Hot answers tagged

84

Number of legs in terrestrial vertebrates Not only do mammals have four legs but actually all terrestrial vertebrates (which include mammals) have four legs. There are slight exceptions though as some lineages have lost their legs. Typically snakes have no legs anymore. Apesteguia and Zaher (2006) discuss the evolution of snakes legs reduction and report a ...


54

Short answer Technically, only mammals lactate. To lactate means to produce milk from the mammaries to feed a baby or young animal. Milk, in turn, is defined as the secretions from mammary glands. However, there are animals other than mammals that produce milk-like substances to feed their young. Background Both male and female pigeons (Columba livia) ...


36

I'll focus on whales and dolphins (cetaceans) as you mention them by name and they are representative for other marine mammals such as seals or manatees. The evolution of cetaceans was one of the fascinating evolutionary mysteries. Clearly, they were mammals, but which mammals were their closest relatives? Clues to solve this mystery began to appear in the ...


36

Really interesting question: The lethal yellow mutation (also abbreviated Ay) affects the agouti signalling protein which plays a major role in pigmentation. Heterozygous expression of it leads to the dominant expression of pheomelanin (which is yellow), causing the mice to express this color (among other effects). To understand why it is homozygous ...


30

1. Sheep are fearless 2. English common names are misleading when it comes to the genetic differences between goats and sheep You posted a picture of Mountain Goats (Oreamnos americanus), which are a different genus than Domestic Goats (Capra aegagrus). Both Capra and Oreamnos are members of the Subfamily Caprinae, as are Domestic Sheep (Ovis aries). ...


28

Producing milk, per se, is a strictly mammalian phenomenon. There are functionally similar processes in non-mammals (e.g., 'crop milk', produced by some birds), but because these processes evolved independently from the evolution of mammalian milk, they are not considered to truly be milk.


26

I'm almost certain that your question is based on the press that Patricia J Yang's research is receiving (e.g., here and here). Yang and her co-authors examined the structure and mechanics of some dead wombats to investigate this question further. They found that varying degrees of pressure in the latter portion of the wombat's intestines (in conjunction ...


20

I know of an ER doctor who had a patient who removed (by biting and pulling) every last part of her tongue, she survived that (although, her ability to speak was probably shot). The stump of her tongue clotted before she could even go into shock (at least where it was really serious). Here is a quote from the book Angels in the ER (this is a paramedic ...


16

I think I might interpret your question as asking, not just why don't mammals have more than four limbs, but why arthropods have more variety. Insects have six, but others have eight, ten, or more. Partly there are just many more species of arthropods. 80% of animal species are some sort of arthropod, and some lineages of arthropods are distantly related ...


15

It is probably true that toilets and other resting-ish area are always a great place to think about biology, I agree $\ddot \smile$. Why do we urinate? In short, urine contains the waste from our blood while defecation is just the stuff that we haven't digested. Kidneys are the organs responsible for draining wastes (mostly nitrogen-containing, or ...


15

Male mice lack nipples too. Mice are frequently used for embryonic research as they are small and reproduce quickly. It is thought that male mice do develop nipples, but that they regress during development (Wysolmerski, 1998). In general, it is thought that mammalian organisms develop as females by default when there is no male (Y) chromosome present (...


14

Tree jumping. The obvious answer is that having a balancing ballast is incredibly handy for some of the death defying jumps squirrels perform. The tail is needed for that. A big bushy tail might be a good counter to predation. You make the assumption that an inconspicuous tail would be bad for predation. I would challenge that assumption, but I am making an ...


13

Most mammalian males have nipples. The duck-billed platypus does not have nipples but you begin to see development of nipples in marsupials (Park and Lindberg 2004) like the opossum and kangaroo. Development of a complete nipple begins in the eutherian (placental) mammals. The mammary glands develop early in the embryo along a pair of ridges called the ...


13

I agree with you that the question is ambiguous, and also that the most sensible answer would be C. However, one could make a more or less reasonable argument in favor of several other answers, too. a. The common ancestor of whales and fish possessed genes for fins. Technically, this statement is true. At least some of the fins of whales and fish are ...


12

You should also bear in mind that the fact that they are great climbers does not make them fearless. For example, if I were to find myself floating 500 meters above the ground, I would be terrified. The fact that birds do not appear to be scared in the same situation does not make them fearless, it just makes them fliers. Similarly, I am sure a fish would ...


