39</p> Signup and view all the answers

    The Atlantic Manta Ray is one of the ray species found in the Western North Atlantic region.

    <p>True</p> Signup and view all the answers

    Name one species of ray that can be found in the Western North Atlantic region.

    <p>Atlantic Torpedo Ray, Atlantic Manta Ray, Pelagic Stingray, Roughtail Stingray</p> Signup and view all the answers

    Match the following ray species to their descriptions:

    <p>Atlantic Manta Ray = Known for its large size and wing-like fins Atlantic Torpedo Ray = Specialized in electric shock for defense Pelagic Stingray = Resides in open waters and has a long tail Roughtail Stingray = Recognized for its unique roughtail structure</p> Signup and view all the answers

    Which of the following is NOT a type of skate found in the Western North Atlantic region?

    <p>Horseshoe Skate</p> Signup and view all the answers

    The Arctic Skate is one of the skates found in the Western North Atlantic region.

    <p>True</p> Signup and view all the answers

    Name one species of skate found in the Western North Atlantic region.

    <p>Thorny Skate</p> Signup and view all the answers

    Match the skate species with their unique characteristics:

    <p>Bigelow's Skate = Named after the biologist who described it Richardson's Skate = Has a notable rounded shape Round Skate = Common in shallower regions Spinytail Skate = Features prominent spines on its tail</p> Signup and view all the answers

    The Whale Shark is a filter-feeding species.

    <p>True</p> Signup and view all the answers

    The __________ Shark is known for its unique ability to survive in colder waters.

    <p>Greenland</p> Signup and view all the answers

    Match the following sharks with their notable characteristics:

    <p>Blue Shark = Known for its striking blue color and agility Tiger Shark = Recognized for its tiger-like stripes and broad diet Dusky Shark = Important for commercial fishing and has a dark hue Porbeagle Shark = Similar in appearance to the Great White but smaller</p> Signup and view all the answers

    Which structure is unique to the male reproductive system of skates?

    <p>Claspers</p> Signup and view all the answers

    Some species of skates can walk using their pelvic fins.

    <p>True</p> Signup and view all the answers

    What is the primary locomotion method of skates?

    <p>Undulatory pectoral fin movement</p> Signup and view all the answers

    What is the primary function of spiracles in elasmobranchs?

    <p>To act as a water breathing passage</p> Signup and view all the answers

    Spiracles help in the ventilation process of elasmobranchs.

    <p>True</p> Signup and view all the answers

    Where are spiracles located on elasmobranchs?

    <p>On the top of the head between the eye and gill slits.</p> Signup and view all the answers

    The spiracle valve permits ______ and ______.

    <p>opening, closing</p> Signup and view all the answers

    Match the following facts about spiracles with their descriptions:

    <p>Found on the top of the head = Location of spiracles Acts as a water breathing passage = Function of spiracles Leads to the oral cavity = Respiratory pathway Permits opening and closing = Spiracle valve function</p> Signup and view all the answers

    Which method of ventilation involves a shark swimming to move water over its gills?

    <p>Ram Ventilation</p> Signup and view all the answers

    Buccal Pump Ventilation is achieved by sharks swimming rapidly to force water across their gills.

    <p>False</p> Signup and view all the answers

    What is the function of buccal movements in sharks?

    <p>To suction water into the mouth and across gills for oxygenation.</p> Signup and view all the answers

    Sharks using _________ can extract oxygen from water while swimming.

    <p>ram ventilation</p> Signup and view all the answers

    Match the ventilation methods with their descriptions:

    <p>Buccal Pump Ventilation = Suction water into the mouth and across gills Ram Ventilation = Swim to move water over gills</p> Signup and view all the answers

    What triggers tonic immobility in sharks?

    <p>Rapid inversion of body</p> Signup and view all the answers

    All shark species are buccal pumping species.

    <p>False</p> Signup and view all the answers

    What is the primary reason for tonic immobility in sharks?

    <p>To feign death</p> Signup and view all the answers

    Match the ventilation types with their characteristics:

    <p>Buccal Pumping = Slows down respiration, continues ventilation Ram Ventilation = Requires swimming for gill irrigation Intermediate Species = Can exhibit traits of both buccal and ram ventilation</p> Signup and view all the answers

    Which of the following metabolic effects is associated with tonic immobility?

