Pterorytis pacanana new species (Gastropoda: Muricidae): circumstantial evidence for late Pliocene El Nino events in southern Peru

2005·2.4 MB·

THE NAUTILUS 119(4):164-168, 2005 Page 164
Pteronjtis pacanana new species (Gastropoda: Muricidae):
circumstantial evidence for late Pliocene El Niiio events in
southern Peru
Thomas DeVries
J.
Burke Museum ofNatin-al Histoiy and Culture
University ofWashington
Seattle, WA 98195 USA
ABSTRACT United States, and the northwestern Pacific Ocean. Its
lone appearance in a collection of endemic cool-water
Ptcronitis pacanana new species was discovered in upper muricids is another example of a thermally anomalous
Pliocene bioclastic sandstone near Chala, southern Peru,
molluscan species encountered in upper Pliocene and
Although it was found faitlier south than other Pterori/tis Pleistocene beds of southern Peru (Muizon and
species fromthe eastern equatorial Pacific Ocean, P. pacanana
most resembles P. roxaneae Petuch, 1994, from the PHocene DeVries, 1985; DeVries, 1986; Ortheb et al, 1990). A
Pinecrest beds of Florida. Its presence among endemic reasonable h}'pothesis is that these equatorial species
late Pliocene cool-water moUusks from high-energy shoreface were introduced to higher austral latitudes by warm-
paleoenvironments is thermally anomalous in die same sense water inciu'sions during the Pliocene and Pleistocene
as die rare occurrence of odier species from northern Peru comparable to modern incursions that cany Panamic
and Ecuador in upper Pliocene and Pleistocene strata molluscan lai-vae poleward duilng El Niiio events
from southern Peru. By analogy with modern thermally (DeVries, 1988; Arntz and Tarazona, 1990; Paredes et
anomalous mollusks that appear episodically off the coast of
al., 1998).
southern Peru and Chile, the Pliocene and Pleistocene
examples are circumstantial evidence forthe occasional south-
ward incursion of warm equatorial waters during former EI Geology
Niiio events.
Bioclastic sandstone and gravel and balanid coquina
overlie igneous basement in roadcuts along a series of
INTRODUCTION sweeping curves in the Panamerican Highway where it
descends towards the beach at Playa Huacllaco
Pliocene deposits in southern Peru arenotedforavariety (Figure 1). The sediments represent high-energy fore-
of muricid gastropods, most belonging to genera still shore and intertidal paleoenvironments that once
represented by extant species (e.g., Acantliina Fischer flanked steep cliffs. The section, prex-iously published
von Waldheim, 1807; Chorus Gray, 1847; ConchoJcpas
Lamarek, 1801; Crassilabnim Joiisseaume, 1880; Mitr-
egina Vermeij, 1998; Stramonita Schumacher, 1817; jr^r~rw.
Xanthochonis Fischer, 1884), but some from genera
entirely or locally extinct (e.g., Herminespina DeVries
and Vermeij, 1997; Traphon, Montfort, 1810) (DeVries,
1995, 1997,' 2000, 200.3, in press a, in press b; DeVries
and Vermeij, 1997). Specimens of most Phocene
muricids are not exceedingly difficult to find.
A well-preserved muricid from Pliocene bioclastic
sandstone south ofChala is, literally, the rare exception.
None have been found odier tlian a single shell plucked
irom a roadcut of the Panamerican Highway that
overlooks Playa Huacllaco. The lamellar fimbriate
varices of the Huacllaco specimen invite comparison SCALt
with ocenebrincs from Ecuador, the soutlieastern Contourintervalis100m
''isjiire 1. Type locality oi Ftcron/li.\ piKiinniui new species
'Mailing address: P.O. Box 1.^061, Burton, WA 98013 USA if)\ 1628).
T. DtAVies. 2005 Page 165
J.
