The tail of the Ordovician fish<i>Sacabambaspis</i>

Pradel, Alan; Sansom, Ivan J.; Gagnier, Pierre-Yves; Céspedes, Ricardo; Janvier, Philippe

doi:10.1098/rsbl.2006.0557

Cited by 18 publications

(17 citation statements)

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“…The South American discoveries opened up a wealth of information on the genus Sacabambaspis , which has led to a number of papers focussing specifically on the palaeobiology of this taxon (for example see Gagnier 1993 a , b ; Sansom et al. 2005; Pradel et al. 2007).…”

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confidence: 99%

Ordovician Fish From the Arabian Peninsula

Sansom¹,

Miller

Heward³

et al. 2009

Palaeontology

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Over the past three decades Ordovician pteraspidomorphs (armoured jawless fish) have been recorded from the fringes of the Gondwana palaeocontinent, in particular Australia and South America. These occurrences are dominated by arandaspid agnathans, the oldest known group of vertebrates with extensive biomineralisation of the dermoskeleton. Here we describe specimens of arandaspid agnathans, referable to the genus Sacabambaspis Gagnier, Blieck and Rodrigo, from the Ordovician of Oman, which represent the earliest record of pteraspidomorphs from the Arabian margin of Gondwana. These are among the oldest arandaspids known, and greatly extend the palaeogeographical distribution of the clade around the periGondwanan margin. Their occurrence within a very narrow, nearshore ecological niche suggests that similar Middle Ordovician palaeoenvironmental settings should be targeted for further sampling.

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confidence: 99%

Ordovician Fish From the Arabian Peninsula

Sansom¹,

Miller

Heward³

et al. 2009

Palaeontology

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“…Kiær 1932; Kermack 1943; Obruchev 1964; Stensiö 1964; Romer 1966) has subsequently been questioned (see Denison 1971), especially after new discoveries of well‐preserved, nearly symmetrical articulated tails in several species (Broad and Dineley 1973; Dineley 1976; Dineley and Loeffler 1976; Soehn and Wilson 1990; Pellerin and Wilson 1995). However, a recent survey of the tail condition in major living and fossil taxa spanning agnathan phylogeny provides phylogenetic support for the hypocercy of heterostracan tails (Pradel et al . 2007), even if these authors accepted that the position of the notochord remains unknown.…”

Section: Descriptionmentioning

confidence: 84%

“…Some authors (Pernègre 2002; Pradel et al . 2007) suppose that the external symmetry of the tails is widespread in heterostracans, if not general for them.…”

Section: Discussionmentioning

confidence: 99%

“…The asymmetrical arrangement of digitations and lobes in heterostracan tails can be considered as clear evidence of their hypocercal condition. The position of the intermediate digitations appending along the dorsal edge of the ventral lobe suggests that it contained the notochordal mass, and supports the idea of Pradel et al (2007) that the apparently diphycercal (symmetrical) aspect of the caudal fin in some heterostracans is a particular case of the hypocercal condition.…”

Section: The Heterostracan Tail Typementioning

confidence: 99%

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On the tail ofErrivaspisand the condition of the caudal fin in heterostracans

Mark-Kurik

Botella

2009

Acta Zoologica

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Mark-Kurik, E. and Botella, H. 2009. On the tail of Errivaspis and the condition of the caudal fin in heterostracans. -Acta Zoologica (Stockholm) 90 (Suppl. 1): 44-51Articulated caudal fins of heterostracans are preserved in very rare cases. Their morphology and internal structure are completely unknown for the majority of species. One of the few preserved caudal fins belongs to the Early Devonian pteraspidid Errivaspis waynensis from the Welsh Borderland, UK. There are two different reconstructions of the tail: (1) strongly asymmetric, with a considerably longer ventral lobe, and a rather concave posterior margin (e.g. White 1935); and (2) almost symmetrical with an only slightly longer ventral lobe and a small notch in the posterior margin (e.g. Blieck 1984). A new reconstruction of the Errivaspis caudal fin, based on a detailed study of White's specimens is presented here. The ventral lobe is longer than the dorsal one but not so much as in White's reconstruction, and the notch in the posterior margin of the fin is less deep. The comparatively massive ventral lobe and 'en echelon' arrangement of three digitations, supporting the fin web and branching off from this lobe, indicate the hypocercal condition of the asymmetrical tail. The same internal structure is present in other heterostracans with nearly symmetrical caudal fins (e.g. Doryaspis , Nahanniaspis , Dinaspidella and Athenaegis ) where all, or most, of the intermediate digitations branch off from the ventral lobe.

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“…4) are found in most jawless fishes: lampreys (Marinelli & Strenger, 1954), euconodonts (Donoghue et al, 2000), anaspids (Blom & Märss, 2010), heterostracans (Pradel et al, 2007;Mark-Kurik & Botella, 2009), and thelodonts (for a review, see Pradel et al, 2007). Caudal-fin structure remains unknown in pituriaspids and in galeaspids; it is unclear whether the heterocercal tails of galeaspids (e.g.…”

Section: Finsmentioning

confidence: 99%

The characters of Palaeozoic jawed vertebrates

2014

Zoological Journal of the Linnean Society

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Newly discovered fossils from the Silurian and Devonian periods are beginning to challenge embedded perceptions about the origin and early diversification of jawed vertebrates (gnathostomes). Nevertheless, an explicit cladistic framework for the relationships of these fossils relative to the principal crown lineages of the jawed vertebrates (osteichthyans: bony fishes and tetrapods; chondrichthyans: sharks, batoids, and chimaeras) remains elusive. We critically review the systematics and character distributions of early gnathostomes and provide a clearly stated hierarchy of synapomorphies covering the jaw-bearing stem gnathostomes and osteichthyan and chondrichthyan stem groups. We show that character lists, designed to support the monophyly of putative groups, tend to overstate their strength and lack cladistic corroboration. By contrast, synapomorphic hierarchies are more open to refutation and must explicitly confront conflicting evidence. Our proposed synapomorphy scheme is used to evaluate the status of the problematic fossil groups Acanthodii and Placodermi, and suggest profitable avenues for future research. We interpret placoderms as a paraphyletic array of stem-group gnathostomes, and suggest what we regard as two equally plausible placements of acanthodians: exclusively on the chondrichthyan stem, or distributed on both the chondrichthyan and osteichthyan stems.

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The tail of the Ordovician fishSacabambaspis

Cited by 18 publications

References 8 publications

Ordovician Fish From the Arabian Peninsula

Ordovician Fish From the Arabian Peninsula

On the tail ofErrivaspisand the condition of the caudal fin in heterostracans

The characters of Palaeozoic jawed vertebrates

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