    <p>Elevated lactate levels</p> Signup and view all the answers

    Tonic immobility in sharks results in an increase in blood oxygen levels.

    <p>False</p> Signup and view all the answers

    What happens to carbon dioxide levels in sharks during tonic immobility?

    <p>They increase.</p> Signup and view all the answers

    During tonic immobility, blood oxygen levels _____ while lactate levels _____.

    <p>decrease, increase</p> Signup and view all the answers

    Match the following effects with their outcomes during tonic immobility:

    <p>Blood oxygen levels = Decreases Carbon dioxide levels = Increases Lactate levels = Increases Active ventilation = Ceases</p> Signup and view all the answers

    What is the typical range of gestation time for sharks?

    <p>6 to 36 months</p> Signup and view all the answers

    All shark species mate in the same region and at the same time of the year.

    <p>False</p> Signup and view all the answers

    What is the maximum length of resting periods between shark reproduction?

    <p>3 years</p> Signup and view all the answers

    What percentage of sharks are oviparous and lay eggs?

    <p>40%</p> Signup and view all the answers

    All skates are viviparous and do not lay eggs.

    <p>False</p> Signup and view all the answers

    What provides nutrients to the growing embryo inside the egg capsule?

    <p>yolk</p> Signup and view all the answers

    The size of the egg cases of sharks ranges from _____ to _____ cm in length.

    <p>10, 25</p> Signup and view all the answers

    What is oviparous reproduction?

    <p>Oviparous reproduction is when eggs are fertilized in the womb and then a shark lays the eggs where they later hatch</p> Signup and view all the answers

    What is the main characteristic of ovoviviparous reproduction?

    <p>Embryos develop inside eggs but are born alive</p> Signup and view all the answers

    In ovoviviparous reproduction, the embryos receive their nutrients from the mother's placenta.

    <p>False</p> Signup and view all the answers

    What is the source of food for embryos in ovoviviparous reproduction?

    <p>single egg yolk</p> Signup and view all the answers

    Ovoviviparous reproduction is described as __________ viviparity.

    <p>aplacental</p> Signup and view all the answers

    What is the main process through which embryos receive nutrients in placental viviparity?

    <p>Via the placental cord</p> Signup and view all the answers

    All rays are classified as oviparous organisms.

    <p>False</p> Signup and view all the answers

    What is the reproductive outcome of viviparous reproduction?

    <p>Live birth</p> Signup and view all the answers

    In _____ viviparity, the yolk sack develops into a placenta.

    <p>placental</p> Signup and view all the answers

    Overfishing drives ___ of all sharks and rays toward global extinction.

    <p>1/3</p> Signup and view all the answers

    Sharks and rays make up ___% of all species threatened with extinction.

    <p>36</p> Signup and view all the answers

    What is the main threat to Pristiformes, commonly known as sawsharks?

    <p>Overexploitation through targeted fisheries</p> Signup and view all the answers

    What are the two types of fishing that primarily threaten sharks and rays?

    <p>Targeted fisheries and incidental catches.</p> Signup and view all the answers

    Study Notes

    Elasmobranch Palaeontology

    • Elasmobranchs are a class of cartilaginous fish that include sharks and rays, with a rich evolutionary history spanning over 400 million years, originating in the Ordovician period.
    • Batoids, which encompass skates and rays, have a more recent evolutionary appearance, emerging approximately 150 million years ago in the lower Jurassic period.
    • Sharks are known for their strong dental fossil record; their large teeth are commonly found in paleontological sites, providing valuable insights into their evolution and diversity.
    • Skates and rays leave behind fewer fossil traces compared to sharks, making it challenging for paleontologists to trace their lineage and understand their ancient origins fully.

    Ecosystem Importance of Sharks, Skates, and Rays

    • Vital for maintaining stability in marine food webs through top-down control.
    • Large sharks exert strong top-down impacts, influencing the distribution and population dynamics of prey species (predator release).
    • As apex predators, they help regulate populations of various marine organisms, promoting biodiversity.
    • Risk effects induce behavioral changes in prey, altering habitat use and benefiting other species beyond direct predation.
    • Prey species play a crucial role in the diet of these predators, maintaining the balance within marine ecosystems.
    • Scavenging by these species contributes to nutrient cycling and cleanup of organic material in ocean environments.
    • They assist in the removal of invasive species, helping to maintain ecological balance and native biodiversity.
    • By targeting weak and diseased individuals, they can limit the spread of illnesses within marine populations.
    • Facilitate nutrient movement across ecosystems, enhancing the health of various marine habitats.
    • Engage in habitat disturbance and bioturbation, which can create diverse environments for other marine life.
    • Their foraging behaviors can create opportunities and improve access to resources for other species, contributing to ecosystem complexity.
    • Overall, the presence of sharks, skates, and rays leads to healthier and more resilient marine ecosystems.

    Elasmobranch Diversity in Canadian Waters

    • The Canadian Arctic and Atlantic waters are home to 39 species of elasmobranchs, a group that includes rays, sharks, and skates.
    • This diversity is significant due to the unique marine ecosystems present in these regions.

    Notable Ray Species

    • Atlantic Manta Ray: Known for its large wingspan and filter-feeding habits, this species plays a crucial role in marine ecosystems.
    • Atlantic Torpedo Ray: Recognized for its ability to deliver electric shocks, it uses this feature for hunting and self-defense.
    • Pelagic Stingray: Found in offshore waters, this species is known for its agility and prominent sting, which it uses as a defense mechanism.
    • Roughtail Stingray: Notable for its distinctive rough tail, this species prefers shallow coastal waters and is often found in sandy or muddy substrates.

    Western North Atlantic Region Skates

    • Skates are a type of flat-bodied fish belonging to the family Rajidae, primarily found in the Western North Atlantic region.
    • Species include a variety of skates, each with unique physical and ecological characteristics.

    Abyssal Skate

    • Adapted to deep-sea environments, typically found at significant depths of the ocean.
    • Characterized by a flattened body and prominent pectoral fins.

    Arctic Skate

    • Inhabits cold Arctic waters, showcasing adaptations to survive in frigid temperatures.
    • Often has a lighter skin coloration to blend with the seafloor.

    Barndoor Skate

    • Features a wide pectoral fin structure, resembling a barn door when viewed from above.
    • Primarily found in coastal waters and known for its large size.

    Bigelow's Skate

    • Named after ichthyologist George Brown Goode, this species is less commonly encountered.
    • Typically found in the continental shelf regions.

    Jensen's Skate

    • A relatively smaller species with a distinctive coloration pattern.
    • Mostly resides in shallower waters compared to other skate species.

    Richardson's Skate

    • Recognized for its rough texture and thorn-like structures on its dorsal side.
    • Commonly found in deeper waters, with limited sightings in shallower coastal areas.

    Round Skate

    • Distinguished by its rounded body shape and smooth skin.
    • Predominantly inhabits sandy or muddy substrates.

    Smooth Skate

    • Known for its sleek body structure, which allows for efficient swimming.
    • Typically found in northern Atlantic waters.

    Soft Skate

    • Features soft, flexible cartilage which contributes to its unique movement.
    • Habitat includes a range of depths, often associating with the seabed.

    Spinytail Skate

    • Recognizable by its spiny tail, which serves as a defense mechanism against predators.
    • Lives in deeper waters, often near underwater structures.

    Thorny Skate

    • Name derived from the prominent thorny projections along its back.
    • Typically prefers cooler waters and often found on the continental shelf.

    White Skate

    • This skate species exhibits a pale coloration, making it less visible in its habitat.
    • Inhabits deeper ocean areas, often near the ocean floor.

    Winter Skate

    • Specializes in colder water environments, active during the winter months.
    • Known for its robust body and strong swimming capabilities.

    Western North Atlantic Region Sharks

    • Atlantic Sharpnose Shark: Commonly found in shallow coastal waters; known for its small size and distinctive pointed snout.

    • Basking Shark: Second-largest shark species; feeds primarily on plankton through filter feeding, often seen near the surface.

    • Black Dogfish: A small species, typically found in deep waters; known for its dark coloration and elongated body.