12

This is a white morph red fox, not an arctic fox. As noted in the question, this fox has larger, more pointy ears than an arctic fox, and the second picture shows it to have a longer muzzle as well. Another clue is that these pictures were taken in the springtime or early summer (which you can tell from the new growth on the plants in the picture), and ...


11

Until someone has a better method to determine this, and I'm willing to go with idea of that this question is not answerable, I put forward the two likely forms of selection criteria: Which mammal has the highest percentage of keratin in it's body for the highest density, and which has the highest percentage of gas (over the day) for the lowest. I also ...


11

It's probably a dugong, based on the location, lack of a dorsal fin, split tail, lack of a blowhole, and narrowing of the snout. The prominent vertebral column looks unusual, but that might come from the strange posture it is being held in or from malnutrition. This publication from the Australian government shows necropsy of several dugongs (note, this ...


10

Among the great apes, chimpanzees and gorillas live in very hierarchical, male-dominated clans that are often in violent conflict with other clans. Bonobos, on the other hand, lead very peaceful lives, and are female-dominated, using sexual contact as a manner of communication to reduce tension within and between groups. Orangutans are largely solitary ...


10

I don't think, there is a precise answer about the evolutionary mechanisms, but "mechanically": mammals have principally just two types of pigments: eumelanin and pheomelanin, both of which have their color variants, but within a known range. Bird pigments, besides melanins, include carotenoids and porphyrins. Arthropods generally have carotenoids, melanins ...


10

The answer by Remi.B is excellent, I'll just attempt an explanation by way of gene networks: In genetics we see new genes "linking" to the older genome by regulation pathways and by being "fit" only in the context of the existing genome. This has the effect of making the older genes indispensable. Change them and you rupture the whole mesh. If you want to ...


10

@JM97 is correct. According to National Geographic >> The gestation period of a Red Kangaroo is 33 days and it's baby at birth weighs a mere 0.03 oz. To put it into a more precise perspective, on birth, the baby weighs 1/100,000 of an adult red kangaroo's weight. Second place goes to the baby of a Giant Panda; at birth it weighs 3.2oz which is 1/900 of ...


10

Sloths have long, thick, sticky tongues covered in a carpet of tiny, rear-ward pointing spikes that they can pull leaves in with. So the tongues are quite different from human tongues and likely much less "soft" to touch and more "rough". According to scanning electron microscopy studies on the topography of a sloth's tongue, the following results were ...


9

The answer really depends on what aspect of the urine and feces one is considering. On the atomic level, no, urine and feces are composed entirely of atoms taken from our environment. As one would expect, as there is no "Humanium" on the periodic table. In fact, all the atoms in urine and feces were originally created by stars. On the molecular level, yes. ...


9

The number of mammary glands a species has is related to litter size. The relationship generally follows the "one-half rule," which states that the average litter size is equal to half the number of mammaries. The number of mammaries also tends to put an upper limit on litter size. It's not necessarily a hard limit, but survival tends to drop noticeably when ...


9

Apparently the most noticeable research on this subject of a rabbit's white behind has been done by Dr Dirk Semmann of the University of Goettingen. He proposes that these spots actually confuse predators because of their very noticeable nature. By focusing on the bright spot, the would-be predator ignores the larger body of the animal. Then, when ...


9

Here is a more morphologic, less genetic answer: According to Sansom 2013, the 2 sets of paired appandages (shoulder and pelvic) was set in stone when agnathans transitioned into gnathostomes (ie. when the first vertebrate organisms began to evolve jaws, an anatomic change that allows for classification of different stages of history found in the fossil ...


9

Feral camels have environmental, economic and cultural impacts in Australia's Northern Territory (Dept of Land Resource Management, Australia). In central Australia, camels feed on more than 80% of the available plant species. Feral camels severely defoliate and suppress the recruitment of some shrub and tree species, with such impacts being greatly ...


9

On a more serious note than my comment, and as a supplement to theforestecologist's answer, it's worth pointing out that a cube with rounded corners and edges has larger surface area to volume ratio than a spherical dropping, making it more efficient for the reabsorbtion of moisture, which would be an evolutionary advantage in a place where water is in short ...


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