Orders Not Yet Discussed Cetaceans. These aquatic mammals—whales, dolphins, porpoises, etc.– include the largest animals ever known. Rabbits. These small herbivores are built to move fast, and they exploit cellulose by a double-cycling, hindgut-fermentation strategy. Hyraxes. These small African herbivores are distantly related to elephants and to sea cows. Sea cows. Manatees and dugongs are large, entirely aquatic herbivores. Elephant shrews. These are small African insect-eaters, typically with monogamous mating systems. Tree shrews. Once thought closely related to primates, these Southeast Asian mammals are mostly insect-eaters. Colugos, flying lemurs, or dermopterans. These arboreal animals of the Southeast Asian rainforests are the best gliders in the Class Mammalia. Aardvark. This African mammal exploits colonial insects and is a world-class digger.
Whales • Large to very large, entirely aquatic mammals. • Two living Suborders (baleen & toothed); 1 extinct Suborder. • About 10 Families. • About 78 species. • Often inhabit higher latitudes (in summer), where long daylight & concentrations of dissolved O2 produce abundant life.
Phylogenetic relationships of Whales • Archaeocetes are extinct. • Baleen whales are large & form a coherent group defined by foraging technique. • Modern “toothed whales” are a diverse group, ranging from smallish to very large.
Thoughts on whale evolution • The earliest whale fossils are from the Eocene, perhaps about 50MYBP. • Some primitive whales had external rear legs (no modern whales do), and all early varieties had teeth. • The relationship between whales and other mammals is now well established: • A few authorities once classified whales in a loose group with elephants-hyraxes-sirenians, or even w/ perissodactyls. • At one time some biologists thought that toothed whales had their own separate ancestry, from carnivores. • Now most mammalogists with any sense believe that all cetaceans are distantly related to hippopotamid artiodactyls (next slide).
Whale ancestry • Of course whales are highly derived, so affiliations are not obvious from fossils. • However, by 1880’s clever mammalogists noticed foot similarities between atriodactyls and animals like Ambulocetus. • In 1950, Boyden & Gemeroy compared serum proteins of cetaceans against all other mammal orders (except rabbits). Artiodactyls were closest.
Some anatomical properties of living whales • Whales have streamlined bodies w/ tails flattened into horizontal flukes. • Limbs: • Traces of femurs and pelvic girdles are present in some species. • Arm bones (humerus, radius, & ulna) shortened; however, fingers 2 & 3 (& occasionally others) lengthened to support paddle-like swim-fins. • Nostrils exit through “blowholes” on the top of the head. • In almost all species these are displaced high & far back; resulting alterations in the structure of the mammalian skull are impressive. • Two blowsholes in baleen whales, one in toothed whales • The skin of adults is hairless, but a thick layer of blubber (subcutaneous fat) provides insulation. • All whales exhibit an extensive suite of anatomical, physiological, and behavioral specializations connected with aquatic existence and deep diving.
More whale anatomy: • Rear legs are absent. • Front legs are modified as “flippers.” • Cervical vertebrae are fused. • Backbone is modified for vertical flexing.
Size & the physics of swimming • Most cetaceans cruise at approximately “brisk bicycle” speeds; orcas have been clocked at 55kph. • Speeds are a function of power-input/drag ratio. • Reducing drag (=minimize turbulence/laminar flow): • Protrusions eliminated; shape sculpted… • Skin evolved to minimize local pressure fluctuations… • Increasing ratio: • Drag is a function of X-sectional area (a “squared” quantity). • Power is a function of muscle-mass, which is a function of body-volume (a “cubed” function). • Therefore, get big (and get long)!
Baleen (“whale-bone”) whales • The toothless whales take their name from the baleen with which they strain out their food from the H2O. Basic feeding strategy is to eat fairly low on the food chain! • Structure of baleen: • Formed in triangular, flat plates, which are composed from strands of horny epithelium embedded in a less durable material. • At the edges of a baleen plate, the less durable material erodes away and leaves a comb-fringe of the epithelial material. • Mouths of baleen whales: • 130-400 baleen plates hang from each side of the whale’s upper jaw. • The plates are arranged so that their fringes form a continuous strainer. • Baleen whale feeding: • Whale takes in a huge gulp of H2O. • Then the animal closes its mouth (not tightly). • As the whale then raises its huge tongue, H2O is forced out through the baleen strainer—thereby retaining small food-organisms (see next slide). • Some baleen whales skim the surface (slide after next). • Gray whale scrapes the bottom & strains the muck (not illustrated).