    • Blue Shark: Recognized for its sleek, slender body; widely distributed and often migratory, inhabiting both coastal and oceanic waters.

    • Deepwater Catshark: Prefers deep-sea environments; nocturnal and possesses a unique ability to camouflage within its surroundings.

    • Dusky Shark: Known for its large size and robust body; typically found in warmer waters and is an active predator.

    • Great Lantern Shark: One of the smallest shark species; notable for its bioluminescent properties that help it in communication and camouflage.

    • Greenland Shark: Inhabits cold Arctic waters; known for its longevity, potentially living up to 400 years, making it one of the longest-lived vertebrates.

    • Longfin Mako Shark: Noted for its speed and agility; capable of reaching high speeds, making it a formidable predator in open waters.

    • Oceanic White Tip Shark: Prefers warm, open ocean waters; known for its characteristic long, white-tipped fins and active hunting strategy.

    • Porbeagle Shark: A cold-water species; closely related to the great white shark, recognized for its distinctive torpedo-shaped body.

    • Portuguese Dogfish: A small, deep-water species; known for its distinctive long, slender body and sharp teeth.

    • Sand Tiger Shark: Unique for its protruding teeth and flattened body; often seen resting on the ocean floor, providing a frightening appearance.

    • Shortfin Mako Shark: Renowned for being one of the fastest sharks; capable of swimming up to 45 mph, primarily preying on fish and squid.

    • Smooth Dogfish: Inhabits temperate waters; characterized by its smooth skin and smaller size compared to other dogfish species.

    • Smooth Hammerhead Shark: Distinguished by its unique hammer-shaped head; aids in enhancing sensory capabilities while hunting.

    • Spiny Dogfish: A small shark species known for its spines located on its dorsal fins; commonly found in both coastal and deep waters.

    • Thresher Shark: Recognized for its long, whip-like tail which it uses to stun prey; typically solitary and found in deeper oceans.

    • Tiger Shark: Known for its distinctive stripes and powerful jaws; considered an apex predator, often preying on a variety of marine animals.

    • Whale Shark: Largest shark species and the largest fish in the ocean; a filter feeder that primarily eats plankton and small fish.

    • White Shark (Great White Shark): Renowned as a top predator; characterized by its impressive size, keen sense of smell, and powerful bite.

    Overview of Skates (Rajiformes)

    • Comprise approximately 14 genera and around 300 species.
    • Found in various habitats: uncommon near coral reefs and in shallow tropical seas; many species inhabit temperate to arctic waters.
    • Some skates adapt to brackish water environments.

    Physical Characteristics

    • Body shape is predominantly disc rhomboid, coupled with a long tail.
    • Possess two dorsal fins, along with a small caudal fin.
    • Pelvic fins feature two lobes; certain species exhibit the ability to "walk" using their pelvic fins.
    • Skin texture is rough, characterized by dermal denticles, primarily concentrated along the spine.

    Locomotion and Movement

    • Move through undulatory pectoral fin motion, known as rajiform locomotion, enabling effective swimming.

    Reproductive Systems

    • Males possess testes and claspers, which help in reproduction.
    • Females have a more complex reproductive system, including ovaries, a shell gland, uterus, and urogenital sinus.

    Spiracles Overview

    • Spiracles are located on the upper part of the head, positioned between the eyes and gill slits.
    • Serve as a critical passageway for aquatic respiration, allowing organisms to breathe underwater.
    • These structures function as a dorsal orifice that leads directly to the oral cavity, facilitating the intake of water for gas exchange.
    • Equipped with a spiracle valve, which controls the opening and closing of the spiracle, regulating airflow.
    • Play a significant role in ventilation, aiding in the effective respiration process of aquatic animals.

    Buccal Pump Ventilation

    • A respiratory method utilized by some sharks to extract oxygen from water.
    • Involves the shark making buccal (mouth) movements to create suction.
    • Water is drawn into the shark's mouth and then pushed across the gills for oxygenation.

    Ram Ventilation

    • An efficient respiratory technique used by many active shark species.
    • Occurs when sharks swim continuously, forcing water into their mouths.
    • Water flows over the gills as the shark moves, facilitating oxygen exchange without the need for buccal pumping.

