Fresvillia constricta Kennedy 1986 (TaxonConcept

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Species Fresvillia constricta Kennedy 1986


[1]


[2]

[1] text-fig. 12e-f Ifrim et al. (2004) [2] text-fig. 13d-e Ifrim et al. (2004)

Diagnosis / Definition:

Kennedy (1986):
Description. Holotype and only known specimen (Pl. 14, figs. 39-42) an internal mould of part of the phragmocone and body-chamber with maximum whorl height 8•5 mm and length 47•0 mm. Straight, slowly expanding, with circular whorl section. Surface ornamented by growth striae and feeble riblets. Ornament effaced on dorsum, flexed back and strongly concave on dorsolateral area, periodically strengthened into crescentic ribs separated by a distance equal to three times median whorl height. Ribs and striae strongly prorsiradiate on flank, curving back and crossing ventrolateral region and venter in broad eonvexity, branching into groups of two or three with additional intercalatories of variable strength and looped over venter. Growth striae strongly projeeted on dorsolateral area, passing more or less straight aeross aorsum. Marked distant constrietions on ventrolateral and ventral region, effacing at mid-flank. Suture (text-fig. lOA) with moderately subdivided bifid lobes and saddles with trigonal outline.
Ifrim et al. (2004):
Description: The straight test has a low expansion rate and an apical angle of c. 3 degrees. Shell is circular with a WBIWH ratio of c. 1. The phragmocone is smooth except for rare constrictions that are strongly projected forward on the flanks but disappear at middle-flank. They cross the dorsum in a wide arch. Striae are directed parallel to the constrictions but are extremely faint. The simple baculitid suture line is composed of moderately incised, symmetrical, bifid lobes and saddles with trigonal outline, and similar depths and heights. The dorsal saddle is slightly wider than other saddles and not strictly symmetrical. The ventral saddle is incised centrally at all growth stages.

Discussion / Comments:

Kennedy (1986):
Discussion. F. teres, the second species referred to Fresvillia, has a similar whorl section and course of growth lines, which are only slightly less projected. It is easily separated by its elose, even constrictions, quite different from the distant ones of F. constricta. The typically baculitid suture distinguishes F. constricta from fragments of the superficially homoeomorphous smoothing diplomoceratids such as Polyptychoceras, Phylloptychoceras, Astreptoceras, and their allies, while cross-section, form of ribs, and constrictions separate it from all contemporaneous baculitids. Differences from the Albian-Cenomanian Lechites and Cenomanian- Turonian Sciponoceras are noted under the generic discussion.
Ifrim et al. (2004):
Remarks: The circular whorl section and even suture line with triangular elements distinguish Fresvillia from Baculites; the conspicuous constrictions on the otherwise smooth internal moulds characterize the species and enable easy determination. Specimens with completely smooth surfaces are considered to belong to F. constricta because they are fragments without the distant constrictions. Fresvillia teres (Forbes) differs from F. constricta in having faint annular to ventrally prorsiradiate ribs. Occurrence: Fresvillia constricta Kennedy is known so far on1y from the Upper Maastrichtian Calcaire a Baculites, north-west France (Kennedy 1986b)

Systematics:

36
Ordo Ammonoidea
  Subordo Ancyloceratina
   Superfamilia Turrilitaceae
    Familia Baculitidae
     Genus Fresvillia
      Species Fresvillia constricta

39
  Ordo Ammonoidea
   Subordo Ancyloceratina
    Familia Baculitidae
     Genus Fresvillia
      Species Fresvillia constricta

Synonym list:

Ifrim et al. (2004):

1986 Fresvillia n sp. n. gen constricta Kennedy. - Kennedy : p.62 pl. 14, figs. 39-42; text-fig. 10a

2004 Fresvillia constricta Kennedy. - Ifrim et al. : 31, 34 text-figs. 12e-f, 13d-e

Stratigraphy - relative ages:

upper Maastrichtian, Ifrim et al. (2004): Ifrim et al. (2004)

References:

Kennedy,W.J.. (1986):
The ammonite fauna of the Calcaire à Baculites (Upper Maastrichtian) of the Cotentin Peninsula (Manche, France) . Palaeontology Vol. 29(1) p. 25-83

Ifrim,C..; Stinnesbeck,W.. and López-Oliva,J.G.. (2004):
Maastrichtian cephalopods from Cerralvo, north-eastern Mexico . Palaeontology Vol. 47(6) p. 1575–1627

Anonymous: Unedited TaxonConcept data

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