A: Open mouth of baleen whale, showing hanging sheets of baleen and large tongue. • B: A triangular sheet of baleen, frayed toward the bottom to form a strainer. • C: Cross-section of baleen whale’s head. 2 sets of baleen sheets show as dark triangles hanging from upper jaws. Tongue is drawn almost entirely raised—& would be forcing water out of mouth, through the baleen “strainer.” • D: Reduced skeleton of a whale within the outline of the animal’s body. Tongue
Two (of 3) baleen-whale feeding methods: straining (left) and skimming (right):
Biggest baleen whale • Size: ave 27m; 150,000kg (XX somewhat larger than XY). • The blue whale’s year: • Spend 3-4 months/yr in higher latitudes. • As weather cools, blues move equatorially, pregnant XX’s first. • Young born near equator; nursed until they have enough blubber to withstand polar summer. • New mothers & young return ASAP to feeding waters (offspring must grow, & XX’s must recover energetic expenses of repro). • XX w/o calves mate in tropics; on return to feeding grounds they eat like crazy to carry them through 11-mo gestation & subsequent lactation. • XY’s—esp. adolescents—leave feeding grounds later than XX’s.
Toothed whales (Odontoceti) • This Suborder includes 6 Families with about 35 genera and 67 Recent species. In contrast to baleens, odontocetes eat high on food chain. • Odontocetes occur in a bewildering array of forms–medium, large, and very large. • Some species are particularly adapted for fresh water (in South America and Asia). • The Suborder’s most interesting adaptations include sounds: • Narrow-band continuous tones (whistles & squeaks used for intraspecific commo). • Broad-band clicks used for echolocation.
Odontocete mysteries: • Echolocation: How does it work? (Next slide.) • “Death Rays”: Evidence from sperm whales suggests that some odontocetes can focus sounds very precisely, emitting waves of high frequency and extraordinary intensity…. • Geomagnetic navigation. It appears that some (many?) odontocetes (and some baleen whales?) can orient with respect to the earth’s geomagnetic field…. • Neither of these latter 2 suppositions has been definitively demonstrated.
Echolocation • Sound is generated by movement of air through amplifying nostrils. • Sound bounces off dorsal surface of cranium and is “focused” by melon (complex lipids, “slow” center & “fast” shell). • Reception is through thin mandible and associated fat running from snout to ear. • Some species can pretty much substitute echolocation for sight. Ganges river dolphin
Sperm Whale (Physeter macrocephalus) • XY maybe to 30m, mass 45,000-70,000kg. • XX much smaller (c. 10m & 17,000kg). • Social organization: • XX near-tropical, in groups of 10-40 (+ dependent young). • XY worldwide, w/competition for harems. • Preferred food probably giant squid; also eat fish, octopus, crustaceans. Consume 3-4% body mass daily.
Dolphins (Dephinidae, worldwide) are the most familiar & abundant cetaceans. (B.N.D.’s are called “porpoises” in South Carolina!) • Range in size from person-sized miniatures to killer whales (7m & 4,500kg). • Evolved in late Miocene, c. 10MYBP). • Food: • Species w/long beaks & many cone-like teeth: fish-eaters. • Species w/shorter beaks & larger teeth: squid-eaters (but orcas…). • Bottlenose dolphins have huge brains. • Evidence suggests this is associated w/ hearing & processing of echolocative sounds. • Individual animals have unique whistles. • Bottlenoses associate in large groups that fracture into smaller groups of definite composition.
Narwhale (above) 4.25m; 1250kg (XY slightly larger than XX) Some other toothed whales Beluga (above): XY 5m, 1600kg; XY: 3.75m, 350kg B.N.D. (right) 4m 635kg Dall’s porpoise (below): 1.8-2.1m; 135-220kg
Next Order: Lagomorpha • Includes two living Families: • Ochotonidae (pikas): 1 genus, c. 14 species. • Leporidae (rabbits): 8 genera, > 50 species. • Evolutionary history: • Ancient group, probably Cretaceous in origin. • Earliest fossils are Paleocene of Mongolia. • By Eocene both Families in Eurasia & N. America. • Basically, lagomorphs are small herbivores able to exploit relatively wretched vegetation because of unusual fermentation strategies.
Lagomorpha “Lattice-work” rostrum and somewhat mobile, almost “hinged” cranium • 2 Families, c. 80 species. • Most major landmasses (not Australia, southern South America, Madagascar, or Antarctica). • Known from Paleocene. • Possibly related to rodents. • Small herbivores. Incisors 2/1 Rodent-like diastoma
Ochotonidae (pikas) 2 genera, 26 sps. • Pikas are round animals, c. 150-200g, resembling fat squirrels w/o tails (or resembling big-eared voles). • Mountains of western North America, + steppes & mountains of Asia. • Live colonially in rock jumbles. • Dry vegetation for “silage” & base territory around defense of these hay piles.
