Conus burckhardti harrisi

Conus burckhardti (Bose, 1906)

Descrizione e caratteristiche:

Shell of moderate size, subcylindric with a high, even, conic spire; spire whorls about six plus, flat, with close sutures, except for the upper whorls which are slightly carinate; the surface of the spire whorls is nearly smooth except for a few faint spirals; the last or body whorl is strongly sculptured with wielt spaced and sub-regular grooves; these grooves form about 14 wide, spiral bands about the lower 3-4^th of the last whorl; the upper 4^th below the shoulder angle forms a wide, smooth band; below, the spiral bands are generally smooth except those about the lower half of the shell, which may become, mesially divided and bear a few small granulations or beads about their upper half; aperture sublinear ⁽¹⁾.

A single specimen of this elegant species was collected from the Gatun of Banana River. It is a specie of the Conus burckhardti (Bose, 1906) type but much larger and when perfect reaching a length of nearly 60 mm. The sculpture is of wide bands formed by deep, and regularly spaced grooves about the lower 3-4ths of the shell ⁽¹⁾.

Remarks ⁽⁴⁾.— Conasprella burckhardti was described by Böse (1906) from Tuxtepec in the Tehuantepec region of Oaxaca, México from deposits that both Woodring (1966, 1970) and Beu (2009) reported as middle Miocene in age. An artificial cast (PRI 70566) of the type specimen (IGM 170; Fig. .1, 4.2) was kindly provided by Dr. Perrilliat at the Colección Nacional de Paleontología, Instituto de Geología. Woodring (1970) was the first to apply the name C. burckhardti to material from the Gatun Formation, and his circumscription of the material he examined from the Gatun Formation is consistent with the features of IGM 170. Conasprella burckhardti was the second most commonly collected species at UF locality YN020.

Woodring (1970) treated Conus harrisi Olsson, 1922 (Fig. 4.5) as a subspecies of Conus burckhardti. The specimen (USNM 645754; Fig. 4.4) figured by Woodring (1970) differs from typical C. burckhardti in the very narrow width of its shell (RD 0.44), but it is otherwise consistent in shell characteristics with other C. burckhardti. Conasprella burckhardti harrisi is thus treated here simply as C. burckhardti. While Woodring (1970) only reported C. burckhardti burckhardti from the middle and upper Gatun Formation, most of the shells found at UF locality YN020 (lower Gatun Formation) are more consistent with this wider form than they are with the narrower Conasprella burckhardti harrisi morphology. Both morphologies span the Gatun Formation ⁽⁴⁾.

Conus burckhardti ⁽³⁾

Plate V figs. 39, 40

mm. 25 x 10

Conus burckhardti

IGM 793

Conus burckhardti harrisi (Olsson, 1922)

Shell of moderate size, subcylindric with a high, even, conic spire; spire-whorls about 6 plus, flat, with close sutures, except for the upper whorls which are slightly carinate; the surface of the spire-whorls is nearly smooth, except for a few faint spirals; the last or body whorl is strongly sculptured with widely spaced and sub-regular grooves; these grooves form about 14 wide, spiral bands about the lower ¾ th of the last whorl; the upper 4th below the shoulder angle forms a wide, smooth band; below, the spiral bands are generally smooth except those about the lower half of the shell, which may become, mesially divided and bear a few small granulations or beads about their upper half; aperture sublinear ⁽¹⁾.

Height 51, diameter 23 mm.

A single specimen of this elegant species was collected from the Gatun of the Banana River. It is a species of the Conus burckhardti type but much larger and when perfect reaching a length of nearly 60 ram. The sculpture is of wide bands formed by deep, and regularly spaced grooves about the lower ¾ th of the shell.

Gatun Stage: Hill No. 3, Banana River.

Resembling Conus burckchardti burckhardti, but outline more slender. Carinate and tuberculate shoulder appearing near end of first post-protoconch whorl and spiral cords on upper part of mature body whorl wider. Tubercles gradually disappearing on second or third whorl. Spiral sculpture on anal fasciole limited to faint lineation ⁽⁵⁾.

Height 37,7 mm, diameter 13,5 mm (figured specimen) ⁽⁵⁾.

Type: Paleontological Research Inst. 20899.

