Agnathans recent and fossil, and the origin of jawed vertebrates

Forey, Peter L.

doi:10.1007/bf00043003

Cited by 53 publications

(46 citation statements)

References 36 publications

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“…In comparison to previous histological interpretations of arandaspids, our conclusions are entirely congruent with the distribution of histological characters in existing cladograms of early vertebrates which consistently place the arandaspids as a sister group to the heterostracans sensu stricto (Forey & Janvier 1993;Gagnier 1993b;Forey 1995;Janvier 1996b;Donoghue et al 2000;Donoghue & Smith 2001). This is reinforced by our parsimony analysis of the cladistic dataset compiled by Donoghue & Smith (2001; and revised in line with our reinterpretation of arandaspid dermoskeletal histology) which resolves arandaspids as the sister-group to Astraspis, rather than heterostracans sensu stricto (figure 3).…”

Section: Implications and Concluding Remarkssupporting

confidence: 89%

Histology and affinity of the earliest armoured vertebrate

2005

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Arandaspids are the earliest skeletonizing vertebrates known from articulated remains. Despite a wealth of data, their affinity remains questionable because they exhibit a random mixture of primitive and derived characteristics. We constrain the affinity of arandaspids by providing the first detailed characterization of their dermoskeleton which is revealed to be three-layered, composed of a basal laminated, cancellous middle and tubercular superficial layers. All three layers are composed of acellular bone but the superficial layer also includes dentine and enameloid, comprising the tubercles. As such, the composition of the arandaspid dermoskeleton is common to heterostracans and astraspids, supporting existing hypotheses of early vertebrate phylogeny. This emphasizes the peculiarity of existing interpretations of aranadaspid anatomy and there is need for a complete reappraisal of the existing anatomical data.

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Section: Implications and Concluding Remarkssupporting

confidence: 89%

Histology and affinity of the earliest armoured vertebrate

2005

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“…In this sense, it is likely that the lack of raldh2 expression in the lamprey RP is a derived feature. Although lampreys display ancestral vertebrate characteristics, Haikouichthys, Myllokunmingia and other agnathan fossils indicate that primitive vertebrates already had prototypes of bilateral fins represented by a pair of continuous mediolateral fin-folds spanning the AP axis, implying that fin absence in extant agnathans is a derived feature of lampreys (Forey, 1995). Thus, it is possible that raldh2 expression was lost from the RP owing to a secondary loss of paired fins in lampreys (Forey, 1995).…”

Section: Research Articlementioning

confidence: 99%

Insights into the organization of dorsal spinal cord pathways from an evolutionarily conserved raldh2 intronic enhancer

Castillo¹,

Cravo²,

Azambujá³

et al. 2010

Development

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SUMMARYComparative studies of the tetrapod raldh2 (aldh1a2) gene, which encodes a retinoic acid (RA) synthesis enzyme, have led to the identification of a dorsal spinal cord enhancer. Enhancer activity is directed dorsally to the roof plate and dorsal-most (dI1) interneurons through predicted Tcf-and Cdx-homeodomain binding sites and is repressed ventrally via predicted Tgif homeobox and ventral Lim-homeodomain binding sites. Raldh2 and Math1/Cath1 expression in mouse and chicken highlights a novel, transient, endogenous Raldh2 expression domain in dI1 interneurons, which give rise to ascending circuits and intraspinal commissural interneurons, suggesting roles for RA in the ontogeny of spinocerebellar and intraspinal proprioceptive circuits. Consistent with expression of raldh2 in the dorsal interneurons of tetrapods, we also found that raldh2 is expressed in dorsal interneurons throughout the agnathan spinal cord, suggesting ancestral roles for RA signaling in the ontogenesis of intraspinal proprioception.

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“…They offer anatomical information from geological epochs close in time to the ancestry of major clades of the vertebrates, including the gnathostomes (Forey and Janvier 1993;Forey 1995;Janvier 1996Janvier , 2008Dono− ghue and Sansom 2002;Hou et al 2002;Novitskaya 2006). Their phyletic evolution is of much value for re− fining the stratigraphic correlation between regions and provides a basis for zonation of strata devoid of other guide fossils.…”

Section: Introductionmentioning

confidence: 99%

The Early Devonian Armoured Agnathans of Podolia, Ukraine

Voichyshyn¹

2011

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Agnathans recent and fossil, and the origin of jawed vertebrates

Cited by 53 publications

References 36 publications

Histology and affinity of the earliest armoured vertebrate

Histology and affinity of the earliest armoured vertebrate

Insights into the organization of dorsal spinal cord pathways from an evolutionarily conserved raldh2 intronic enhancer

The Early Devonian Armoured Agnathans of Podolia, Ukraine

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