First Jurassic brittlestar from Neuquén Basin, Argentina
Articulated fossil ophiuroids from South America were reported for the Devonian, Cretaceous, Eocene, and Miocene. Here we report the first Jurassic record of an articulated ophiuroid from the Sierra Chacaicó Formation (early Pliensbachian– Sinemurian) in Neuquén Basin, Argentina, and discuss the t...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Institute of Paleobiology PAS
2023-03-01
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| Series: | Acta Palaeontologica Polonica |
| Subjects: | |
| Online Access: | https://www.app.pan.pl/archive/published/app68/app010322022.pdf |
| Summary: | Articulated fossil ophiuroids from South America were reported for the Devonian, Cretaceous, Eocene, and Miocene. Here
we report the first Jurassic record of an articulated ophiuroid from the Sierra Chacaicó Formation (early Pliensbachian–
Sinemurian) in Neuquén Basin, Argentina, and discuss the taphonomic processes that allowed its preservation. The Sierra
Chacaicó Formation represents the onset of the Early Jurassic extensive marine transgression in the basin. The basal
section comprises shoreface and offshore Gilbert-type delta system, which was affected by hyperpycnal discharges. The
middle and upper sections are represented by offshore deposits, affected by storms and eroded by hyperpycnal channel-levee
systems. The ophiuroid specimen was found in levels of massive, fine, tuffaceous sandstone beds and covered
by coarse sandstone containing a large amount of plant debris and organic matter. It was preserved articulated, with a
complete disc and almost complete arms. Based on the microstructure of the spine-bearing lateral arm plates, the ophiuroid
is assigned to Sinosura, an extinct genus of the family Ophioleucidae, widespread in the Lower Jurassic deposits
of Europe but previously unknown from other parts of the world. The posture of the ophiuroid, with one arm curved
distally and extended in one direction and the other four arms symmetrically oriented in the opposite direction, suggests
a walking or escape movement frozen in time. This implies that the ophiuroid was buried alive by sediment thick enough
to prevent successful escape. The taphonomic and sedimentologic evidence indicates that the fossil material was found in
hyperpycnal deposits accumulated in offshore positions, which carried a high concentration of sediment in suspension. |
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| ISSN: | 0567-7920 1732-2421 |