Ancistrolepis carolineae, SQUIRES, 1984

Squires, Richard L., 2022, The earliest Ancistrolepis (Gastropoda: Buccinidae) and its geologic implications, PaleoBios 39 (2), pp. 1-11 : 5-7

ANCISTROLEPIS CAROLINEAE SQUIRES, 1984

FIG. 4A–I

Ancistrolepis? carolineae Squires, 1984 . p. 30, figs. 8d–e. Groves and Squires. 2021. p. 191.

Primary type material— Holotype LACMIP 10554 [originally UCLA 59401 ], LACMIP Locality 7242.35 . Paratype LACMIP 10555 , LACMIP Locality 7242.36; paratype LACMIP 10556 , LACMIP Locality 7242.37; and paratype LACMIP 10557 , LACMIP Locality 22312.14. These three paratypes were originally referred to as lot UCLA 59402 , which was, at some point in the past, split into the three lots listed here. LACMIP Locality 7242 is equivalent to UCLA Locality 22312 (originally UCLA Locality 2312 (collected by W.P.Popenoe classes, April 19, 1946 and 1950).

Dimensions of holotype — Length 32 mm, width 20 mm (specimen is missing most its anterior siphonal canal).

Secondary type material— LACMIP hypotype 14904, LACMIP Locality 40444.2; LACMIP hypotype 14905, LACMIP Locality 40374.75; LACMIP hypotype 14906, LACMIP Locality 40374.76; and LACMIP hypotype LACMIP 14907 , LACMIP Locality 40374.77 .

Number of specimens examined— Seventeen specimens. All are from four localities (7242, 40374, 40444, and 40479) in the “Stewart bed”of the Llajas Formation on the north side of Simi Valley , Ventura County, southern California. Nearly all the specimens are from the Las

Llajas Canyon area: LACMIP Localities 7242 and 40374, ribs on ante-penultimate whorl, 3 ribs on penultimate which are in the immediate vicinity of each another, and whorl, and 6 (on most specimens) to 8 (rarely) ribs on Locality 40444, which is a short distance northwest- last whorl. Several widely spaced secondary spiral ribs wardly. The one exception is a specimen from LACMIP can be present inside of surface of apertural area and Locality 40479, approximately 3 km westardly of the represent continuations of primary ribs on main surface localities in Las Llajas Canyon. of last whorl. Spacing of spirals usually consistent at 3

Description– Shell ovate fusiform, shell very thin mm apart but can be as much as 4 mm apart, even on a (“paper thin”), up to 30.4 mm height and 17.7 mm single specimen. Spiral ribs beveled (not square-edged); width, with corresponding h/w = 1.72; average h/w of interstitally (especially on columellar inner lip) with five all specimens = 1.59. Protoconch/shell apex missing, bands of spiral microscopic threads alternating with upper spire incomplete on most specimens. Teleoconch bands of five spiral submicroscopic threads; comprising up to 5 whorls; commonly only four teleoconch whorls a grand total of 25 threads. Columella has almost none present. Suture impressed and coincident with spiral to only slight twist to left; no columellar teeth; anterior rib. Only spiral ribs (widely spaced); no radial sculpture. part of columella can have a few intermediate-strength Earliest two teleoconch whorls smooth (ribs apparently ribs, becoming obsolete anteriorward and interiorward. eroded off), 2 ribs on pre-ante penultimate whorl, 2 Siphonal canal moderately long. Outer lip “terminal varix,” 3 mm thick, smooth, solid, and flattish but with beveled on both outermost and innermost edges; minute threads axially parallel to edge of outer lip.

Remarks— The holotype has been missing for several decades. A copy of a Kodrachrome 35-mm slide of the holotype, taken by the author 30 years ago, is shown on the “Cover” of this present paper. The specimens of A. carolineae all have moderately poor to poor preservation because of weathering, which has caused some of the shells, which had thin shells to begin with, to become to steinkerns or nearly so. Weathering has probably caused the spiral ribs to be somewhat rounded.

