Week 1c: Evolution and morphology

Question 1

Parallel evolution

Answer 1

Cetacea (mystecetes and odontocetes)
Sirenia (sea cows)
Carnivora (pinnipeds, polar bears and sea otter (fissipeds))

Cetaceans and Sirenians showed up first in the Eocene age (50-60 mya) and within Carnivoras, pinnipeds showed up later in the oligocene era (25-30 mya) and sea otters and polar bears showed up the latest in the pliocene age (1-3 mya).

Question 2

Cetacean origin

Answer 2

First records from the Eocene epoch (50-55 mya).

Evolved from aquatic artiodactyla (even-toed ungulates)(cows, camels, deer) in India

Closest living relative are hippos

Global distribution; two major groups:
- Mystecetes: 4 families and 14 species
- Odontocetes: 10 families and 73-76 species

Made a major dietary change during the transition from artiodactylates to cetaceans

Question 3

Indohyus

Answer 3

The raoellid Indohyus is similar to whales in its structure of its ears and premolars, in the density of its limb bones and the stable oxygen isotope composition of its teeth.

They were aquatic waders, which indicates that aquatic life in this lineage occurred before the origin of cetaceans (order).

Aquatic escape behavior

Question 4

Cetacean morphological changes from land to sea.

Freshwater semi-aquatic –> Brackish water –> salt water

Answer 4

Freshwater semi-aquatic habitat:
- They got a thick, bony wall around the middle ear

Brackish water habitat:
- Large powerful tail; shorter legs
- Fat pad in jaw for hearing underwater

Salt water habitat:
- Nasal opening shifted back and eyes moved to the side of the head
- They got tail flukes and very small hind legs
- Nasal opening moved further back
- Complete loss of hind legs, nasal opening=blow hole
- Echolocation in odontocetes and baleen + large increase in bodyseize in mystecetes

Question 5

Cetacean skull evolution

Answer 5

Telescoping of rostrum (elongation of skull)

Nasal opening shifting towards the back of the skull

Eyes moving to the side of the head

Multiple adaptations to breathing, senses and foraging.

Question 6

Skeletal anatomy and function

Answer 6

Cervical (neck), Thorax (chest), Lumbar (back) and Caudal (tail)

Cervical: Vertebrates compressed and fused. V7

Thorax: Vertebrates with ribs. V13-14

Lumbar and Caudal: LV2-30 and CV13-49. With elongated processes and variable number of vertebrae.

Functions:
- Protect organs in the thorax
- Production of blood cells
- Endocrine (hormone) regulation
- The chevron bones are for muscular support.

Loss of hind limbs. The little bone is the pelvis, only thing left of hind limbs.

Question 7

Hyperphalangy

Answer 7

They have elongated digits (fingers) with an increased number of phalanges (bones in the fingers)

In order of increasing number:
Orca<Sperm whale<Right whale<Humpback<Ichthyosaur

Question 8

Areas with large variation among cetaceans

Answer 8

Chevron bones
Number of vertebra
Pelvic bones remnants
Shape of skull
Shape of scapula
Number and shape of hand bones

Also many external differences.

Question 9

Evolution of filter feeding (baleen)

Answer 9

34 to 24 million years from teeth, to teeth+baleen to baleen.

Skim filter feeding
Bulk filter feeding
Lateral suction filter feeding
Lunge filter feeding

All baleen whales have teeth as a foetus, but these are gradually replaced by baleen during fetal development.

First few months they have teeth, around six months they have teeth and baleen and around the nine months they have baleen only.

Question 10

Coronodon havensteini

Answer 10

Relative of modern baleen-bearing whales, but retains teeth.

Its molars are large, multi-cusped and overlapping.

Question 11

Pinnipeds

Answer 11

Carnivores
Sister group to Mustelids

Modern pinnipeds:
- Phocids (true seals)
- Otarids (eared seals)
- Walrus

Question 12

Early pinnipeds

Answer 12

First fossil from the oligocene 30-40 million years ago.

High diversity of fossils in Northeast Pacific, so it’s questioned wether this is the geographical origin of pinnipeds.

Question 13

Pinniped evolution and phylogeny

Answer 13

There are many extinct families and species

The only modern families are phocidae, otaridae and odobendae.

These families include both extinct and modern species.

The walrus is the only modern species of odobendae.

around 40 mya, the pinnipeds split into their own group.

23 mya, the earless seals split from the eared seals.

14 mya, the earless seals split into the northern and southern earless seals.

Question 14

General pinniped morphological changes

Answer 14

Overall increase in body seize (possibly for diving)

Thicker and shorter limbs, elongated fingers, flexible spine

Teeth modified, larger eyes and alteration of bulla (ear)

Question 15

Otarids vs Phocids

Answer 15

Otarids (eared seals):
- Extra ridge on scapular (swimming and walking)
- Large cervical vertebrae (balance and flexibility)
- Support on front and hind limbs (walking)
- Primarily swimming with front limbs

Phocids (true seals; earless seals):
- Long transverse process on lumbar vertebrae (swimming)
- Elongated 1st and 5th digits (swimming and movement on land)
- Primarily swimming with hind limbs

Question 16

Sirenia (sea cow) evolution

Answer 16

First recorded from Eocene (50-60 mya)

Loss of hind limbs; paddle-life front limbs; tail fluke

Herbivores (unlike all other marine mammals)

Their closest living relative are elephants and hyraxes

Question 17

Polar bear (Ursus) evolution

Answer 17

Pleistocene (1-1.5 mya)… or more recent?

Closely related to brown bear

Question 18

Polar bear adaptations to cold temp

Answer 18

Black skin for warmth

Hair is clear and hollow to help keep bear warm

Large paws with fur underneath

Question 19

Polar bear adaptations to swimming

Answer 19

Strong neck and leg muscles for swimming

Small ears flatten when swimming

Nostrils close when swimming

3 eyelids

Question 20

Plate tectonics and cooling

Answer 20

Eocene, 50 mya:
- Antarctic cooling

Oligocene, 35 mya:
- Drake passage (30 mya)
- Tasmani Antarctic passage (35 mya)

Miocene, 20 mya:
- Artic ice-sheet (10 mya)
- Closure of Tethys sea (10 mya)
- Indo-pacific closure (5-3 mya)
- Panama Isthmus (3 mya)

Pleistocene, 50 Kya:
- Major coolings at both ends

Question 21

Primary productivity

Answer 21

Increased primary productivity driven by cooling, upwelling and ocean circulation.

energy is converted by photosynthetic organisms (such as plants, algae, and some bacteria) into organic matter through the process of photosynthesis. They are then eaten by other organisms and provide energy to them.

The north and south poles have high primary productivity.

High primary productivity provided food-base for evolution of large body size (gigantism)

Question 22

Separation by temperature, land or food can result in new species

Answer 22

Ex: Anti-tropical distribution. Warm equatorial water acts as a barrier, causing two new subspecies of dolphin.

Ex: Inshore-offshore distribution.

Question 23

Summary

Answer 23

All marine mammals originate from land

Gradual morphological and behavioural adaptations to the sea
- Polar bear: few aquatic adaptations
- Pinnipeds/otter: semi-aquatic
- Cetaceans/sirenians” fully aquatic

Evolution shaped by plate tectonics, increased cooling and increased primary productivity.