Xenarthra anteaters, sloths, & armadillos

Pholidotapangolins

Xenarthra is from the Greek, meaning “strange-jointed ones.” With minor exceptions Xenarthrans are and have always been South American animals.

Pholidota means “scaled-skin animals.” Pangolins are scaly ant- and termite-eaters of Africa and Southeast Asia.

Zoogeographical & taxonomic riddles currently being solved:

• Xenarthrans are ancient, Southern-Continent animals. How come they are not found in Africa or Australia? – Xenarthrans probably arose in Cretaceous, but first fossils

date from c. 60MYBP; Africa had separated by 80-65MYBP.– South America-Antarctica-Australia don’t break until c.

35MYBP, but climate stops land-dispersal c. 64MYBP.– Thank you, geologists and paleontologists!

• At one time xenarthrans & pangolins were put in one Order (Edentata). What really is their relationship? – Formerly ambiguous, the resemblance is now known to be

the result of extreme convergence.– Pangolin’s closest relatives are probably carnivores.– Thank you, molecular taxonomists!

Almost all mammalogists now accept three major clades of eutherian mammals, but…

• The fossil record gives us no decent clues as to which split is most profound.

• Statistical analysis of molecular evidence gives approximately equal support to each of the three hypotheses at right.

• What do you think that geo-history might suggest?

The Living Xenarthra

65MYBP

55MYBP

Some Xenarthran & Geological History• The Xenarthrans (MYBP)

– 80-65: Order originates– 65-63: Armadillos split– 55: Sloths & AA’s split– 55-3.5: Moderately rapid

speciation; “background” extinction

– 3.5-2: Increased rates of speciation & extinction.

– 11KYBP: Extinction of almost all N.Am. Xenarthra

– 10KYBP: Extinction of 90% of S. Am. Xenarthra

– 4KYBP: Extinction of 100% of Caribbean Xenarthra.

• The Geo-Ecology (MYBP)– 65: End of Cretaceous– 55-3: World increasingly

seasonal (dry in places)– 3MYBP-10KYBP: Ice ages

& Inter-glacials– 2.5MYBP: Panama rises;

great faunal interchange– 10KYBP: Rapid warming,

increased rain; sea-level rise, people in Americas; mammals w/mass> 50kg:

• North America: lose 75%• South America: lose 80%

– 5-4KYBP: People into Caribbean.

Probable patterns of xenarthran evolution:

• Earliest types:– Ancestral form was probably a sloth-like, leaf-eating,

cellulose fermenter.– Offshoots eventually included:

• Armadillos (the hard-skinned xenarthrans; many fossils) were the first to split off. These were and remain successful ground-scroungers.

• Sloths and anteaters split later. These 2 groups eat very different stuff, but both groups’ food-types are “difficult.” Exact ancestry of anteaters is not definitively known.

• More on patterns of extinctions:– Circa 2MYBP: Armadillos and specialists are more likely to

survive; overall losses less than formerly believed.– Circa 10KYBP: Big stuff is more likely to become extinct.– Perhaps ecologists should not succumb to physics-envy.

Characteristics of living xenarthrans

• Backbone is highly flexible, but in 1 dimension only.• Teeth (if present) lack enamel and are simple &

single-rooted.• Smell is emphasized over other senses.• All exploit “difficult” food resources (armadillos less so

than sloths and anteaters).• All survivors (except armadillos) are extreme

specialists.• All try to save thermoregulatory energy:

– By low body temps and/or heterothermy.– By behavior.– By choice of habitat and/or microhabitat.

Some Representative Living Xenarthrans

Sloths in general

• Taxonomic diversity– once much greater; 60 fossil genera are known– 2-toed & 3-toed varieties are convergent; 2-toed

now classed w/ground sloths (Megalonychidae)

• But ecological similarity among living sloths.• The problems of a leaf-diet:

– Tropical ecology & detoxifying leaves…– Digesting cellulose & energetics

Adaptations (?) that are probably related to “sloth energetics”:

• Fermentation in compartmented stomach– Cost of microbial symbiants– Month-long throughput

• Feces and urine– About 1-2 times per week (500ml urine!)– Climb down from the tree; why?

