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Kyphosis and other Variations in Soft-shelled Turtles

BY

HOBART M. SMITH

University of Kansas Publications
Museum of Natural History

Volume 1, No. 6, pp. 117-124
July 7, 1947

UNIVERSITY OF KANSAS
LAWRENCE
1947

UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

Editors: E. Raymond Hall, Chairman, Donald S. Farner,
Donald F. Hoffmeister

Volume 1, No. 6, pp. 117-124
July 7, 1947

UNIVERSITY OF KANSAS
Lawrence, Kansas

PRINTED BY
FERD VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS
1947

[Illustration]

21-6301




Kyphosis and other Variations in Soft-shelled Turtles

By

HOBART M. SMITH


Kyphotic (hump-backed) soft-shelled turtles have been known for many
years in Asia and America. Gressitt (Peking Natural History Bulletin, 2
(pt. 4): 413-415, figs. 1-5, 1937) has reviewed accounts of such
turtles, and recorded the anomaly in _Amyda sinensis_ (Wiegmann) and _A.
steindachneri_ (Siebenrock) of Asia and in unidentified species in the
United States. Records of kyphosis in American species apparently are
few.

Three skeletons in the University of Kansas Museum of Natural History
demonstrate occurrence of the condition in at least 3 American species:
_Amyda emoryi_ (Agassiz), _A. mutica_ (Le Sueur) and _A. spinifera_ (Le
Sueur). The specimen of _A. emoryi_ (Catalog No. 2219) was taken at
Phoenix, Maricopa Co., Arizona, by Victor H. Householder, on May 1,
1926. The second specimen, called to my attention by C. W. Hibbard, was
taken in 1936 from the Kansas River at Lawrence, Douglas Co., Kansas, by
Max Wheatley, to whom I am indebted for the accompanying photographs and
permission to describe the specimen which he has added to the Museum's
collections (No. 23230). The identity of No. 23230 is established as _A.
mutica_ by the absence of spines (see fig. 3) and by a number of cranial
characters. The specimen of _A. spinifera_ (No. 23026) is without
locality data; its identification is verified by the presence of spines
on the front of the carapace.

In the specimen of _A. mutica_ (see figures) the hump forms a smooth,
high curve, closely resembling the condition in Gressitt's specimens of
_A. steindachneri_ (_op. cit._: fig. 1). In the other two the hump is
lower and its apex forms a relatively sharp angle; in the specimen of
_A. spinifera_ the posterior face of the hump is more nearly vertical
than the anterior face. In _A. emoryi_ the rear edge of the apex is
sharply inclined (at an angle of about 45°), whereas the remainder of
the surface slants at an angle of about 35°.

In the accompanying table of measurements of specimens in the University
of Kansas Museum of Natural History the height is measured from the end
of the rib opposite the highest elevation to the crest of the elevation,
by projected lines. The length is measured from the anterior border of
the nuchal plate to the posterior edge of the last costal plate. The
width is measured from tip to tip of the longest ribs. Catalogue
numbers of the specimens, with indication of the localities of capture
are as follows: Nos. 2215-9, 2803, 2824, 2837, Phoenix, Maricopa Co.,
Arizona; Nos. 19459-60, Ozark, Franklin Co., Arkansas; Nos. 2225-9,
Lewisville, Lafayette Co., Arkansas; Nos. 1867-70, 1874-6, 1879, 1881,
1930-1, 2666, 2761-2, 2826, 2838-42, Devalls Bluff, Prairie Co.,
Arkansas; No. 16528, Orange Co., Florida; Nos. 1872, 1878, 1943, 1964,
Doniphan Lake, Doniphan Co., Kansas; No. 2220, Douglas Co., Kansas; No.
23230, Kansas River, Douglas Co., Kansas; No. 18159, Harper Co., Kansas;
No. 2757, Smoky Hill River, Trego Co., Kansas; No. 23026, no data.

