Evolution of Pinnipeds and Sirenians

Cladis'cs  •  Phylogeny  

– Hypothesis  about  evolu'onary  rela'onships  •  Clades  

– Groups  of  related  taxa  and  their  descendants  

Cladistics • Character

–Diverse, heritable attributes  

–Used in phylogenetic analysis

• Character state –Condition expressed in the individual

• Limb number (0,2,4,6,8) • DNA sequence (GGGAATT)  

Origin of Features • Homologous structures

Similar features resulting from common ancestry • Bones of a flipper & hand  

Origin  of  features  

•  Analogous  structures  structures  with  similar    func'on  that  evolved    separately  Convergent  evolu'on  e.g.  wings  of  a  bat  &  bird  

•  Parsimony  fewest  evolu'onary  steps/changes  is  accepted  as  the  best  

Tools used to study evolution Bones and Teeth

• saved in fossil record • structure used to infer diet (ecology)  

• limbs, pelvis - shows how animal moved

Tools used to study evolution

Immunology

• similar response shows relatedness    

• used with extant species

Biochemistry & Molecular tools

• DNA sequencing

• DNA recombinations – more  connections shows relatedness

Mammalian Tree

  Marine mammals: monophyletic group?

Malcolm A. Ferguson-Smith & Vladimir Trifonov Nature Reviews Genetics 8, 950-962 (December 2007)

NO

 CONVERGENT

evolution from land to sea

Triassic // 200 million years ago

Wildman D E et al. PNAS 2007;104:14395-14400

Laurasiatheria /Cetartiodactyla (cow)

Afrotheria (elephant) Xenarthra

(armadillo)

Euarchontoglires (monkey)

Order Carnivoria Includes 5 Families of Marine Mammals Mustelidae – Sea otter Ursidae – Polar bear Phocidae – Seals (true seal) Otariidae – Sea lions (eared seals) Odobenidae - Walrus

Pinnipeds  

MARINE MAMMAL EVOLUTION

Pinniped Evolution Diphyly: Fossil & morphological support    Monophyly: molecular & revised morphological support

Bear   Pinnipedimorph   Otariid   Odobenid   Phocid  

Pinniped  Skeletal  Morphology    

Chronological  Ranges  for  Marine  Carnivora  

Puijila  t    

Pinniped Evolution When & where?

• 27-25 mya (late Oligocene)    

• N. Pacific and Canadian Arctic    

• Arctoid ancestors (bear like)

Puijila darwini Enaliarctos spp.  

N Rybczynski et al. Nature 458, 1021-1024 (2009) doi:10.1038/nature07985

Puijila  darwini  skeleton  (NUFV  405,  holotype).  

Enaliarctos spp.

Pinniped  Cladogram  

Divergence of Early Otariids

• Pithanotaria spp. • 11 mya (late Miocene), CA

• Thalassoleon spp. • 8-6 mya, CA, Mexico, & Japan

• Callorhinus • 5-4 mya, extant

Present day Otariids

Precursor to Phocids

• Desmatophocidae – 21-20 mya

• derived from Enaliarctos

• not true phocid but evolutionary link    

• N. Pacific coastal (CA, OR, Japan)    

• Large, sexually dimorphic

• Allodesmus & Desmatophoca

Early Phocids

• Monotherium spp. & Leptophoca spp.

• 15-14 mya

• Appeared in N. Atlantic      

• Split into many lineages

Monotherium & Leptophoca

Desmatophoca

Moved through Central American Seaway or through the Arctic Basin

Present day Phocids

Early Odobenids • Relationship to Otariids & Phocids

unclear

• Very diverse group (3 suborders)

• Proneotherium & Neotherium spp.

• Ancestral walrus 16 mya & 14mya    

• Eastern N. Pacific    

• Fish eaters

Modern Odobenids

• Evolved in N. Atlantic

• Prorosmarus, early Pliocene

• Re-invaded Pacific through Bering Strait ( < 1mya)

• Odobenus rosmarus

Order Sirenia

• Family Dugongidae

• Family Trichechidae – Manatees

Sirenian  EVolu'on  Sirenian  

Evolu'on    •  Caribbean  region  

•  Herbivorous  mammals  

Sirenia Evolution Earliest Ancestors:

• herbivorous mammals

• 50 mya, Caribbean region

Sirenian  evolu'on  •  Prorastomas  –  early  Eocene  (50  Ma),  Jamaica  

– Long  trunk,  rela'vely  short  legs  – 4  sacral  vertebrae:  increased  flexibility  -­‐  undula'on  – Strong  and  long  tail  –   Par'ally  aqua'c  

Order  Sirenia  Sirenians,  proboscideans  (elephants),  &  desmostylians  (ex'nct)  termed  Tethytheria    

Order Desmostylia

• Only extinct order of marine mammal    

• N. Pacific, Late Oligocene (33-10 Ma) • 10 species

• hippopotamus-like amphibious quadrupeds

• Paleoparadoxia & Desmostylus Most closely related to elephants

Unique Teeth Structure: