Bio 1300, Ch 35 Vertebrates

Chapter Overview: Vertebrates

Introduction

Vertebrates are a significant subphylum within the phylum Chordata, characterized by the presence of a backbone or vertebral column. This chapter explores the evolution, diversity, and distinctive characteristics of vertebrates, highlighting their ecological roles and adaptive strategies throughout history.

1. Ancestral Vertebrates

• Cyclostomata (lampreys and hagfish): These are jawless fish considered to be some of the most primitive vertebrates. They lack eyes, jaws, and traditional vertebrae but possess a flexible notochord and a cartilaginous skull.

  • Hagfish: Notable for being blind, these creatures rely on their enhanced sense of smell to navigate and find food. They have the unique ability to produce large amounts of slime as a defense mechanism against predators.

  • Lampreys: These have a rudimentary vertebral column and undergo metamorphosis. Some species are parasitic, attaching to fish to feed on their blood.

Evolutionary Innovations

• Gnathostomes: The emergence of jawed vertebrates from earlier forms, with jaws evolving from modified gill arches. This development allowed for improved feeding strategies and diversification.

  • Key Clades:

    • Chondrichthyes: Cartilaginous fishes including sharks, skates, and rays, adapted for life in aquatic environments.

    • Actinopterygii: Ray-finned fishes, the most abundant group of vertebrates, exhibiting a vast range of forms and adaptations.

    • Sarcopterygii: Lobe-finned fishes, recognized for their fleshy, lobed fins which are precursors to limbs in terrestrial vertebrates.

• Amniotes: This group includes reptiles and mammals, recognized for the evolution of the amniotic egg, allowing reproduction away from a water source.

2. Vertebrate Characteristics

• Common Features: Vertebrates possess a backbone, a cranium, and an endoskeleton composed of either cartilage or bone. Their diversity of internal organs and complex morphologies is largely influenced by numerous Hox gene interactions, which govern body plan development.

Clades and Characteristics Table

3. Functional Anatomy of Vertebrates

• Cyclostomata:

  • Hagfish: Their unique slime-producing adaptation has vital roles in their survival and ecological interactions, despite lacking complex anatomical features.

  • Lampreys: Active in aquatic ecosystems, many species play crucial roles as parasites that can influence fish populations.

Jaws and Their Evolution

• Jaws, a significant evolutionary feature, evolved from modifications of gill structures, enabling early jawed vertebrates, termed gnathostomes, to capture and consume prey more effectively, which significantly altered food web dynamics.

4. Clade Chondrichthyes

• This group has adapted various features to thrive in marine environments. Their skeletons are primarily made of cartilage, which is lighter than bone, aiding in buoyancy.

  • Chondrichthyes must maintain buoyancy through fin movements and a large oil-filled liver.

  • Breeding strategies vary, incorporating internal fertilization methods that include oviparous (egg-laying), ovoviviparous (live birth with eggs retained in the body), and viviparous (live birth) methods.

  • This clade exhibits super-senses, such as electroreception, which enhance their ability to detect prey in various water conditions.

5. Bony Fish – Osteichthyans

• Among the most diverse groups of vertebrates, bony fishes are classified into two distinct clades:

  • Actinopterygii: Known for their operculum, which covers the gills, allowing efficient respiration while swimming.

  • Sarcopterygii: These lobe-finned fishes include significant evolutionary links to land vertebrates, showing transitional forms.

Transition to Tetrapods

• Tetrapods: Evolved from lobe-finned fish ancestors, showcasing vital adaptations crucial for terrestrial life, including skeletal and respiratory modifications facilitating movement and gas exchange in air.

• Hox Gene Expression: Changes in gene activity resulting in limb formation and adaptation to new environments.

• Transition Species: Tiktaalik rosae is a pivotal species that provides insight into the transition from aquatic to terrestrial life.

6. Diversity of Amphibians

• Amphibians are unique due to their dependence on aquatic environments for reproduction, showcasing varied life cycles often beginning with larval aquatic stages.

• Orders of Amphibians:

  • Anura: Includes both frogs and toads, well-known for their distinct metamorphosis.

  • Apoda: Comprised of legless caecilians, these burrowing amphibians mostly inhabit tropical regions.

  • Urodela: Salamanders that retain larval characteristics in adulthood, often showcasing vibrant colors and complex behaviors.

• Decline Factors: Amphibian populations face significant challenges from habitat destruction, disease, pollution, and climate change, leading to worldwide declines.

