Understanding Vertebrates: From Fish to Mammals

Posted on Nov 19, 2024 in Biology

Vertebrates

Vertebrates have bilateral symmetry and are equipped with a skull that protects the brain and a cartilaginous or bony skeleton, including a vertebral column. The typical vertebra has the body clearly divided into three regions: head, trunk, and tail.

Chordata

Deuterostomia, bilateral symmetry, segmented body, triploblasty (three germ layers), well-developed coelom (lost in some groups).

Features:

  • They have a hollow, tubular nerve cord, dorsal to the gut (epineurium). From this ridge, in more complex animals, the brain and the neural spine develop.
  • They have a support structure in the dorsal position, called a notochord. It extends throughout the body. In some groups, it persists throughout life; in others, it is replaced by the spine.
  • They have pharyngeal slits (pharyngotremes) at some stage of development. In terrestrial vertebrates, these slits are lost in the adult animal.
  • With endostyle pharynx (Urochordata and cephalochordates) or homologous (thyroid gland) in vertebrates.
  • They have a complete digestive tract (mouth and anus) with specialized regions.
  • They reproduce sexually; most have separate sexes.
  • Heart ventral to the digestive tract.
  • Segmented musculature.
  • Postanal muscular tail and locomotor development in some state.
  • Radial holoblastic, subequal segmentation.
  • Tadpole larva stage at some point in development.

Fish

  • The body is covered with scales.
  • Their extremities are shaped like fins. Their body ends in a stronger flap that forms the tail.
  • Their skeleton is the simplest of the vertebrates. Most fish have a bone skeleton with a bone-shaped spine. Some fish, including sharks and rays, have a cartilaginous skeleton made up of softer and more flexible parts than bones, called cartilage.
  • The body temperature is variable, meaning it depends on the temperature of the water in which they find themselves. That’s why we say they are cold-blooded animals.
  • Almost all fish have a swim bladder, which is like a bag full of air that prevents them from sinking.
  • Fish breathe through gills, which are a group of thin plates arranged in several rows. The gills are located behind the head and allow them to get the oxygen dissolved in water.

Amphibians

The head is attached directly to the trunk, so there is no neck. It has a mouth, eyes with upper and lower eyelids, nostrils, ears, and paratoid glands. The skin, which helps with cutaneous respiration, is naked (contains no kind of tegumentary annex, such as hairs or scales). The skin contains several layers and is renewed periodically by a process of molting. The skin glands are more developed than in fish; there are two types: mucous glands and venomous glands. Mucous glands secrete a colorless liquid that prevents desiccation. Venomous glands have a defensive function in response to predation because they produce irritating or poisonous substances. The color is usually cryptic, meaning it has the purpose of concealing or confusing the animal with its environment. The arrangement of bones and muscles of the anterior and posterior limbs of tetrapods is an amazing record, despite the different uses intended. The mouth is large enough, sometimes being provided with small, weak teeth. The tongue is fleshy and in some groups is supported by the anterior and free from behind so it can be projected to the outside for capturing prey. The cloaca is a chamber into which the digestive, urinary, and reproductive systems empty, with a single outlet to the outside. Respiration is by gills (external or internal). They have separate sexes, with internal and external fertilization, being mostly oviparous. Eggs hatch, and larvae, often called tadpoles, emerge. The larvae of amphibians live in freshwater, while adults usually lead a semi-terrestrial life.

Reptiles

  1. They are terrestrial vertebrates, with the body usually covered with scales.
  2. They have short limbs, which are lateral or absent.
  3. They have scaly skin, shields, or horny plates.
  4. They are cold-blooded and spend the winter hibernating.
  5. They breathe with lungs and skin.
  6. They reproduce by eggs that usually hatch because they have internal fertilization.
  7. Their heart has two atria and a ventricle with one or two cavities.

Birds

Birds are vertebrates, warm-blooded, walking, jumping, or maintained only on the hindlimbs, while the forelimbs are modified as wings. Like many other unique anatomical features, these are adaptations for flying, but not all birds fly. Their bodies are covered with feathers and, in today’s birds, a toothless horny beak. To reproduce, they lay eggs that hatch. Birds inhabit all terrestrial biomes and all oceans.

Mammals

  • Their bodies are covered with hair.
  • Females have breasts that secrete milk to feed their young.
  • They have lips and teeth. Their lips suck the milk without causing harm. Some whales have teeth replaced by thin sheets called baleen.
  • The limbs are usually turned into legs, which serve to move. Aquatic mammals have fins turned into limbs, and flying mammals, like bats, have membranes in their forelimbs turned into wings, which they use to fly.
  • They have a constant temperature (warm-blooded): the temperature of their body does not change with the exterior.
  • They breathe with lungs. Aquatic mammals have to go out to the water surface to take oxygen from the air.
  • Their circulation is double and complete.
  • Most are viviparous.

Carnivora

  • The head:
    • The ears: They are stiff, small, and with fine hearing.
    • The eyes: They glow with changing pupils, depending on whether there is more or less brightness.
    • The muzzle: It is small, short, and surrounded by long whiskers.
    • The nostrils: For breathing. They have lung respiration.
    • The mouth: With pointed teeth, tusks, and well-developed carnivorous teeth.
    • The tongue: With many papillae to lick wounds.
  • The trunk: It is very flexible and agile. The hair on the back electrifies easily.
  • The legs: They are formed by four legs which end in four fingers. The supporting fingers rest on a soft cushion, making their departure very quiet. They have long fingernails or curved retractable claws. The claws are cramped and extended when attacking their prey.
  • The digestive system: The mouth has lips, teeth with cavities for chewing, the stomach is simple, and there is a large intestine but no cloaca.

Herbivores

Their feet are adapted for running to escape in case of danger. Their stomach is divided into four compartments; they swallow a lot of food in a short time and later crush it. They have a very particular way of eating (eating plants). Their stomach is divided into four compartments: rumen, reticulum, omasum, and abomasum.

Water Mammals

The known mammalian animals, pinnate mammals, have their limbs transformed into wings, which enables them to live in water and have a fish-like form. Their tail is very robust for propulsion. The pelvic limb is atrophied or not diverted, and they use the pectoral and tail for locomotion.

Primates

They are placental animals. They have complete dentition similar to that of humans, prehensile limbs, an omnivorous regime, and a thumb opposed to the other digits, at least in the forelimbs. They have forward vision and eyes in relief. They have a pair of pectoral breasts. They lead an arboreal life.