The three abnormal specimens vary in width/height ratio from 1.83 to
3.14. In the 37 normal turtles measured, the corresponding ratio is 4.64
to 7.85. The ratio of 4.64 is possibly subject to correction since the
shell tends to warp in some specimens, especially in those retaining the
skin about the periphery of the shell. The warping does not produce a
marked convexity in transverse section, but does so in longitudinal
section. Accordingly the height as here measured is little effected, and
the comparison with width rather than length of shell provides for the
lesser error from warping. There appears to be no close correlation of
proportions with either size or sex.

It is of interest that _Amyda ferox_ is the most distinctive in
proportions of the carapace. Its carapace is longer in relation to its
width than that of any of the other species. The average relative length
of the carapace of _A. emoryi_ is intermediate between that of _A.
ferox_ and the averages of _A. spinifera_ and _A. mutica_, but the
overlap in range with the latter two is complete.

The cause for kyphotic anomalies is unknown. That it is accompanied by a
greater degree of growth in the vertebral column than in the periphery
of the costal plates is obvious. There seems to be no well-established
accommodation for the difference in growth, since the hump produced by
it varies considerably in form.

There is no trend from small to large specimens in size of the hump;
large and small humps occur in both large and small specimens.
Accordingly it seems that the humped condition is developed in the late
embryo or early post-embryonic life, and does not later change.

An apparently reasonable hypothesis is that the costal plates ankylose
distally with the ribs early enough in embryonic life so that any
differential in growth rate between them and the vertebral column is
translated into abnormal contortions of the body. Agassiz and others
have shown that the costal plates normally do not fuse with the ribs by
the time of hatching; the fusion then does not normally occur in the
embryonic stage. Presumably, once fused, the costal plates and vertebral
column normally have equal growth rates, since the height/width ratio
does not change significantly with increased size. It is well known that
fusion takes place in young specimens soon after hatching; in all
skeletons examined of this genus, from the smallest (62 mm. in length)
to the largest (295 mm.), the fusion has occurred. Therefore, the normal
time of fusion must be approximately at the time of hatching.

Although costal plates and the vertebral column grow in direct
proportion to each other throughout life from a period shortly after
hatching, the vertebral column apparently grows more rapidly than the
costals shortly before and possibly also shortly after hatching, at
least in kyphotic and probably also in normal specimens. An
exceptionally early date of fusion of costal plates and ribs would thus
result in a kyphotic condition, and it may well be assumed that the
earlier the fusion, the greater the hypertrophy would be. Whether or not
this hypothesis correctly accounts for kyphosis in turtles can be
ascertained only by further study.

Stejneger (Bull. Mus. Comp. Zoöl., 94: 12, 1944) regards the presence of
8 neurals as opposed to 7 as an important peculiarity of _A. mutica_.
The 42 specimens for which the number of neurals is recorded reveals,
however, that there is greater variation than previously supposed: in 16
_A. mutica_ more than half (9) have 7 neurals and the remainder (7) have
8. Eight neurals were recorded also in 2 of 18 _spinifera_, and in 1 of
7 _A. emoryi_. Seven neurals are present in the single specimen of _A.
ferox_ examined.

It is of interest also that the number of costals, which has been
reported to be consistently 7 in New World species and 8 in Old World
species, varies markedly. In New World specimens, one _A. mutica_ has 7
on one side, 8 on the other, and 8 occur on both sides of one other (of
a total of 16 examined). One of twenty _A. spinifera_, and one of eight
_A. emoryi_ have 8; the single _A. ferox_ (Schneider) has 7. Accordingly
the suggestion by H. M. Smith (Field Mus. Nat. Hist. Zoöl. Ser., 23:19,
1939) that _Platypeltis_ Baur be resurrected for the American
soft-shelled turtles on the basis of the occurrence of only 7 costals,
is untenable.

