Which vertebrates have internal fertilization

Development of the pelvic fins of Acipenser ruthenus. New data for the theory of the paired fins of fishes. Reproduction in the Middle Triassic actinopterygians; complex fin structures and evidence of viviparity in fossil fishes. Schultze, H. Early growth stages in coelacanth fishes. New Biol. Lund, R. Viviparity and interuterine feeding in a new holocephalan fish from the Lower Carboniferous of Montana. Science , — Miles, R. Observations on the ptyctodont fish, Rhamphodopsis Watson.

The relationships of placoderm fishes. Anatomical Studies on the Arthrodiran Head. Svenska Vetensk. Download references. We thank M. Brazeau for access to his manuscript before publication, A. Ritchie for discussions, and G.

Young and G. Edgecombe for reviewing the manuscript. We also thank K. Bifield for the photograph of WAM Author Contributions All three authors contributed equally to the description of the new embryos and arthrodire pelvic structures, and to the general discussion; J.

You can also search for this author in PubMed Google Scholar. Correspondence to John A. Reprints and Permissions. Devonian arthrodire embryos and the origin of internal fertilization in vertebrates.

Download citation. This was a key development since fertilization in insects can be timed with environmental or food conditions that are optimal for offspring survival. Vertebrates have similar structures i. Non-mammals, such as birds and reptiles, have a common body opening, called a cloaca, for the digestive, excretory, and reproductive systems. Coupling between birds usually involves positioning the cloaca openings opposite each other for transfer of sperm.

In mammals, there are separate openings for the systems in the female and a uterus for support of developing offspring. Depending on the type of species, there are differences in the uterus. In species that produce large numbers of offspring, the uterus has two chambers.

In other species that produce one offspring, such as in primates, there is a single uterus. Another development in the evolution of reproduction is the means by which sperm is transferred. All of these methods of sperm transfer represent the varying ways reproduction has evolved and become specialized to specific organisms. Privacy Policy. Skip to main content. Animal Reproduction and Development. Search for:. External and Internal Fertilization External and internal fertilization are forms of reproduction that vary in method and embryo development.

Learning Objectives Compare and contrast external and internal methods of fertilization. Key Takeaways Key Points External fertilization is characterized by the release of both sperm and eggs into an external environment; sperm will fertilize the egg outside of the organism, as seen in spawning.

Internal fertilization is characterized by sperm fertilizing the egg within the female; the three methods include: oviparity egg laid outside female body , ovoviparity egg held within female , and viviparity development within female followed by live birth. Internal fertilization protects the fertilized egg or embryo from predation and harsh environments, which results in higher survival rates than can occur with external fertilization.

Ovoviparity is characterized by an organism retaining a fertilized egg inside the body where development occurs and nourishment is received from the yolk.

An international team of researchers reached this conclusion after examining fossil antiarchs and spotting some previously overlooked telltale anatomy: male copulatory claspers and female dermal plates, similar to what is found in modern-day sharks. The researchers think that antiarch males used those bony protuberances to grasp the female from the side, and that her two dermal plates helped facilitate that exchange.

Whether antiarchs' choice reproductive strategy represented the norm for all early vertebrates or whether they alone had figured out the anatomical secret for internal fertilization remains unknown. External fertilization usually occurs in aquatic environments where both eggs and sperm are released into the water. After the sperm reaches the egg, fertilization can then take place. Most external fertilization happens during the process of spawning where one or several females release their eggs and the male s release sperm in the same area, at the same time.

The release of the reproductive material may be triggered by water temperature or the length of daylight. Nearly all fish spawn, as do crustaceans such as crabs and shrimp , mollusks such as oysters , squid, and echinoderms such as sea urchins and sea cucumbers.

Pairs of fish that are not broadcast spawners may exhibit courtship behavior. This allows the female to select a particular male. The trigger for egg and sperm release spawning causes the egg and sperm to be placed in a small area, enhancing the possibility of fertilization.

External fertilization in an aquatic environment protects the eggs from drying out.