𝑃ℎ𝑎𝑡𝑡ℎ𝑎𝑙𝑢𝑛𝑔𝑜𝑐𝑒𝑟𝑎𝑠 𝑠𝑟𝑖𝑠𝑢𝑘𝑖 A New Genus and Species of Triassic Nautiloid Cephalopod (Cephalopoda, Orthoceratoidea, Orthoceratidae) from Eastern Peninsular Thailand

Abstract

𝑃ℎ𝑎𝑡𝑡ℎ𝑎𝑙𝑢𝑛𝑔𝑜𝑐𝑒𝑟𝑎𝑠 𝑠𝑟𝑖𝑠𝑢𝑘𝑖 gen. et sp. nov. (Orthoceratidae) has been collected from Khao Ok-Thalu, Chaiburi Formation, Triassic Strata in Phatthalung province, in eastern peninsular Thailand and is described as a new genus and species based on the characteristics of the internal mold of the phragmocone. The new genus is distinguished from other family members by its elliptical cross section of the conch as well as suborthochoanitic septal neck and free endosiphuncular deposit. Ornamentation is absent.

Full text

Phuket mar. biol. Cent. Res. Bull. 75: 13–18 (2018)
Phatthalungoceras srisuki A NEW GENUS AND SPECIES OF TRIASSIC NAUTILOID
CEPHALOPOD (CEPHALOPODA, ORTHOCERATOIDEA, ORTHOCERATIDAE) FROM
EASTERN PENINSULAR THAILAND
Kittichai Tongtherm1 and Jaruwat Nabhitabhata2*
1 Department of Biology, Faculty of Science, Prince of Songkla University,
Hatyai, Songkhla 90112, Thailand
2 Excellence Centre for Biodiversity of Peninsular Thailand (CBIPT), Faculty of Science,
Prince of Songkla University, Hatyai, Songkhla 90112, Thailand
*Corresponding author: Email: jaruwat.n5@gmail.com, jaruwat.n@psu.ac.th
INTRODUCTION
The eastern part of peninsular Thailand
geologically belongs to the Shan-Thai or Sibumasu
microplate or terrane (DMR, 2001; 2014). Khao
Ok-Thalu or Khao Thammalai in Phatthalung
province (Changwat Phatthalung; 07º37´N, 100º 05´E)
is one of several isolated limestone monadnock
scattered in the Quaternary plain of the Phatthalung
area. The hill is about 2 km in length with a 245 m
peak above sea level and is located at the 100º
longitude line, about 2 km northeast of Amphoe
Muang Phatthalung, (Fig. 1). The marine carbonate
rocks in the area belong to the Chaiburi Formation,
which are of Early to Late Triassic age based on
micropaleontological evidence (Ampornmaha, 1995;
Sardsud, 2001; Sardsud et al., 2017). Khao Ok-Thalu
belongs to the lower/middle/upper member of the
Chaiburi Formation, the Chiak Limestone Member,
which consists of laminated mudstone and bioclastic
mudstone. These strata strike N10°W and dip 55-
60°E (DMR, 2001; 2014; Sardsud, 2001). Fossils
of radiolarians, ostracods, gastropods and echino-
GHUPV IRXQG LQ WKLV PHPEHU DUH ¿OOHG ZLWK FOHDU
calcite cement, and geopetal fabrics (Ampornmaha,
1995; Sardsud, 2001). Conodonts date this member
as Early Anisian to Late Carnian (Sardsud, 2002;
Sardsud et al., 2017).
Cephalopod fossils in Thailand are known
from only a few localities. In peninsular Thailand,
nautiloids have been recorded only from Ordovician
Silurian, Carboniferous and Triassic strata (Tongtherm
et al., 2016a; b; 2017). Moreover, previous records of
Anisian Triassic orthocerids elsewhere are relatively
rare. The present specimen of this nautiloid fossil
was collected from Khao Ok-Thalu, Phatthalung
province (Changwat Phatthalung), peninsular Thailand
as an outcrop fossil by Mr. Paladej Srisuk.
MATERIALS AND METHODS
One specimen of nautiloid fossil was collected
from Khao Ok-Thalu, Phatthalung province
(Changwat Phatthalung), peninsular Thailand
(07o37´N, 100o05´E) (Fig. 1), by Mr. Paladej Srisuk
on 2 September 1973. The systematic terminology of
morphology and measurements generally follows
Teichert et al. (1964). The description of nautiloid
specimens was made using the following abbreviations
for shell dimensions: Pl = Phragmocone length, Paw
= Phragmocone anterior width, Ppw = Phragmocone
posterior width, Nc = Number of chambers, Cl =
Chamber length. The type specimen is deposited in
Palaeontological Research and Education Centre,
Mahasarakham University (PRC), Thailand, with
SUH¿[HG FDWDORJXH QXPEHU 35&6+0.2
7KDLZRUGVXVHGLQWKHWH[WDUH.KDRPHDQVPRXQWDLQ
or steep hill, Muang means city and Changwat
means province.
ABSTRACT: Phatthalungoceras srisuki gen. et sp. nov. (Orthoceratidae) has been collected from Khao
Ok-Thalu, Chaiburi Formation, Triassic Strata in Phatthalung province, in eastern peninsular Thailand and
is described as a new genus and species based on the characteristics of the internal mold of the phragmocone.
The new genus is distinguished from other family members by its elliptical cross section of the conch as
well as suborthochoanitic septal neck and free endosiphuncular deposit. Ornamentation is absent.
Keywords: new genus, new species, Triassic, nautiloid, Thailand.

