Why even the jaguar fears a mere anteater

The giant anteater (https://en.wikipedia.org/wiki/Giant_anteater and https://www.cambridge.org/core/journals/journal-of-zoology/article/abs/morphology-evolution-and-function-of-feeding-in-the-giant-anteater-myrmecophaga-tridactyla/A17370E51494B916705EEDA3F12440D2) and its small relatives the tamanduas (https://en.wikipedia.org/wiki/Tamandua) seem surprisingly nonchalant, for small-brained, toothless mammals with such slow metabolism that they cannot outdistance most predators.

This confidence may be based on a 'superpower' unique to the anteaters of central and South America.

The triceps (https://en.wikipedia.org/wiki/Triceps) is a major muscle on the upper fore limb which straightens the limb (think of pushups). It is particularly well-developed in the Myrmecophagidae. These anteaters find food by scratching into hard surfaces with their fore limbs, which are twice as muscular as their hind limbs.

However, the giant anteater and tamanduas are unusual among mammals in that the triceps is attached not only in the usual way to the ulna, but also by means of an extended tendon to the main claw-bearing digits (https://periodicos.uem.br/ojs/index.php/ArqMudi/article/view/55345 and https://books.google.com.au/books?hl=en&lr=&id=CxZjAAAAcAAJ&oi=fnd&pg=PA1&dq=Triceps+myrmecophaga&ots=zSWmSTmxKF&sig=Nfn_Pc4zKr4iEqsh0j70FnjgrFE#v=onepage&q=Triceps%20myrmecophaga&f=false and https://onlinelibrary.wiley.com/doi/10.1002/jmor.1051570307 and https://bioone.org/journals/journal-of-zoo-and-wildlife-medicine/volume-47/issue-3/2015-0236.1/GROSS-ANATOMY-AND-SURGICAL-APPROACH-TO-THE-HUMERAL-SHAFT-IN/10.1638/2015-0236.1.short and https://academic.oup.com/mspecies/article/50/956/1/4968042?login=true and https://anatomypubs.onlinelibrary.wiley.com/doi/abs/10.1002/ar.24502.

The apparent result is that:

  • the muscular power whereby these animals squeeze-impale attackers with their claws is that of not only the 'forearm' but also the 'upper arm', and
  • maximum force can be applied by the claws while the fore limb is stretched out, keeping the opponent safely at arm's length.

The unusual development of this flexion mechanism (which facilitates both breaking into termitaria/wood and talon-like stabbing) helps to explain why the giant anteater can sometimes stare down even the jaguar (Panthera onca), and why tamanduas choose to stand confidently with fore legs spread when approached.

Effectively the giant anteater has substitutes for canine teeth, longer than the teeth of the jaguar, and these are powered by muscles and tendons superior to the jaw muscles of the jaguar.

It is this largely unapparent weaponry that seems to be the basis for the warning colouration on the forequarters, and most distinctly on the fore foot of the giant anteater.

The aposematic pattern of the giant anteater includes a dark bar on the pale fore feet, as if to draw particular attention to the hazard hidden there (https://www.inaturalist.org/observations/66556791 and http://ianloydwildlife.blogspot.com/2013/09/ and https://www.youtube.com/watch?v=7xjImFKyEY4 and https://www.gettyimages.com.au/detail/news-photo/newborn-baby-giant-anteater-rides-on-the-back-of-his-mom-news-photo/108204761 and https://www.quora.com/What-are-ways-anteaters-protect-themselves).

In tamanduas, the dark band on the otherwise pale shoulders does not emphasise the fore limbs particularly (see video in https://didyouknowpets.com/having-a-tamandua-as-a-pet/). However, the defensive posture displays the claws and the brawniness of the fore limbs (http://justfunfacts.com/wp-content/uploads/2016/09/anteater-standing-up.jpg and https://www.memecenter.com/fun/1617805/aggressive-ant-eater/comments).

When juveniles ride the mothers, the banding on the shoulders is reinforced rather than disrupted, suggesting self-advertisement rather than camouflage.

See:

These anteaters differ from unambivalently aposematic mammals such as skunks because their conspicuous features of colouration remain partial/subtle enough to allow the animals to blend in when stationary. In the case of the giant anteater, the plain-coloured tail balances the functions of the bold markings. It can alternately cover and disguise the sleeping body, or expand in profile to exaggerate the body size of the animal in defensive display.

In the case of tamanduas the conspicuous pattern is absent in many individuals in a complex system which includes plain, all-pale and all-dark colour-morphs within a given population, plus geographic variation among populations.

However, warning colouration is well-developed enough, overall, in these anteaters to give pause to relatively big-brained carnivores such as felids and canids. In tamanduas the aposematism may be based largely on the noxious secretions of the anal glands, but in the giant anteater it is surely based on claws, the power of which is not self-evident.

הועלה ב-אוקטובר 29, 2021 11:56 לפנה"צ על ידי milewski milewski

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The giant anteater seems to be diurnal by preference, and tamanduas seem as active by day as at night. This readiness to appear in broad daylight contrasts with the giant armadillo (Priodontes maximus) and the aardvark (Orycteropus afer), which are nocturnal. The daytime activity of Myrmecophaga and Tamandua may indicate not only the confidence they have in their anti-predator defences, but also the warning function of their colouration. This is because aposematism depends on sufficient illumination: the sinister patterns of colouration need to be visible to predators.

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