Rabbits • Informally split into two subfamilies: • Rabbits: altricial young (e.g., cottontails) • Hares: precocial young (e.g., jack “rabbits”) • Nutritional strategy: • Eat coarse vegetation high in cellulose. • Hindgut fermenters w/ high surface/volume ratios. • Re-ingestion of caecotrophic feces (next slide). • Reproductively an extreme r-species (next + 1) • Social systems (2 basic types): • Dispersed, somewhat like forest artiodactyls. • Warrens w/ dominance hierarchies (especially important among XX’s).
Rabbit digestion • Rabbits eat a lot! • Mass: 6%-8% body mass • Calories: 54kcal/kg-day • Cellulose: • Mostly separated out. • Even if fermented in caecum, cellulose is poorly digested (c. 14%). • Very rapid throughput! • Importance of caecum is poorly understood…. • Problems w/calcium metabolism…. • Food input • Stomach; regular emulsification, etc. • Small intestine; absorption of proteins, starches, sugars…. • Large intestine; recovery of water, etc. • Caecum; Amino acids (?), water-soluble vitamins, fatty acids, etc. • Hard feces (“rabbit pellets”). • Caecotrophic pellets; re-ingested.
Rabbit reproduction • Gametogenesis: • Winter quiescence; reactivation by photoperiod. • Males more easily activated. • Ova mature in response to FSH (if sufficient food); their development is arrested in sub-mature stage. • Courtship and copulation: • Faint heart never won fair rabbit! • Feedback through pituitary: LH surge in < 1hour; ovulation within 10 hours. • Pregnancy (28-day gestation): • Corpora lutea are initial progesterone-secreting structures. • Later, placenta; CL regress; FSH, ova to sub-mature stage • Recycling: • Post-partum copulation • If insufficient milk, total resorption in days 8-15.
South Carolina rabbits • The most common state-wide is cottontail, left. • Exploits successional habitats. • Populations vary from year to year. • The marsh rabbit is a coastal-plain species. • Eats mostly semi-aquatic vegetation. • Swamp rabbit is restricted to Pickens, Anderson, & Oconee Counties. • This is a big rabbit of river bottoms and canebrakes.
Other rabbits • I.P.R. is an endangered, small cottontail. • Tropical rabbits of Southeast Asia are poorly known. • Jackrabbits (hares) of the American west compete with domestic livestock. • The snowshoe hare (left) is a large, northern animal varying seasonally in color. It makes huge caloric demands. S.E. Asian forest rabbit Snowshoe hair Idaho pygmy rabbit Jackrabbit
Hyracoidea 3 genera, 6 species • This Order includes a single living Family, the Procaviidae, which has 3 genera and 11-12 species. • Formerly widespread, hyraxes are now restricted to Africa and a tiny segment of the Middle East. • Extinct varieties included rat-sized and rhino-sized animals; living members are rabbit-size. • Hyraxes are thought to be related to elephants and sea cows, part of an Afrotherian radiation (next slide) into drier, herbivorous niches….
Hypothesized components of the Afrotherian Radiation: • Aardvarks (later in this presentation) • Elephant shrews (later in this presentation) • Golden moles (treated as “insectivores”) • Tenrecs (treated as “insectivores”) • A proto-ungulate radiation: • Hyraxes (the Order of present consideration) • Sea cows (later in this presentation) • Elephants (considered as a separate topic) • Hyraxes were most successful; why have they declined so much?
Hyraxes • Rock hyraxes are highly social animals living in groups of 5-50. • Food is vegetation, often heavy in cellulose, fermented in the hindgut. • Perhaps to conserve energy, hyraxes have labile body temperatures. • “Group huddles” on cold mornings help hyraxes thermoregulate.
Hyrax digestive system • Hyraxes might have been the first efficient mammalian fermenters. • 2-compartment stomach, small intestine, two different caeca, and joining large intestine all have different digestive rolls. • Uh, but different roles are not well understood by me!
Hyrax technical characters • Skull and teeth: • Convergence w/rodents: • Ever-growing upper incisors • Dental diastoma • Note deep lower jaw • Feet (rear illustrated): • 3 syndactylus toes w/nails instead of claws • Sole evolved for superior traction • Foot structure is associated with the Order’s survival and its limits!