Figures 2-8. Ptcronjiis species. 2, 3, 5. Pterorytis pacanana new species. Upper Pliocene. Holohpe, liW'BM 97772, length =
.30.9 nnn, width = 19.6 nnn. 2. Apertural view. 3. Abapeitural xdew. 5. Obhqiie xiew olspire. 4, 6-8. Ptcron/fis rvxaneae Petuch,
1994. UpperPliocene. Holotspe. Florida MuseumofNatural Histoiy, Gainesville, UFfi(S254, length = .33.3 nnn,width = 21..5 mm.
4. LateRil view. 6. Apertural view. 7. Abapertunil view. 8. Obli<jue view ofspire.
bv DeVries (2003), consists of four stratigraphic units. SYSTEMATICS
The ocenebrine specimen was found at the liase of Unit
III, just below strata where roiuided clasts of blackened Family Muricidae Rafinesque, 1815
andesite first appear in great numbers and below beds Subfamily Ocenebrinae Cossmann, 1903
where specimens oi Concliolepas andAcanihina acquire Genus Pferon/tis Conrad, 1862
dieir modem form (DeVries, 2000, 200.3). Subgenus Pteron/tis sensu stricto
The age of die HuacUaco beds is bracketed by basal
beds \\idi specimens of Concholepas nodosa Hupe, Type Specie.s: Murcx umhrifcr Conrad, 1832, by
1854, Acanthina triangularis DeVries, 2003, and Her- monot\pv.
minespina mirahilis (Moricke, 1896), which collectively
indicate an earlv late Pliocene age (DeVries and Ptcronjiis pucinKiiid new species
Frassinetti, 2003), and the uppermost and oldest of (Figures 2, 3, 5)
several marine terraces, whose elevation and largely
extant taxa suggest a latest Pliocene age (Muizon and Diagnosis: Shell small; textiu'e \va\y, shell thin. Five
De\ nes, 1985). lamellar, fimbriate varices; inten-arical nodes absent.
Three spiral cords; shoulder spiral cord strong. Sutnral
platform horizontal. Labral tooth absent.
MATERIALS AND METHODS
mm
Description: Shell 30.9 long (first teleoconch
The specimen from Peru described in this study was whorls missing), quadrate in profile, very thin, with
found bv die audior. Dimensions affected b\' breakage waxy texture. Spire estimated to be about 40 percent ol
are enclosed bv parentheses. The holotvpe is deposited shell length. Siphonal canal about 20-25 percent ofshell
at die Uni\"ersitv of Washington's Burke Musevmi of length. Protoconch and earliest teleoconch whorls
Natural Histor\' and Culture in Seattle, Washington missing. Upper sides of whorls planar, vertical; base of
(UWBM). body whorl shaiply constricted. Shoulder orthogonally
Page 166 THE NAUTILUS, Vol. 119, No. 4
angulate, sutures deeply impressed; sutural platform The absence of a closed siphonal canal does not argue
horizontal to slightlyconcave. Three lastwhorls with five against assignment oftlie single Huacllaco specimen to
lamellarvarices extending from fasciolar ridge to suture, Pteronjtis or Ocinebrelhis, sincejuvenile and some adult
each varLx joining across suture with varix of prevdous specimens ofthe two genera may have an open siphonal
whorl. Lamellae broader basally, narrower adapicall)-, canal. The Permdan specimen, itself partly abraded,
extended adapically at shoulder but not spinose; might be ajuvenile specimen or have a broken siphonal
fimbriate on adapertural face; erect or recun'ed canal.
adapertiu'ally except apertiu-al lamellae, which is weakly Distinguishing Pteronjtis from Ocinebrellus for place-
recun'ed abaperturally. Intervarical nodes absent. Spiral ment of the Huacllaco specimen is problematic.
