Amussiopecten protistus (Woodring, 1982)
WOODRING, W. P. 1982. Geology and paleontology of Canal Zone and adjoining parts of Panama. United States Geological Survey Professional Paper, 306-F: 1-759, pls. 83-124. [p. 583, pl. 87, fig. 15; pl. 92, figs. 10, 16-17]
1982 Flabellipecten gatunensis protistus Woodring, 1982
W. P. Woodring, 1982, plate 87.
W. P. Woodring, 1982, plate 92.
|
«Of medium size, right valve slightly convex, left valve practically flat to slightly convex. Right valve sculptured with 16 to 20 inverted U-shaped ribs (histogram peak at 18); strong throughout, except at posterior end, at least to height of 46 mm, or lower on ventral third. Ribs wider to much wider than interribs. Left valve sculptured with 16 to 18 ribs, inverted U-shaped throughout, or lower and more arched on ventral third. Ribs narrower than interribs, or of about same width. Interior lirae fading out short distance from ventral margin.
Length (almost complete) 71 mm, height (practically complete) 73 mm, convexity about 7 mm (type). Length 72.3 mm, height 72.9 mm (paratype). Type (thin-shelled right valve) USNM 646974. Paratype (thin-shelled left valve) USNM 646975. Paratype (thick-shelled right valve) USNM 646976. Paratype (thick-shelled left valve) USNM 646977. Type and paratype locality: 56 (USGS 6025, about 200 m south of southern end of switch at Bohio Ridge station. relocated Panama Railroad (south side of Bohio Peninsula), Canal Zone), Cairnito formation. Paratype locality: 60 (USGS 17685, northward flowing tributary of Rio Mandinga, pebbly calcareous tuffaceous sandstone, 3.31 km southwest of west end of Gamboa bridge), Caraba formation. Flabellipecten gatunensis protistus is identified in three late Oligocene formations and one early Miocene (the early half of early Miocene)— a total of 19 valves. The specimens from the Panama formation lack the outermost part of the shell and that from the La Boca is an external mold. The type was chosen as the most complete right valve, although it cannot be properly cleaned. It and the accompanying left-valve paratype of about the same size are thin shelled, so thin that they are translucent, and their ribbing is subdued on the ventral part. An incomplete thick-shelled right-valve paratype (pI. 92, fig. 10) has ribbing like that of the typical form of the nominate subspecies. The two thin-shelled and nine thick-shelled incomplete valves collected at the type locality presumably represent different environments. Whether they were found in the same bed is not known. A strongly ribbed left-valve paratype, from the Caraba formation, is shown on plate 87, figure 15. This subspecies is smaller than the nominate subspecies and has fewer ribs: 16 to 20 on right valves (histogram peak at 18), compared with 20 to 24 (peaks at 22 and 23). One middle Gatun right valve of the nominate subspecies is only slightly convex, and the ribs of a few right valves and of one left valve are subdued. One other late Oligocene American Flabellipecten is on record: the Antiguan species, Pecten duplex (Cooke, 1919, p. 140, pI. 11, figs. 10a, 10b), which was assigned to Flabellipecten by Olsson and Richards (1961, p. 5, pI. 1, figs. 5, 6) when they recorded it from the Guajira Peninsula of Colombia. The ventral part of its ribs on both valves is divided. Occurrence: Caimito, Caraba, and Panama formations (late Oligocene), and La Boca formation (early Miocene). Caimito formation, localities 56, 57a (Flabellipecten? sp.). Caraba formation, locality 60. Panama formation, locality 44. La Boca formation, Gaillard Cut area, locality 102a.» WENDELL PHILLIPS WOODRING, 1982
|
«In Figure 5 the species from which Leopecten is derived, Amussiopecten protistus, is the same taxon that Woodring (1982) regarded as the oldest subspecies of his F. gatunensis lineage. In the present study, however, this taxon is elevated to species rank and is placed in the genus Amussiopecten. Like most members of this genus, and unlike members of the genus Leopecten, A. protistus has a distinct pair of intermediate teeth on the hinge of its right valve and disk plicae that decrease in amplitude distally. Also, the shell of A. protistus is higher (dorsoventral dimension) than long (anterior-posterior dimension), like the shell shapes of many species in Amussiopecten but unlike the broader, more flaring shells of Leopecten. Contrary to Woodring’s (1982, p. 583) assertion that there is an unbroken lineage, the available collections (including material studied by Woodring) do not demonstrate a morphological transition between A. protistus and L. gatunensis in hinge structure or shell shape. The disk ribs of the earliest L. gatunensis, although of low amplitude, do not decrease in amplitude or disappear near the distal margins as in Amussiopecten. Thus far A. protistus is known only from the Oligocene and Lower Miocene formations of Panamá (Woodring, 1982, p. 583). Its highest stratigraphic occurrence is in the La Boca Formation, considered to be early Miocene (Burdigalian) in age (Blacut and Kleinpell, 1969; Bold, 1972; Woodring, 1982).»
WALLER, T. R. 2007. The evolutionary and geographic origins on the endemic Pectinidae (Mollusca: Bivalvia) of the Galápagos Islands. Journal of Paleontology, 81 (5): 929–950, figs. 1-9. [p. 936]
|
Phylogeny of Leopecten; T. R. Waller, 2007, The evolutionary and geographic origins on the endemic Pectinidae of the Galápagos Islands, figure 5.
|