3 major adaptations allowed mammals to retain their embryos in their reproductive tract and become viviparous. Mammals reproduce sexually through internal fertilization. Another adaptation of sea turtles to the sea is a hinge in the lower portion of the turtle that allows them to take in much more air and come up for air less often. The progeny feed on a skin layer that is specially developed by the adult in a phenomenon known as maternal dermatophagy. The surface cells of the morula become the trophoblast and the inner cell mass gives rise to the embryo (the formative cells) and also its yolk sac, amnion, and allantois. b. Crocodilians and chelonians (turtles) have a penis (phallus), a median thickening in the floor of the cloaca consisting of two cylinders of spongy vascular erectile tissue, the corpora spongiosa. The clasper, supported by modified fin cartilages, contains a groove along which sperm are conveyed into the uterus and is raised, or erected, by muscles at its base. A layer of endoderm is formed adjoining the cavity of the blastocyst, and an amniotic cavity develops, enclosing the embryo; in lower placental mammals, the allantois also develops. This attachment, or implantation, a crucial step in the development of a mammal, is attained through the action of the trophoblast, which forms extensions, known as villi, that penetrate the uterine wall. In higher mammals the penis has been modified. Aquatic: mammals trained to live in aquatic environments, both in fresh and salt water. Reproductive strategies of species are diversified into numerous adaptations to a large variety of aquatic environments. In the initial stages of pregnancy, the continued existence of the embryo in the uterus depends on the hormone progesterone, which is secreted by the corpora lutea, “yellow bodies,” that develop in the ovary after an egg has been released. Similarly, all sirenians are obligate swimmers. 4. The latter begins on the pelvic floor as the bulb of the penis and contains a dilation of the urethra (urethral bulb). All mammals have internal fertilization and an erectile penis. This diversity may concern sexuality, spawning and parental behaviour, sensitivity to environmental fact … In placental mammals, the reproductive structures have become specialized to facilitate giving live birth. When the spongy bodies are no longer filled with blood, the retractor muscle returns the penis to the cloacal floor. Skeletal adaptations during mammalian reproduction B.M. In hyenas, the clitoris is large and often mistaken for a penis, and female scrotal pouches, lacking gonads, are present. The caudal tip of the penis protrudes into the cloaca as a genital tubercle, or glans penis. Adaptations for internal fertilization Fertilization among vertebrates may be external or internal, but internal fertilization is not always correlated with viviparity or the presence of intromittent (copulatory) organs. Author information: (1)Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvagen 18 D, 752 36 Uppsala, Sweden. How is sexual reproduction an advantage for terrestrial mammals? 2. Berlin S(1), Smith NG. Mammals with adaptations to jumping: The most prominent are the lagomorphs , their long hind limbs enable them to run and make great jumps. The male reproductive system consists of external organs. All living organisms reproduce. Home / Pets & Animals / Animal Reproduction / What Are the Adaptations of Terrestrial Animals? A mammal’s adaptations for attack and defense and its specializations for finding, capturing, chewing, swallowing, and digesting food all determine a mammal’s shape and habits. In a few mammals (some rodents, insectivores, lemurs, and hyenas) the urethral canal becomes enclosed within the clitoris, as in males. The male urodele deposits a spermatophore that the female picks up with the lips of her cloaca. Reproduction in Mammals A. In the young spider monkey Ateles, the clitoris is six or seven centimetres (2.4 to 2.8 inches) long. Except in ruminants (i.e., cud-chewing animals, such as cattle and deer), cetaceans, and some rodents, the penis terminates in a glans penis, a swelling of the corpus spongiosum that caps the ends of the corpora cavernosa and contains the urinogenital aperture. In some cattle, a sigmoid, or S-shaped, flexure bends the penis, which otherwise would be too long to fit into the preputial sac. The spermatic duct opens on one side of the papilla. Contraction of the uterine wall first releases the fetus from the uterus; the fetal parts of the placenta (the afterbirth) follow. Hemipenes protrude independently of each other and are often covered with spines. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. One example of adaptation is the lungs of mammals being adapted explicitly for breathing on dry land, while fish have gills adapted for breathing in water. Yaks, rabbits, cows, hippopotamuses, bats and humans all fall within this category. While implantation takes place, the formative cells arrange themselves in the form of a disk under the trophoblast. The mesodermal layer adjoining the notochord becomes thickened and, by transverse crevices, subdivided into sections called somites. Rather early the mesodermal mantle splits into two layers, the outer parietal (somatic) layer and the inner visceral (splanchnic) layer, separated by a narrow cavity that will expand later to form the coelomic, or secondary, body cavity. 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