Agnathans and the origin of jawed vertebrates

Article Abstract:

Recent fossil discoveries have forced a revision in the prevailing theory for how the jawed vertebrates (gnathostomes) evolved from the jawless fishes (agnathans). Anatomical comparison of the two surviving groups of agnathans, the lampreys and the hagfishes, with the newly unearthed fossil agnathans supplemented the new understanding of vertebrate evolution gained from fossil discoveries. The gnathostomes and the lampreys are more akin to each other than either is to the hagfishes, which developed from the heterostracans. Lampreys and hagfishes are not closely related despite their similar forms.

Vertebrates, Evolution (Biology), Origin, Hagfishes, Fishes, Fossil, Lampreys, Fossil fishes

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Conodonts join the club

Article Abstract:

Conodonts, which are small tooth like or comb like fossils found from the Cambrian era to the Triassic era, have been classified as vertebrates on the basis of the presence of the large notochord, the chevron shaped muscle blocks, radials in the caudal fins and the presence of eyes. This classification however does not take into account the absence of any form of gill apparatus and the position of the eyeballs on the head. Although the conodonts are believed to resemble the ancient vertebrates they may have been more evolved than that.

Identification and classification, Taxonomy (Biology), Conodonts

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A primitive fossil fish sheds light on the origin of bony fishes

Article Abstract:

Living gnathostomes include osteichthyans or bony fishes, which are divided into actinopterygian and sarcopterygian lineages. It is uncertain how the two lineages took on their respective characteristics. A reconstruction of a 400-million-year-old fossil fish from China has been undertaken. It combines features of sarcopterygians and actinopterygians, but has large paired fin spines, previously only seen in two extinct gnathostome groups, providing a morphological link between osteichthyans and non-osteichthyan groups.

Observations, Osteichthyes

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