There are many controversies present about the origin and Ancestry of Subphylum Vertebrata but no one is yet can be assumed to be actual. There are so many hypotheses that try to explain the time and place of origin of Subphylum Vertebrata but none of them is accurate but yet we will discuss all the hypotheses regarding the origin and Ancestry of Subphylum Vertebrata.
Time of Origin of Subphylum Vertebrata
If we talk about the exact time when Subphylum Vertebrata came on earth first, then we can tell the exact time but we can tell a range of time. During the late Silurian period and middle Devonian period vertebrates originate first in water, so we can say that freshwater Vertebrate came on earth first but they are now extinct and they were known as Ostracoderms.
Cyclostomata and Ostracoderms are primitive Vertebrates present under Group Agatha, Agnatha does not have the jaw-bordered mouth and they do not have paired appendages. They generally filter feeders and they respire through the paired pharyngeal gill slits but they do not show advanced Vertebrate features.
The Ostracoderm fossil was found during the late Cambrian but it may be possible that Vertebrate was also present before the Cambrian period but we did not get any fossil evidence. Maybe the ancestors Vertebrata before the Cambrian period were freshwater Habitatans so there was no chance for forming strong fossil evidence as we find in the case of Ostracoderms.
Place of Origin of Subphylum Vertebrata:
It is clear to us that Vertebrate originates in water first not on land but it is the question Vertebrate comes first on freshwater or in seawater. There is no evidence for the freshwater fossil so can not say surely that Vertebrate came on freshwater but we can get assumptions based upon the modern study.
Some workers assumed that the first Vertebrate originate on freshwater and their body fluids were much diluted as compared to the seawater. And the first freshwater Vertebrate was adapted to expel the excess water outside to maintain the osmotic pressure.
But some workers doubt the origin of Vertebrate in freshwater because there is some logic that raises questions about the origin of Vertebrate in freshwater. Most of the invertebrates were marine so during evolution the marine invertebrates evolve into vertebrates and live in marine water and we also get evidence of primitive Vertebrate on marine water. The excretory organ of primitive Vertebrates like Hagfish has the excretory organ for extracting the nitrogenous waste materials, not for osmoregulation. So it can be assumed that the first Vertebrate originate in marine water, not on freshwater, it is controversial that vertebrates originate on marine water or freshwater.
Hypothetical Ancestor of Vertebrate:
The true ancestors of Subphylum Vertebrate are hypothetically known as Prevertebrate but the Prevertebrate are only hypothetical. There is no fossil evidence for the Prevertebrate and the reason may be the ancestors of Vertebrate were soft-bodied and maybe they were freshwater.
The Protochordata, Subphylum Urochordata, Subphylum Cephaochordata, Subphylum Hemichordata show great similarity with the Vertebrate. Protochordate has pharyngeal gill slits, dorsal hollow nerve cord, notochord also present in Vertebrate, it is true that the skull and vertebral column are not present in Protochordata. But the similarities of Protochordata and Vertebrate are not a negligible fact, workers study them intensively and reconstructed an average prototype of Vertebrate ancestors.
Some workers assume that the ancestors of Subphylum Vertebrata were free-swimming fish-like animals live in freshwater and they show bilateral symmetry.
Detailed Study On Subphylum Vertebrata Definition Characteristics Classification Examples and Diagram
Reference
Basis of Classification in Subphylum Vertebrata
Phylogeny of Subphylum Vertebrata
An Overview of Classification in Subphylum Vertebrata
Subphylum Vertebrata and its Diversity
Cephalochordata Characteristics Features Classification Examples and Diagram
Urochordata Classification Morphology Characteristic Features
Characteristics Features of Hemichordata
General Comparison of Hemichordata Urochordata and Cephalochordata
Comparative Study of Digestive System in Hemichordata Cephaochordata and Urochordata
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