sculpture ofprominent but ill-defined rounded primary Ocinebrelhis has fourprimaiyspiral cords on the swollen
cord atshoulderangulation and tvvo additional broad low portion ofthe bodywhorl, posteriortothe labral tooth, if
spiral cords anteriorly, almost obsolete. Additional broad present (Vermeij and Vokes, 1997; Amano and Vermeij,
low secondaiy cords barely \isible adjacent to adaper- 1998a). Pteronjtis and the Huacllaco specimen have
tural face ofvarices. Lamellar limbria slightly extended three priniaiy spiral cords, with an additional weak
at intersection with primaiy spii'al cords. Apertiire with primaiy spiral between the shoulder and suture. On
invertedtear-drop shape. Parietal rib, anal sulcus absent; smoother specimens of both genera the number of
parietal area unexcavated. Columella smooth, inner lip primaiy spiral cords can be difficult to enumerate, and
very weakly concave, adherent anteriorly. Outer lip on strongK- sculptured specimens the distinction be-
witliout dentition on inner edge. Labral tooth absent. tAveen primaiy and secondaiy spiral cords is unclear if
Siphonal canal open, slightly recused to right. Siphonal the ontogeny is unknown.
fasciole strongly arched, without rostrae. Pseudo-umbi- Other features are equally unsatisfactoiy for distin-
licus narrow, extending adapically beyond siphonal guishing the two genera. The reflection of lamellar
canal. varices is not reliable, since the lamellae may be
Holotj'pe: UWBM 97772, DV 162S-5, lower Upper adaperturally reflected, or not, in Ocinebrelhis (Amano
and Vermeij, 1998a), abaperturally reflected or erect in
Pliocene, length (30.9) nun, width 19.6 mm. Plerortjtis (Vermeij and Vokes, 1997), and erect or
Type Locality: Roadcut along the Panamerican High- reflected in either direction on the Huacllaco specimen.
way, 10 km south of Chala, on a winding descent from The angularity ofthe shoulder also fails as a distinguish-
a 200 m elevation terrace towards Playa Huacllaco, ing character. Most specimens of Ocinebrelhis have an
locality DV 1628, north side of first sweeping outside angulate shoulder and a horizontal sutural platform (as is
curve from base of outcrop, south side of road, near the case for the Huacllaco specimen), but some have
outcropWofigneous basement rock (Figure 1), 1.5^52' S, rounded shoulders. Most specimens of Pteronjtis have
74"10' (Chala 1:100,000 (luadrangle). broad, planar, steeply sloping sutural platforms, but
some have narrower, less inclined sutural platforms
Occurrence: Upper Pliocene, southern Peru. more like those of typical Ocinebrelhis and the
Huacllaco specimen.
Etymology: "Paca,' Quechua for 'high, and "nan,'
Quechua for 'p;ith.' rderring to the horizontal to The presence or absence of a labral tooth is not
concave sutural platform bordered above and below b\' diagnostic. Some ocenebrines actjuire a labral tooth only
in adulthood; the Huacllaco specimen might be a juve-
vertical walls ofthe whorls.
nile. Species of Pteronjtis that normally have a tooth (P.
Remarks: Pterorytis or Ociiifhrcllus Jousseaume, iiinbrifer Conratl, 1832; P. fliiviana ball, 1890) have
1880, is the most appropriate genus in which to place specimens lacking a tooth. Specimens of P. roxoneae
the Huacllaco specimen, which has five varices on at Petuch, 1994, never have a labral tooth (Vermeij and
least the last three whorls, consistent with the three to Vokes, 1997). Species oiOcinebrelhis (sensu Amano and
nine varices observed on fossil Atlantic species of Vermeij, 1998a) that normally lack a labral tooth have
Pteronjtis (Emerson, 1959; Vermeij, 2001), the four to specimens with a tooth. (In tlie more restrictive
five varices on the modern eastern Pacific Pteronjtis classification ol Houart and Sireiiko (2003), species of
hamatus (Hinds, 1844) (Emerson, 1985), and three to OciiH'brelhis do not have a labral tooth.)