    Tonic Immobility in Sharks

    • Tonic immobility refers to the state when sharks exhibit a brief feigned death, often as a defensive mechanism.
    • This response is typically triggered by physical factors such as rapid body inversion, nose contact, or being entrapped/encircled by a line.
    • Sharks employing buccal pumping can slow down their respiration while still ventilating, allowing them to manage oxygen intake during tonic immobility.
    • In contrast, ram ventilators, which rely on water flowing over their gills to breathe, may face challenges during tonic immobility as they cannot effectively irrigate their gills.
    • Species that fall between buccal pumpers and ram ventilators may exhibit varied responses during tonic immobility, showcasing different physiological adaptations.

    Buccal Pump Ventilation and Ram Ventilation

    • Buccal pump ventilation involves sharks using mouth movements to draw water in and pass it over gills for oxygen.
    • Ram ventilation occurs when sharks swim, forcing water into their mouths and across their gills.

    Tonic Immobility

    • Tonic immobility is a state where sharks appear to feign death.
    • This phenomenon can be induced through various methods, such as rapid body inversion or physical entrapment.
    • Buccal pumping species can continue ventilation while slowing down respiration, whereas ram ventilators need constant water flow over gills.
    • Metabolic impacts may lead to cessation of active ventilation, decreased blood oxygen, increased carbon dioxide, and elevated lactate levels.

    Elasmobranch Palaeontology

    • Elasmobranchs have existed for over 400 million years, dating back to the Ordovician period.
    • The Batoids group (including skates and rays) emerged later, approximately 150 million years ago in the lower Jurassic period.
    • Sharks typically leave behind large teeth, providing clear paleontological evidence, whereas skates leave fewer identifiable traces, complicating their fossil record.

    Ecosystem Importance

    • Sharks, skates, and rays play crucial roles in maintaining the stability of ocean ecosystems.
    • Large sharks exert a strong top-down influence on prey, affecting marine community structures.
    • They serve as predators, impacting prey behavior and habitat use, thereby influencing non-target species.
    • These elasmobranchs also impact nutrient movement, habitat disturbance, and biological interactions such as scavenging and invasive species control.

    Western North Atlantic Region Ray Species

    • There are 39 species of elasmobranchs in the Canadian Arctic and Atlantic waters, including:
      • Atlantic Manta Ray
      • Atlantic Torpedo Ray
      • Pelagic Stingray
      • Roughtail Stingray

    Western North Atlantic Region Skates

    • Notable skate species include:
      • Abyssal Skate
      • Arctic Skate
      • Barndoor Skate
      • Bigelow's Skate
      • Jensen's Skate
      • Richardson's Skate
      • Round Skate
      • Smooth Skate
      • Soft Skate
      • Spinytail Skate
      • Thorny Skate
      • White Skate
      • Winter Skate

    Western North Atlantic Region Sharks

    • Significant shark species are:
      • Atlantic Sharpnose Shark
      • Basking Shark
      • Black Dogfish
      • Blue Shark
      • Deepwater Catshark
      • Dusky Shark
      • Great Lantern Shark
      • Greenland Shark
      • Longfin Mako Shark
      • Oceanic White Tip Shark
      • Porbeagle Shark
      • Portuguese Dogfish
      • Sand Tiger Shark
      • Shortfin Mako Shark
      • Smooth Dogfish
      • Smooth Hammerhead Shark
      • Spiny Dogfish
      • Thresher Shark
      • Tiger Shark
      • Whale Shark
      • White Shark

    Skates, The Rajiformes

    • Consist of about 300 species within 14 genera, often found outside tropical coral reefs in cooler waters.
    • Some species inhabit brackish environments.
    • Characterized by a disc-shaped body with a long tail, two dorsal fins, and a small caudal fin.
    • Pelvic fins are lobed, allowing for limited 'walking' motion on the seafloor.
    • Skin is rough with dermal denticles, particularly along the spine.
    • Utilize rajiform locomotion, moving by undulating pectoral fins.

    Spiracles

    • Positioned on the top of the head, between the eyes and gill slits, spiracles act as an alternative breathing passage.
    • Serve as a dorsal opening to the oral cavity for respiration.
    • Equipped with a valve that controls opening and closing for effective ventilation.

