What is a Vertebrate?
Here’s a fun question: What do you have in common with all other mammals, birds, amphibians, reptiles, and fish? The answer is, a backbone or nerve cord. While that may not seem like anything special, it’s something that 90% of the animal kingdom doesn’t have.
The backbone is a very useful adaptation. It protects the vulnerable spinal cord and provides structure for the rest of the body. The bony spinal column and bony skeleton found in most vertebrates allows more muscle attachment and complicated movement than most invertebrate animals. It also allows us to grow bigger than the vast majority of invertebrate animals, because we aren’t constrained by an external skeleton.
Since we need big brains to move our big, complicated bodies, vertebrates tend to be significantly more intelligent than invertebrates. Some invertebrates, like jellyfish and sea stars, don’t even have brains! The exception to this rule is cephalopods like octopuses, which have been shown to be incredibly intelligent for an invertebrate.
The first vertebrates appeared on Earth around 500 to 600 million years ago, with is very recent compared to most invertebrate lineages. Early vertebrates resembled the hagfish that live on earth today, and had a nerve cord but no bony spinal column.
Over time, these primitive fishes evolved both a spinal column and jaw that was made of bone, though the rest of their skeleton was likely made of cartilage like modern sharks and rays. Eventually some fish evolved a full bone skeleton and the rest, as they say, is history.
It’s hard to believe since they look nothing like us, but our closest relatives in the invertebrate world are echinoderms like sea stars, brittle stars, and sea cucumbers. We all belong to a group of animals called “deuterostomes”, which are grouped together because during embryo development the anus forms before the mouth.
Pippir, Jochen (photographer). (2015). Spine Backbone Vertebrae [photography]. Retrieved from