twelve varices on specimens of OcinebrcUiis (Amano and Taking into account this taxonomic ambiguit\', the
Vermeij, 1998a). The ocenebrine genera Ccratostoma Huacllaco specimen is assigned to Pteronjtis. Species of
Herrmannsen. 1846, Ptcropuiyura Jousseaume, 1880, Pteronjtis (P. iinibrifer, F. fliiviana. P. roxaneae) t\pically
and Microrlu/ti.s Emerson, 1959, in contrast, have three have smooth-shelled variants such as the specimen from
prominent lamellar varices on all or at least the last two Huacllaco. Most specimens of Pteronjtis, like the
whorls (Vermeij and Yokes, 1997; Amano and Vermeij, Huacllaco specimen, feature a prominent primaiy spiral
1998a, 1998b). Specimens of Ceratostoma, Pteropiir- cord at the shoulder, but nonetheless usually lack spines
pura, Micri)iiii/tis, and some Ocenebra Gray, 1847, also or angulations tspicallv seen in specimens of Ocineb-
have intei-v'arical nodes, wliich are absent on the relhis.
Huacllaco specimen and specimens of Ptcron/fis and Pliocene Ecuadorian specimens assigned to Ocineb-
Ocinebrelhis. relhis by Vokes (1988) are smootli, ha\e a prominent
T. T. DeNries, 2005 Page 167
shoulder spiral bordering an inclined sutural platform, Table 1. Molliiscan species associated with Ptcrnnjtis paca-
and ha\-e \-arices that are onl\-\\eakl\- angulate; the\- nia\' nana, new species, which was found at the base ofUnit III of
be referred to Pteronjtis ecuodoria (Olsson, 1964). The\' the Upper I^Iiocene beds above PIa\a Huacllaco, Peru.
have a more fusiform profile and greater number of (* = Extiiu-tV
varices tlian the Huacllaco specimen.
The specimen of Pteronjtis pacanana most closelv Unit Ill4-I\' (\i)ungerj
resembles specimens ofthe Pliocene Ptcron/tis (Pteror- Acanthina unicornis (Bruguiere, 1789)
CanccUaria huccinoides Sowerbv, 1832
ijtis) roxaneae Petuch, 1994, (Figures 4, 6-8) from
Choromi/tilus chorus (Molina, 1782)
the Phocene Pinecrest beds of Florida (Vermeij and
* Chonis nrandis (Philippi, 1887) / C. gigantcns (Lesson,
\'okes. 1997). Specimens of both species are thin with
1846)
a \va\"S' textiu'e, have reduced spiral sculpture, and lack * Concholepas camerata DeVries, 2000
a labral tooth. Pinecrest specimens differ from the Concholepas concholepas (Bruguiere, 1789)
Huacllaco specimen in having four varices, not five, Crassilahnim crassilahnnn (Sowerbv, 1834)
\'aric;il lamellae that are broader adapicallw not abapi- Crcpidula dilafafn (Lamarck. 1822)
callw and a weak peripheral spiral cord bordering Eiirhoinalea lenticuhiiis (Sowerbv, 1835)
a sloping sutural platform, rather than the strongly Ghjci/mcris ovata (Broderip, 1843)
Mcsodcsma donacinni (Lamarck, 1818)
defined horizontal sutural platform of P. pacanana.
Mulinia edulis (King, 1831)
Contran'to\'ermeij andYokes (1997), the holotvpe ofP. Oliva peruviana Lamarck, 1811
roxancoc is neither excessi\el\' worn nor lacking the * Piscoaciitia new species
labral \ail\. Prisogaster niger (Wood, 1828)
Sinum cijmba (Menke, 1828)
Xanthochorus cassidifonnis (Blainxille, 1832)
DISCUSSION
Unit I+Il (older)
* Acanthina tiiangulnri'~ De\'ries. 2003
Pteronjtis pacanana is the third or fourth species of * Acmaeids
Pteronjtis recognized in tlie eastern Pacific Ocean, after Chlamijs cf. C, vidah (Philippi, 1887)
P. ecuadoria (Pliocene, Ecuador), P. hamatus (Recent, Chorormjtilus chorus (Molina, 1782)
nortliern Peiii [.\lamo and \'aldivieso, 1997], a species * Chonis grandis (Philippi, 1887)
\\\\h a protoconch unlike that of Ocinehrellus or any * Concholepas camerata DeVries. 2000
otlier ocenebrine [R. Houart, personal communication, * Concholepas nodosa (Moricke, 1896)
2005]), and an unnamed Recent ocenebrine from Fissurella spp.