• Slow movement• Labile body temperature

– 28oC-35oC (system-failure possible at 18o ambient)– Range-restriction to tropical rainforest

• Adaptations to save energy:– Move slowly (hence the name…)– Insulate well & have low body temperatures (must therefore

live in tropics)

Three-toed sloth(Bradypodidae)

• Bradypus variegatus.

• 40-70cm; 2.2-6.2kg.

• 8-9 cervical vertebrae; flexible neck.

• Much slower than 2-toed sloth.

• Eats from one tree for very long time.

• “Green” fur (longitudinal slits and specific algae).

• 11+ month gestation; extensive maternal care….

2-toed sloth(count on front feet)

• Choloepus hoffmanni• 6-8 cervical vertebrae• More active, fiercer, and

more catholic of diet than 3-toed variety.

• 50-55cm, 5-8.5kg.• Highly variable body

temps (24oC-35oC).• Gestation 4-6months;

maternal care is protracted.

• Female-biased sex ratio (reportedly 11 to 1) in wild. (Why?)

• Animal is long-lived (often > 20 years).

Sloth status and conservation• They usually dominate

Amazonian-mammal biomass:– 2-toed: 2.7/ha– 3-toed: 7/ha

• The prefer Cecropia over other trees:– This genus thrives in

second-growth forest.– So habitat is not

endangered.

• But they are reservoirs of Leismaniosis—which you don’t want!

Giant ground sloths

(extinct)

• Ground sloths are placed in the Family Megalonychidae.– Recall that two-toed sloths are

placed in the same Family as ground sloths.

– Thus their resemblance to three-toed sloths is due to convergence.

• Ground sloths invaded North America before Panamanian land-bridge.– At max diversity (c. 20KYBP):

• 15 genera of S. Am. ground sloths

• 4 genera of N. Am. ground sloths

– So extinction is probably not due to competition.

– What else might caused it?

Think 200kg-3000kg!

Anteaters (3 basic types)

• In the Neotropics, much of the zoomass is concentrated in colonial insects; anteaters eat nothing else.

• Front legs are powerful; each has a single, greatly enlarged claw (3rd digit). Guess why.

• Teeth are absent, but rostra are elongated & ridged. Tongues are long & sticky.

• Pyloric region of stomach is thickened and may serve as a “gizzard” for grinding chitinous exoskeletons (and as a protection against concentrated formic acid).

Type 1: small & entirely arboreal

• Cyclopes didactylus• 350g, <50cm head-body.• Entirely nocturnal.• One author estimated 700-5000

ants/day (former is much too low).• Only xenarthran for which paternal

care reported (but is it true?).• “Male-overlap” territorial pattern.

Type 2: Medium sized; partly arboreal

& partly terrestrial

• The genus Tamandua (> 2 species) enters North America in southern Mexico.

• 2-7kg, 60cm head-body.• Eats ants & termites (about

9000/day).• “Tripod” defense.• 1 baby (rarely twins),

extensive maternal care for up to about 1 year.

• Most common anteater.

Type 3: Large & entirely terrestrial

• Myrmecophaga tridactyla.

• 20-40kg, 180cm total length.

• Female bears one young per year, nurses for 6mo., carries on back for about one year.

• Often diurnal where not molested by people.

• Male-overlap territory.

• Most endangered by conversion of habitat for cattle ranching.

Ecologyof M. tridactyla:

How do they manage???

• Adults need 14,000-28,000 insects/day– Termites seldom eaten?– Termites dominate diet?

• Taking so many from a single colony would destroy resource piecemeal.

• Giant anteaters typically hit c.100 colonies per day, eating c. 150-175 insects from each.

• Mourão radio-tracked 7 for 10mo.; ranges did not asymptote.