Phuket mar. biol. Cent. Res. Bull.
14
Figure 1. Type locality; Khao Ok-Thalu, Changwat Phatthalung, Peninsular Thailand: 1. Phukhaothong
Dolomite, Khao Khuha-Sawan; 2. Chiak Limestone Member, the eastern zone of Khao Ok-Thalu; 3. Specimen
FROOHFWLRQVLWHFLUFOH1(0RGL¿HGIURP*RRJOHPDSQXPEHUVGHQRWHKLJKZD\QXPEHUV
RESULTS
Order Orthocerida Kuhn, 1940
Family Orthoceratidae M’Coy, 1844
Phatthalungoceras gen. nov.
Fig. 2
Tienoceras sp. A; Tongtherm et alDS௅
௅¿J௅
Tienoceras sp. A; Tongtherm et alES௅
¿JF௅K
Type species: Phatthalungoceras srisuki sp. nov.,
designated herein.
Material examined
Holotype: PRC-SKM-KO-151, Phragmocone
internal mold, Phragmocone length 16.97 mm,
Chaiburi Formation, Triassic (Anisian), Khao
Ok-Thalu, Changwat Phatthalung, Peninsular Thailand,
07o37´N, 100o05´E, collector P. Srisuk.
Description. Shell smooth, cross section elliptical,
GHSUHVVHG GRUVXP FRQYH[ YHQWUXP ÀDWVWUDLJKW

