Conus
(Hemiconus) leroyi (Tracey & Craig, 2017)
The earliest record of Conidae is the late Thanetian
species Hemiconus leroyi (1).
The teleconch whorls of the single Paleocene Hemiconus, H.leroyi
Tracey & Craig, n. sp., and the Ypresian species bicoronatus Melleville,
fallax Pacaud, concinnus Sowerby, diastictus Cossmann, and
rouaulti d’Archiac, all share a similar morphology, being ornamented
with a row of beads immediately below the suture, a row of larger tubercles on the
periphery (i.e. shoulder), 2-4 spiral cords overriding the tubercles, and 1-3
weaker cords on the upper part of the whorl (1).
Type stratum and
locality of H. leroyi n. sp. : Paleocene (mid Thanetian), Châlons-sur-Vesle Formation, niveau 4 of LEROY et al. (2014), Cauroy-ès -Hermonville (Marne) France (1).
Distribution of H.
leroyi n. sp. : Known only from the
type locality and from Jonchery-sur-Vesle (COSSMANN, 1913) where a
similar horizon was formerly exposed (1).
Etymology of H.
leroyi n. sp.: Named in honour of
Arnaud LEROY, discoverer of the type locality and the first to illustrate an example
of this species (1).
Description of H.
leroyi n. sp. : Moderately small,
narrowly biconical shell, spire c. 32% of shell height ; whorl profile
slightly convex with 8-9 large, low rounded tubercles crossed by 2 spiral cords
and a prominent and strongly beaded subsutural collar with 3-4 finer spiral
threads below it. Tubercles persist to the last whorl where they form a broad,
rounded, nodular shoulder. Last whorl covered in close, fine spiral threads.
Sinus wide and shallow, aperture narrow with parallel sides ; paries long and
straight, columella short (1).
Holotype 14,1 x 6,1 mm.
Discussion of H.
leroyi n. sp. : Although COSSMANN first recorded what
was probably this species in 1913, that record has not been substantiated and
has been overlooked since. Subsequently the earliest conids have long been
considered to date from the early Eocene (middle Ypresian) (KOHN, 1990).
Although the whereabouts of the specimen recorded by COSSMANN is unknown, it is
assumed, in view of the rarity of cones in the Paleocene, that this was in fact
another example of H. leroyi n. sp.. Recently, LEROY et al. (2014) figured
this species and observed that it reached about twice the size of the Ypresian H.
bicoronatus (Melleville, 1843) but they did not formally describe it as
new. H. leroyi n. sp. differs from H. bicoronatus (Melleville,
1843) not only in its larger size but also in its more attenuated shape (1).
It more closely
resembles the Ypresian H. concinnus (Sowerby, 1821) which has, however,
a smooth upper body whorl, granulated cords on the whorl tops and 15 or more
tubercles per whorl. While the protoconch is as yet unknown, it is likely that
a multispiral state was plesiomorphic for the stem group of the Conidae.
Three of the four
Ypresian species that followed H. leroyi n. sp. also had multispiral
protoconchs, as did at least two later Eocene Hemiconus, i.e. H.
macrocentrus (Bayan, 1873) and H. scabriculus (Solander, 1766) and
indeed many other Eocene to Recent species of Conidae. We regard this as the
earliest species that can confidently be referred to the Conidae and its
shell morphology suggests that its latest common ancestor might have been
shared with the Turridae (sensu lato). Difficulties of preservation, owing to
fragility of some shells from this horizon, mean that certain details of its
ontogeny have yet to be described (1).
Paleocene: Hemiconus leroy
Ypresian: H.
bicoronatus, H. fallax, H. concinnus, H. diastictus, H, rouaulti
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Fig. 1 a-c Hemiconus leroyi Tracey &
Craig, n. sp. Holotype NHMUK PI TG 26839 (leg. S. TRACEY) mm. 14,1 x 6,1 Thanetian, Cauroy-les-Hermonville
(Marne) |
Bibliografia Consultata