Cranial morphology of the Carboniferous rhizodontid<i>Screbinodus ornatus</i>(Osteichthyes: Sarcopterygii)

Jeffery, Jonathan E.

doi:10.1080/14772019.2011.595961

Cited by 7 publications

(3 citation statements)

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“…Both Eusthenopteron and Sauripterus are hypothesized to have been fully aquatic and to have used their pectoral fins primarily for swimming (20,33,37,38) and perhaps, also to prop the animal up while resting on benthic substrate. Third, we studied the elpistostegid Tiktaalik roseae , the most crownward finned tetrapodomorph (39)(40)(41) known from at least 20 individuals that are estimated to range from 1.25 to 2.75 m in length (12,42). Based on study of the endoskeleton and girdle, the pectoral fin of Tiktaalik is hypothesized to have been capable of holding the body up in an elevated posture on the substrate, and the animal is predicted to have occupied a benthic aquatic niche in littoral zones (12,42,43).…”

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Fin ray patterns at the fin-to-limb transition

Stewart

Lemberg

Taft

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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The fin-to-limb transition was marked by the origin of digits and the loss of dermal fin rays. Paleontological research into this transformation has focused on the evolution of the endoskeleton, with little attention paid to fin ray structure and function. To address this knowledge gap, we study the dermal rays of the pectoral fins of 3 key tetrapodomorph taxa—Sauripterus taylori (Rhizodontida), Eusthenopteron foordi (Tristichopteridae), and Tiktaalik roseae (Elpistostegalia)—using computed tomography. These data show several trends in the lineage leading to digited forms, including the consolidation of fin rays (e.g., reduced segmentation and branching), reduction of the fin web, and unexpectedly, the evolution of asymmetry between dorsal and ventral hemitrichia. In Eusthenopteron, dorsal rays cover the preaxial endoskeleton slightly more than ventral rays. In Tiktaalik, dorsal rays fully cover the third and fourth mesomeres, while ventral rays are restricted distal to these elements, suggesting the presence of ventralized musculature at the fin tip analogous to a fleshy “palm.” Asymmetry is also observed in cross-sectional areas of dorsal and ventral rays. Eusthenopteron dorsal rays are slightly larger than ventral rays; by contrast, Tiktaalik dorsal rays can be several times larger than ventral rays, and degree of asymmetry appears to be greater at larger sizes. Analysis of extant osteichthyans suggests that cross-sectional asymmetry in the dermal rays of paired fins is plesiomorphic to crown group osteichthyans. The evolution of dermal rays in crownward stem tetrapods reflects adaptation for a fin-supported elevated posture and resistance to substrate-based loading prior to the origin of digits.

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confidence: 99%

Fin ray patterns at the fin-to-limb transition

Stewart

Lemberg

Taft

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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“…22C) with a distinctive ornament of tubercules or ridges (cf. Jeffery, 2012) and three indeterminate rhizodont teeth (Fig. 22G), which have a shape similar to that of Strepsodus , but an ornament of well-defined striae similar to that of Archichthys (Jeffery, 2006).…”

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confidence: 99%

A Tournaisian (earliest Carboniferous) conglomerate-preserved non-marine faunal assemblage and its environmental and sedimentological context

Clack

Bennett

Davies

et al. 2019

PeerJ

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A conglomerate bed from the Tournaisian Ballagan Formation of Scotland preserves a rich array of vertebrate and other nonmarine fossils providing an insight into the wider ecosystem and paleoenvironment that existed during this pivotal stage of Earth history. It challenges hypotheses of a long-lasting post-extinction trough following the end-Devonian extinction event. The fauna recovered includes a wide size range of tetrapods, rhizodonts, and dipnoans, from tiny juveniles or small-bodied taxa up to large adults, and more than one taxon of each group is likely. Some fauna, such as actinopterygians and chondrichthyans, are rare as macrofauna but are better represented in the microfossil assemblage. The fauna provides evidence of the largest Carboniferous lungfish ever found. The specimens are preserved in a localized, poorly-sorted conglomerate which was deposited in the deepest part of a river channel, the youngest of a group of channels. In addition to the fossils (micro- and macro-), the conglomerate includes locally-derived clasts of paleosols and other distinctive elements of the surrounding floodplains. Charcoal fragments represent small woody axes and possible larger trunk tissue from arborescent pteridosperms. Preservation of the fossils indicates some aerial exposure prior to transport, with abrasion from rolling. The findings presented here contrast with other published trends in vertebrate size that are used to interpret a reduction in maximum sizes during the Tournaisian. The richness of the fauna runs counter to the assumption of a depauperate nonmarine fauna following the end-Devonian Hangenberg event, and charcoal content highlights the occurrence of fire, with the requisite levels of atmospheric oxygen during that stage.

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“…Common associations are Archichthys / Strepsodus and Screbinodus / Rhizodus , which has long had a confounding effect on the taxonomy of these genera (Andrews ; Jeffery ). Screbinodus is a small rhizodont, with a length of 1.5–2 m; Strepsodus and Rhizodus are both large rhizodonts, with length estimates of 3–5 and 5–7 m, respectively (Jeffery ). Given the limited material, size estimates have not been produced for Archichthys .…”

Section: Discussionmentioning

confidence: 99%

A fish and tetrapod fauna from Romer's Gap preserved in Scottish Tournaisian floodplain deposits

et al. 2018

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The end‐Devonian mass extinction has been framed as a turning point in vertebrate evolution, enabling the radiation of tetrapods, chondrichthyans and actinopterygians. Until very recently ‘Romer's Gap’ rendered the Early Carboniferous a black box standing between the Devonian and the later Carboniferous, but now new Tournaisian localities are filling this interval. Recent work has recovered unexpected tetrapod and lungfish diversity. However, the composition of Tournaisian faunas remains poorly understood. Here we report on a Tournaisian vertebrate fauna from a well‐characterized, narrow stratigraphic interval from the Ballagan Formation exposed at Burnmouth, Scotland. Microfossils suggest brackish conditions and the sedimentology indicates a low‐energy debris flow on a vegetated floodplain. A range of vertebrate bone sizes are preserved. Rhizodonts are represented by the most material, which can be assigned to two taxa. Lungfish are represented by several species, almost all of which are currently endemic to the Ballagan Formation. There are two named tetrapods, Aytonerpeton and Diploradus, with at least two others also represented. Gyracanths, holocephalans, and actinopterygian fishes are represented by rarer fossils. This material compares well with vertebrate fossils from other Ballagan deposits. Faunal similarity analysis using an updated dataset of Devonian–Carboniferous (Givetian–Serpukhovian) sites corroborates a persistent Devonian/Carboniferous split. Separation of the data into marine and non‐marine partitions indicates more Devonian–Carboniferous faunal continuity in non‐marine settings compared to marine settings. These results agree with the latest fossil discoveries and suggest that the Devonian–Carboniferous transition proceeded differently in different environments and among different taxonomic groups.

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Cranial morphology of the Carboniferous rhizodontidScrebinodus ornatus(Osteichthyes: Sarcopterygii)

Cited by 7 publications

References 50 publications

Fin ray patterns at the fin-to-limb transition

Fin ray patterns at the fin-to-limb transition

A Tournaisian (earliest Carboniferous) conglomerate-preserved non-marine faunal assemblage and its environmental and sedimentological context

A fish and tetrapod fauna from Romer's Gap preserved in Scottish Tournaisian floodplain deposits

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