Cetacean Systematics &
Evolution
Lisa T. Ballance
SIO 133 – Marine Mammal Biology
Spring 2017
Prologue
i. Definitions
• Systematics
– The study of biological diversity that emphasizes phylogeny
(evolutionary history of organisms)
• Cladistics (phylogenetic systematics)
– Method of reconstructing evolutionary history based on shared,
derived characters (“synapomorphies”) and the assumption that these
provide evidence of common ancestry (“homology”)
• Characters
– diverse, heritable attributes (e.g., DNA base pairs, anatomical and
physiological features, behavioral traits)
– Character states: two or more forms of a given character
Shared, derived characters
identify monophyletic groups
(e.g., tetrapods)
ii. Cladogram – representation of
evolutionary history
Lineages
Synapomorphies
Speciation Events
Time
How do you determine if characters are
derived or ancestral?
• Outgroup comparison (widely used)
– Character states found in close relatives
(outgroup) are likely to be ancestral to the group
of study (ingroup)*
– Analysis includes multiple outgroups if possible
– Most important is the most closely related (sister
group)
– See Fig 2.2 and associated text in Berta et al. 2006
*actually, it’s more complicated than this
iii. The Geologic Time Scale
•
Names from
– Locations of rocks corresponding to that age (e.g., Permian – Perm province in
northern Russia)
– Ancient peoples living in area corresponding to rocks of that age (e.g., Ordovician –
Ordovice tribe in southern England)
– Derivations of time (e.g., Paleocene – ancient (palaeos) division of recent (caenos)
geologic history)
Millions of years
iv. Two ever-changing conditions over
geologic time are relevant to evolution:
a. Configuration of land
masses and oceans
b. Climate
https://www.youtube.com/watch?v=uLahVJNnoZ4
iv-a. Seafloor Spreading and
Continental Drift
http://www.scotese.com/Default.htm
K-Pg Boundary 66 Ma
(K-T Boundary)
iv-b. Global Temperature
Cetacean Systematics & Evolution
Mammalian
Phylogeny
• Cetaceans
• Pinnipeds, sea
otters, polar bears
• Sirenians
http://whozoo.org/mammals/mammalianphylo.htm
Cetaceans are monophyletic*
Deer, Elk,
Moose, Caribou
Order
Cetartiodactyla
Giraffe, Okapi
Bison, Buffalo, Antelope,
Gazelle, Sheep, Goat
Hippopotami
Gatesy et al. 1999
*synapomorphies in Berta et al. 2006
The Archaeocetes (“ancient whales”)*
*
*
*
*
*
*
Adapted from Thewissen
et al. 2001
Major Features Associated with the
Evolution of Cetaceans:
1. Reduction of
the hind
limbs
(adaptive
significance:
increased
hydrodynamic
efficiency)
Major Features Associated with the
Evolution of Cetaceans:
2. Hyperphalangy
(adaptive
significance:
use of
forelimbs for
locomotion in
water)
– Increased
number of
bones in digits
Greyhound
Major Features Associated with the
Evolution of Cetaceans
3. Telescoping of the skull (adaptive
significance: nares on top of head)
–
–
–
–
–
–
Maxillae - rostrum
Pre-maxillae – nares
Nasals
Occipital
Parietals
Frontals
Major Features Associated with the
Evolution of Odontocete Cetaceans:
4. Homodonty and Polydonty
(adaptive significance: prey
capture)
– Teeth of the same type
– Increase in tooth number
Early Eocene (60-50 Mya)
Pakicetidae
•
•
•
•
Early – Middle Eocene (50 mya)
Wolf/fox-size
Predominantly terrestrial
Partially aquatic?
– Fossils in modern-day Pakistan,
near coastal Tethys Sea
– Earbones adapted for
underwater hearing
Middle Eocene (45 mya)
Ambulocetidae
•
•
•
•
•
•
•
•
Ambulocetus natans “walking whale
that swims” (most complete
specimen found to date)
Middle Eocene (45 mya)
3 m, 300 kg; thick limbs
Amphibious (back legs more adapted
to swimming than walking)
Shallow, swampy marine and fresh
water environments
Ecological niche similar to today’s
crocodiles
Cetacean-like features: teeth; ear
bones; nose adapted for underwater
swallowing; no external ears
Transition: fresh-marine; land-water
Walking with
Prehistoric Beasts
BBC
https://www.youtube.com/watch?v=LveL3L2YLjY
Remingtonocetidae
Kutchicetus
• Middle Eocene (45
mya)
• Amphibious
• Coastal marine
environments
• Long, narrow skull
and jaw (suggesting
diet of fastswimming prey)
• Small orbits
(suggestion vision
not important)
• Ears adapted for
underwater hearing
Protocetidae
• Middle Eocene (45 mya)
• Widespread (fossils from
Europe, Africa, Asia, N
America) – first
Archaeocetes to disperse
to all shallow sub-tropical
oceans
• Lagoon, coastal, *and*
open marine forms
• Nasal openings large and
half-way up the snout
• Some possibly with flukes
Rodhocetus
Protocetus
Basilosauridae “king lizard”
•
•
•
•
•
•
Late Eocene – Early Oligocene (41-35
Mya)
Initially mistaken for a marine reptile
Oldest known (with Dorudontids)
obligate marine forms (no freshwater
forms)
Small brains (suggesting non-social)
Widely distributed in tropical and
sub-tropical oceans of the world
Fully recognizable cetaceans
– Nostrils close to position of modernday blowholes
– Functionally modern cetacean ear
structure (incl air-filled sinus
between ear bones and skull)
– Tiny external hind limbs but pelvic
bones not connected to vertebral
column
•
Of note:
– Large body size (12-25 m!)
– Extreme elongation of lumbar vertebrae
– Tail with fluke but likely not the main
propulsive organ
•
Fish remains found with fossils
Dorudontidae
• Late Eocene – Early Oligocene (41-35 mya)
• Very similar to Basilosaurids *except*:
– Dolphin-like (~5 m)
– Tail with fluke that formed main propulsive organ
Modern Mysticetes and Odontocetes likely
diverged from these forms
Oligocene (35 mya)
Modern Cetaceans
• Odontocetes and Mysticetes are each
monophyletic*
35 mya
*synapomorphies in Berta et al. 2006
Early Mysticetes:
a) the toothed forms
• Known only from the Southern
Ocean and N Pacific (none from
Atlantic)
• Primitive degree of skull
telescoping; nares midway btwn tip
of rostrum and orbit
• Heterodont dentition
• Likely (though contested) possessed
some form of baleen (in addition to
teeth)
• Extinct before beginning of Miocene
Aetiocetus weltoni
Four Families of Toothed Mysticetes
= 20 cm
• Three ~ smaller-bodied
families (2-3m total length)
– Janjucetidae
• Includes species with large
orbits relative to skull length
(suggesting acute vision)
– Mammalodontidae
– Aetiocetidae
• Most diverse of the four (3-4
genera; 7 species)
• Longer rostrum relative to other
two small-bodied families
• Llanocetidae
– including oldest Mysticete:
Llanocetus denticrenatus
– Large (2m skull)
Janjucetus hunderi
Mammalodon
collivieri
Aetiocetus weltoni
Berta & Deméré 2009
Baleen
= 10 cm
• Poorly documented in the
fossil record
• Hypothesized step-wise
evolution:
– Toothed forms
– Intermediate forms with
teeth and baleen
– Derived forms with baleen
only
• Evidence: Osteological
– Extant Mysticetes have highly
vascularized palate with
distinct foramina for blood
supply and innervation of
baleen plates
Aetiocetus weltoni
Balaenoptera acutorostrata
Berta & Deméré 2009
Early Mysticetes:
b) toothless forms
• Eomysticetidae
Cetotherium
– Late Oligocene
– Medium size (skull ~ • Cetotheriidae
1.5m)
– Late Oligocene – Late Pliocene
– Primitive features, e.g.,
– 3-10 m in size
• Anteriorly placed
– Diverse (>30 genera; > 45
blowholes
species described)
– Derived features, e.g.,
– Non-monophyletic
• Edentulate
• Flattened rostrum
• Laterally bowed
mandibles
Mysticete Phylogeny
All of the early
Mysticete
lineages are
extinct
Deméré et al. 2008
Early Odontocetes
• Mid Oligocene – Mid
Miocene (33-14 mya)
• Rostra of various
lengths
• Primitive dentition
• Squalodontidae
– Telescoping of skull
– first hypothesized
echolocation
Squalodon
Odobenocetops “walrus whale”
• Early Pliocene
• Convergent on walrus
• Asymetrical tusk length
(1.4m vs 25 cm)
Reading
• Pp. 51-64; 68-71 in Berta, A., J.L. Sumich, K.M.
Kovacs. 2006. Marine mammals: evolutionary
biology. Second Edition. Academic Press.
– http://www.sciencedirect.com/science/book/978
0120885527