STUDIES ON THE FAUNA OF CURAÇAO AND OTHER
CARIBBEAN ISLANDS: No. 35.
Fossil Rodents from Curaçao and Bonaire
by
D.A. Hooijer
(Rijksmuseum van Natuurlijke Historié, Leiden)
with Plates I-III
The fossil remains of rodents described in the present paper are
from various localities. The large extinct musk rat Megalomys occurs in reddish-brown phosphatic “oolite” fillings of irregular cavities marine in a limestone found by Mr. P. H. DE BUISONJÉ in the north-western part of the Duivelsklip, eastern Curaçao, about 50 m above sea-level. The “oolite” also contains scanty remains of lizards, snakes, and of a bat. Fragmentary molluscs
include Cerion present possibly uva (L.), a recent, very common, terrestrial as well other species, as gastropods, many opercula of which were found.
Samples of a phosphatic “oölite” deposit collected in 1937 by
Dr. P. HUMMELINCK from WAGENAAR an escarpment near Fontein,
Bonaire, proved to contain jaws, with teeth, of a genus of hespero- myine rodents, Thomasomys a single snake vertebra; and mollusc remains what be their including seem to coprolites.
Finally, teeth of the South American capybara, Hydrochoerus,
found Prof. were by Dr. H. J. MAC GILLAVRY and Mr. P. H. DE
BUISONJÉ in reddish-brown phosphatic "oolite", deposited after
of the consolidation underlying marine limestone and located at a
of present height about 160 m above sea-level on the Tafelberg
Santa Barbara, eastern Curaçao. No other vertebrates have been recovered from this deposit.
The limestone is considered to be Quaternary in age.
1 2
Marine molluscs contained in the Santa Barbara "oolite" have been identified
by Mrs. W. S. S. VAN DER FEEN (née VAN BENTHEM JUTTING) and Mr. H. E. COO-
MANS, independently of each other, as Livona pica (L.), Nerita cf. tesselata Gm.,
and Nerita ci. versicolor Gm.
It is of interest to find that the "oolite" deposits of Duivelsklip and Santa Bar-
been identified Dr. bara contain the same species of land crab, which has by L. B.
HOLTHUIS Coenobita - land hermit crab is as clypeatus (Herbst) a which common all the West and is in over Indies frequently met with Curaçao. Coenobita clypeatus
the is found from the high-tide mark on coast to far inland. It lives in the shells of
but various species of gastropod molluscs, seems to prefer those of Livona pica.
Permission collect the of "oolite" the to samples fossil contents of which are
described in the the Cura- present paper was kindly given by "Mijn-Maatschappij
Mr. R. and Dr. W. P. Fuik çao", manager J. MESNEY, by MAAL, owner of Plantation.
I much indebted to H GILLAVRY and to H. WESTERMANN am Prof. Dr. . J. MAC Dr. J. for the fossil rodent material to thanks to passing me for description. My are due Mr. R. W. HAYMAN of the British Museum (Natural History), for kindly sending me measurements of the type specimen of Megalomys luciae (Major), as well as
other information to the recent rodents of the Antilles. I also pertaining am very
grateful to Mr. P. H. DE BUISONJÉ, who spent a great deal of time in dressing the
at fossil remains from the block of "oolite" collected Duivelsklip, as well as those from the samples from the escarpment near Fontein, Bonaire, by means of acetic
most the acid, thus extracting even the delicate specimens from matrix, which would have been impossible by mechanical methods. It was found that the con- cretions in the matrix contained entire teeth small Duivelsklip not only and very bones, but also tooth and bone fragments. The largest single fragment dressed from the block is of fossil only 15 mm long ; most the specimens do not exceed 5 mm in
diameter. How these small found their into the is moot specimens way deposit a
that I shall into question not go at present.
The fossil material described below is preserved in the Geological Institute of the
University of Amsterdam; the registration numbers are given in each case. The photographs have been taken by Mr. H. F. ROMAN, the text figure is by Mr. H.
Historié. HEIJN, both of the Rijksmuseum van Natuurlijke
All this measurements recorded in paper are in mm, unless otherwise stated.
Megalomys curazensis nov. spec, from Curaçao
DIAGNOSIS: An oryzomyine rodent of large size; length M1-3 ,
7.6 7.9 Width of mm; length M1-3, mm, on an average. palate
1 1 between M s less than combined width of and left right M . Major folds and minor remain open marginally throughout most of the life of the teeth. Major folds well developed in all molars but short in M3 . Minor folds well developed in M 1 and Mi, reduced in M2 and
3 M2, obsolete or absent inM and M3. Primary and secondary folds tend
become isolated from to marginal enamel with prolonged wear. First 3
1-2 primary folds well developed in M and M 1-3; internal portion
3 1-2 isolated in M . Second primary folds well developed in M and
3 1 Mi—2, reduced in M and M3. Anterior median folds rare in M and Mi, never continuous with anterior internal folds. Anterior
1 secondary fold (M ) and anterior primary fold (Mi) small but distinct, marking off anterior cingula. First secondary folds in
M 1-3 and second folds in well secondary MI_3 always defined.
Mesoloph fused with mesostyle, mesolophid fused with mesostylid.
Second secondary folds distinct but small in M1-3 off , marking posterior cingula. First secondary folds distinct in Mi but reduced or obsolete in M2-3. Hypoconid depressed posteriorly. Enterostyles
2-3 incipient or absent, ectostylids present. M with three roots,
inner and M 1 in anterior one two outer; has, addition, an root;
with anterior and Mi—3 one one posterior root; accessory inter- mediate roots in M1 and Incisors may develop Mi. large, ungrooved.
1-2 HOLOTYPE: The M dext., E3187, described and figured in the present paper.
LOCALITY: Duivelsklip, eastern Curaçao, Netherlands Antilles.
AGE: Presumably Pleistocene.
DESCRIPTION OF THE HOLOTYPE SPECIMEN, E 3187
The most complete fossil specimen recovered from the block of "oolite" from
1-2 Duivelsklip, Curaçao, is a fragment of a right maxillary with M in situ (pl. I fig. 1). At the anterior end of the fragment the root supporting the anterocone of
M1 most is exposed along of its length. Medially, a small portion of the palate is
of the lateral preserved, showing part right palatal groove but nothing of the borders the level of incisive foramen or of the posterior palatine foramen. At the of M1 the is broken off the median fragment along palatal suture, indicating a
the the M1 which less than width of palate between s of 4.2 mm, is the combined
1 width of right and left M (5.2 mm). Laterally, the posterior boundary of the
with the anterior zygomatic root begins to curve outward on a level middle of M1, but as its anterior border has not been preserved it is impossible to determine the least anteroposterior diameter of the zygomatic plate. The lateral border of the
to 2 palate is seen curve gently inward just behind M , indicating a transversely
3 narrowed M that is, however, missing in the specimen and has left only the im- pression of its palatal root.