    Respiratory Mechanisms in Sharks

    • Buccal Pump Ventilation: Sharks suction water into their mouth using buccal movements, circulating it across gills for oxygen extraction.
    • Ram Ventilation: Involves sharks swimming to force water over their gills by 'ramming' it into their mouths.

    Tonic Immobility

    • Defined as a state where sharks simulate death, often induced by specific physical interactions (e.g., body inversion, entrapment).
    • Species practicing buccal pumping can maintain respiration during tonic immobility, while ram ventilators cannot, leading to potential metabolic effects.
    • Consequences include cessation of active ventilation, decreased blood oxygen levels, increased CO2, and higher lactate concentrations.

    Elasmobranch Paleontology

    • Elasmobranchs boast a paleontological history of over 400 million years, dating back to the Ordovician period.
    • The Batoids (skates and rays) emerged approximately 150 million years ago in the lower Jurassic period.
    • Sharks contribute significant fossil records via large teeth, while skates leave fewer traces, complicating the study of their evolutionary history.

    Ecosystem Importance

    • Sharks, skates, and rays play crucial roles in marine ecosystems, contributing to food web stability and influencing prey behavior, known as "predator release."
    • They help regulate populations by preying on weaker or diseased specimens, controlling disease spread, and assisting in nutrient movement.
    • Their behaviors can lead to habitat disturbance and bioturbation, thereby promoting ecosystem health.

    Western North Atlantic Region Ray Species

    • Total of 39 elasmobranch species identified in Canadian Arctic and Atlantic waters, including notable species such as:
      • Atlantic Manta Ray
      • Pelagic Stingray
      • Roughtail Stingray

    Western North Atlantic Region Skates

    • Notable skate species include:
      • Abyssal Skate
      • Arctic Skate
      • Barndoor Skate
      • Round Skate

    Western North Atlantic Region Sharks

    • Diverse shark species present include:
      • Basking Shark
      • Great White Shark
      • Whale Shark
      • Thresher Shark

    Characteristics of Skates (Rajiformes)

    • Comprise around 300 species across 14 genera, commonly found in temperate to arctic waters; some inhabit brackish environments.
    • Have a distinctive disc-shaped body with long tails and two dorsal fins.
    • Possess rough skin covered in dermal denticles, especially along the spine.
    • The pelvic fins feature two lobes, with some species capable of walking using them.

    Spiracles

    • Located on the dorsal side of the head between eyes and gill slits, functioning as respiratory passageways.
    • Allow water intake through a valve that opens and closes, supporting ventilation while stationary.

    Shark Reproduction

    • Mating preferences vary among shark species, with some choosing specific regions and times of the year to mate, while others may mate throughout the year.
    • Sharks often experience resting periods between reproductive cycles, which typically last from 1 to 3 years, allowing time for recovery and growth.
    • The gestation period for sharks can range significantly, taking anywhere from 6 to 36 months depending on the species.
    • Reproductive methods differ among shark species, with some laying eggs (oviparous) and others giving birth to live young (viviparous or ovoviviparous).

    Oviparous Reproduction in Sharks

    • Oviparous reproduction involves internal fertilization followed by the laying of eggs outside the womb, leading to hatching.
    • About 40% of shark species are oviparous, meaning they reproduce by laying eggs rather than giving live birth.
    • Skates, a group of cartilaginous fish related to sharks, exclusively reproduce through oviparous methods.

    Egg Cases

    • Egg cases of sharks are multi-layered structures designed to protect developing embryos.
    • They possess cord-like growths that function as anchors, securing the eggs to substrates in their environment.
    • Size of egg cases typically ranges between 10 cm to 25 cm in length, indicating a variety of species adaptations.

    Nutritional Aspects

    • Each egg capsule contains a yolk that supplies essential nutrients to the embryo as it develops, providing a critical source of energy until hatching.

    Buccal and Ram Ventilation

    • Buccal pump ventilation involves sharks suctioning water into their mouths, passing it over gills for oxygen.
    • Ram ventilation occurs when sharks swim, forcing water into their mouths and over gills without additional pumping.

