The most distinctive feature of also had two rows of ventral paired fins, one ro
ID: 252178 • Letter: T
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The most distinctive feature of also had two rows of ventral paired fins, one row on each side, each fin preceded by a spine. Number of fins in a row was variable, and the presence of the rows has been cited as evidence of the fin-fold theory of the origin of paired fins (and tetrapod limbs). a. Ostracoderms b. Acanthodians c. Placoderms d. Conodonts 20 was the stout, ornamented spines in front of all fins. Earliest forms Matching Fossil Fishes 23 24 Acanthodians Ostracoderms Placoderms Conodonts Fossils of small fishes or fish-like chordates called - mostly known from small teeth (mineralized bone- like substance)- are abundant in marine sediments of late Cambrian490 mya); although they are usually classified as agnathans, their relationship with vertebrates is not well known. a. b. Jawed fishes (first major radiation) with heavy external bony plates; appeared in Silurian (-420 mya), c. Jawed fishes (oldest-known specimens) with large eyes, paired fins, dentine-tipped scales; appeared in d. Air-breathing jawed fishes with several features intermediate between fishes and first amphibians dominated in late Devonian, extinct in lower Carboniferous (-350 mya); freshwater/marine species Silurian (440 mya); most were small (Explanation / Answer
20 Ans: b. The most distinctive feature of Acanthodians was the stout, ornamented spines in front of all fins. Earliest forms also had two rows of ventral paired fins, one row on each side, each fin preceded by a spine. Number of fins in a row was variable, and the presence of the rows has been cited as evidence of the fin-fold theory of the origin of paired fins(and tetrapod limbs).
21. Ans. C. Jawed fishes (oldest-known specimens) with large eyes, paired fins, dentine-tipped scales; appeared in Silurian (~440 mya); most were small (<20cm long) freshwater/marine species.
22.Ans. e. Jawless fishes with external bony plates; appeared in marine deposits of Ordovician (~460 mya).
23. Ans. B. Jawed fishes (first major radiation) with heavy external bony plates; appeared in Silurian (~420mya), dominated in late Devonian, extinct in lower Carboniferous (~350 mya); freshwater/marine species.
24. Ans. A. Fossils of small fishes or fish-like chordates called conodonts mostly known from small teeth (mineralized bone like substances) conodonts are abundant in marine sediments of late Cambrian (~490 mya); although they are usually classified as agnathans, their relationship with vertebrates is not well known.
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