Preserved Vertebrates
Examining animals defined by backbones and internal skeletons.
Overview
Vertebrata is a subphylum of chordates that includes animals with a backbone or spinal column. Approximately 57,739 vertebrate species have been described. Vertebrates first evolved around 530 million years ago during the Cambrian explosion, with the earliest known vertebrate identified as Myllokunmingia. The name Vertebrata is derived from the vertebrae, the bones that form the spinal column.
General Characteristics
Vertebrates represent the largest subphylum of chordates and include many animals familiar to humans, such as fish, amphibians, reptiles, birds, and mammals. Most vertebrates possess a muscular system organized into paired masses and a central nervous system that is at least partly enclosed within the backbone.
Defining Features
Vertebrates are often defined by the presence of a backbone, brain case, and internal skeleton, although these traits are not universal across all members. Jawless vertebrates such as lampreys lack some of these defining features. A more consistent characteristic of vertebrates is the presence of a distinct head with concentrated sensory organs, particularly eyes, and a high degree of cephalization. This distinguishes vertebrates from other chordates such as lancelets, which lack a true head.
Skeleton and Body Structure
The internal skeleton of vertebrates is composed of cartilage, bone, or a combination of both. The earliest vertebrates developed external bony armor, which may have served as a phosphate reservoir while also providing protection. The skeleton supports the body during growth and allows vertebrates to reach larger sizes than most invertebrates.
In most vertebrates, the skeleton includes a skull, vertebral column, and two pairs of limbs. In some groups, such as snakes and whales, one or both pairs of limbs have been reduced or lost over evolutionary time.
Major Vertebrate Groups
Preserved vertebrate specimens commonly represent major groups that illustrate structural diversity, evolutionary history, and adaptations to different environments. These include jawless fishes, amphibians, reptiles, birds, mammals, and multiple lineages of fish.
Agnatha
Agnatha, meaning “no jaws,” is a paraphyletic superclass of jawless fishes. The two surviving groups are lampreys and hagfish, with approximately 60 living species combined.
Amphibians
Amphibians (class Amphibia) are vertebrates that include tetrapods lacking amniotic eggs. These ectothermic animals typically divide their lives between aquatic and terrestrial environments and lack many of the adaptations required for a fully terrestrial existence.
Birds
Birds are bipedal, warm-blooded, egg-laying vertebrates characterized by feathers, forelimbs modified as wings, and lightweight hollow bones.
Chondrichthyes
Chondrichthyes, or cartilaginous fishes, include sharks and their relatives. These jawed fishes possess paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made primarily of cartilage rather than bone.
Mammals
Mammals are vertebrates distinguished by mammary glands that produce milk for nourishing young, the presence of hair or fur, and endothermic, or warm-blooded, physiology.
Osteichthyes
Osteichthyes, or bony fishes, form a major superclass that includes ray-finned fishes (Actinopterygii) and lobe-finned fishes (Sarcopterygii). This group represents the largest diversity of fish species.
Reptiles
Reptiles are tetrapods and amniotes whose embryos develop within an amniotic membrane. Living reptiles are represented by four surviving orders: Crocodilia, Rhynchocephalia, Squamata, and Testudines.