Are sharks tetrapods, and how did they evolve? Learn about the Phylogeny of tetrapods and the evolution of their tongues. In addition, you’ll learn about viviparous sharks. If you’d like to learn more about the evolution of tetrapod tongues, read these articles. They’ll help you make your decision!
Phylogeny of tetrapods
Recent genetic analyses of the ribosomal RNA genes of tetrapod sharks have revealed a resemblance between the true sharks and skates, but some differences remain. The phylogeny of tetrapod sharks is monophyletic within the sarcopterygian order, tetrapoda. Scientists at the University of Colorado, Boulder, and LSU, for example, determined that the rays and skates of the Silurian period are closely related to those of the Selachii, but the tetrapods of the current day are very different.
In addition to differences in limb-type and structure, tetrapods differ from apes in their evolution. Their limbs and fins have separate axes, and the front of their skull is longer than the hind fin. Despite this similarity, tetrapods evolved four distinct methods of respiration to survive: the gills, the muscles and the tongue.
Origin of tetrapods
The origin of tetrapods in shark species was first proposed more than a million years ago, and it is still debated today. The earliest tetrapods had flat skulls with eyes on top and an elongated front end, allowing them to see and hear in the air. When tetrapods moved onto land, they developed tall skulls with eyes facing forward.
After evolution of tetrapods, these fish evolved gills and lungs, and the first tetrapod-like fish was Panderichthys. Its limb-like fins were adapted for life in shallow, muddy waters. Later, tetrapods evolved limb-like fins to survive in oxygen-poor seas.
The earliest tetrapods had eight digits on each limb. Over time, some digits were lost. Later, there were seven-digit animals, and finally, five-digit tetrapods became common. Although the evolutionary timeline of tetrapods is still controversial, the Tiktaalik fossil shows the earliest tetrapods had digits.
Evolution of tetrapod tongue
Scientists typically investigate the evolution of limbs in ancient animals, such as tetrapods. But a recent study suggests that early tetrapods acquired the ability to eat on land and developed tongues. That evolution is similar to amphibious fish, which emerge onto land with mouths full of water. The evolution of the tetrapod tongue may offer clues about the origin of this organ.
The transition from fins to limbs began in the water, where buoyancy favored flexibility and movement over support. This transition would have resulted in limbs that pushed the fish-tetrapod forward. It is probable that the fish limbs first developed the elbow, wrist, and knee joints. The limbs of a fish tetrapod likely began development of a knee, elbow, and ankle joints.
In early tetrapods, the tongue evolved in order to carry food to their mouths. Essentially, they would have crawled along the Devonian shorelines, bringing their food to their mouth. Once they arrived, they would have tilted their heads backward and dropped their prey in their mouths. The tongue then moved the food to their throat, where it would be swallowed. This motion is similar to that of fish, where they suction food into their mouths.