Location and interpretation of ontogenetic relics in the shell of adult brachiopods

Abstract

Baker, Peter G. 1989 07 15: Location and interpretation of ontogenetic relics in the shell of adult brachiopods. Lethaia, Vol. 22. pp. 241–245. Oslo. ISSN 0024–1164. Careful sectioning of critically orientated adult Ornithella bathonica (Rollier) shells has revealed, close to the umbo in the secondary fibrous shell layer of the brachial valve, relics of early ontogenetic structures which can be directly correlated with those of early juveniles of Zeilleria leckenbyi (Davidson ex Walker MS). It is now confirmed that very early in ontogeny, the brachial valve of O. bathonica possessed a septal pillar identical with that found in Z. leckenbyi and many terebratellacean species. *Brachiopoda. Terebratellidina, Ornithellidae, ontogenetic relics, buried microstructure.

A New Early Jurassic Rhynchonellid Brachiopod From the Western Tethys and Implications for Systematics of Rhynchonellids From the Triassic–jurassic Boundary

“…The between-section distance used in brachiopod studies is mostly 0.1 m m or more. As was shown by Baker (1989), a section interval of approximately 0.02 m m can be used for a detection of early ontogenetic structures in the posteriormost parts of adult brachiopod shells. Although specimens were not tilted in order to observe juvenile structures (cf.…”

“…Although specimens were not tilted in order to observe juvenile structures (cf. Baker, 1972Baker, , 1989, cardinalia characters and crural terminations can be very fine even in adult brachiopods (e.g., Dewing, 2001). This can be especially impor tant for relatively small species (below 20 mm).…”

Support from early juvenile Jurassic, Cretaceous and Holocene thecideoid species for a postulated common early ontogenetic development pattern in thecideoid brachiopods

“…Data may be obtained (Baker 1989 b ) from the study of ontogenetic relics preserved in adult shell fabrics. Unfortunately, although the high magnification available in SEM photographs of coated specimens enables individual grain boundaries to be easily differentiated, the scale of the much larger field of view required for the study of shell fabric boundaries necessitates the use of uncoated cellulose acetate peels viewed with the aid of transmitted light microscopy.…”

The early ontogeny of Jurassic thecideoid brachiopods and its contribution to the understanding of thecideoid ancestry

“…1E). Extrapolation still closer to the origin is possible using the technique of shell fabric mapping (Baker 1989 b ) to identify unresorbed early juvenile skeletal elements buried in the fabric of adult shells (Baker 1970, 2005; Baker and Manceñido 1997). Serial sectioning of the outer layers of the umbonal region of adult dorsal valves shows that the earliest juvenile shell had a fibrous secondary shell lining, was atuberculate and lacked a subperipheral rim although scattered endopunctae were already present.…”