The two molars are excellently preserved; for an explanation of the various terms used in the description of the teeth reference should be made to the stylized
diagrams of enamelpatterns on page 5.
The M1 anterior molar, dext., is moderately worn, and consists of an anterior lobe and two of The internal (anterocone) pairs cusps, transversely placed. cusps
are larger than those on the external side, and are separated from the latter by 4
NAMES OF CUSPS, LOPHS, AND CINGULA
Upper Lower
1. Paracone 1. Protoconid
2. Protocone 2. Metaconid
3. Metacone 3. Hypoconid
4. Hypocone 4. Entoconid
5. Anterocone 5. Anteroconid
6. Anteroloph 6. Anterolophid
7. Anterior cingulum 7. Anterior cingulum
8. Mesoloph 8. Mesolophid
9. Mesostyle 9. Mesostylid
10. Enterostyle 10. Ectostylid
11. Posterior cingulum 11. Posterior cingulum
NAMES OF FOLDS ( upper and lower)
MAF Major fold
MIF Minor fold
PF1 First primary fold
PF2 Second primary fold
SF1 First secondary fold
SF2 Second secondary fold
AIF Anterior internal fold
AMF Anterior median fold
APF Anterior primary fold
ASF Anterior secondary fold 5
Stylized diagrams of enamel patterns of upper right and lower left molar series nomenclature after WOOD & and ; WILSON (1936)
HERSHKOVITZ For (1944). explanation see opposite page. 6
distinct enamel folds, which enter the crown externally, and curve inward and
backward in front of and metacone These two paracone respectively. primary folds have just about lost the communication with the marginal enamel. On the
there two enamel folds less far into internal side are extending the crown; these,
the of the the minor and the major folds, open broadly to internal wall crown.
Their low down the and will entrances are on crown, consequently they never
the become isolated from the margin. The plane of wear is distinctly oblique, in- ternal down than the external. side being more worn
More detailed examination of the specimen reveals the following. The antero-
the coneis asymmetrical, internal part beingrounded and broader anteroposteriorly than the external part. It will be observed that the anterocone thereby tends to
in the of the of duplicate appearance structure transversely placed pairs cusps behind. The external part is pinched in by the anterior secondary fold; between this fold and the first primary fold behind there is an enamel projection: the anterior
cingulum.The anterior surface of the anterocone is slightly depressed in the median line near the occlusal surface, but becomes gently rounded from side to side near the base the this median the of crown; depressionrepresents anterior median fold, which most the the There enamel is evidently marked near top of crown. is an island in the of the which is and have centre anterocone, elongatedtransversely, may formed part either of the anterior secondary fold or of the anterior median fold in a less advanced stage of wear.
The is widest the anterior of main feature crown transversely over pair cusps, a which is mainly due to the bulging-out of the protocone internally. The minor fold, between anteroloph and protocone, is well developed and slightly curved forward at its The the transverse in end. major fold, behind protocone, is longer, its course,
the line the the external and extends outward just about to median of crown. On side, the first primary fold (between the anterior cingulum and the paracone) curves inward and then backward well beyond the median line ; its entrance forms
above the and has almost been reached a pass just one mm crown base, by wear, as a result of which the fold becomes isolated from the crown margin. Behind the
there is enamel fold that is in its it extends inward paracone an transverse course ; only to the median line of the crown, and is already constricted off from the external margin: this fossette represents the first secondary fold. Between the latter fold andthe second fold behind there is continuous enamel primary a strip of representing mesoloph and mesostyle.
The of than the in front posterior pair cusps, slightly narrower transversely pair
of it, is essentially similar in structure. The second primary fold, between meso- loph and metacone, closely resembles the first, and is likewise almost cut off from the external marginal enamel. Behind the metacone, in the postero-external angle
the of crown, we observe a distinct second secondary fold, marking off the posterior
cingulum.
the M1 the The anteroposterior diameter of crown of is 3.5 mm, greatest width is 2.6 mm.
The 2 1 M of the present specimen has all the characters of an M without the
but of in less The anterocone, is, course, a slightly advanced stage of wear. crown
is wider anteriorly than posteriorly. The minor fold is only a faint depression at the antero- antero-internal angle of the crown, and the anterior cingulum forms the
external angle. The first and second primary folds are still open externally, and
to be less curved than those of M1 The first fold is dis- appear slightly . secondary 7
at its inner and there is of enamel into tinctly expanded end, a tiny spur projecting
it from the border of the It is closed off from the external posterior paracone. just margin. Between the first secondary fold and the second primary fold we again find
transverse a strip of enamel, the mesolophostyle complex. The second secondary fold is than that in M1 and the posterior cingulumis therefore quitedistinct. deeper ,
The 2 posterior surface of the crown of M is rounded behind instead of nearly flat
1 of there of as in M because less interproximal is as yet hardly trace a , wear; any
contact facet with M3 .
the M2 the anterior The length of crown of is 2.6 mm, width 2.3 mm
The characters that can be observed in this single specimen point to its belonging to the cricetine to the of rodents rodents, more specifically group oryzomyine
the anterior well fused characterized by presence of and posterior cingula as as by a
and 12 author calls the anterior mesoloph mesostyle (GOLDMAN, 1918, p. (this
1 2 cingulum of our terminologythe "secondary parastyle" (M ) or "parastyle" (M ));
11 GYLDENSTOLPE, 1932, p. (idem); HERSHKOVITZ, 1944, p. 12-13, 1955, p. 654).
However, in addition to the fine specimen just described, numerous isolated teeth
have been recovered from the block of "oolite" from Duivelsklip, representing
all the and lower molars of the same as that to which the upper evidently species 1-2 It there- M dext. belong, and yielding much additional information. seems best,
fore, to defer comparison of the present fossil species with the recent and subfossil
oryzomyines until all the material now available has been considered.
UPPER MOLARS
there of the first Includingthe specimen described above are 33 specimens upper
molar, viz., 17 from the right, and 16 from the left side (E 3187—E 3219). These
amount specimens display a certain of variation in size, as is shown in table 1. All
the similar in Mis are remarkably structure, differingonly in unimportant details
the of or in of the anterior median fold depending upon stage wear, development The less in number and of enterostyles. roots are more or completely preserved a
of specimens; these could not be studied in the type.