7. Amniotes and Their Innovations

• Amniotes are distinguished from amphibians through the adaptation of a desiccation-resistant egg, allowing for successful reproduction in arid environments.

• Key Features of Amniotic Egg: The egg is characterized by structures such as the amnion, yolk sac, allantois, and chorion, each with specialized functions enhancing embryo protection and nourishment.

• Reptilian Diversity: The amniotes include a wide array of reptiles and birds, showcasing remarkable adaptations for diverse ecological niches.

• Evolution of Birds: Birds, a clade derived from theropod dinosaurs, exhibit unique attributes such as feathers which are not only for flight but also for thermoregulation, and air sacs that enhance respiratory efficiency.

8. Mammalian Characteristics

• Mammals are defined by their possession of hair and mammary glands, which play crucial roles in insulation and nurturing offspring.

• Major Clades:

  • Monotremata: Includes egg-laying mammals like the platypus and echidna, which exhibit unique reproductive behaviors.

  • Theria: This clade encompasses marsupials, which typically give birth to underdeveloped young that continue to develop in maternal pouches, and eutherians, or placental mammals, which gestate their young internally for extended periods.

Lecture Questions

35.1

•In addition to the 4 key features of chordates, what 3 additional features do vertebrates have?

In addition to the four key features of chordates (notochord, dorsal hollow nerve cord, pharyngeal slits, and post-anal tail), vertebrates possess three additional features:

1. A backbone or vertebral column - providing structural support and protecting the spinal cord.

2. A cranium - which encases and protects the brain.

3. An endoskeleton made of cartilage or bone - facilitating movement and providing a framework for muscle attachment.

•There are 10 main clades of vertebrates- what are they?

The 10 main clades of vertebrates are:

1. Cyclostomata - Jawless fish, including lampreys and hagfish.

2. Chondrichthyes - Cartilaginous fishes, including sharks, skates, and rays.

3. Actinopterygii - Ray-finned fishes, which are the most abundant group of vertebrates.

4. Sarcopterygii - Lobe-finned fishes, including coelacanths and lungfishes.

5. Amphibia - Includes frogs, toads, and salamanders.

6. Reptilia - Includes turtles, lizards, snakes, and birds.

7. Mammalia - Mammals, including monotremes, marsupials, and placental mammals.

8. Agnatha - Another term for cyclostomes, often treated as a superclass.

9. Tetrapoda - Legged vertebrates that include amphibians, reptiles, and mammals.

10. Osteichthyes - Represents bony fishes, inclusive of both actinopterygii and sarcopterygii.

•Clade Cyclostomata contains what 2 species? One of the species in this clade lacks several of the important features of vertebrates; why are they still considered vertebrates? What are the features of the other species in this clade?

Clade Cyclostomata contains two species: lampreys and hagfish. Hagfish, one of these species, lacks several important features typically associated with vertebrates, such as eyes, jaws, and a traditional vertebral column. Despite this, they are still considered vertebrates because they possess a flexible notochord, a cartilaginous skull, and other defining characteristics of vertebrate lineage.

Lampreys, the other species in this clade, have a rudimentary vertebral column and undergo metamorphosis, with some species being parasitic and feeding on the blood of other fish.

35.2

• What does the term gnathostome mean? What was the earliest diverging gnathostome? How did jaws evolve in gnathostomes (what specific features changed)? This group contains 6 clades- what are they?

The term "gnathostome" refers to jawed vertebrates. The earliest diverging gnathostome is thought to be an ancestral form that lived over 400 million years ago, most likely resembling modern-day jawless fish before evolving jaws. Jaws in gnathostomes evolved from modifications of gill arches, allowing these organisms to effectively capture and consume prey, significantly altering food web dynamics.

The six clades within the gnathostomes are:

1. Chondrichthyes - Cartilaginous fishes like sharks, skates, and rays.

2. Actinopterygii - Ray-finned fishes, the most abundant group of vertebrates.

3. Sarcopterygii - Lobe-finned fishes.

4. Amniotes - Includes reptiles and mammals, recognized for the evolution of the amniotic egg.

5. Tetrapoda - Includes legged vertebrates such as amphibians, reptiles, and mammals.

6. Osteichthyes - Represents bony fishes, encompassing both actinopterygii and sarcopterygii.

• Clade Chondrichthyes contains what types of organisms? What is the defining feature that they share? What are the forms of internal fertilization that this group demonstrates? What are the notable "super senses" of this clade?