The generic allocation of American soft-shelled turtles has varied
considerably in recent years: Smith (_loc. cit._) uses _Platypeltis_;
Pope (Turtles of the United States and Canada, p. 343, 1939) uses
_Trionyx_ Geoffroy; and Stejneger (_op. cit._, p. 8) uses _Amyda_
Geoffroy. As stated above, use of _Platypeltis_ at the present time is
unwarranted, since no constant difference has been discovered that would
support generic separation of Asiatic and American members of this
group. New World turtles should be placed either in _Trionyx_ or in
_Amyda_, depending upon the interpretation of type designation for the
latter name. Malcolm Smith (Bull. Raffles Mus. 3:2, 1930) and others
have considered that, as a part of the original description, Geoffroy
(Ann. Mus. Hist. Nat. Paris, 14:20, 1809) designated the type species of
his new generic name _Trionyx_ as _aegypticus_ E. Geoffroy (=
_triunguis_ Forskål a well-recognized species). Stejneger argues that
Geoffroy did not adequately designate a type from among the many species
he treated in his genus _Trionyx_, and that it remained for Fitzinger
(Syst. Rept., p. 30, 1843) to select one of these as a type; he chose
_coromandelicus_ Geoffroy, which is a synonym of _granosa_ Schöppff, a
species belonging to a different genus (as now recognized) from that to
which _triunguis_ belongs, although Geoffroy had made the mistake of
considering both groups as members of his genus _Trionyx_. Now if
Fitzinger's type designation is accepted, the name _Trionyx_ is to be
applied to that group containing _granosa_ (only one other form is known
in the genus, and both forms occur only in India and Burma), whereas the
name _Amyda_ of Geoffroy (_op. cit._, p. 1) is applied to the genus (as
now recognized) which includes _triunguis_ and some 20 other species of
Asia and North America. The type of _Amyda_ is a typical member from
Asia (_cartilagineus_ Boddaert). On the other hand, if Geoffroy's type
designation is accepted, the American forms (and the others of that
genus) would take the generic name _Trionyx_, of which _Amyda_ would be
a synonym, and the genus to which _granosa_ belongs would take the name
_Lissemys_ Malcolm Smith (Fauna Brit. India, Rept. Amph., 1:154, 1931).

Stejneger discussed the various aspects of this problem (_op. cit._, pp.
6, 7), and I can add nothing to his discussion. His arguments for the
acceptance of Fitzinger's type designation rather than that of Geoffroy
are well founded upon the statement of the International Rules of
Zoölogical Nomenclature, while those of Smith are not. In weighing these
two alternatives, the practical value of maintenance of the "status quo"
is not here important, for the whole system of nomenclature in this
field is completely upset; _any_ conclusive decision would be of great
practical value and one alternative holds no special, practical
advantage over the other. Accordingly, it seems reasonable to consider
the matter closed with Stejneger's analysis, retaining _Amyda_ for the
American and related species of soft-shelled turtles. That this
assemblage contains natural subgroups that may warrant subdivision into
other genera is obvious, but to none of these will the name _Trionyx_ be
applicable.


Table of Data on _Amyda_

Transcriber's note: Legend has been created for the column headings to
make the table fit.

Column headings:

A: Number
B: Sex (M = male, F. = female)
C: Width (mm.)
D: Length (mm.)
E: Ratio, width-length
F: Height (mm.)
G: Ratio, width-height
H: Neurals
I: Costals