The anterior internal fold is isolated from the enamel in marginal every specimen,
no matter how slightly worn, but in several molars it is barely closed off from the
in anterior secondary fold entering the crown externally, as can be seen a slightly
1 worn M sin. (E 3204) shown on pl. I fig. 5. Two rather large and moderately worn
x I show indication of right M s (E3188 and E3189; pl. figs. 2-3) do not any an
but 1 anterior median fold, in a much worn left M (E 3205 ; pl. I fig. 4) the anterior
surface of the anterocone is distinctly flattened. In a few specimens (E 3208 and
there is the surface E 3213) a faint cingular ledge on anterior of the anterocone,
in true which and one specimen (E 3193) there is a anterior median fold, divides
the anterocone into two conules but does not, however, communicate with the
anterior internal fold.
in the In a very few molars only (e.g., E 3203), enterostyles (not shown type)
enamel the entrance to the fold. are seen as very tiny points, blocking major
1 There are three main roots in M : the largest is located internally, supporting
protocone and hypocone ; the second largest is that of the anterocone, and the third
is that of the metacone. In addition, there are either one or two much smaller roots
the in E 3204 I supporting paracone (shown specimen ; pl. fig. 5). 8
TABLE 1
Measurements of M 1 of curazensis 3187-E Megalomys nov. spec. (E 3219)
No. of specimen 1 2 3 4 5 6 7 8 9 10 11
Anteroposterior 3.4 3.5 3.8 3.4 3.4 3.8 3.5 3.2 3.2 3.3 3.2
Transverse 2.6 2.6 2.5 2.2 2.5 2.6 2.3 2.3 2.2 2.2 2.3
No. of specimen 12 13 14 15 16 17 18 19 20 21 22
Anteroposterior 3.6 3.4 3.1 3.3 3.3 3.3 3.2 3.5 3.4 3.5 3.6
Transverse 2.6 2.4 2.2 2.2 2.4 2.2 2.2 2.6 2.3 2.4 2.5
No. of specimen 23 24 25 26 27 28 29 30 31 32 33
Anteroposterior 3.2 3.2 3.3 3.2 3.0 3.0 3.4 3.3 3.3 3.1 3.3
Transverse 2.3 2.4 2.3 2.4 2.1 2.0 2.3 2.3 2.4 2.2 2.4
The second M 2 is somewhat less well than is M1 upper molar, , represented .
There are 27 entire or almost entire specimens; nos. 1—17 from the right, and nos.
18-27 from the left side (E 3187 and E 3220-E 3245). No. 1 is that in the holotype.
M 2 rather constant in its characters. In of the first is, again, early stages wear secondary fold is expanded at its inner end (E 3221; pl. II fig. 1); it is isolated
earlier than the two and recedes and the externally primary folds, more more from margin, as can be seen in a much worn left M2 (E 3236; pl. II fig. 2). The meso-
all and the anterior lophostyle complex is distinct in specimens, so is cingulum.
In the the has most worn specimens second secondary fold disappeared entirely; in the specimen on pl. II fig. 2 (E 3236) it is represented by a tiny enamel island postero-externally. Enterostyles are so weak as to be practically absent. The major fold remains the life of the but the minor open internally throughout tooth, fold, which is but in M2 is out in old faintly developed even slightly worn s, worn age.
roots M2 in the The of are three number: largest is elongated anteroposteriorly in cross section and is located internally; the second largest supports the metacone ; and the third is that of the An paracone. incipient accessory root, placed postero- the The internally from paracone root, is developed in E 3225. measurements of the in table 2. specimens are given
TABLE 2
Measurements of M2 of curazensis 3187 and E 3220-E Megalomys nov. spec. (E 3245)
No. of specimen 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Anteroposterior 2.6 2.5 2.2 2.5 2.4 2.2 2.5 2.6 2.4 2.4 2.2 2.3 2.3 2.4
Transverse 2.3 2.4 2.1 2.3 2.2 2.0 2.1 2.2 2.1 2.3 2.2 1.9 2.0 2.2
No. of specimen 15 16 17 18 19 20 21 22 23 24 25 26 27
Anteroposterior 2.3 2.2 2.2 2.4 2.2 2.3 2.3 2.2 2.3 2.2 2.3 2.2 2.1
Transverse 2.2 2.1 2.3 2.2 2.0 2.1 2.2 2.1 2.3 2.0 2.2 2.0 2.0
The 3 is M2 is last M is built on the same plan as but smaller both upper molar, , , 9
ways; its posterior portion is much reduced. The first primary fold is isolated from its internal portion even in the least worn specimens, the internal portion forming a conspicuous rounded enamel island. The second primary fold is markedly re-
duced, being transverse in its course and even shorter than the second secondary fold behind it (M3 dext. E 3246; pl. II fig. 3). In E 3247 (pl. II fig. 4) the second primary and second secondary folds have coalesced internally. The first secondary
and in in E M3 II fold is rather variable, some cases (as 3262, an sin. (pl. fig. 5), and in E 3269) In E 3247 II it is cut into appears duplicated. (pl. fig. 4) by a pos- terior from the The is projection paracone. mesoloph-mesostyle ridge, however, always present. The major fold is short but very distinct, the minor fold obsolete.
M3 like the other molars, has internal and external the internal , upper one two roots ; root is not, however, enlarged in relation to the others.
Of the last molar have 25 the of which will upper we specimens, measurements be found in table 3. Nos. 1-16 are from the right side, the other specimens are from the left (E 3246-E 3270).
TABLE 3
Measurements of M3 of curazensis 3246-E Megalomys nov. spec. (E 3270)
No. of specimen 1 2 3 4 5 6 7 8 9 10 11 12 13
Anteroposterior 2.0 1.9 2.0 2.0 1.9 2.0 1.9 1.9 2.1 2.1 2.1 2.1 1.8
Transverse 1.8 1.7 1.7 1.7 1.7 1.8 1.7 1.7 2.0 1.9 1.9 1.9 1.7
No. of specimen 14 15 16 17 18 19 20 21 22 23 24 25
Anteroposterior 2.0 2.1 1.9 1.8 1.8 2.0 2.0 2.1 2.0 2.0 2.0 1.7
Transverse 1.7 1.9 1.8 1.7 1.7 1.6 1.8 1.9 1.8 1.8 1.7 1.6
LOWER MOLARS
Of the lower molars only a few specimens still remain in situ in portions of the
A in mandible. much worn left M2, incomplete antero-internally, is situ in a left ramus of the mandible the incisor of which is, however, gone. Neither the height of the mandible the the the the body of nor length of diastema can be given, but
and alveolar of alveoli of Mi of M3 are visible, revealing an length MI_3 7.8 mm.
The the in the mental foramen, on labial side front of Mi, is just anterior to the masseteric the the A crest; nothing of ascending portion of ramus is preserved. right Mi and M2 (Mi incomplete anteriorly) are in situ in a mandible fragment the height of which cannot be given either. All the remaining specimens of lower molars
their are isolated, many with roots partially preserved.