nortliern Peru (Radwin and D'Attilio, 1976). These ta,\a * Henninespina inirahilis (Moricke. 1896)
define an eastern tropical Pacific complement to a clade Lithophaga sp.
* Piscoacritia coUapsa De\'ries and Hess, 2004
o{Pteronjtis species fromtlie southeastern United States * Straintinita new species
whose oldest members date to the late Miocene. * Tegida {Chlorostoma} new species
OcincbrcUus. w^hich ma\' be endemic to the northwest- Xaiithochonis buxeus (Broderip, 1833)
em Pacific (Amano and Vermeij, 199Sa; Houart and * Xanthochorus new species
Sirenko, 2003), extends back to the Earlv or Middle
Miocene. Ocinehrellus seems moi"phologicalIv more
similar to Pteronjtis than otlier ocenebrine clades, but
the trail offossil species that might lead from Japanese Sechura coastline of northern Peru {5'S) (Alamo and
Ocinehrellus to Panama and the Caribbean and beyond Valdi\ieso, 1997), are occasionally found in upper
to Peru\ian and Floridian Pteronjtis has yet to be Pleistocene terrace deposits near San Juan de Marcona
discoxered (Amano and X'ermeij, 1998a). (15°20'S), Sacaco (15"30'S), and Ilo (17°40'S) (DeVries,
The specimen of Pteronjtis pacanana from 16 S is 1986, 1988; Ortlieb et al., 1990). Ortlieb et al. (1990)
remarkable for its singular occurrence and equatorial proposed that the late Pleistocene thermalK' anomalous
affinits'. Associatedtaxa (Table 1) are entirelyendemic or species were introduced southward from equatorial
cool-water species that became prexalent after a pro- latitudes during El Niiio events. Several such immigra-
\incial mid-Phocene extinction that coincided with tions of equatorial mollusks have been documented
a global coohng event (Dowsett et al., 1996; DeVries, during modern El Niiios events (Arntz and Tarazona,
2001). The rare appearance of Pteronjtis in southern 1990; Paredes et al., 1998). The rare Phocene equatorial
Peru resembles that ofa mangrove bivahe, Anadara cf. species in southern Peru were probably introduced in
A. grandis (Broderip and Sowerbv. 1829), whose speci- tlie same manner.
mens are foundin small numbers in uppermost PHocene
ACKNOWLEDGMENTS
beds at 15'.30' S with cool-water species (Muizon and
DeX'ries. 1985; De\'ries, 1986). In a more recent
example, specimens of Chione hrog^gi (Pilsbrs- and 1 would like to thank Brandur Karlsson ol Re\4'ja\ik,
Olsson. 1943,1 and Cerithium stercusmuscanim X'alenci- Iceland, for his assistance in the field and Greg Herbert
ennes, 1833, both li\ing today only as far south as the (University of South Florida) for helpful discussions on
Page 168 THE NAUTILUS, Vol. 119, No. 4
ocenebrine taxouomv. G. J. V'ernieij and R. Houart De\'ries, T. J. and C^. D. Frassinetti. 2003. Range extensions
provided helpful critiques in their reviews of the and biogeographic implications of Ghilean Neogene
manuscript. moUusks lound in Peru. Boletin del Museo de Historia
Natural, Chile 52: 141-157.
DeVries, T. and G. Vermeij. 1997. Hcnnlnespina: New
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