There are about 57,000 vertebrate species, which is a tiny amount when compared to the 1 million insect species on the planet. What vertebrates lack in quantity, they make up for in diversity, with traits such as body mass differing significantly. Vertebrates include the largest creatures to ever walk on earth, plant-eating dinosaurs weighing up to 40,000 kg (more than 13 pickup trucks).

The blue whale, which may weigh more than 100,000 kg, is the largest mammal known to have lived on Earth. On the opposite end of the scale, the fish Schindleria brevipinguis is just 8.4 mm long and weighs about 100 billion times less than a blue whale.

Chordates have a notochord and a hollow dorsal nerve cord.

Vertebrates are chordates, which are part of the phylum Chordata. Chordates are bilaterian (bilaterally symmetrical) creatures that belong to the Deuterostomia group of animals within Bilateria. There are two families of invertebrate deuterostomes that are more closely linked to vertebrates than to other invertebrates: cephalochordates and urochordates. As a result, these two invertebrate taxa, together with vertebrates, are classed as chordates.

Lancelets (Cephalochordata), which receive their name from their bladelike form, are the most basal (earliest diverging) group of extant chordates (as shown in the image attached). Lancelets have a notochord, a dorsal, hollow nerve cord, many pharyngeal slits, and a post-anal tail as larvae. The larvae feed on plankton in the water column, swimming upward and sinking passively. Plankton and other suspended particles are trapped in the larvae's throat as they sink.

Adult lancelets can grow to be 6 cm long. They maintain essential chordate characteristics and resemble the idealized chordate.

A mature lancelet swims down to the seabed and wriggles backward into the sand, leaving just its anterior end exposed after transformation. Cilia pour seawater into the mouth of the lancelet.

As water flows through the pharyngeal slits, a net of mucus produced across the openings eliminates small food particles, and the trapped food reaches the gut. Gas exchange occurs mostly over the exterior body surface, with the pharynx and pharyngeal slits playing a minor role.

A lancelet will often exit its burrow to swim to a new site. Despite being poor swimmers, these invertebrate chordates exhibit the swimming mechanism of fishes in a simplified manner.

Although lancelets and tunicates are relatively unknown creatures, they play important roles in the development of life and can shed light on the origins of vertebrates.

As you may know, lancelets exhibit essential chordate characteristics as adults and their lineage branches from the chordate evolutionary tree's base. These findings imply that the ancestral chordate resembled a lancelet, featuring an anterior end with a mouth, a notochord, a dorsal, hollow nerve cord, pharyngeal slits, and a post-anal tail.

Lancelet’s research has also provided crucial insights into the development of the chordate brain. Lancelets lacks a full-fledged brain and instead have a little enlarged tip on the anterior end of their dorsal nerve cord, as shown in the image attatched. However, the same Hox genes that organize key areas of vertebrates' forebrain, midbrain, and hindbrain express themselves in a similar way in this tiny cluster of cells in the lancelet's nerve cord. This implies that the vertebrate brain evolved from an evolutionary structure comparable to the simple nerve cord terminal of the lancelet.

In the case of tunicates, several of their genomes have been entirely sequenced and may be used to identify genes that are likely to be present.

Vertebrates are chordates (animals with a backbone).

A lineage of chordates gave rise to vertebrates half a billion years ago during the Cambrian epoch. With a more complicated neural system and a skeletal structure than their forebears, vertebrates were more effective at two crucial tasks: collecting food and avoiding being devoured.

Developmental gene expression in lancelets and vertebrates. Hox genes (particularly BF1, Otx, and Hox3) regulate the development of key brain areas in vertebrates.

In both lancelets and vertebrates, these genes are expressed in the same anterior-to-posterior order. Each colored bar is placed above the region of the brain whose development that gene regulates.

Humans are animals that walk on two legs and have big brains.

Human-derived characteristics include bipedalism, a bigger brain, and a smaller jaw as compared to other apes.

Hominins—humans and animals more closely related to humans than chimps—emerged in Africa some 6 million years ago. Although early hominins had a tiny brain, they most likely walked upright.

The earliest evidence of tool usage dates back 2.5 million years. The first completely bipedal, large-brained hominid was Homo ergaster. The first hominid to leave Africa was Homo erectus.

From around 350,000 to 28,000 years ago, Neanderthals inhabited Europe and the Near East.