    Tonic Immobility

    • A behavioral state where sharks appear to feign death, often induced by rapid body inversion or physical entrapment.
    • Buccal pumping species continue to ventilate, while ram ventilators require water movement for gill irrigation.
    • Metabolic effects include cessation of active ventilation, decreased blood oxygen, increased CO2, and elevated lactate levels.

    Reproduction in Sharks

    • Different shark species exhibit varied mating preferences for locations and times, with some mating year-round.
    • Resting phases can last from one to three years, while gestation periods range from six to thirty-six months.
    • Sharks display diverse reproductive strategies, with some laying eggs and others giving live birth.

    Oviparous Reproduction

    • Oviparous species fertilize and develop eggs within the womb, laying them to hatch later.
    • Approximately 40% of sharks are oviparous, including all skates.
    • Egg cases feature multi-layer structures with cord-like growths for anchoring, ranging from 10cm to 25cm.
    • The egg capsule nourishes the embryo with a yolk.

    Elasmobranch Palaeontology

    • Elasmobranchs have existed for over 400 million years, dating back to the Ordovician period.
    • Batoids (skates and rays) have a shorter evolution, emerging around 150 million years ago in the Jurassic.
    • Large shark teeth are common in fossil records, while skates leave fewer traces complicating origin studies.

    Ovoviviparous Reproduction

    • Known as "aplacental viviparity," embryos develop inside eggs and are born as live young.
    • The single egg yolk provides necessary nutrients for the developing embryo.

    Ecosystem Importance

    • Sharks, skates, and rays play crucial roles in maintaining ocean ecosystems and food web stability.
    • Large sharks exert strong top-down influences on prey populations, shaping marine communities.
    • They contribute to prey behaviors, scavenging, and removal of invasive species.
    • Their presence facilitates nutrient movement, habitat disturbance, and overall ecosystem health.

    Western North Atlantic Region Ray Species

    • 39 species of elasmobranchs inhabit Canadian Arctic and Atlantic waters.
    • Key species include Atlantic Manta Ray, Atlantic Torpedo Ray, Pelagic Stingray, and Roughtail Stingray.

    Western North Atlantic Region Skates

    • Prominent skate species encompass Abyssal Skate, Arctic Skate, Barndoor Skate, and others with variations in habitat and visibility.

    Western North Atlantic Region Sharks

    • A diverse range of shark species includes Atlantic Sharpnose, Basking, Blue, Great White, Whale, and Tiger Sharks alongside others.

    Skates, The Rajiformes

    • Comprised of approximately 300 species across 14 genera, skates are often found in temperate to arctic waters, less common in shallow tropical areas.
    • Characterized by a flattened body, long tail, and unique pelvic fins equipped for locomotion.
    • Reproductive systems include testicular structures in males and ovaries with associated glands in females.

    Spiracles

    • Located between the eye and gill slits, spiracles aid in respiration by directing water to the oral cavity.
    • Includes a valve for regulating airflow, facilitating ventilation while the shark is at rest or buried in substrate.

    Viviparous Reproduction

    • Placental viviparity found in all rays; yolk sac develops into placenta.
    • Embryos receive nutrients from the mother via the placental cord, resulting in live births.

    Buccal Pump Ventilation

    • Sharks use buccal movements to create suction, drawing water into the mouth and across gills for oxygenation.

    Ram Ventilation

    • Sharks swim to move water over their gills, pushing it into their mouths and across the gills through swimming motion.

    Tonic Immobility

    • A phenomenon where sharks feign death.
    • Induced by body inversion, nose contact, or entrapment, leading to varied metabolic responses.
    • Buccal pumping species maintain respiration, while ram ventilators require active gill irrigation.
    • Metabolic effects include cessation of active ventilation, decrease in blood oxygen, increase in CO2, and elevated lactate levels.

    Reproduction

    • Mating preferences vary among shark species regarding regions and seasons; some mate year-round.
    • Resting periods between mating can last from 1 to 3 years.
    • Gestation typically ranges from 6 to 36 months, with some species laying eggs and others giving live birth.

    Oviparous Reproduction

    • Fertilized eggs are laid by sharks, with about 40% of species engaging in this method.
    • Skates reproduce exclusively through egg-laying.
    • Egg cases have multiple layers and cord-like structures for anchoring in the environment.
    • Sizes of egg cases vary from 10 cm to 25 cm; yolk inside provides nutrients for the developing embryo.