Clade Chondrichthyes contains cartilaginous fishes, including sharks, skates, and rays. The defining feature that they share is that their skeletons are primarily made of cartilage rather than bone.

In terms of internal fertilization, this group demonstrates three forms: 1) Oviparous (egg-laying), 2) Ovoviviparous (where eggs develop inside the body and are retained until they hatch), and 3) Viviparous (live-bearing).

Notable "super senses" of this clade include electroreception, which enhances their ability to detect prey by sensing the electrical signals produced by other organisms, allowing them to thrive in various aquatic environments.

• What does the term Osteichthyans mean? What are the two clades within this group? What features make this group distinct from the Chondrichthyes?

The term Osteichthyans refers to bony fishes, which are a diverse group of vertebrates characterized by having a skeleton primarily composed of bone. The two major clades within this group are: 1) Actinopterygii (ray-finned fishes) and 2) Sarcopterygii (lobe-finned fishes).

The features that make Osteichthyans distinct from Chondrichthyes (cartilaginous fishes) include:

• Skeleton Composition: Osteichthyans have bony skeletons, whereas Chondrichthyes have skeletons made of cartilage.

• Swim Bladder: Many Osteichthyans possess a swim bladder, which aids in buoyancy control, while Chondrichthyes use an oil-filled liver for buoyancy.

Operculum: Osteichthyans have an operculum, a bony flap covering the gills that improves respiration efficiency, unlike Chondrichthyes, which do not have this feature.

• Actinopterygii describes what types of organisms?

Actinopterygii describes ray-finned fishes, which are the most abundant group of vertebrates. They are characterized by their operculum covering the gills, an ossified skeleton, and a single gill opening. This group exhibits a vast range of forms and adaptations, enabling them to inhabit various aquatic environments.

• Sarcopterygii describes what types of organisms?

Sarcopterygii describes lobe-finned fishes, which are characterized by their fleshy, lobed fins. These fins are significant as they are recognized as the precursors to limbs in terrestrial vertebrates, exhibiting strong skeletal support that allows for various adaptations.

• What features make Actinopterygii distinct from Sarcopterygii?

Actinopterygii, or ray-finned fishes, are distinct from Sarcopterygii (lobe-finned fishes) due to several key features:

1. Fin Structure: In Actinopterygii, the fins are supported by long, thin rays of bone or cartilage, which provide a more flexible and maneuverable structure for swimming. In contrast, Sarcopterygii possess fleshy, lobed fins that are more robust and are precursors to limbs.

2. Skeleton Composition: Actinopterygii have an ossified (bony) skeleton, while Sarcopterygii, while they also have a bony skeleton, have the traditional lobe-finned structure that supports their heavier body.

3. Swim Bladder: Most Actinopterygii possess a swim bladder, which allows them to maintain buoyancy in water. Sarcopterygii have a more complex respiratory system, historically used for breathing air and buoyancy control.

4. Gill Structure: Actinopterygii have a single gill opening and an operculum, a bony flap that covers the gills, enhancing respiratory efficiency. Sarcopterygii have multiple gill openings.

35.3

• What does the term Tetrapod refer to? What evolutionary changes had to occur for this transition? What do we mean by transitional taxa? Examples? There are 3 main groups of animals included in the term tetrapods- what are they?

Tetrapod refers to a superclass of animals that have four limbs, which evolved from lobe-finned fish and adapted to life on land. The evolutionary changes that occurred for this transition include the development of limbs capable of supporting the animal's weight on land, modifications in the skeleton and musculature for movement, and adaptations in the respiratory system for breathing air.

Transitional taxa are species that exhibit traits common to both ancestral groups and their descendant groups, providing evidence of evolutionary processes. An example of a transitional taxon is Tiktaalik rosae, which displays features of both fish and early tetrapods.

The three main groups of animals included in the term tetrapods are:

1. Amphibians (e.g., frogs, toads, and salamanders)

2. Reptiles (e.g., turtles, lizards, snakes)

3. Mammals (e.g., monotremes, marsupials, eutherians)

• What are Amphibians? What are their distinctive features? There are 3 orders within Amphibians. What are they, and what organisms do they include?

Amphibians are a class of vertebrates that are uniquely adapted to both aquatic and terrestrial environments, displaying distinctive features such as a moist skin which aids in respiration, a three-chambered heart, and a life cycle that typically includes an aquatic larval stage and a terrestrial adult stage. They generally require water for reproduction, laying eggs that do not have a protective shell.