Four of the 17 Llajas Formation specimens of A. carolineae have an obvious, relatively wide, flat, and sturdy thickening (callus) of the outer lip (terminal varix) of the aperture. A search of the available literature revealed that no other ancistrolepine (fossil or extant) has such a wide and flat outer lip callus, although a few extant species can have a very thin, narrow ridge callus. A terminal “varix” is common in warm, shallow-marine gastropods, but is rare in polar and deep-marine habitats ( Webster and Vermeij 2017), therefore, the presence of this feature on A. carolineae might be another indication that A. carolineae lived in an environment quite different than the extant Ancistrolepi s spp.

Ancistrolepis carolineae most closely resembles Ancistrolepis rategiensis Titova, 1993 (p. 12, figs. 2A–2D) from the upper Eocene Rategian Formation at Podkagernaya Bay, northwestern Kamchakta. The Llajas Formation species is similar in its ovate-fusiform shell shape, approximately five rounded whorls, rounded base on last whorl, subtriangular to triangular spiral ribs, about seven spiral ribs (can be variously spaced) on last whorl, and interstitial ribs on last whorl of some specimens. Ancistrolepis carolineae differs from this Kamchakta species by having a smaller size shell, fewer spiral ribs on the spire whorls, many fewer and much less closely spaced spiral ribs on the siphonal canal, and the presence of a terminal varix on the outer lip.

Titova (1993) reported that Ancistrolepis rategiensis Titova, 1993 shows much similarity to Ancistrolepis matchgarense ( Makiyama, 1934: p. 165, pl. 7, figs. 56, 57) from the upper Oligocene Asagai Sandstone near Matchgar in northern Sakhalin. The Llajas Formation species is similar, therefore, to A. matchgarense , but this latter species, which has a small shell (like A. carolineae ) has rather poor preservation (interstitial threads not visible) and its siphonal canal is missing. The Llajas Formation species differs by having a “terminal varix” on the outer lip. Ancistrolepis matchgarense occurs with calcareous concretions containing Turritella , which is a shallow-marine gastropod.

Ancistrolepis carolineae , A. rategiensis , and A. matchgarense differ from most other species of this genus by having subtriangular spiral ribs, rounded whorls, and a rounded shell base. Four other species, all from the Kuschiro coal fields in Japan, that share these particular properties are A. chizuzenensis ( Matsui, 1958) ; A. onbetsuensis ( Matsui, 1959) ; A. subcarinata ( Matsui, 1958) ; and A. ezoana Takeda, 1953 .

Previous workers ( Titova 1993, Egorov and Barsukov 1994) have placed various species of Ancistrolepis into two informal groups, referred commonly to as the eucosmius “stock” and the grammatus “stock.” The eucosmius “stock,” bearing the name of the type species of Ancistrolepis , is supposedly characterized by relatively small shells with relatively few spiral ribs, which are narrow and have a square shape. The grammatus “stock,” has larger shells with much stronger spiral ribs, commonly referred to as “T” ribs

Figures

Figure 4A–I. Ancistrolepis carolineae Squires, 1984. “Stewart bed,” Llajas Formation, north side of Simi Valley, Ventura County, southern California. Apertural (A) and abapertural (B) views, 1.7x, length 32 mm, width 20 mm, plasto-holotype, LACMIP 10554 [=UCLA 59401], Locality LACMIP 7242.35. Apertural (C) and abapertural (D) views, x1.8x, length 28.8 mm, width 18.4 mm, hypotype, LACMIP 14904, LACMIP Locality 40444.2. Apertural (E) view, 1.8x, length 26.3, width 14.9, hypotype, LACMIP 14905, LACMIP 40374.75. Apertural (F) and abapertural (G) views, x2.3, length 22 mm, width 15.8 mm, hypotype, LACMIP 14906, LACMIP Locality 40374.76. Right-lateral apertural, with aperture end tilted up slightly (H) and oblique lower columellar (I) views, x2.5, length 28.5 mm, width 29.8 mm, hypotype, LACMIP 14907, LACMIP Locality 40374.77.