Fishes jawless

Ordovician 500 Myr Diversification of echinoderms, other invertebrate phyla, jawless fishes. Mass extinction at end of period (ca. 85To of all species disappear)... 

Silurian 440 Myr Sea levels rise, two large continents form, hothouse climate. Diversification of jawless fishes, first bony fishes invasion of land by vascular plants and arthropods... 

Braun C.B. (1996). The sensory biology of the living jawless fishes a phylogenetic assessment. Brain Behav Evol 48, 262-276. 

Freitag J., Beck A., Ludwig G., von Buchholtz L. and Breer H. (1999). On the origin of the olfactory receptor family receptor genes of the jawless fish (Lampetra fluviatilis). Gene 226, 165-174. 

Jawless fish (450xl06 years) As for (2) with olfactory system and a cerebellum for maintaining posture while viewing. Very small cortex and telencephalox... 

Jawless fish (Cambrian) As above second hydroxylation giving norepinephrine and amidated peptides copper chemistry in vesicles Recovery additionally by hydrolysis Zinc enzymes... 

Migrating male sea lampreys, Petromyzon marinus, are attracted to water from conspecific larvae (Teeter, 1980). This Jawless fish originates in the Atlantic Ocean but has invaded the Great Lakes, where it parasitizes fish populations,... 

Figure 7.21. The Lamprey. A jawless fish whose ancestors diverged from bony fish approximately 400 million years ago, the lamprey contains hemoglobin molecules that contain only a single type of polypeptide chain. [Brent P. Kent.]... 

Fig. 2 Phylogenetic tree of the species discussed in this review. The five teleost species, for which completed genomes are available, are shown together with the nodes for divergence from tetrapods, cartilaginous, and jawless fish (human, shark, and lamprey, respectively)...

The many remaining questions concerning the function of AHRs in jawless fish make this a fertile area of future research. It is too soon to know whether studies on AHR pathways in lamprey and hagfish will reveal features of ancestral (ligand-independent ) AHR functions, developmental changes in AHR signaling, or unique modifications of AHR function in these highly specialized fish. 

Concerning broader hypotheses of early vertebrate diversity, the view that diversity patterns and the extinction of most clades of jawless fish reflect competition between agnathans and gnathostomes or between specific clades of jawless and jawed fish, although widely held, must be regarded as untested, and at present untestable, speculation. The available data for feeding habits, palaeogeographic distribution, and habitats are inadequate for this purpose, and the possibility that members of two contemporary clades were potential competitors can be neither confirmed nor refuted. Competitive interactions are just one of a number of possible explanations of the pattern of early vertebrate diversity. 

Janvier, P. (1993) Patterns of diversity in the skull of jawless fishes , in Hanken, J. and Hall, B.K. (eds) The skull, vol. 2. Patterns of structural and systematic diversity, Chicago and London The University of Chicago Press, pp. 131-88. 

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