Which Phylum Are Reptiles In?

All living organisms are classified first by the kingdom to which they belong: Animalia (animals), Plantae (plants), Protista (single-celled organisms), Fungi (mushrooms, mold, and yeast) and Monera (bacteria). Within the kingdom Animalia, which encompasses all animals, there are fourteen Phylum, which begin to break down the kingdom into more recognizable categories. The best-known Phylum within the animal kingdom is Chordata: animals with skeletons including spinal chords.

  1. What is a Reptile?

    • Reptiles are four-legged creatures who dwell primarily on land and lay eggs. Reptile eggs have hard, waterproof shells containing amniotic fluid in which offspring develop and grow. Some reptiles have adapted to spending time in the water, such as crocodiles, alligators and turtles. While some live in water, all reptiles breathe through lungs and have, or had, legs with feet, toes and claws.

    Snakes

    • While snakes move in a unique fashion that makes it appear they are boneless, or at least spineless, they do in fact have spines, a ribcage and skulls. Snakes have very complex spines with up to 200 individual vertebrae that allow them more flexibility in their slithering movement. They do not, however, have legs, which would seem to eliminate them from being reptiles. In fact, snakes did have four legs at some point in their evolution, and are thus still classified as tetrapods and, consequently, still reptiles.

    Birds

    • Birds have spines, lay eggs and have scaly skin, visible on their legs, that protect them from drying out, as does all reptile skin. Birds are descendents of small meat-eating dinosaurs and meet all the criteria of reptiles, including membership in the same phylum. Birds are classified as reptiles. Birds begin to differ from other reptiles in the next taxonomical level, Order, in which birds are classified as Aves.

    Phylum of Reptiles

    • Because all reptiles have spines, all reptiles are members of the Phylum Chordata. Chordates have a dorsal spinal cord culminating in a brain. In addition to this cord, chordates have notochords, which allow them to move. In most reptiles, the notochord, usually a semi-flexible rod running the length of the body, hardens into vertebrae at some point in development. As in the case of snakes, the notochord can be made of up to 200 vertebrae to allow for flexibility needed for the animal's movement. The final trait shared by all chordates is pharyngeal slits, or gills, which are also present on reptiles during early stages of their development. Chordates that have adapted to live on land lose these, usually before birth, or hatching in the case of reptiles.