| Titre | Mind the gape: the solution to the life habits of Rafinesquina alternata may turn on a 3D-printed hinge |
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| Auteur | Morse, A; Dattilo, B; Dewing, K ; Hagadorn, J W |
| Source | Geological Society of America Annual Meeting 2018; Geological Society of America, Abstracts With Programs vol. 50, no. 6, 236-12, 2018 p. 1, https://doi.org/10.1130/abs/2018AM-323792 |
| Liens | Online - En ligne
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| Image |  |
| Année | 2018 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20180258 |
| Éditeur | Geological Society of America |
| Réunion | GSA 2018 - Geological Society of America 130th Annual Meeting; Indianapolis, IN; US; Novembre 4-7, 2018 |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.1130/abs/2018AM-323792 |
| Media | papier; en ligne; numérique |
| Formats | html; pdf |
| Sujets | fossiles; morphologie des fossiles; positions des fossiles; modèles; Brachiopodes; paléontologie |
| Programme | Réseau des laboratoires scientifiques |
| Diffusé | 2018 11 01 |
| Résumé | (disponible en anglais seulement)
Rafinesquina alternata is at the center of a debate over whether free-living concavo-convex brachiopods lived concave side up or down. Whereas epibionts and
bio-sedimentary structures indicate a concave-down life position, the counter-argument is that the downturned narrow gape would have been buried in the muddy substrate preventing water circulation to the lophophore.
This biomechanical constraint
hinges on the assumption that Rafinesquina gaped at <5° as observed in most modern brachiopods. However, modern thecideide brachiopods open their valves to ~90°, and Rafinesquina lever systems allow a gape of ~50°. Nevertheless, the structure of the
hinge could limit gape, and should not be neglected.
The challenge of studying a precision mechanism like the Rafinesquina hinge is that separated valves show internal detail but are unlikely to have been life pairs and will not fit precisely.
The hinge cannot be observed directly on still-articulated valves because these are generally cemented together with calcite.
Using serial sagittal sections of hinges on articulated valves, it is possible to estimate muscle leverage but one
cannot determine how features in different sagittal planes interact, including hinge function. For example, the hinge, more than muscle leverage, is sensitive to the precise position of the fulcrum, but the exact fulcrum line cannot be determined
from sagittal slices or examining isolated valves.
We addressed this knowledge gap by serial grinding of typically preserved specimens and microCT scanning silicified specimens to generate, enlarge and print 3D models of articulated valves. These
models were articulated and manipulated from the outside to approximate the movement that would have resulted from muscle contraction.
The fulcrum articulation is clear when manipulated. Shell structures previously attributed to the fulcrum
actually stabilize closed valves. Two radiating rows of teeth on each valve mesh progressively like shears as the valves open or close. At the full gape the valves fit together on a few radial crenulations in the interarea. Interarea alignment allows
gape angle of any articulated valves to be measured directly at ~50°.
This hinge analysis confirms a wide gape, and indicates that concave-down life position was possible. |
| Sommaire | (Résumé en langage clair et simple, non publié)
La coquille d'un brachiopode de strophoménide fossile a été scannée à l'aide d'un microCT. Un modèle 3D de la coque agrandi dix fois a été
imprimé à l'aide d'une imprimante 3D. Ce modèle 3D est utilisé pour illustrer que les coques pourraient s'ouvrir à environ 50 degrés. Cela aide à répondre à une controverse de longue dure sur les habitudes de vie de ce type de brachiopode. |
| GEOSCAN ID | 312992 |
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