Type locality: Rio Banana, Limon Prov., Costa Rica, middle Miocene.

This slender subspecies of Conus burckhardti is represented by 22 specimens from the lower and middle parts of the Gatun formation. An exceptionally slender shell from the upper part in the eastern area is doubtfully identified, as the shoulder and the spire whorls are missing. The slender outline and greater width of the spiral cords on mature body whorls are the most diagnostic features distinguishing C. burckhardti harrisi from the nominate subspecies. The other differences mentioned in the brief description are of no significance. In both Costa Rica and Venezuela C.burckhardti harrisi reaches a larger size (height about 60 mm) than in the Canal Zone. Both subspecies are in the collection from locality 155, but that collection is not narrowly controlled stratigraphically ⁽⁵⁾.

C. alaquaensis Mansfield (1935, p. 18, pi. 1, fig. 7; upper Miocene, Florida) is wider at the shoulder and sharply carinate ⁽⁵⁾.

Occurrence: Lower, middle, and possibly upper parts of Gatun formation (middle Miocene). Lower part, localities 136, 136a, 138a, 138c, 138d. Middle part, eastern area, localities 139c, 139e, 155. Upper part, eastern area, locality I77d (identification doubtful) ⁽⁵⁾.

Deposits of early (?) Miocene age, Ecuador. Middle Miocene deposits, southeastern Costa Rica. Punta Gavilan formation (late Miocene), Venezuela⁽⁵⁾.

Conus harrisi ⁽¹⁾

Gatun Stage

mm. 51 x 23

Banana River – Costa Rica

Conus harrisi ⁽⁴⁾

Hoilotype PRI 20899

Banana River, Panama

portion of SL preserved

53,0 mm

Conus harrisi ⁽²⁾

USNM 643939

mm. 36

Mompiche – Portete

Ecuador

Plate 11 Fig. 6

Figure 4. ⁽⁴⁾

Conasprella burckhardti (Böse, 1906)

(1, 2, 4–8) photographed under regular light;

(3, 9–23) photographed under UV light;

specimens are from UF locality YN020 unless otherwise indicated.

(1, 2) Artificial cast of IGM 170 (PRI 70566), holotype of Conus burckhardti Böse, 1906, Tuxtepec, Oaxaca, Mexico, portion of SL preserved 21.6mm (measured from a digital image);

(3) USNM 645752, specimen figured by Woodring (1970, pl. 57, fig. 19),

SL 42.3 mm, Panama Canal Zone, Woodring locality 155, middle Gatun Formation;

(4) USNM 645754, specimen figured by Woodring (1970, pl. 57, fig. 17), SL 37.8 mm, Panama Canal Zone, Woodring locality 138a, lower Gatun Formation;

(5) PRI 20899, holotype of Conus harrisi Olsson, 1922, Banana River, Panama, portion of SL preserved 53.0 mm;

(6, 12) UF 270984, SL 17.2 mm, showing features of the protoconch and early postnuclear whorls; (7, 19) UF 270985, SL 26.0 mm, showing growth lines on the sutural ramp, indicating the shape of the subsutural flexure;

(8) UF 259819, showing ornamentation features of the last whorl;

(9, 10) UF 270986, SL 34.9 mm;

(11) UF 259811, SL 30.5 mm;

(13) UF 270987, SL 25.9 mm;

(14) UF 270988, SL 31.0 mm;

(15) UF 270989, SL 24.5 mm;

(16) UF 270990, SL 33.3 mm;

(17) UF 259831, SL 26.6 mm;

(18) UF 270991, SL 25.1 mm;

(20) UF 259813, SL 23.3 mm;

(21) UF 270992, SL 21.2 mm;

(22) UF 270993, SL 26.7 mm;

(23) UF 270994, SL 30.3 mm.

Scale bar to left of (1) is 1 cm and pertains to all but (6–8), which are focus-stacked

composite images; (6) scale bar equals 0.5mm and (7, 8) scale bars equal 1 mm.

Bibliografia Consultata

· (1) - Olsson (1922) “The Miocene of Northern Costa Rica”

· (2) - Olsson (1964) “Neogene Mollusks from Nortwestern Ecuador”

· (3) - Bose (1906) “Sobre algunas faunas terciarias de Mexico”