Abstract
How long-extinct jawless fishes fed is poorly understood, yet interpretations of feeding are an important component of many hypotheses concerning the origin and early evolution of vertebrates. Heterostracans were the most diverse clade of armoured jawless vertebrates (stem gnathostomes), and the structure of the mouth and its use in feeding are the subjects of long-standing and heated controversy. I present here evidence that heterostracan feeding structures exhibit recurrent patterns of in vivo wear, are covered internally by microscopic oral denticles, and that the mouth may have been less flexible than has been thought. These data, particularly the absence of wear at the tips of oral plates, and the evidence that the mouth was lined with delicate outwardly directed denticles, effectively falsify all but one hypothesis of feeding in heterostracans: heterostracans were microphagous suspension feeders. This has a direct bearing on hypotheses that address ecological aspects of early vertebrate diversity and evolution, contradicting the widespread view that the pattern of early vertebrate evolution reflects a long-term trend towards increasingly active and predatory habits.
Full Text
The Full Text of this article is available as a PDF (2.7 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Donoghue P. C., Forey P. L., Aldridge R. J. Conodont affinity and chordate phylogeny. Biol Rev Camb Philos Soc. 2000 May;75(2):191–251. doi: 10.1017/s0006323199005472. [DOI] [PubMed] [Google Scholar]
- Gans C., Northcutt R. G. Neural crest and the origin of vertebrates: a new head. Science. 1983 Apr 15;220(4594):268–273. doi: 10.1126/science.220.4594.268. [DOI] [PubMed] [Google Scholar]
- Gans C. Stages in the origin of vertebrates: analysis by means of scenarios. Biol Rev Camb Philos Soc. 1989 Aug;64(3):221–268. doi: 10.1111/j.1469-185x.1989.tb00471.x. [DOI] [PubMed] [Google Scholar]
- Northcutt R. G., Gans C. The genesis of neural crest and epidermal placodes: a reinterpretation of vertebrate origins. Q Rev Biol. 1983 Mar;58(1):1–28. doi: 10.1086/413055. [DOI] [PubMed] [Google Scholar]
- Postlethwait J. H., Yan Y. L., Gates M. A., Horne S., Amores A., Brownlie A., Donovan A., Egan E. S., Force A., Gong Z. Vertebrate genome evolution and the zebrafish gene map. Nat Genet. 1998 Apr;18(4):345–349. doi: 10.1038/ng0498-345. [DOI] [PubMed] [Google Scholar]
- Smith M. M., Coates M. I. Evolutionary origins of the vertebrate dentition: phylogenetic patterns and developmental evolution. Eur J Oral Sci. 1998 Jan;106 (Suppl 1):482–500. doi: 10.1111/j.1600-0722.1998.tb02212.x. [DOI] [PubMed] [Google Scholar]
- Wistow G. Protein structure and introns. Nature. 1993 Jul 8;364(6433):107–108. doi: 10.1038/364107b0. [DOI] [PubMed] [Google Scholar]
- Zimmer C. Evolution. In search of vertebrate origins: beyond brain and bone. Science. 2000 Mar 3;287(5458):1576–1579. doi: 10.1126/science.287.5458.1576. [DOI] [PubMed] [Google Scholar]