• More

Folks say that big mammals can’t be insect-specialists, but:

50% fruit

Armadillos: the most successful living xenarthrans

• Roughly 30 living species, mostly South American (one species USA).

• Armor (bone & horn-like substance) is arranged in bands & plates connected by flexible skin. (Shoulder & hip shields, armored head & legs, rings around body, underside soft….)

• Food is mostly invertebrates though small vertebrates & considerable plant matter are also consumed.

• Respiration often anaerobic; low metabolic rate.

Dasypus novemcinctus:

successful invader of USA from the

South

• Total length about 75cm; mass c. 5kg (XX) & 6.5kg (XY).

• Range is probably constrained by…well, who knows? (Dramatic range extensions in twentieth century.)

• In USA, > 90% of diet is invertebrates.

• Reproduction is by monozygotic polyembryony (not characteristic of Order).

How did they get there? How far can they go?

• US range extensions:– Natural movements

plus…– Introductions– Hitch-hiking

• Limits (& non-limits) to range:– Physiological constraints

perhaps not primary• Vasoconstriction, shivering,

increased metabolism…• (Look at Mo, Ok, Tx, Ks.)

– Food-supply may be more critical

– Global Warming & the Armadillos that ate Manhattan?

Priodontes maximus

• 100cm h-b, 70kg (? still, largest living xenarthran).

• Once widespread across South American plains.

• Digs shelters, often in active termite mounds.

• Main food is termites (+ a few ants; feeding strategy not like giant anteater).

• Highly endangered by habitat modification and direct exploitation.

Cabassosus tatouay• 20-45cm h-b,

5kg.• Main food is

fossorial insects (mostly ants & termites?); sticky tongue.

• Middle claw greatly enlarged (root-cutting).

• Usually produces 1 baby/litter.

• Endangered by habitat destruction.

Tolypeutes matacus• 30cm h-b, 1.5-1.8kg.• Probably eats mostly

ants & termites.• Karyotypically very

different from all other armadillos (2n=38; all other armadillos 2n=50-64).

• Bears single young.• Only armadillo genus that

can roll into a complete ball.

Chaetophractus: Fairy armadillos• This variable genus

includes at least 3 species of small (c. 25cm) armadillos.

• Thermoregulatory strategy includes burrows several meters long.

• Chaetophractus includes much plant material in diet. It is known for burrowing under carcasses to obtain maggots.

Euphractus sexcinctus

• 40cm h-b, 3-7kg.• South American dry

& seasonally inundated prairies.

• Spends most of day in burrow.

• Not commonly exploited for food.

Zaedyus: the pichi• Head-body length

is 25-35cm.• Food is typical of

armadillos though pichis are said to include a fair amount of plant material in diet.

• These armadillos inhabit sandy soils in southern South America.

• Litter is 1-3 young; weaning occurs at about 6 months.

Family Glyptodontidae (extinct)• Glyptodonts were distant

relatives of armadillos.– More completely armored.– Larger; grazers.

• Once, successful invaders of the North (including South Carolina).

• Possible causes of extinction:– Competition?– Climate?– People?

Order Pholidota (pangolins)• Taxonomic position unclear; once classified

with xenarthrans in Edentata; now believed to be more closely related to Carnivora.

• No teeth. Long, sticky tongues. Bodies covered with scales derived from agglutinated hairs.

• Pangolins can be highly selective in diet, often moving great distances (at night) and scraping in soil only lightly for preferred ant type.

• Pangolins pay role in traditional medicine and folklore (& are heavily exploited in some areas).

African pangolins

• Manis tetradactyla (top)

• M. temmincki (bottom)• 60cm, 7-15kg.• Burrow well and climb

OK.• Eat mostly termites

(plus some ants).• Mother carries single

young on back or curled in tail.

• Can ball up completely.

Manis javanica: an Asian pangolin

• Total length 80-90cm.– Males are larger and

are known to fight violently over females.

• Less armored than African species.

• An ant and termite predator estimated (uh, by whom?) to take about 70 million insects per year.