Sirenian Evolution & Systematics

MARE 390Dr. Turner

Order Sirenia

Only herbivorous marine mammals

2 Families of Sirenians

Trichechidae – manatee (3 species)Dugongidae – dugong (1 species)

Order Sirenia

Fossil record from early Eocene (50 mya)

Sirenian Biogeography

Sirenians first evolved in theCaribbean (Jamaica)

By end of the Eocene – occupied tropical Atlantic & Pacific

Dugongids – most diverse & successful sirenians; appeared in Mediterranean

“No, mon, let's go home to Jamaica. I and I been in Babylon too long. I want to pass the dutchie on the left-hand side!” – Homer Simpson

Sirenian Biogeography

Dugongids – most diverse & successful sirenians; appeared in Mediterranean

Manatees – diverged from Dugongids in late Eocene; occupied coastal estuaries of South America

Order Sirenia

Earliest partially aquatic quadrupedsMorphology consistent – aquatic existence

Order Sirenia

Sirenians, proboscideans (elephants), & desmostylians (extinct) termed Tethytheria

Order Sirenia

Manatee Dugong

Hydrostatic Adaptions

Sirenian skeleton – thick compact bone

Heavy bones & horizontal lungs – neutral buoyancy

Muscular diaphragm

Whatever Sea Cow!

Sea Elephants?

“This is the greatest case of false advertising I've seen since I sued the movie ‘The Never Ending Story’.” - Lionel Hutz Attorney at Law

Family TrichechidaeTrichechus senegalensis- West African manatee

Trichechus inunguis- Amazonian manatee

Trichechus manatus- West Indian manatee2 subspecies:Trichechus m. latirostris- Florida manatee Trichechus m. manatusAntillean manatee

Family Dugongidae

Dugong dugong- Dugong

Hydrodamalis gigas- Steller’s sea cow

Family Dugongidae

More diverse in the past than manatee

19 extinct genera; some cold adapted

Many had tusks

Steller’s Sea Cow

Known for 27 yrs (1741-1768)

Large sized sirenian (7.5-7.9 m)

Cold-temperate waters of Bering Sea

Fed in water column – Kelp

Small in number & range when describedQuickly wiped out by sailors, sealers, & fur traders

Hunted for food, skins, & blubber

Order Desmostylia

Only extinct order of marine mammals

At least 6 genera; 10 species

Hippo-sized amphibious quadrapeds

Estuarine/coastal – subtropical/temperate

Order Desmostylia

Similar locomotion to polar bears

Herbivore – marine algae & seagrasses