Cetacean Systematics & Evolution. Lisa T. Ballance SIO 133 Marine Mammal Biology Spring 2018

Transcription

1 Cetacean Systematics & Evolution Lisa T. Ballance SIO 133 Marine Mammal Biology Spring 2018

2 Prologue

3 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)

4 ii. Cladogram representation of evolutionary history Lineages Synapomorphies Speciation Events Time

5 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 *actually, it s more complicated than this

6 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

7 iv. Two ever-changing conditions over geologic time are relevant to evolution: a. Configuration of land masses and oceans b. Climate

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9 iv-a. Seafloor Spreading and Continental Drift

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12 K-Pg Boundary 66 Ma (K-T Boundary)

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16 iv-b. Global Temperature

17 Cetacean Systematics & Evolution

18 Mammalian Phylogeny Cetaceans Pinnipeds, sea otters, polar bears Sirenians

19 Cetaceans are monophyletic* Deer, Elk, Moose, Caribou Order Cetartiodactyla Giraffe, Okapi Bison, Buffalo, Antelope, Gazelle, Sheep, Goat Hippopotami Gatesy et al *synapomorphies in Berta et al. 2006

20 The Archaeocetes ( ancient whales )* * * * * * * Adapted from Thewissen et al. 2001

21 Major Features Associated with the 1. Reduction of the hind limbs (adaptive significance: increased hydrodynamic efficiency) Evolution of Cetaceans:

22 Major Features Associated with the 2. Hyperphalangy (adaptive significance: use of forelimbs for locomotion in water) Increased number of bones in digits Evolution of Cetaceans: Greyhound

23 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

24 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

25 Early Eocene (60-50 Mya)

26 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

27 Middle Eocene (45 mya)

28 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

29 Walking with Prehistoric Beasts BBC

30 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

31 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

32 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

33 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

34 Oligocene (35 mya)

35 Modern Cetaceans Odontocetes and Mysticetes are each monophyletic* 35 mya *synapomorphies in Berta et al. 2006

36 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 Aetiocetus weltoni Heterodont dentition Likely (though contested) possessed some form of baleen (in addition to teeth) Extinct before beginning of Miocene

37 Four Families of Toothed Mysticetes 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 Berta & Deméré 2009 = 20 cm Aetiocetus weltoni

38 Baleen 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 = 10 cm Balaenoptera acutorostrata Berta & Deméré 2009

39 Early Mysticetes: b) toothless forms Eomysticetidae Late Oligocene Medium size (skull ~ 1.5m) Primitive features, e.g., Anteriorly placed blowholes Derived features, e.g., Edentulate Flattened rostrum Laterally bowed mandibles Cetotherium Cetotheriidae Late Oligocene Late Pliocene 3-10 m in size Diverse (>30 genera; > 45 species described) Non-monophyletic

40 Mysticete Phylogeny All of the early Mysticete lineages are extinct Deméré et al. 2008

41 Early Odontocetes Mid Oligocene Mid Miocene (33-14 mya) Rostra of various lengths Primitive dentition Squalodontidae Telescoping of skull first hypothesized echolocation Squalodon

42 Odobenocetops walrus whale Early Pliocene Convergent on walrus Asymetrical tusk length (1.4m vs 25 cm)

43 Reading Pp ; in Berta, A., J.L. Sumich, K.M. Kovacs Marine mammals: evolutionary biology. Second Edition. Academic Press