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Marine vertebrates > Cetaceans > Flashcards

Cetaceans Flashcards

1
Q

Where and when did cetaceans evolve?

A

Cetaceans evolved along the Tethys Seaway in the early Eocene (53–45 mya), with the earliest fossils found in India and Pakistan.

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2
Q

What is the ancestral group of cetaceans?

A

Cetaceans are derived from artiodactyls (even-toed ungulates), which include hippos, antelopes, and giraffes.

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3
Q

Who were the Archaeoceti, and why are they significant?

A

Archaeoceti were an early cetacean radiation, transitioning from semi-aquatic to fully marine forms during the middle to late Eocene.

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4
Q

What are Neoceti, and when did they appear?

A

Neoceti are the modern cetaceans, including Odontocetes and Mysticetes, which diversified in the late Eocene and Oligocene (around 34 mya).

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5
Q

What characterizes odontocetes?

A

Possess teeth and are known for echolocation.

Include dolphins, porpoises, and sperm whales. First appeared in the North Atlantic around 32 mya.

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6
Q

What is echolocation, and why is it significant for odontocetes?

A

Echolocation allows odontocetes to navigate and hunt using sound waves, likely evolved early in their lineage.

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7
Q

What distinguishes Mysticetes from Odontocetes?

A

Mysticetes have baleen plates for filter feeding instead of teeth.

They lack a melon, have symmetrical skulls, and possess paired blowholes.

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8
Q

Name the four families within Mysticetes.

A

Balaenidae (right whales, bowhead).

Neobalaenidae (pygmy right whales). Eschrichtiidae (gray whales). Balaenopteridae (rorquals, including blue and humpback whales).

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9
Q

What are key features of right whales?

A

Highly arched rostrum with long baleen plates.

Large heads, making up one-third of their body length. Feed by surface skimming.

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10
Q

What is notable about bowhead whales?

A

Bowhead whales can live over 200 years, as evidenced by harpoons found in their bodies.

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11
Q

What makes rorquals unique among Mysticetes?

A

Possess ventral throat pleats for gulp-feeding.

Include species like blue, fin, sei, and humpback whales.

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12
Q

What are the feeding and migratory habits of rorquals?

A

Most rorquals migrate between high-latitude summer feeding grounds and warmer overwintering grounds. They feed on zooplankton, krill, and schooling fish.

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13
Q

How do gray whales feed?

A

Gray whales are benthic feeders, filtering food from the seafloor using their baleen plates.

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14
Q

What makes gray whales unique among baleen whales?

A

They are the most coastal of baleen whales and often host amphipod parasites (whale lice).

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15
Q

How are cetaceans categorized by size?

A

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).

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16
Q

What adaptations enable baleen whales to filter feed?

A

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.

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17
Q

How does diet vary among baleen whales?

A

Blue whales: Primarily krill.

Minke, humpback, and sei whales: Schooling fish. Fin whales: Generalists feeding on krill, copepods, and fish.

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18
Q

Why do baleen whales migrate?

A

To follow seasonal prey availability, moving to high latitudes in summer for feeding and lower latitudes in winter for calving.

19
Q

What is unique about Bryde’s whales among rorquals?

A

They remain in tropical waters year-round and do not exhibit long migrations.

20
Q

What are the main clades of odontocetes?

A

The main clades are: Delphinidae (dolphins), Phocoenidae (porpoises), Ziphiidae (beaked whales), Physeteridae and Kogiidae (sperm whales).

21
Q

What distinguishes odontocetes from mysticetes?

A

Odontocetes possess teeth, a single blowhole, and are capable of echolocation.

22
Q

What are the members of the sperm whale group?

A

Sperm whale (Physeter macrocephalus), Pygmy sperm whale (Kogia breviceps), Dwarf sperm whale (Kogia sima).

23
Q

What is the spermaceti organ, and what is its function?

A

A structure in the sperm whale’s head filled with spermaceti oil, likely aiding in buoyancy control and sound production for echolocation.

24
Q

What are notable characteristics of the sperm whale?

A

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.

25
Q

Why are sperm whales considered successful despite historical hunting?

A

Their deep-water habits, specialized diets, and distant-water ranges limit overlap with human activities.

26
Q

How many species of beaked whales exist, and what is their size range?

A

23 species, ranging from the pygmy beaked whale (4m) to Baird’s beaked whale (13m).

27
Q

What are key characteristics of beaked whales?

A

Spindle-shaped body with maximum girth at midsection, small, foldable pectoral fins, reduced dentition (males often have tusk-like teeth for intraspecific combat), deep divers (record depth: 2,992m; record duration: 3 hours, 48 minutes).

28
Q

Why are beaked whales understudied?

A

Their deep-water lifestyle makes them elusive, and they are rarely observed directly.

29
Q

What human activities pose a threat to beaked whales?

A

Plastic ingestion, mid-frequency military sonar linked to mass strandings (possibly causing panic ascents leading to decompression sickness).

30
Q

How many species of dolphins exist, and what is their global range?

A

37 species in 17 genera, found from the ice edge to the equator, with the highest diversity in tropical and warm temperate waters.

31
Q

What are unique features of dolphins?

A

Spindle-shaped bodies with a single blowhole, left-skewed cranial asymmetry, advanced echolocation, conical teeth (unlike porpoises’ spade-shaped teeth).

32
Q

What is the social structure of dolphins?

A

Dolphins exhibit complex social behavior, with some species forming matrilineal societies and cooperative hunting methods.

33
Q

What is known about dolphin intelligence?

A

High brain-to-body ratio (second only to humans), comprehension of abstract commands, syntax, and self-recognition in captivity, use of tools and premeditated hunting strategies in the wild.

34
Q

How are porpoises different from dolphins?

A

Porpoises lack an external beak (paedomorphism), spade-shaped teeth instead of conical, smaller size (no species exceeds 2.5m), lack strong social bonds and cooperative hunting behavior.

35
Q

What is unique about porpoise life history?

A

Rapid ontogeny (females reach maturity by age 3), annual reproduction, often lactating and pregnant simultaneously, shorter lifespan (rarely exceeding 20 years).

36
Q

What are key threats to porpoises?

A

Bycatch in fisheries (e.g., gill nets, shrimp nets), the critically endangered vaquita (fewer than 100 individuals) is at risk of extinction due to bycatch.

37
Q

What is the geographical range of monodontids?

A

Narwhals: Atlantic Arctic region, closely tied to pack ice. Belugas: Circumpolar distribution, occupying coastal areas in winter and offshore regions in summer.

38
Q

What is the narwhal’s tusk, and what is its purpose?

A

A modified tooth (typically the left one) in males that extends into a tusk, possibly used for mating displays and dominance.

39
Q

How do narwhal and beluga diets differ?

A

Narwhal: Narrow dietary breadth (Greenland halibut and squid in winter). Beluga: Generalists, feeding on both benthic and pelagic prey.

40
Q

What are the main threats to narwhals and belugas?

A

Climate change impacting Arctic ecosystems, polar bears and killer whales as natural predators, human hunting (more common for belugas).

41
Q

What makes beaked whales vulnerable to sonar?

A

Mid-frequency sonar causes panic, leading to rapid ascents and decompression injuries.

42
Q

Why is the vaquita critically endangered?

A

Bycatch in fishing nets, with fewer than 100 individuals remaining, and limited effective mitigation.

43
Q

How does climate change threaten narwhals?

A

Their restricted range, dependence on pack ice, and narrow dietary preferences make them particularly vulnerable.

Marine vertebrates (9 decks)

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