Sea cows • Part of Afrotherian radiation, these big, aquatic herbivores have oar-like arms, vestigial hindlimbs, & paddle-shaped tails. • The nostrils are high on the skull, behind the anterior margin of the small eyes. The lips are large & flexible. The upper lip has numerous vibrissae-like whiskers, but the sea cow body is otherwise hairless. • All living sirenians lack canine teeth. • Dugongs: XY dugongs have 1 blade-like incisor in each upper jaw. Molarform teeth are un-enameled. A dugong’s jaws can appear to be covered with horny plates—something like those seen in many turtles. • Manatees: Adult manatees lack incisors as well as canines. Their molarform teeth are adapted for grinding massive quantities of aquatic vegetation. These teeth are lost from the front and replaced in the rear, as with their distant relatives, the elephants (but manatees have more teeth).
Recent Sea-Cow Species • Manatees: • Amazonian manatee. A fresh-water animal feeding in floating meadows of aquatic vegetation. • West Indian manatee. Mostly salt water entering fresh water in N. Am. mostly for warmth. (Slide.) • West African manatee. Late Pleistocene re-immigrant from New World. Fresh & salt water. • Dugongs: • Dugong. Indian Ocean & South Pacific. (Slide.) • Steller’s Sea Cow. Bearing Sea. To 10,000kg (largest non-whale). Discovered 1741; extinct 1768.
Manatees • These are large (c. 400kg) New World & West African animals. • Insulation is not good, so despite small S/V ratio, manatees are restricted to warm H2O. • Feeding, & Nutritional physiology: • Diet low in nutrition • Teeth (6-7/quad, horiz. replace.) • Huge digest.-tract (40m long) • Very slow throughput • Very high extractive efficiency • Groups ephemeral; multiple XY’s chase receptive XX’s. • Manatees make many sounds that carry great distances & convey social information • Interbirth interval is c. 3 years; social maturity for XY is at 9-10 years; XX mature more rapidly. Lifespan is long.
More on manatees T. senegalensis? • Bones are very heavy (no marrow cavities in longbones or ribs). • Shape and position of lungs; breathing efficiency…. • Bone-weight, CH4, diaphragm, and buoyancy…. • Brain is relatively small and relatively simple. • Low metabolic rate, K-selection, general life strategy.
Dugong • Appearance: • Dugong: indented tail. • (Manatee: paddle-like tail.) • Range: • East coast of Africa, south coast of Asia; South Pacific to Australia & Caroline Islands. • Size: 250cm; 300kg. • Feeding: • Strong lips for eating sea grasses. • Other: • Large incisors apparently used in XY-XY combat.
Macroscelidia (elephant shrews) Giant Short-eared Checkered Golden- rumped
Elephant shrews • Once classified w/ Insectivora; now called members of Afrotheria. • Fossils known only from Africa (as early as Eocene of Tunisia). • 4 genera and 15 living species. • Size: • Large mouse (50g) to large rat (450g) • Food is primarily insects (termites & ants in one studied species).
More on elephant shrews • Elephant shrews are monogamous, with XX & XY scent-marking territories & defending against same-sex conspecifics. • Gestation is long; twins are produced, XY does a little child-care, but…. • Pairs maintain trail systems (important), with XY doing most trail maintenance.
Tree Shrews (Scandentia) • The Order has one Family, about 5 genera and perhaps 19 living species. • Range includes much of South & Southeast Asia. • Classification: • Once placed w/primates because of skull features. • Now considered sister Order to primates, bats, and dermopterans (and rabbits?????????????). • Social system: • Long-term bonds between XY & multiple XX’s. • Territories defended against same-sex conspecifics. • Mothers deal with their babies about 1 time/2 days, feeding w/ large quantities (to 20% body-mass) of high-quality milk (10% protein, 26% fat).
Two Treeshrews ( Tupaia tana & Dengrogale minuta) • Three shrews were formerly thought to be largely insectivorous (because of teeth). • Now they are known to consume much fruit. • Rapid pass-through rate (13-29 min!) is like fruit-eating bats– and makes tree shrews important seed dispersers.
Dermopterans • 1 genus, 2sp. of S.E. Asian arboreal leaf eaters. • 1-1.75kg; h-b 34-42cm; tail 25cm; 70cm wing-span (note tail). • Hindgut fermenters, so low-energy creatures. • Crepuscular or nocturnal gliders in forests with broken canopies. • 1 altricial young clings to mother’s underside. Protected orbits Multi-cusped canines
1-1.75kg; h-b 34-42cm; tail 25cm; 70cm wing-span (note uropatagium). • Hindgut fermenters, so low-energy creatures. Colugo Dermopteran “Flying lemur” Cynocephalus variegatus
The Noble Aardvark • H-b 100-160cm; mass 50-100kg! • Ancestor of artiodactyls? Member of Afrotheria? • Have regular foraging routes & exploit termites (wet season) and ants (dry season) in ways reminiscent of giant anteaters. • Dig enormous burrows shared by many vertebrates.