The three orders within Amphibians are:

1. Anura: This order includes frogs and toads, known for their distinct metamorphosis from tadpoles to adults.

2. Urodela: Comprising salamanders, this order retains larval characteristics in adulthood, often showcasing vibrant colors and complex behaviors.

3. Apoda: This order includes legless caecilians, which are burrowing amphibians mostly inhabiting tropical regions.

35.4

• What are Amniotes? What key feature sets them apart from Amphibians? What are the 4 membranes that make up the egg? What is the purpose of each?

Amniotes are a group of vertebrates distinguished by their adaptation of a desiccation-resistant egg, which allows for successful reproduction in arid environments. This key feature sets them apart from amphibians, which generally require water for reproduction.

The amniotic egg is composed of four membranes, each serving a specific purpose:

1. Amnion: This membrane surrounds the developing embryo, providing a protective sac filled with amniotic fluid that cushions and helps maintain a stable environment.

2. Chorion: This outer membrane facilitates gas exchange, allowing oxygen and carbon dioxide to pass between the embryo and the external environment.

3. Allantois: This membrane collects waste from the embryo and also plays a role in gas exchange, contributing to the overall metabolic functions of the developing embryo.

4. Yolk sac: This membrane contains the yolk, which provides nutrients to the developing embryo until it is capable of independent feeding.

Together, these membranes help support the developing organism in a variety of environments, increasing the range of habitats suitable for amniote reproduction.

• Reptiles include what 4 classes of extant animals? What are the distinctive features of each class? What organisms are included?

Reptiles include four extant classes of animals, each with distinctive features and organisms:

1. Testudines (Turtles):

   • Distinctive Features: Characterized by a bony or cartilaginous shell that protects their body.

   • Included Organisms: Turtles and tortoises, which can be found in both aquatic and terrestrial environments.

2. Squamata (Lizards and Snakes):

   • Distinctive Features: Features scales and a flexible skull, allowing for the consumption of prey larger than their head; lizards often have limbs while snakes are limbless.

   • Included Organisms: Iguanas, snakes, chameleons, and geckos.

3. Crocodylia (Crocodiles and Alligators):

   • Distinctive Features: Heavy, elongated bodies with a long snout, armored skin, and the presence of a secondary palate for simultaneous breathing and eating.

   • Included Organisms: Alligators, crocodiles, and caimans.

4. Aves (Birds):

   • Distinctive Features: Feathers for insulation and aerodynamics, a lightweight skeletal structure, and the laying of hard-shelled eggs.

   • Included Organisms: All known bird species, such as eagles, sparrows, and penguins.

• What are the 2 extinct classes of reptiles? What organisms are included?

The two extinct classes of reptiles are:

1. Plesiosauria:

   • Included Organisms: These marine reptiles were characterized by their long necks and flippers. Notable examples include the well-known Plesiosaurus.

2. Dinosauria:

   • Included Organisms: This diverse group included all dinosaurs, such as theropods (like Tyrannosaurus rex

35.5

• What are the key identifying features of Mammals? What are the additional features that most, if not all mammals share?

The key identifying feature of mammals is the presence of hair or fur and mammary glands, which allow females to produce milk for nourishing their young. Additional features that most, if not all mammals share include a three-bone structure in the middle ear, which enhances hearing, a specialized set of teeth adapted for their diets, enlarged brain within a large skull, and warm-blooded physiology, which maintains a stable body temperature.

• There are 2 subclasses within Mammals. What are they, and what organisms do they include? What are distinctive features and species within order Monotremata?Subclass Theria contains 2 clades. What are they, and what organisms do they include? What are the distinguishing feature of each clade?

There are two subclasses within Mammals:

1) Monotremata

2) Theria.

• Monotremata: This order includes egg-laying mammals like the platypus and echidna. Distinctive features include laying eggs and possessing a cloaca, similar to reptiles, rather than specialized openings.

• Theria: This subclass contains two clades: 1) Metatheria (marsupials) and 2) Eutheria (placental mammals).

  • Metatheria (Marsupials): Includes organisms like kangaroos and koalas. They typically give birth to underdeveloped young that continue to develop in maternal pouches.

  • Eutheria (Placental Mammals): Includes humans, dogs, and elephants. They have longer gestation periods during which the embryo develops inside the mother, receiving nutrients through a complex placenta.