Me (as2et5. 1) 
Bull. nat. Hist. Mus. Lond. (Zool.) 68(1): 27-37 
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Issued 27 June 2002 

A redescription of Sousa chinensis (Osbeck, 
1765) (Mammalia, Delphinidae) and 
designation of a neotype 

L.J. PORTER 
The Swire Institute of Marine Science, The University of Hong Kong, Cape d’Aguilar, Shek O, Hong Kong 
Special Administrative Region, China. 
Synopsis. The holotype of the delphinid Sousa chinensis, held in the collection of the Royal College of Surgeons, London, was 
destroyed during the Second World War. The neotype is described herein from a male specimen obtained from the waters of Hong 
Kong (the Hong Kong Special Administrative Region of China since | July 1997). This dolphin was found newly dead in May 
1996 and death determined as heart failure brought about by entanglement with fishing gear. There is currently debate over 
divisions within the genus Sousa although recent reviews suggest that the five nominal species currently designated likely 
comprise but one. A description of the neotype’s external appearance and skeletal elements is given and compared with the 
information that remains for the holotype and for other specimens obtained from Hong Kong waters. 
INTRODUCTION 
The species Sousa chinensis (formerly Delphinus sinensis) (Osbeck, 
1765) was designated after observations were made of a population 
of delphinids within the Pearl River Estuary, Guangdong Province, 
Southern China, i.e. close to Hong Kong. It was over one hundred 
years after the species was named, however, that the first skeleton 
was described from an almost entire individual collected from 
Xiamen (formerly Amoy), Fujian Province, approximately 700km 
northeast of Hong Kong (Flower, 1870). This specimen and, thus, 
the holotype of the species was held in the collections of the Royal 
College of Surgeons, London, but was subsequently destroyed 
during the Second World War. 
Osbeck’s original account noted ‘Snow-white Dolphins tumbled 
about the ship; but at a distance they seemed nothing different from 
the common species, except in their white colour’. The holotype was 
physically mature and although the external appearance of this 
particular individual was not described, the typical coloration of 
members of the Xiamen population was noted to be ‘milky white, 
with pinkish fins and black eyes’ (Flower, 1870). The individuals 
that remain in the Pearl River and Jiulong Jiang River (Xiamen) 
Estuaries today, are similar in external appearances (Porter, 1998). 
Four other species are included in the genus Sousa (Table 1), 
although there has been debate as to where the taxonomic divisions 
within it, if any, actually occur (Pilleri & Gihr, 1972; Mitchell, 1975; 
Zhou et al., 1980; Wang & Sun, 1982; Ross et al., 1994). The most 
recent classification of the genus as comprising one species was 
based upon a morphological review (Ross ef al., 1996) and a 
molecular investigation of the genus concurred with this definition 
(Cockcroft et al., 1997). Both of these publications, however, noted 
that the limited availability of data from parts of the species’ range, 
particularly Asia, did not allow definitive segregation at a sub- 
specific level and, as such, the taxonomy of the genus is not 
resolved. 
There have been many strandings of Sousa chinensis in Hong 
Kong waters, which comprise the eastern portion of the Pearl River 
Estuary, since 1990 (Porter et al., 1998) although the cause of death 
in many cases could not be determined due to either the decomposi- 
tion of, or damage to, the remains. In May 1996, however, a fresh 
© The Natural History Museum, 2002 
specimen identified as S. chinensis was retrieved and on which a full 
necropsy was performed. The cause of death was determined as 
heart failure, most likely due to entanglement with fishing gear, as 
deduced by the presence of fresh net abrasions on the rostrum and 
neck area. This specimen has been chosen for designation as the 
neotype of S. chinensis because: (a), it was obtained from the area 
from which the species was originally identified; (b), it was neither 
significantly different from the description of the extant holotype 
nor other individuals measured from the Hong Kong population of 
S. chinensis; (c), its death was perceived to be accidental rather than 
a consequence of any ailment or abnormality and (d), its remains 
were intact. 
MATERIALS AND METHODS 
A modification of the criteria described by Perrin (1975) was used to 
measure the skeleton obtained from Hong Kong and herein desig- 
nated as the neotype. The tympanoperiotic bones were measured in 
accordance with Kasuya (1973). Other skeletal remains of the same 
species were also examined and measured to obtain a better range of 
values for the species in this component of its range. All measure- 
ments were made with EPI precision calipers and recorded to the 
nearest millimetre or, in the case of smaller bones, 0.1 mm. Each 
measurement was taken several times until a confident value was 
established. An inventory of the measurements recorded for the 
neotype is included as Appendix I. 
The neotype and other Hong Kong specimens were aged from 
three teeth, selected from the upper left jaw, which were sliced to a 
thickness of 110um. The sections were etched for one hour by 
emersion in 5% formic acid and the dentinal growth layer groups 
then counted under a light microscope. One pair of dark and light 
stained layers is equivalent to one dentinal growth layer group 
which is assumed to be gained annually (Kasuya, 1976). 
The equivalent holotype measurements of Sousa chinensis 
(Flower, 1870) were transformed into metric units and compared 
with corresponding values for the neotype. The original drawings of 
Flower’s (1870) and photographs of the neotype were also com- 
pared. The skeletal characters of both the holotype and neotype were 
