The protostome developmental sequence arosejust once in evolutionary history, re
ID: 5191 • Letter: T
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The protostome developmental sequence arosejust once in evolutionary history, resulting in two main subgroups- Lophotrochozoa and Ecdysozoa. What does this findingsuggest? Division of these two groups occurred after theprotostome developmental sequence appeared. These two subgroups have a common ancestor thatwas a protostome. The protostomes are a monophyletic group. All of the above apply. The protostome developmental sequence arosejust once in evolutionary history, resulting in two main subgroups- Lophotrochozoa and Ecdysozoa. What does this findingsuggest? Division of these two groups occurred after theprotostome developmental sequence appeared. These two subgroups have a common ancestor thatwas a protostome. The protostomes are a monophyletic group. All of the above apply. Division of these two groups occurred after theprotostome developmental sequence appeared. These two subgroups have a common ancestor thatwas a protostome. The protostomes are a monophyletic group. All of the above apply. Division of these two groups occurred after theprotostome developmental sequence appeared. These two subgroups have a common ancestor thatwas a protostome. The protostomes are a monophyletic group. All of the above apply. Division of these two groups occurred after theprotostome developmental sequence appeared. These two subgroups have a common ancestor thatwas a protostome. The protostomes are a monophyletic group. All of the above apply. Division of these two groups occurred after theprotostome developmental sequence appeared. These two subgroups have a common ancestor thatwas a protostome. The protostomes are a monophyletic group. All of the above apply. Division of these two groups occurred after theprotostome developmental sequence appeared. These two subgroups have a common ancestor thatwas a protostome. The protostomes are a monophyletic group. All of the above apply. Division of these two groups occurred after theprotostome developmental sequence appeared. These two subgroups have a common ancestor thatwas a protostome. The protostomes are a monophyletic group. All of the above apply. Division of these two groups occurred after theprotostome developmental sequence appeared. These two subgroups have a common ancestor thatwas a protostome. The protostomes are a monophyletic group. All of the above apply. Division of these two groups occurred after theprotostome developmental sequence appeared. These two subgroups have a common ancestor thatwas a protostome. The protostomes are a monophyletic group. All of the above apply. Division of these two groups occurred after theprotostome developmental sequence appeared. These two subgroups have a common ancestor thatwas a protostome. The protostomes are a monophyletic group. All of the above apply. Division of these two groups occurred after theprotostome developmental sequence appeared. These two subgroups have a common ancestor thatwas a protostome. The protostomes are a monophyletic group. All of the above apply. Division of these two groups occurred after theprotostome developmental sequence appeared. These two subgroups have a common ancestor thatwas a protostome. The protostomes are a monophyletic group. All of the above apply.Explanation / Answer
Another difference between protostomes and deuterostomesis that in protostomes the embryo displays spiral cleavage, wherethe position of each cell is deterministic. In deuterostomes, whichdisplay radial cleavage, there is less certainty in wheredifferentiated cells ultimately end up. The protostomes'embryological development might therefore be considered relativelyconservative and predictable. Unsurprisingly, protostomes encompassthe world's simplest animals, including the earliest bilateralanimals to appear in the fossil record, such as arthropods andmolluscs.
When it comes to species count, protostomes win overdeuterostomes. While there are many millions of protostome species,especially thanks to phylum Arthropoda, there are only about 70,000species of deuterostomes, though these encompass all fairly complexanimals. Protostomes encompass all simple animals, but theirabundance is a testimony to their success. Ignoring fish andwhales, protostomes make up the majority of biomass in the world'soceans, though they are less dominant on land, where the vertebratebody plan has proven highly successful. The suspension qualities ofwater make a spinal column much less necessary.
Protostomes and deuterostomes are thought to have splitat least 558 million years ago, and possibly much earlier. This isinferred by the existence of Kimberella, a primitivemollusk, 555 million years ago, which is a known protostome.However, just because Kimberella existed at the time, whydoes that mean that deuterostomes didn't evolve later, branchingoff from protostomes? There is little solid consensus on thesubject, but apparently some Late Ediacaran (older than 542 millionyears) fossils, Ernettia, have a likely deuterostomeaffinity, though consensus on the classification of Ediacaranfossils is frequently absent. In any case, it is certain thatprotostomes and deuterostomes had separated by the dawn of theCambrian, 542 million years ago.
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