Such a scenario would also explain why the lancelet amphioxus, a 'primitive' chordate
, has a notochord with both cartilage and muscle.
It clearly identifies the planet's most primitive chordate
At some point in their development from embryo to adult, all chordates
have a "notocord", a flexible rod supporting a nerve cord running down the back.
In the case of amphibian's phylogeny it's imply the rearrangement of the cells toward a tridermic organisms and within this process the evolution to early chordate
For example, the natural pigmentation of Styela embryos enabled classic studies of chordate
development (Conklin 1905; Gehring 2004).
51) more or less fusiform in long section, three-angled/triangular in cross section, stalked, ending in a short acute style; bristles three, bearing retrorsed teeth; bracts three, thickened, chordate
with long, acuminate tips.
A little more hazily, I recall highlights of my cellular journey long before the first chordate
In particular the deep sea species show how a primitive animal with some chordate
characteristics but no tail or limbs can drag itself across the sea floor using a muscular collar to gather food and then float above the sea floor to new feeding sites.
For example, in the Convolvulaceae family, leaves tend to begin with simple chordate
leaves and over time develop larger, more deeply lobed shapes.
Eggs from gastropods Nassarius obsoletus (Say, 1822) and Crepidula maculosa (Conrad, 1846), and chordate
4 billion years ago, multicellular animals are thought to have developed about 800-700 million years ago, and the biodiversity of modern life forms, including the first known chordate
, is known to have evolved by about 500 million years ago with the Cambrian explosion (Gould 1990; Meyerowitz 2002).
What makes a sea squirt a chordate
is the notochord in the animal's larval stage.
We think the sea squirt is valuable as a developmental model to study these connections because it is a simple chordate
that is the closest living relative of vertebrates, including humans," said developmental biologist Mike Levine.
One thing that stands out so far is the genetic similarity to chordate
as opposed to invertebrate organisms.
These gene clusters were duplicated twice during early chordate
evolution such that there are four paralogous groups.