Cetaceans Flashcards
Where and when did cetaceans evolve?
Cetaceans evolved along the Tethys Seaway in the early Eocene (53–45 mya), with the earliest fossils found in India and Pakistan.
What is the ancestral group of cetaceans?
Cetaceans are derived from artiodactyls (even-toed ungulates), which include hippos, antelopes, and giraffes.
Who were the Archaeoceti, and why are they significant?
Archaeoceti were an early cetacean radiation, transitioning from semi-aquatic to fully marine forms during the middle to late Eocene.
What are Neoceti, and when did they appear?
Neoceti are the modern cetaceans, including Odontocetes and Mysticetes, which diversified in the late Eocene and Oligocene (around 34 mya).
What characterizes odontocetes?
Possess teeth and are known for echolocation.
Include dolphins, porpoises, and sperm whales. First appeared in the North Atlantic around 32 mya.
What is echolocation, and why is it significant for odontocetes?
Echolocation allows odontocetes to navigate and hunt using sound waves, likely evolved early in their lineage.
What distinguishes Mysticetes from Odontocetes?
Mysticetes have baleen plates for filter feeding instead of teeth.
They lack a melon, have symmetrical skulls, and possess paired blowholes.
Name the four families within Mysticetes.
Balaenidae (right whales, bowhead).
Neobalaenidae (pygmy right whales). Eschrichtiidae (gray whales). Balaenopteridae (rorquals, including blue and humpback whales).
What are key features of right whales?
Highly arched rostrum with long baleen plates.
Large heads, making up one-third of their body length. Feed by surface skimming.
What is notable about bowhead whales?
Bowhead whales can live over 200 years, as evidenced by harpoons found in their bodies.
What makes rorquals unique among Mysticetes?
Possess ventral throat pleats for gulp-feeding.
Include species like blue, fin, sei, and humpback whales.
What are the feeding and migratory habits of rorquals?
Most rorquals migrate between high-latitude summer feeding grounds and warmer overwintering grounds. They feed on zooplankton, krill, and schooling fish.
How do gray whales feed?
Gray whales are benthic feeders, filtering food from the seafloor using their baleen plates.
What makes gray whales unique among baleen whales?
They are the most coastal of baleen whales and often host amphipod parasites (whale lice).
How are cetaceans categorized by size?
Small cetaceans (<3m): Dolphins and porpoises (47 species).
Intermediate cetaceans (3-10m): Larger dolphins, beaked whales, pygmy right whales, and minke whales (31 species). Large cetaceans (>10m): Sperm whales and most mysticetes (11 species).
What adaptations enable baleen whales to filter feed?
Keratinous baleen plates with frayed inner edges.
Tongue action forces water out and traps prey. Right whales skim, while rorquals gulp large volumes of water.
How does diet vary among baleen whales?
Blue whales: Primarily krill.
Minke, humpback, and sei whales: Schooling fish. Fin whales: Generalists feeding on krill, copepods, and fish.
Why do baleen whales migrate?
To follow seasonal prey availability, moving to high latitudes in summer for feeding and lower latitudes in winter for calving.
What is unique about Bryde’s whales among rorquals?
They remain in tropical waters year-round and do not exhibit long migrations.
What are the main clades of odontocetes?
The main clades are: Delphinidae (dolphins), Phocoenidae (porpoises), Ziphiidae (beaked whales), Physeteridae and Kogiidae (sperm whales).
What distinguishes odontocetes from mysticetes?
Odontocetes possess teeth, a single blowhole, and are capable of echolocation.
What are the members of the sperm whale group?
Sperm whale (Physeter macrocephalus), Pygmy sperm whale (Kogia breviceps), Dwarf sperm whale (Kogia sima).
What is the spermaceti organ, and what is its function?
A structure in the sperm whale’s head filled with spermaceti oil, likely aiding in buoyancy control and sound production for echolocation.
What are notable characteristics of the sperm whale?
Largest toothed whale (males: up to 16m and 45 tons), extreme sexual dimorphism, deep divers (targets squid and deep-sea fish), large brain (~8kg), complex social structures.