Of Mi only 17 entire or almost entire specimens have been recovered, 11 of them from the right side (E 3271-E 3281, E 3283-E 3288). This tooth consists of an
anterior lobe (anteroconid) behind which follow two transverse pairs of cones, those on the external side being larger than the internal. The two primary folds
the enter crown internally, behind metaconid and entoconid respectively, and curve outward and forward. On the external side the minor and major folds mark the threefold division of the crown; these folds are less deep, and have lower en-
than the in the molars. The of trances, primary folds, just as upper crown Mi narrows distinctly from back to front. 10
The anteroconid of Mi has a central depression, the anterior internal fold; this is elongated transversely, and is of great relative depth, so that it remains as an enamel island evenin the most worn specimens (e.g., Mj sin. E 3285; pl. II fig. 8).
The anterior primary fold, which enters the anteroconid internally,is still shown in this much smaller internal to the central island. In specimen as a island, just less
II worn specimens, such as the Mi sin. E 3283 (pl. fig. 7), the anterior primary
is to extend from the internal the central fold seen margin into depression (the
anterior internal fold). The specimen just mentioned also shows a slight but distinct
depression in the anterior wall of the anteroconid ; this is the anterior median fold, only exceptionally apparent in molars in more advanced stages of wear. On the
external side of the anteroconid only the minor fold is seen, separating the antero- lophid from the protoconid. It is curved forward at its end, as shown both in the
to. slightly worn and in the much worn left Mi already referred
On the internal side, just in front of the metaconid, there is a small fold, the first secondary fold; it is just behind the anterior primary fold already referred to
above. Between the two last-mentioned folds the anterior cingulum is found,
first distinct in all stages of wear (cf. pl. II figs. 6-9). The primary fold, behind and
in to the be with the first medially relation metaconid, may confluent secondary
fold, thus marking offthe whole of the metaconid. Between metaconid and entoconid
there is of distinct from both this enamel a transverse ridge enamel, cusps; ridge
is the mesolophid-mesostylid complex. In two moderately worn Mis, one from the
right side (E 3271 ; pl. II fig. 6) and one from the left side (E 3284; pl. II fig. 9),
this is distinctive character readily seen. In the much worn Mi sin. E 3285 (pl. II
fig. 8) the second secondary fold which marks the mesolophid off posteriorly is just
visible small island. The last fold to be observed the internal as a very transverse on
side of the crown is the second primary fold, curving outward and forward behind
the entoconid. It marks off the posterior cingulum.
On the external side, the major fold enters the crown between protoconid and
it is wide its and level with the fused mesolo- hypoconid; very at entrance just on a
phid and mesostylid. There is an enamel point at its entrance, a low cingular elevation called the ectostylid. The major fold is isolated from the marginal enamel
only in the most advanced stages of wear (e.g., in E 3275 and E 3282; the last-
mentioned is anincomplete Mi dext. not included in table 4). The posterior surface
of the shows weak feature characteristic hypoconid a depression or "dimple", a very
of the lower molars.
TABLE 4
Measurements of M1 of Megalomys curazensis nov. spec.
(E 3271-E 3281, E 3283-E 3288)
No. of specimen 1 2 3 4 5 6 7 8 9
Anteroposterior 1 3.3 3.6 3.2 3.0 3.4 3.0 3.2 3.1 3.0
Transverse 2.2 2.2 2.1 2.0 2.0 2.0 2.1 2.0 1.9
No. of specimen 10 11 12 13 14 15 16 17
Anteroposterior 3.3 3.0 3.1 3.1 3.2 3.3 3.4 3.2
Transverse 2.1 2.0 2.2 2.2 2.1 2.1 2.3 2.1 11
the The root system of anterior lower molar is as follows. Below the anteroconid there is a large root, either rounded or antero-posteriorly elongated in cross section.
extended root. Behind, supporting hypoconid and entoconid, there is a transversely
Between two roots in these main are a pair of accessory roots; a few specimens there to be three of which the central is the smallest. appear even accessory roots,
The lower second molar is the best represented tooth in the collection from
from the and Duivelsklip. There are 35 specimens; nos. 1—20 are right side, nos.
21—35 from the left (E 3289—E 3323). Four specimens, all from the right side and in different show the characteristic of the tooth stages of wear, features (E 3289-
Ill In the the E3292; pl. figs. 1-3, 6). unworn state, crown exhibits a reduced minor fold antero-externally, marking off the anterolophid, which remains distinct
in old The first off the anterior even age. secondary fold, marking cingulum, is,
obsolete in the it be enamel however, unworn crown although may seen as an pit in the later stages figured, especially in E 3290. The first primary fold is closed
off from the internal marginal enamel already in the unworn crown E 3289, and so is the second primary fold. The second secondary fold, which is behind the mesolo- phid-mesostylid complex, is likewise closed off internally. Only the major fold remains open duringmost of the life of the tooth. In much-worn molars the ecto-
the of the fold is touched stylid invariably developed at entrance by wear, upon which even this fold loses its continuity with the marginal enamel. The postero-
external of the "dimple" crown can be observed in most specimens. The M2 dext.
E is in external view Ill the 3293 represented on pl. fig. 5; it shows height of the
the (unworn) crown, ectostylid at the entrance of the major fold, the high antero- lophid in front, and the "dimple" in the posterior surface of the hypoconid.
There are only two main roots to M2, one below the anterior, and one below the
of roots have not been observed. posterior pair cusps; accessory
TABLE 5
Measurements of M2 of Megalomys curazensis nov. spec. (E 3289-E 3323)
No. of specimen 1 2 3 4 5 6 7 8 9 10 11 12
Anteroposterior 2.4 2.5 2.3 2.5 2.5 2.3 2.3 2.4 2.5 2.2 2.4 2.5
Transverse 2.1 2.3 2.0 2.2 — 2.2 2.0 2.1 2.1 2.0 2.0 2.3
No. of specimen 13 14 15 16 17 18 19 20 21 22 23 24
Anteroposterior 2.6 2.5 2.3 2.3 2.4 2.4 2.5 2.5 2.4 2.3 2.5 2.5
Transverse 2.2 2.1 2.1 2.0 2.1 2.2 2.1 2.1 2.2 2.0 2.3 2.2
No. of specimen 25 26 27 28 29 30 31 32 33 34 35
Anteroposterior 2.2 2.4 2.4 2.2 2.6 2.4 2.3 2.4 2.5 2.4 2.3
Transverse 1.9 2.0 2.0 2.0 2.2 2.1 2.0 2.2 2.1 2.0 2.1
Of the last lower molar 30 specimens are available, 17 from the right, and 13 from the left side (E 3324-E 3353). In relation to the second molar it is less reduced than the last molar. The antero-internal that the first upper pit represents secondary
fold is visible in both slightly and much worn specimens (E 3341 and E 3343, both
M3 sin.; pl. Ill figs. 4, 7). The first primary fold is shaped like that in M2, but the second primary fold is reduced. The second secondary fold, and the fused mesolophid. 12
the and mesostylid in front of it, are distinct in all specimens. The minor fold, antero-externally, is seen only in less than one-half of the specimens, and is very
if at all. The wide extends weakly developed, present major fold, open externally, about entrance. half-way across the crown, and has anectostylid at its The postero- external but "dimple" is incipient discernible in slightly worn crowns.
roots two and The are in number, the anterior is extended transversely, the posterior is extended obliquely from antero-internal to postero-external ; the latter is the heavier.