    Elasmobranch Paleontology

    • Elasmobranchs have existed for over 400 million years, originating in the Ordovician period.
    • Batoids (skates and rays) have a shorter evolutionary history, appearing about 150 million years ago.
    • Sharks are recognizable in the fossil record by large teeth; skates leave fewer traces, complicating origin assessments.

    Ovoviviparous Reproduction

    • Known as "aplacental viviparity," embryos develop in eggs that are retained inside the mother, resulting in live births.
    • Nutritional support comes from a single yolk.

    Ecosystem Importance

    • Sharks, skates, and rays play crucial roles in marine ecosystems, maintaining food web stability.
    • Large sharks exert top-down influences on prey populations, shaping marine communities and behaviors.
    • They provide scavenging benefits, aid in controlling invasive species, and help in removing weak or diseased specimens, promoting ecosystem health.
    • Activities contribute to nutrient cycling, habitat disturbance, and overall resilience of ecosystems.

    Western North Atlantic Region Ray Species

    • 39 species of elasmobranchs found in Canadian Arctic and Atlantic waters include:
      • Atlantic Manta Ray
      • Atlantic Torpedo Ray
      • Pelagic Stingray
      • Roughtail Stingray

    Western North Atlantic Region Skates

    • Notable skate species include:
      • Abyssal Skate
      • Arctic Skate
      • Barndoor Skate
      • Bigelow's Skate
      • Jensen's Skate
      • Richardson's Skate
      • Round Skate
      • Smooth Skate
      • Soft Skate
      • Spinytail Skate
      • Thorny Skate
      • White Skate
      • Winter Skate

    Western North Atlantic Region Sharks

    • Diverse shark species present such as:
      • Atlantic Sharpnose Shark
      • Basking Shark
      • Black Dogfish
      • Blue Shark
      • Deepwater Catshark
      • Dusky Shark
      • Great Lantern Shark
      • Greenland Shark
      • Longfin Mako Shark
      • Oceanic White tip Shark
      • Porbeagle Shark
      • Portuguese Dogfish
      • Sand Tiger Shark
      • Shortfin Mako Shark
      • Smooth Dogfish
      • Smooth Hammerhead Shark
      • Spiny Dogfish
      • Thresher Shark
      • Tiger Shark
      • Whale Shark
      • White Shark

    Skates – The Rajiformes

    • Comprise approximately 300 species across 14 genera; typically absent from coral reefs and tropical shallow waters, many reside in temperate to arctic habitats.
    • Features include a disc-shaped body with a long tail, two dorsal fins, small caudal fin, and pelvic fins with two lobes for movement.
    • Notable anatomical traits include rough skin and dermal denticles, particularly along the spine, and rajiform locomotion using undulatory pectoral fins.
    • Male reproductive anatomy encompasses testes and claspers; females have ovaries, a shell gland, uterus, and urogenital sinus.

    Spiracles

    • Located on top of the head between the eyes and gill slits, serving as breathing passages for water.
    • Provides a pathway to the oral cavity for respiration, with a valve that controls opening and closure.

    Threats to Marine Species

    • Pristiformes refers to a group known as sawsharks, which face significant threats.
    • Rhino rays, also known as guitar fishes, represent some of the world's most endangered marine fish species.
    • Overexploitation is the primary threat, driven by targeted fisheries that support the global fin trade and demand for meat, liver oil, and gill rakers.
    • Approximately one-third of threatened sharks and rays are subjected to targeted fishing practices.
    • Over 50% of sharks and rays entering the fin trade are classified as threatened species.
    • Habitat degradation, alteration, and loss contribute to the decline of marine species, in addition to persecution and climate change.
    • Population control measures for sharks, such as shark nets and culling, further exacerbate the threats to these marine animals.

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    Description

    Explore the fascinating paleontological history of elasmobranchs, which have existed for over 400 million years. Learn about the origins of batoids like skates and rays that emerged during the Jurassic period. Discover the significance of shark teeth in the fossil record and the challenges in tracing the origins of skates.

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