Phatthalungoceras srisuki a new genus and species of Triassic nautiloid cephalopod
15
lateral acute angle absent; cameral deposit present,
on mural, episeptal and connecting ring; siphuncle
VXEFHQWUDO VHJPHQWHG H[SDQGHG HQGRVLSKXQFXODU
deposit free; suture 1 saddle on dorsum, 2 on
ventrum.
Etymology. The name is an arbitrary combination
of Phatthalung province (Changwat Phatthalung),
the type locality, in combination with the Latin
³FHUDV´IRUKRUQHGVHUSHQW*HQGHURIJHQXVQHXWHU
Remarks. Phatthalungoceras shares many characters
of the genus with the Permian Tienoceras but
GL൵HUV LQ PRUSKRORJ\ RI WKH FURVV VHFWLRQ RI WKH
conch which is lenticular with acute-angular
lateral sides in Tienoceras (Chao, 1954; p. 36, pl.
¿J&KDRGLGQRWDVVLJQTienoceras to
DQ\ KLJKHU WD[RQRPLF UDQN EHFDXVH WKH KRORW\SH
was not well preserved. T. lenticulare is the only
species of the genus. We suggest that Tienoceras
should belong to the Order Orthocerida Kuhn,
1940, Superfamily Orthocerataceae, Family Ortho-
ceratidae, based on its orthochoanitic to subortho-
choanitic phragmocone and the free endosiphuncular
deposit. Such characteristics are also presented
in Phatthalungoceras. It is notable that the two
JHQHUD DUH IURP GL൵HUHQW V\VWHPV Tienoceras is
IURPWKH3HUPLDQ+XQDQSURYLQFH&KLQD&KDR
1954; Teichert et al., 1964) and Phatthalungoceras
is from Triassic strata.
Phatthalungoceras srisuki sp. nov.
Fig. 2
Material examined. As for description of genus.
Description. Phragmocone fragment, orthoconic
longicone, 4 chambers preserved, length 16.9 mm,
conch depressed, ornament absent; cross section
width anterior 5.7 mm, posterior 4.5 mm, dorsum
FRQYH[ YHQWUXP ÀDWWHQHG YHQWURODWHUDO DQJOH
round; chamber dense, length 2.9 mm; cameral
deposit present, secondary, mural thick; septal
QHFNVXERUWKRFKRDQLWLFVLSKXQFOHFHQWUDOH[SDQGHG
VHJPHQWHGGLDPHWHU ௅PPHQGRVLSKXQFXODU
deposit free; suture one dorsal saddle, 2 ventral
saddles with 1 median lobe.
Measurements and counts. Pl. 19.7 mm, Paw 5.7
mm, Ppw 4.5 mm, Nc 4 chambers, Cl 2.9 mm.
Etymology. The name ‘srisuki’ (Latin for “Srisuk”)
commemorate the type-specimen collector, Paladej
Srisuk, Palaeontological Research and Education
Centre, Mahasarakham University.
Remarks. The characters that distinguish
Phatthalungoceras srisuki from the similar species
T. lenticulare have already been discussed on the
basis of their generic characters.
DISCUSSION
Phatthalungoceras srisuki LVWKH¿UVWQHZJHQXV
and species described from peninsular Thailand.
Occurrence of orthocerid nautiloids from Triassic
VWUDWDLVUDUHDQGWKHQHZWD[RQLVDOVRWKH¿UVWRQH
in this region, the mainland of Southeast Asia.
ACKNOWLEDGEMENTS
The authors would like to thank the Palaeon-
tological Research and Education Centre, Ma-
hasarakham University, Thailand, for the loan of
WKHVSHFLPHQLQ WKLV VWXG\:HDOVR WKDQNVWD൵RI
WKH([FHOOHQFH&HQWUHIRU%LRGLYHUVLW\RI3HQLQVXODU
7KDLODQG 'HSDUWPHQW RI %LRORJ\ DQG 3ULQFHVV
0DKD&KDNUL6LULQGKRUQ1DWXUDO+LVWRU\0XVHXP
Faculty of Science, Prince of Songkla University
for their assistance in the laboratory work. Our
warmest thanks are dedicated to Dr. Janek von
%\HUQ&RUH)DFLOLW\&HOO,PDJLQJDQG8OWUDVWUXFWXUH
Research, University of Vienna. This work was
DOVRVXSSRUWHGE\ WKH +LJKHU(GXFDWLRQ5HVHDUFK
Promotion and National Research University Project
RI 7KDLODQG 2൶FH RI WKH +LJKHU (GXFDWLRQ
Commission and ASEA-UNINETS research grant,
University of Vienna. Also thanks to the late Dr.
%ULDQ+RGJVRQDQG'U$QQD&KDWWKRQJIRUDVVLVWDQFH
with the English language corrections.

Phuket mar. biol. Cent. Res. Bull.
16
Figure 2. Phatthalungoceras srisukiJHQHWVSQRY+RORW\SH35&6+0.2DDQGEGRUVDOYLHZ
of the phragmocone with suture on the posterior; 2a. and 2b. cross section of anterior view of the phragmo-
FRQHODWHUDOYLHZZLWKVXWXUHRQDQWHULRUWRSRVWHULRUVXWXUHGGRUVDOD[LVYYHQWUDOD[LVDDQG
5b. ventral view of the phragmocone with suture on the anterior; 5c. posterior view of the phragmocone
with central siphuncle; 5d. cross section in posterior; 5e. and 5f. segmented siphuncle and suborthochoanitic
septal neck at the posterior. Scale bar = 10 mm.

Phatthalungoceras srisuki a new genus and species of Triassic nautiloid cephalopod
17
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Manuscript received: 10 January 2017
Accepted: 9 January 2018