TABLE 6
Measurements of M3 of Megalomys curazensis nov. spec. (E 3324—E 3353)
No. ofspecimen 1 2 3 4 5 6 7 8 9 10
Anteroposterior 2.2 2.1 2.2 2.2 2.1 2.5 2.2 2.4 2.4 2.3
Transverse 1.8 1.9 1.7 1.8 1.7 2.0 1.8 2.0 2.0 1.9
No. ofspecimen 11 12 13 14 15 16 17 18 19 20
Anteroposterior 2.2 2.2 2.4 2.5 2.2 2.1 2.2 2.1 2.1 2.4
Transverse 1.9 1.7 1.8 2.0 1.7 1.8 1.9 1.8 1.7 1.9
No. ofspecimen 21 22 23 24 25 26 27 28 29 30
Anteroposterior 2.3 2.1 2.3 2.3 2.3 2.2 2.5 2.1 2.3 2.2
Transverse 1.8 1.9 1.9 1.9 1.8 1.7 2.0 1.7 1.8 1.8
INDIVIDUAL VARIATION IN SIZE OF FOSSIL MOLARS
As from tables available of each can be seen 1-6, adequate samples are upper
and lower molar of curazensis it has been found Megalomys nov. spec. Hence,
practicable to employ some statistics.
Table 7 the number of variâtes the of and the gives (n), ranges variation, means
(M) of anteroposterior and transverse diameters. The standard deviation E** i / = L in which e is the deviation from the mean found for a —, every single
a X 100 variate. The of C coefficient variation = . M
The variation coefficients are higher in the upper than in the lower molars. The
most variable tooth is M 2 , the least variable, M2. In both Ml and Mi the length is
more variable than the width; the reverse is the case in M2-3 and M2-3. The variation
coefficients vary only from about 4J to figures typical of linear dimensions
of functional hard parts in mammals, in respect of which the great majority of
such coefficients lie between about 3 and 10 (SIMPSON, 1953, p. 74).
It the follows from these figures that Duivelsklip block contained a fairly homo-
geneous sample of the whole population of Megalomys. There is no evidence that
more than one species is present. 13
TABLE 7
Statistical data on molars of Megalomys curazensis nov. spec.
n range M a c
M 1 , anteroposterior 33 3.0-3.8 3.3 0.19 5.8
transverse 33 2.0-2.6 2.3 0.11 4.8
M 2, anteroposterior 27 2.1-2.6 2.3 0.14 6.1
transverse 27 1.9-2.4 2.1 0.14 6.7
M 3 25 1.7-2.1 2.0 0.12 6.0 , anteroposterior
transverse 25 1.6-2.0 1.8 0.11 6.1
Mi, anteroposterior 17 3.0-3.6 3.2 0.17 5.3
transverse 17 1.9-2.3 2.1 0.10 4.8
M2, anteroposterior 35 2.2-2.6 2.4 0.11 4.6
transverse 34 1.9-2.3 2.1 0.10 4.8
M3, anteroposterior 30 2.1-2.5 2.3 0.13 5.7
transverse 30 1.7-2.0 1.8 0.11 6.1
INCISORS
A number of incisor fragments have also been recovered. Ofthese, noneis grooved in front; the faces of all specimens are smooth. Ten specimens of upper incisors
in is shown in table 8. vary but slightly diameters, as
TABLE 8
Measurements of incisors of curazensis upper Megalomys nov. spec. (E3354-E3363)
No. of specimen 1 2 3 4 5 6 7 8 9 10
Anteroposterior 2.6 2.8 3.0 2.4 2.6 2.7 2.6 2.9 2.7 2.7
Transverse — 1.7 — 1.3 1.7 1.7 1.5 1.7 1.6 1.7
Two sizable fragments of lower incisors, one from the right and one from the left
side, measure 2.6 by 1.6 mm, and 2.8 by 1.6 mm, respectively, in diameters. The
to show the if 3364-E fragments are not sufficiently long recurvature, any (E 3365).
POSTCRANIAL SKELETON
Among the bone fragments which presumably all formed part of the skeleton of the present species, the following may be briefly mentioned : a few incomplete lumbar and caudal vertebrae of uncertain serial position (E 3366-E 3367) ; the
the shaft of left distal part of a humerus, without the trochlea, preserved upward
of with the as far as the deltoid process (E 3368) ; two proximal fragments ulnae olecranon the incomplete (E 3369) ; acetabular portion of a right os coxae (E 3370) ; various distal ends of femora, greatest distal width in two specimens 6-7 mm
the diameter tibia (E 3371); a portion of shaft of a right tibiofibula, of just above 14
of fusion with fibula: 2.7 2.1 two distal of point by mm (E 3372); epiphyses tibio- fibulae (E 3373 and E 3374) ; three entire astragali (one right, two left), proximal width 3.1-3.3 mm, greatest (medial) length 4.6-5.0 mm (E 3375-E 3377) ; a right calcaneum at least 9 mm high, tuber incomplete (E 3378) ; a metatarsal without proximal end, length as preserved 15 mm, distal width 2.2 mm (E3379). (The last is the longest single fragment dressed from the block.) Furthermore, there are
and tarsal and a number of carpal bones, metapodials, phalanges of various sizes the exact position of which remains uncertain (E 3380).
COMPARISON OF Megalomys curazensis NOV. SPEC.
WITH OTHER ORYZOMYINE RODENTS
The of the 2-3 of this diagnosis present species given on p. paper leaves shadow of doubt that it has be classed with the no to ory-
The distinctive characters of this the zomyine rodents. group are
of anterior and and of presence posterior cingula, a mesolophostyle
The complex (HERSHKOVITZ, 1944, p. 12-13; 1955, p. 654). oryzo- myines form a branch of the Tribe of Hesperomyini or New World mice which includes five (Cricetinae), genera, viz., Oryzomys, Megalomys, Neacomys, Scolomys, and Nectomys. Only the last-
mentioned of these has been the subject of recent revision (HERSH-
KOVITZ, 1944).
