Species have been assigned to the Glandulinidae going back to the Jurassic with the modern genus Glandulina recognisable in the Palaeocene (Loeblich & Tappan 1964). The test may be uniserial, biserial or polymorphine (more than two series); a common arrangement is for the test to start out biserial or polymorphine then become uniserial as the individual chambers become larger. In Glandulina, the microspheric generation starts biserial but the megalospheric form is uniserial throughout (Taylor et al. 1985). As the test grows, the internal walls between chambers may be resorbed. The terminal aperture of the test may be radial or slit-like. The most characteristic feature of the family is a tube running into the chamber from the inside of the aperture, referred to as the entosolenian tube. Some glandulinids have been described as lacking an entosolenian tube but such absences are likely artefacts of preservation: the delicate tube is easily dislodged during the fossilisation process (Taylor et al. 1985).
The overall relationships of the Nodosariata remain a question open to investigation. The classification of forams by Loeblich & Tappan (1964) included both multi-chambered and single-chambered (unilocular) forms within the Glandulinidae, with the unilocular forms placed in a subfamily Oolininae. Oolinines resemble glandulinids proper in a number of features including wall structure and the presence of an entosolenian tube. More recent authors, however, have rejected this relationship. Rigaud et al. (2016) entirely excluded unilocular forms from the Nodosariata as a whole, regarding it as improbable that single-chambered forms could have evolved from multi-chambered ancestors (as would seemingly be required by their relative appearances in the fossil record). Do the similarities between glandulinids and oolinines reflect a common ancestry, or are they the result of simple convergence? Unfortunately, with so few significant characters available to inform our understanding of foram higher relationships, the answer you prefer may come down to no more than your own personal feelings about which indicators are more reliable.
REFERENCES
Loeblich, A. R., Jr, & H. Tappan. 1964. Treatise on Invertebrate Paleontology pt C. Protista 2. Sarcodina: chiefly "thecamoebians" and Foraminiferida vol. 2. The Geological Society of America, and The University of Kansas Press.
Rigaud, S., D. Vachard, F. Schlagintweit & R. Martini. 2016. New lineage of Triassic aragonitic Foraminifera and reassessment of the class Nodosariata. Journal of Systematic Palaeontology 14 (11): 919–938.
Taylor, S. H., R. T. Patterson & H.-W. Choi. 1985. Occurrence and reliability of internal morphologic features in some Glandulinidae (Foraminiferida). Journal of Foraminiferal Research 15 (1): 18–23.
No comments:
Post a Comment
Markup Key:
- <b>bold</b> = bold
- <i>italic</i> = italic
- <a href="http://www.fieldofscience.com/">FoS</a> = FoS