Jawless vertebrates

Phylogenetic analysis helps us understand the evolutionary history and mechanism of the extraordinary diversity of the vertebrate OR gene family. The phylogenetic tree shows that the OR gene family can be classified into two groups, type 1 and type 2 (Fig. la). The divergence of these two types predated the split between jawed vertebrates and jawless vertebrates (Fig. lb). The phylogenetic analysis revealed at least... 

Herrin BR, Cooper MD. Alternative adaptive immunity in jawless vertebrates. J Immunol. 2010 185 1367-74. 

Janvier P. microRNAs revive old views about jawless vertebrate divergence and evolution. Proc Natl Acad Sci USA. 2010 107 19137-8. 

Saha NR, Smith J, Amemiya CT. Evolution of adaptive immune recognition in jawless vertebrates. Semin ImmunoL 2010 22 25-33. 

Denison, R.H. (1964) The Cyathaspididae a family of Silurian and Devonian jawless vertebrates , Fieldiana Geology, 13, 309-473. 

Wilson, M.V.H. and Caldwell, M.W. (1998) The Furcacaudiformes a new order of jawless vertebrates with thelodont scales, based on articulated Silurian and Devonian fossils from northern Canada , Journal of Vertebrate Paleontology, 18, 10-29. 

So what is the evidence for competitive interactions between jawless vertebrates and gnathostomes, and between different groups of jawless vertebrates Is it even possible to formulate and test hypotheses of competition I will deal with these questions separately. 

Hypotheses of feeding in jawless vertebrates and scenarios of early vertebrate evolution... 

It is not possible in this short contribution to consider feeding in each of the major clades of jawless vertebrate. Thus, I have limited discussion to just two groups the conodonts and heterostracans. These clades provide a good illustration of some of the problems involved in analysis of feeding (and other aspects of the palaeoecology of fossils) that may lie behind misgivings such as those expressed by Janvier (1996b, quoted above). 

Another consequence of the limited understanding and the lack of consensus regarding the functional morphology of fossil jawless vertebrates is that the possibility that correlated progression was a significant factor in early vertebrate evolution simply cannot be investigated at present. 

MARiuzzA RA, VELiKovsKY CA, DENG L, XU G, PANCER z (2010), Structural insights into the evolution of the adaptive immune system the variable lymphocyte receptors of jawless vertebrates , Biol Chem, 391,753-60. 

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