The cranial and external characters of the fossil Curaçao rat are unknown, and consequently it is necessary to rely exclusively on
dental characters for identification From the purposes. a com-
parison of the fossil teeth with those of Nectomys squamipes (Brants),
in the Leiden it is several skulls of which are Museum collection,
Not the clear that our fossil does not belong to Nectomys. only are
molar in but also characterized crowns higher Nectomys, they are
fused and in the and by a mesostyle paracone upper molars, by a
fused mesostylid and entoconid in the lower molars (HERSHKOVITZ,
characters that do obtain in the fossil from 1944, p. 19), not rat
Curaçao. In their relatively low crowns the fossil molars agree
the and inclusive of with those of Oryzomys, central most genus
rodents. oryzomyine Oryzomys, which comprises one hundred and
from eighty odd species, ranges throughout South America southern
Patagonia northward, the Galapagos Islands, Central America,
Mexico, Lower California, Texas, Alabama, Georgia, Florida, and
north to New Jersey (ELLERMAN, 1941, p. 340). The only records 15
of the genus from the Caribbean islands known to date are
antillarum THOMAS from Oryzomys (1898, p. 177) Jamaica, Oryzomys
victus THOMAS from St. (1898, p. 178) Vincent, and Oryzomys spec, from Curaçao and Margarita (WAGENAAR HUMMELINCK, 1940,
The and St. Vincent believed be p. 69). Jamaican species are to extinct, while the Curaçao and Margarita specimens are mandibles obtainedfrom animals x cave deposits, no living having been found ).
Oryzomys undoubtedly once had a much more extensive range in the
Caribbean area ; it is generally considered that its exterminationin the islands of the Caribbean is of the very recent date, following
introduction of Rattus and of the mongoose from the Old World.
An interesting observation made by Dr. H. E. ANTHONY while exploring cave
deposits in Jamaica in 1919-1920, and related by KOOPMAN & WILLIAMS (1951), is as follows. A number of different layers could be distinguished within the caves, the most superficial of which were the “Rattus layers". Immediately below these
the bones came ”Oryzomys strata", in which the were stained a browner colour and fresh than in the true surface "The had a less appearance those layers. Oryzomys
and the with the were invariably old and rotten not on surface more recent Epimys
material" (Rattus) (1.e., p. 3).
The difference in degree of hypsodonty between Oryzomys and Nectomys has
been observed WINGE ILL 10a lati- already by (1887, p. 12, 182, pl. fig. (Calomys
ceps = Oryzomys) and fig. 12a (Nectomys squamipes) ; see revised nomenclature in
As noted COUTO, 1946). by GOLDMAN (1918, p. 13), in Oryzomys the molar crowns
x ) I have examined the material on which HINTON and HAYMAN'S record of Oryzomys
from spec, Curaçao (in WAGENAAR HUMMELINCK, 1940, p. 69) is based. It consists of
two mandibular rami with M3 in situ, found in the cave of Hato, Curaçao, by Dr. P.
WAGENAAR HUMMELINCK in 1936. The specimens are now in the Zoological Museum at
Amsterdam, and have been kindly loaned to me by Mr. P. J. VAN DER FEEN. The shape
of the mandible and the structure of Ms undoubtedly resemble those of Oryzomys, but
a identification would seem The alveolar is 5.4 specific impossible. length Mi -3 mm, which it the robust forms of the puts among genus. M3 measures 1.7 by 1.2 mm. M2-3
are two-rooted, Mi has two accessory intermediate roots. The fact that the major fold
of extends less than the II M3 half-way across crown (pl. fig. 10) indicates that the
Curaçao cave specimens belong to the O. palustris group, which is known from Central
America, Mexico, and the southern United States, and which also includes the Jamaican
Oryzomys (GOLDMAN, 1918, p. 15-16). It is interesting to note that Rattus, generally
considered a post-Columbian intruder in the West Indies, has also been obtained from
the of Hato: the Leiden Museum three mandibles and cave possesses two maxillae Cave of which collected labelled Hato, Curaçao, were by HUMMELINCK in 1936. These
rather fresh in and Rattus rattus One of the jaws are appearance, belong to (L.) subsp. is the other looks fresh Oryzomys jaws encrusted; as as the Rattus specimens. Dr. HUMME-
LINCK informs that evidence ofstratification of the of Hato has been me no cave deposits
found: both the Rattus and the Oryzomys were picked up by him from the surface on
the same spot and on the same day. The cave of Hato, which is easily accessible, should
be is other thoroughly explored; Oryzomys no longer extant on Curaçao, and remains of
extinct animals to turn in this recently are likely up cave. 16
the lower, but the distinct than in the are, on whole, cusps are more Nectomys ;
and same difference is noted by GYLDENSTOLPE ( 1932, p. 11, 66) by ELLERMAN
As stated the fossil rat molars from have the (1941, p. 337-338). above, Curaçao
relatively low crowns found in Oryzomys, a number of skulls of different South
American for species of which are available direct comparison in the Leiden Museum
collection. Structurally, the molars of Oryzomys resemble those of the fossil Curaçao
characters to rat in detail, save for individual pertaining enterostyles and other
secondary features 1 ).
is little difference between the molar teeth of the various of There genera oryzo-
myine rodents exclusive of Nectomys, except in the matter of size. According to
of GYLDENSTOLPE varies in the tables (1932, p. 136-137), Oryzomys proper length
M1-3 to like that from 3.2 6.3 mm. Neacomys has a dentition of Oryzomys but
M1-3 2.5-3.1 smaller in proportion (GYLDENSTOLPE, I.e., p. 34); length mm (I.e.,
has dentition in but p. 138). Scolomys a "apparently as Neacomys” (I.e., p. 35),
1-3 the smallest smaller still; length M 2.6 mm (I.e., p. 138). Even specimens of
recovered from the block would make molar upper molars Duivelsklip up an upper
6.8 series of mm, which is larger than that found in any Oryzomys. It is in the genus
which of structure Megalomys that we find molars are not only the same but also
of the size those from dealt with in the same as Curaçao present paper.
Megalomys, then, has a distinctly relict distribution in the
it has been found Caribbean area; living only on Martinique and
Santa and exterminated around the of the on Lucia, was beginning
present century. The Martinique species is Megalomys desmarestii
of its (Fischer) ; it is the largest species genus (greatest length of
skull 7 recorded 1885, The Santa cm, as by TROUESSART, p. 7).
Lucia species is smaller; the skull length of Megalomys luciae
is The further record of (MAJOR, 1901, p. 206) 49 mm. only Mega-
lomys known to date is Megalomys audreyae HOPWOOD (1926) from
Barbuda, based on a left ramus of the mandible with M2-3 in situ,
of Pleistocene The fossil found in a cave breccia presumably age.
than the Lucia and Barbuda form seems smaller still Santa species,
it shows the 2 have been is important as range of the genus ) to more
x ) Both GOLDMAN (1918, p. 13) and GYLDENSTOLPE (1932, p. 31) refer to the develop-
in M of and in its an element ment of a "paraconulid" 2 Oryzomys subgenus Melanomys,
considered absent in Nectomys. The element in questionis not a "paraconulid", a term neither mentioned GOLDMAN in his list of elements by crown (I.e., p. 11, copied by detailed of GYLDENSTOLPE, I.e., pi. xvm) nor indicated in the more diagrams WOOD &
WILSON and HERSHKOVITZ 17 It is evident that the element (1936) (1944, p. fig. 1). anterior of in question is the "paraconid" of GOLDMAN, the cingulum our terminology, which be in of and is also discernible may or may not present M2 Oryzomys, occasionally 31 5a and in M2 of Nectomys (HERSHKOVITZ, 1944, p. fig. b).
