Morphology and histology of acanthodian fin spines from the late Silurian Ramsåsa E locality, Skåne, Swede

Jerve, Anna; Bremer, Oskar; Sanchez, Sophie; Ahlberg, Per

doi:10.26879/749

Cited by 1 publication

(3 citation statements)

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“…Several examples are given to show the morphological differences in cross-section. Examples are: (b), Lophosteus [ 24 ]; (c), Nostolepis [ 23 , 32 ], (d), Diplacanthus [ 10 ]; (e) ischnacanthid ([ 23 , 32 ]; (f), Ischyodus [ 41 ]; (g) Chimaera [ 41 ]; (h), Callorhinchus [ 16 ]; (i), Orthacanthus [ 42 , 43 ]; (j), Ctenacanthus [ 16 , 22 ]; (k), Squalus [ 15 , 16 ]; (l), Heterodontus [ 15 ]; (m), Etmopterus [ 15 ]; and, (n), Oxynotus [ 15 ]. The question mark indicates extinct taxa that bear fin spines but currently have no histological data and the null sign indicates the loss of dermal fin spines in crown osteichthyans.…”

Section: Discussionmentioning

confidence: 99%

“…Fin spine composition from the handful of published histological studies shows that some acanthodian spines can be composed of bone and dentine, similar to both Romundina and Lophosteus , but that the proportions of these tissues are reversed, with dentine comprising the main part of the spine. Since acanthodians have been placed as stem chondrichthyans in recent phylogenetic analysis [ 2 , 3 , 12 , 31 ], they may thus help to bridge the gap between the chondrichthyan and Romundina - Lophosteus spine types, and clarify the homology relationships between them (refer to [ 32 ]).…”

Section: Discussionmentioning

confidence: 99%

“…Here, we present a three-dimensional histological study of a dorsal ridge spine from Romundina stellina , produced by synchrotron microtomography, with the dual aim of illuminating the histological organization of the dermal skeleton and understanding the growth of fin spines in early vertebrates. By investigating the three-dimensional architecture and growth mode of a dorsal spine of Romundina stellina , we aim to provide a basis for comparison not only with extant chondrichthyans in which fin spine growth has been studied directly [ 16 ], but also with acanthodians and extinct chondrichthyans that can be imaged the same way, and will provide new data to address the question of fin spine homology [ 31 , 32 ].…”

Section: Introductionmentioning

confidence: 99%

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Vascularization and odontode structure of a dorsal ridge spine of Romundina stellina Ørvig 1975

Jerve

Sanchez

et al. 2017

PLoS ONE

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There are two types of dermal skeletons in jawed vertebrates: placoderms and osteichthyans carry large bony plates (macromery), whereas chondrichthyans and acanthodians are covered by small scales (micromery). Fin spines are one of the last large dermal structures found on micromeric taxa and offer a potential source of histology and morphology that can be compared to those found on macromeric groups. Dermal fin spines offer a variety of morphology but aspects of their growth modes and homology are unclear. Here, we provide detailed descriptions of the microstructure and growth of a dorsal ridge spine from the acanthothoracid placoderm, Romundina stellina, using virtual three-dimensional paleohistological datasets. From these data we identify several layers of dentine ornamentation covering the lateral surfaces of the spine and reconstructed their growth pattern. We show that this spine likely grew posteriorly and proximally from a narrow portion of bone located along the leading edge of the spine. The spine is similarly constructed to the scales with a few exceptions, including the absence of polarized fibers distributed throughout the bone and the presence of a thin layer of perichondral bone. The composition of the spine (semidentine odontodes, dermal bone, perichondral bone) is identical to that of the Romundina dermal plates. These results illustrate the similarities and differences between the dermal tissues in Romundina and indicate that the spine grew differently from the dentinous fin spines from extant and fossil chondrichthyans. The morphology and histology of Romundina is most similar to the fin spine of the probable stem osteichthyan Lophosteus, with a well-developed inner cellular bony base and star-shaped odontodes on the surface. Results from these studies will undoubtedly have impact on our understanding of fossil fin spine histology and evolution, contributing to the on-going revision of early gnathostome phylogeny.

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