RE: Why did God get rid of the Trilobites?
October 22, 2021 at 3:12 am
(This post was last modified: October 22, 2021 at 3:13 am by Anomalocaris.)
“Very closely related” is to distort the truth to an rather extreme. Insects (Hexapoda) and the order that includes prawns (Crustacea) are more closely related to each other than to trilobites or spiders, that is true, but they are not much more closely related.
Hexapoda diverged from Crustacea at least 425 million years ago. While the ancestors of both diverged from trilobites about 540 million years ago. So insects and prawns might be said to be about 80% as distant from each other as either are from trilobites, spiders or millipedes.
Both hexapoda and Crustacea have exoskeletons, but so do members of other branches of arthropods. So that shared trait does not denote closeness or relations between them. look closer and the exoskeletons of Crustacea and hexapoda only resemble each other superficially. They are formed by different biochemical processes. Contrary to what is said on your quote, Hexapoda have three part bodies, but crustacea have only two. Crustacea doe not have separate heads and thorax as Hexapoda do. More significantly, from embryon development perspective, the combined head and thorax in Crustacea are not analogous to the head and thorax in hexapoda in terms of where in the segmented fetal structure they developed from. The segmented legs of Hexapoda may seem to resemble those of crustacea, but they are structurally different. Hexapoda legs are uniramous, that is each leg grows out of the body as a single series of segments attached end to end. Crustacea legs on the other hand, are mostly biramous, that is most leg branch into two separate parallel series of segments where it attached to the body. From embryonic development, it is also clear crustacea legs grow out of different parts in the segmented fetal tissue from Hexapoda legs.
So it is a distinction with quite a deep seated difference in genetics, biochemistry, embryonic development, and morphology.
Hexapoda diverged from Crustacea at least 425 million years ago. While the ancestors of both diverged from trilobites about 540 million years ago. So insects and prawns might be said to be about 80% as distant from each other as either are from trilobites, spiders or millipedes.
Both hexapoda and Crustacea have exoskeletons, but so do members of other branches of arthropods. So that shared trait does not denote closeness or relations between them. look closer and the exoskeletons of Crustacea and hexapoda only resemble each other superficially. They are formed by different biochemical processes. Contrary to what is said on your quote, Hexapoda have three part bodies, but crustacea have only two. Crustacea doe not have separate heads and thorax as Hexapoda do. More significantly, from embryon development perspective, the combined head and thorax in Crustacea are not analogous to the head and thorax in hexapoda in terms of where in the segmented fetal structure they developed from. The segmented legs of Hexapoda may seem to resemble those of crustacea, but they are structurally different. Hexapoda legs are uniramous, that is each leg grows out of the body as a single series of segments attached end to end. Crustacea legs on the other hand, are mostly biramous, that is most leg branch into two separate parallel series of segments where it attached to the body. From embryonic development, it is also clear crustacea legs grow out of different parts in the segmented fetal tissue from Hexapoda legs.
So it is a distinction with quite a deep seated difference in genetics, biochemistry, embryonic development, and morphology.