2 The believed to be not ) genus Megalomys Trouessart, 1881, although separable is considered valid ALLEN from Oryzomys by MAJOR (1901, p. 205), a genus by (1911,
MILLER ANTHONY HOPWOOD p. 179, 214-215), (1912, p. 178; 1924, p. 365), (1926, p. 211), 17
extensive than it was at the beginning of European colonization of the Lesser Antilles.
in The Leiden Museum is fortunate having two skulls of Megalomys, one labelled
"lies Antilles" without further data and another (JENTINK, 1887, p. 219), origina- ting from Martinique, which is one of the cotypes of Megalomys desmarestii (Fischer) presented by Mr. PLÉE and was received by exchange from the Paris Museum in 1825.
two skulls of the than The dentitions of the Leiden Museum collection are larger those of the fossil Curaçao species : thelargest specimens recovered from the Duivels-
block would make M1-3 and klip a series 8.5 mm long, an Mi_3 8.7 mm long (see
in the table 7), whereas recent skulls the length M1-3 is 9.2-9.5 mm, and the length
Mj_3 9.2-9.3 mm. The diameters of the incisors in the two skulls differ more than the diameters of the molars, as is shown in table 9.
TABLE 9
Measurements of incisors of recent and fossil Megalomys
M. desmarestii M. audreyae M. curazensis
Upper I, anteroposterior 3.3-3.9 3.0 2.4-3.0
transverse 2.1-2.6 — 1.3-1.7
Lower I, anteroposterior 3.0-3.6 — 2.6-2.8
transverse 1.7-2.2 — 1.6
In the M1-3 that of Megalomys luciae length is given as 7.5 mm, Mi_3 as 8 mm
HOPWOOD records the (MAJOR, 1901, p. 206). However, (1926, p. 329) length
Mi—3 of Megalomys luciae as 9.4 mm, in which case there would be no difference
the in size between Martinique and Santa Lucia species as far as the molars are
not the concerned !). Incisor diameters are available for Megalomys luciae, but measurements of the molar series as recorded by MAJOR are indicative of molars
just as large as those in an average-sized dentition of Megalomys curazensis (see the diagnosis on p. 2-3).
known from incisor Megalomys audreyae Hopwood, being anM2-3 (and anupper in table included 9), excellently figured (HOPWOOD, 1926, pi. xn), can easily be
with fossil from The is compared our species Curaçao. lengthM2-3 given as 5.2 mm
(estimated length MI_3, 8.3 mm) ; M3 is slightly narrower and shorter than M2,
and the crowns are low, as in our species. The mesostylids are well developed, and
the "protoconulid" (anterolophid of our terminology, marked off by the minor fold)
TATE (1926), (1932, p. 10), ELLERMAN (1941, p. 359), ALLEN (1942, p. 90), SIMPSON
MILLER & KELLOGG and A. E. WOOD As (1945, p. 84), (1955, p. 442), (1955, p. 176). has, and SIMPSON however, been remarked by ELLERMAN (1941, p. 360) by (1956, p. 11),
is close and differentiated Megalomys very to, poorly from, Oryzomys. Generally speaking, size is character for since the number of mere not a good diagnostic genera, but, genera
in is I harm in commonlyrecognized Neotropical Hesperomyini forty, see no retaining
distinct for Caribbean island a generic name these interesting gigantic rats.
Mr. R. W. HAYMAN informs that the alveolar *) kindly me (in litt., June 14th, 1957) lengths of the tooth rows of the type specimen of Megalomys luciae are actually as
follows: M 1-3 8.2 8.4mm. , mm; Mi_3,
Studies Fauna. 7822. 2 18
is slight. The "entostylid" (= posterior cingulum) is well developed in M2, and in
in the both molars a posterior depression or "dimple" is seen hypoconid. In the
Curaçao Megalomys the "dimples" are less strongly marked, especially that in M3.
the the The ectostylids at entrances to major folds are also less strongly marked in the than in the Barbuda molars. HOPWOOD remarks Curaçao (I.e., p. 329) upon the apparent absence of "paraconids" (= anterior cingula) in Megalomys audreyae, and their in but these anterior presence Megalomys luciae, cingula greatly vary
with the obsolescence of the first folds in individually presence or secondary M2-3; in the first folds of Megalomys curazensis secondary M2-3 are reduced or obsolete.
the fossil teeth from In conclusion, Megalomys Curaçao are only slightly different from those of Barbuda, which, in their turn,
with those of the extinct Santa Lucia agree closely recently Mega- lomys. It is remarkable that the teeth of the (presumably) Pleisto-
of cene forms, occurring in the small islands Barbuda and Curaçao,
1,000 km apart as the crow flies, should be so similar. It is unlikely that should have diffe- they not undergone specific or subspecific rentiation least. In the at my opinion, therefore, Curaçao Megalomys
to be I have done the ought differently named, as throughout pres- ent paper.
Thomasomys spec. from Bonaire
The specimens described in the present chapter have been dressed from samples of a phosphatic "oolite" deposit collected at an escarpment near Fontein, Bonaire, by Dr. P. WAGENAAR HUMME-
in 1937. This that of LINCK deposit is very similar to Duivelsklip,
Curaçao, yielding the Megalomys described above, but the frag- ments of fossil bone that it contains are larger: two mandibular
and cranial fragments are over 14 mm long, a fragment is over
sizes found the fossil 9 mm long, only very exceptionally among specimens from the Duivelsklip "oolite". On treatment with acetic
contain of acid, the Bonaire samples proved to a number molars,
in from all in situ jaw fragments, which belong to a genus different that from the Duivelsklip "oolite".
with M1-2 in situ. The E 3399 is a portion of the left maxillary external and
the incisive posterior borders of the left incisive foramen are preserved; foramen
1 terminates posteriorly just in front of M . The median palatal suture is partially seen: the palate must have been at least as wide between the as the combined
1 1 much The width of right and left M . The M sin. is entire but very worn down. anterior surface of the is in the the anterocone depressed middle, indicating presence 19
anterocone of an anterior median fold. The is rather wide transversely, only slightly
of behind. of advanced the less so than the pairs cusps Because wear nothing of anterior The two internal or anterior secondary folds has remained. primary folds
and the first secondary fold are isolated from the external margin; the minor and
folds still There is trace left of the major are open internally. no posterior cingulum.
