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Definition: Osteichthyes refers to bony fishes, an extensive and diverse class of fish characterized by their bony skeletons.
Subclass Sarcopterygii: Includes lobe-finned fishes and their relatives. Comprises seven infraclasses:
- Infraclass Actinistia: Contains coelacanths.
- Extinct Infraclasses: Four extinct groups including Onychodontida, Rhizodontida, Osteolepidida, Elpistostegalia.
- Infraclass Dipnomorpha: Includes a variety of extinct fishes and modern lungfishes.
- Infraclass Tetrapoda: Vertebrates that emerged onto land, leading to the evolution of amphibians, reptiles, birds, and mammals.

Overview: All members classified under the order Coelacanthiformes.
Fossil History: Fossil records indicate that coelacanthimorphs appeared in the Middle Devonian and vanished by the Late Cretaceous, found globally in both marine and freshwater environments.
Coelacanth Discovery: Once believed to be extinct for 80 million years, the first live specimen was caught in 1938 in South Africa. Currently, a small population (approximately 200-600 individuals) exists in the Comoros Islands, with a second species located in parts of Indonesia, South Africa, Madagascar, and Eastern Africa.
Specialized Features:
- Unique spiny dorsal fin rather than a lobate form.
- A three-lobed caudal fin featuring a fleshy, fringed middle lobe.
- Possesses a rostral organ and cavity for electroreception, marked by multiple openings on the snout.
- Viviparous characteristics demonstrated by dissected females showing 5-26 well-developed young with yolk sacs or scars.

Fossils Bridging Gaps: Tiktaalik, a significant fossil, bridging a gap of 20 million years between two key fish species (Panderichthys and Ichthyostega). The fossil serves as an example of early adaptations towards terrestrial life.
Tiktaalik Characteristics:
- Size: Approximately 3 meters in length.
- Identified as an elpistostegalian due to its fishlike traits including: dorsal eyes, gill arches, scales, and pectoral fin rays.
- Features indicating evolution toward tetrapods: shortened skull roof, mobile neck, and a functional wrist joint.
- Morphological details highlighted in dorsal and lateral anatomical views.

Structure: Classified into various subclasses and infraclasses reflecting evolutionary relationships among fish and tetrapods.
Subclass Sarcopterygii (Lobe-finned Fishes): Includes Actinistia (coelacanths) and Dipnomorpha (lungfishes).
Subclass Actinopterygii (Ray-finned Fishes): Encompasses various orders and families of modern bony fishes.

Overview: Commonly known as dipnoans, lungfishes can utilize two methods of breathing; they are well represented in the fossil records across all major continents.
Ceratodontimorphs: First appeared in the Early Triassic, now represented by three families of lungfishes in Australia, South America, and Africa.
Survival Mechanism: African lungfishes demonstrate an ability to survive during desiccation by creating vertical burrows and entering a dormant state with a mucus cocoon.

General Characteristics: Considered primitive actinopterygians; sturgeons and paddlefishes are highly derived but retain some ancestral features.
Divergence: Likely diverged during the Jurassic period, with shared traits such as cartilaginous skeleton, heterocercal tail, and unique jaw suspension mechanisms.

Species Diversity: Over 25 species of sturgeons within the Acipenseridae family, mainly found in the Northern Hemisphere. Some exhibit anadromous spawning behavior, moving between freshwater and marine environments.
Anatomical Features:
- Four barbels located ventrally to the mouth.
- Composite of bony scutes on the body and a cartilaginous endoskeleton.
Life History Traits: Sturgeons have long lifespans leading to vulnerability from overexploitation; females may mature at 5-30 years and only spawn every 3-5 years.
Human Impact: Commercially sought for caviar and other products, creating significant conservation concerns.

Species: Two remaining species: North American Paddlefish and Chinese Paddlefish. Both have specific ecological roles and adaptations in their environments.
Anatomical Features:
- Retain heterocercal tails; cartilaginous endoskeleton but differ from sturgeons in absence of bony scutes.
Feeding Habits: Paddlefish filter feed primarily on zooplankton in large rivers, using their elongated rostrum equipped with ampullary receptors to detect prey in low-visibility waters.

Habitat: Primarily found in North and Central America, living in backwaters and requiring atmospheric air to breathe due to low oxygen levels in their habitats.
Species Diversity: Includes Spotted Gar, Alligator Gar, Shortnose Gar, Longnose Gar.
Ecological Importance: Unique biological characteristics, such as toxic eggs, and ecological roles within fish assemblages.

Species: Bowfin (Amia calva), considered more derived than gars; display a distinct suite of anatomical features.
- Median gular plate formation and specialized swimming mechanics.
Behavioral Adaptations: Potential for lungfish-like estivation in response to drying habitats.

General Overview: Teleosts represent the most diverse assembly of vertebrates, with approximately 30,000 species, referred to as "perfect bone" fish due to evolutionary advancements in their structural integrity.
Taxonomic Diversity: Includes multiple orders and families critical to both ecological systems and fisheries.

Taxonomic Breakdown:
- Order Salmoniformes (Trouts, Salmons, Whitefishes): Characterized by common anatomical traits such as an adipose fin and specific gill structures.
- Order Esociformes (Pikes, Pickerels, Mudminnows): Notable absence of teeth on the maxillary bone.
- Order Argentiniformes: Deep-sea fishes, including peculiar barreleyes.
- Order Stomiiformes: Characterized by adaptive traits for deep-sea living.

Taxonomic Classification: Falls between a cohort and a superorder, referring to a monophyletic group defined by unique cranial and jaw characteristics.
Superorder Cyclosquamata and Scopelomorpha: Includes foundational families such as lizardfishes and lanternfishes that exhibit primitive features while adapting to diverse environments.
Superorder Lamprimorpha: Observations in the unique adaptations of the opah and oarfish showcase the variety within teleosts, primarily in open oceanic ecosystems.