================+==========+===+=====+=====+======+====+======+===+=====
    SPECIES     |    A     | B |  C  |  D  |  E   | F  |  G   | H | I
----------------+----------+---+-----+-----+------+----+------+---+-----
    _emoryi_    |  2219[A] |   |  81 |  62 | 1.30 | 34 | 2.38 |   | 7
       "        |  2215    | M |     |     |      |    |      | 7 | 7
       "        |  2216    |   | 104 |  88 | 1.18 | 18 | 5.77 | 8 | 7
       "        |  2217    |   |     |     |      |    |      | 7 | 8
       "        |  2218    |   | 106 |  93 | 1.14 | 21 | 5.04 | 7 | 7
       "        |  2803    | F | 150 | 132 | 1.13 | 28 | 5.35 | 7 | 7
       "        |  2824    | F | 204 | 198 | 1.03 | 32 | 6.37 | 7 | 7
       "        |  2837    | F |     |     |      |    |      | 7 | 7
       "        | 19460    |   |  97 |  77 | 1.26 | 14 | 6.93 | 8 | 7
                |          |   |     |     |      |    |      |   |
 _ferox mutica_ | 16528    | F | 282 | 295 | 0.99 | 53 | 5.32| 7 |  7
       "        |  2841    | F |  99 |  75 | 1.32 | 16 | 6.18 | 7 | 7
       "        | 23230[A] |   | 101 |  78 | 1.29 | 55 | 1.83 | 7 | 7
       "        |  2838    | F | 106 |  79 | 1.34 | 17 | 6.23 | 7 | 7
       "        |  1964    | M | 110 |  95 | 1.15 | 18 | 6.11 | 7 | 7
       "        |  2839    | F | 115 |  77 | 1.49 | 18 | 6.39 | 7 | 7
       "        |  2840    | F | 115 |  85 | 1.35 | 17 | 6.76 | 8 | 7-8
       "        | 19459    |   | 131 | 106 | 1.23 | 20 | 6.55 | 7 | 7
       "        |  2220    | F | 144 | 116 | 1.24 | 22 | 6.54 | 7 | 7
       "        |  1874    |   | 162 | 137 | 1.18 | 32 | 5.06 | 7 | 7
       "        |  1930    | F | 180 | 138 | 1.30 | 33 | 5.45 | 8 | 7
       "        |  1875    |   | 181 | 164 | 1.10 | 39 | 4.64 | 8 | 8
       "        |  1881    | F |     |     |      |    |      | 8 | 7
       "        |  1868    | M | 185 | 167 | 1.10 | 39 | 4.74 | 7 | 7
       "        |  1876    | F | 190 | 177 | 1.07 | 33 | 5.75 | 8 | 7
       "        |  1870    | F | 194 | 166 | 1.27 | 35 | 5.54 | 8 | 7
       "        |  1943    |   |  98 |  76 | 1.29 | 18 | 5.44 | ? | 7
                |          |   |     |     |      |    |      |   |
  _spinifera_   |  1872    |   | 129 | 101 | 1.27 | 17 | 7.59 | 7 | 7
       "        |  1931    | M | 148 | 102 | 1.45 | 26 | 5.69 | 7 | 7
       "        | 18159    | F | 151 | 129 | 1.17 | 26 | 5.80 | ? | 7
       "        |  1878    | F | 163 | 132 | 1.23 | 25 | 6.52 | 8 | 7
       "        |  2225    | F | 165 | 131 | 1.17 | 21 | 7.85 | 7 | 7
       "        | 23026[A] | F | 170 | 133 | 1.27 | 54 | 3.14 | 7 | 7
       "        |  2227    | F | 191 | 175 | 1.09 | 39 | 4.89 | 7 | 7
       "        |  2228    | F | 196 | 167 | 1.17 |    |      | 7 | 7
       "        |  1867    | M | 207 | 164 | 1.26 | 26 | 7.58 | 7 | 7
       "        |  2757    |   | 213 | 196 | 1.08 | 30 | 7.10 | 7 | 8
       "        |  2229    |   | 215 | 178 | 1.20 | 28 | 6.78 | 7 | 7
       "        |  2762    | F | 219 | 184 | 1.19 | 40 | 5.47 | 7 | 7
       "        |  1879    |   | 223 | 187 | 1.19 | 38 | 5.87 | 7 | 7
       "        |  2761    | F | 233 | 182 | 1.28 | 43 | 5.41 | 7 | 7
       "        |  2666    |   | 234 | 208 | 1.12 | 42 | 5.57 | 8 | 7
       "        |  2226    | F | 239 | 215 | 1.11 | 38 | 6.29 | 7 | 7
       "        |  1869    |   | 245 | 211 | 1.16 | 44 | 5.55 | 7 | 7
       "        |  2842    |   | 245 | 219 | 1.12 | 45 | 5.44 | 7 | 7
       "        |  2826    | F | 245 | 237 | 1.03 | 45 | 5.44 | 7 | 7
----------------+----------+---+-----+-----+------+----+------+---+-----

[Footnote A: Kyphotic]

_University of Kansas, Museum of Natural History, Lawrence, Kansas._

[Illustration: FIGS. 1-3. _Amyda mutica_, Univ. Kans., Mus. Nat. Hist.,
No. 23230, Lawrence, Kansas. All views approximately half natural size.
1, Frontal view. 2, Lateral view. 3, Dorsal view.]