The crown measures 2.4 mm in length, and 2.0 mm in width. The M 2 of the same specimen is somewhat damaged externally, but the two primary folds likewise
to be isolated from the The first fold is appear margin. secondary represented by two enamel islands. The minor fold is absent, and so is the posterior cingulum.
E 3400 is another portion of the palate with M1-2 sin. The M1 is longer and narrower than that just described; it is only slightly worn (pl. Ill fig. 8). The crown is low, and has a broad anterocone, as in the foregoing specimen. There
is a distinct anterior median fold that communicates with the anterior internal fold, dividing the anterocone into two conules of which the internal is the larger.
The anterior secondary fold, although tiny, is present. The two primary folds are
well second first developed; the internal portion of the is isolated as a fossette. The
fold is transverse second and secondary a slit. The secondary fold the posterior
The the of M 1 is 2.6 the cingulum are clearly visible. length of crown mm, width,
1.6 M2 ofthe is at the base of the The minor mm. same specimen damaged hypocone.
is much but is still in the of of the fold reduced, visible early stage wear specimen.
The fold is continuous the first to be with second primary a fold ; appears bipartite,
its internal portion closed off. The second secondary fold and posterior cingulum
have out. The of M2 are present, but would soon been worn crown measures 2.3
by 1.5 mm.
the There are three specimens of anterior lower molar, one from the right side
E (E 3401) and two from the left side, 3402-E 3403 (pl. Ill figs. 9-10). They are
similar in the dext. does not show very characters, except as regards one point : Mi while the In the the an anterior median fold, other two do. more worn of two left
this is distinct. On the occlusal surface of the there Mis fold quite anteroconid are
two enamel islets, the anterior internal and the anterior primary folds, respectively.
The first off the is The two secondary fold, marking anterior cingulum, easily seen.
primary folds, curving outward and forward as usual, are undivided. However, a
to all the entrance to the second peculiarity common specimens is that secondary
fold is quite conspicuous: a vertical groove extends to low down onthe internal wall
of the crown, and leads upward into the second secondary fold, so that there is a
distinct incurvation of the internal marginal enamel just behind the first primary
fold, marking off a strong mesostylid. This enamel infold is still visible when the
primary folds are closed internally, and the external portion of the second secondary
is isolated from and fold the marginalpart, as shown in the figures. The minor major
folds to open widely on the margin, and enterostyles are present. The dimensions
E 2.6 E is of E3401 and 3403 are the same: length mm, width 1.8 mm. 3402
slightly longer, and measures 2.8 by 1.8 mm.
in in left of the broken in E 3402 is situ a ramus mandible, off anteriorly just
front of the mental foramen. The angle of the mandible, and the coronoid and
the alveoli of shown: each condylar processes, are gone. However, M2-3 are molar
has three roots, and the anterior root is duplicated. There is a pit between M3 and
the ascending ramus. The alveolar length of Mi_3 is 6.7 mm.
Another fragment of the left mandibular ramus (E 3404) also shows the alveoli of
M2-3. The roots are the samein number : two anterior and one posterior to each molar. 20
in A E 3403 holds the lower incisor, 2.0 by 1.1 mm diameter. smaller specimen
of lower incisor (E 3405) measures 1.8 by 0.8 mm in cross section. Two isolated
incisors 2.4 1.2 in diameters There is median upper measure by mm (E 3405). no
anterior groove.
Apart from their smaller size the Bonaire molars differ from those of Megalomys
structural follows. The anterocone of M1 is in several details, as relatively wider;
the anterior median fold is much more marked, and is continuous with the anterior
in the The internal the internal fold slightly worn molar. portions of primary
folds may be isolated from their external portions. In Mi the anterior median fold, when present, is more distinct. The second secondary fold, as described above,
with has a lower and more pronounced entrance, an enamel infold visible on the
margin until late in the life of the tooth, and marking off a strong mesostylid.
In the Mi of Oryzomys and Megalomys the second secondary fold is already closed
without infold enamel earlier internally, any of the marginal showing, either than,
at about the or same time as, the primary folds. Finally, in Oryzomys (GOLDMAN,
there and anterior and 1918, p. 12) are only two roots to M2 M3, one one posterior.
It clear that the could not to to seems present specimens belong Oryzomys, or
for that any oryzomyine rodent, matter. Nectomys need not concern us, because
in the in of its much higher crowns, and because Nectomys second secondaryfold Mi is closed off internallyby the fusion of the mesostylid with the entoconid (HERSH-
KOVITZ, 1944, p. 19).
The Bonaire molars described above have the greatest resemblance to a genus of
Hesperomyini named Delomys by THOMAS. A specimen of the genotype, Hesperomys
dorsalis Hensel, has been excellently figuredby HENSEL (1873,pi. 11 fig. 16a, b) !),
and it shows all the most distinctive characters: the anterior median fold, wide
and As remarked GYLDENSTOLPE anterocone, strong mesostylid. by (1932, p. 60),
the molars of Delomys are brachyodont, rather narrow but Oryzomys-like in struc-
and 1 ture, M is of an evenly oblong shape.
the Delomys is at present included in genus Thomasomys Coues, 1884 (ELLERMAN,
the dental of which in GYL- 1941, p. 366; SIMPSON, 1945, p. 84), description genus
DENSTOLPE (1932, p. 51) is identical with that of Delomys given by this author.
The of listed GYLDENSTOLPE in species Thomasomys by (I.e., p. 141) vary length
1-3 7.6 that would include the Bonaire form. M from 3.5 to mm, a range
The genus Thomasomys as now understood comprises fifty-one
the of which British species geographical range covers Guiana, Venezuela, Colombia, Ecuador, Peru, Bolivia, northern Argentina,
and south-eastern Brazil (ELLERMAN, 1941, p. 367). The present
fossil indicate that its also included least specimens range once at
one of the Caribbean islands.
Beside the Oryzomys and Megalomys already mentioned above,
one more form of Hesperomyini is known to occur in the Caribbean
? Aruba HUMME- islands, viz., Hesperomys spec, on (WAGENAAR
x ) For another good figure, see SCHAUB, 1925, pl. V figs. 8, 10. 21
LINCK, 1940, p. 69); if the generic allocation proves to be correct
than the dis- this occurrence would be an even greater surprise
of for is covery Thomasomys on Bonaire, at present Hesperomys not
north of known to occur anywhere Peru (ELLERMAN, 1941, p. 446).
a full revision of the in which more Pending genus Thomasomys , attention should be given to the teeth than is commonly paid to the dentition in neozoological descriptions, the Bonaire fossil rat
be recorded may simply as Thomasomys spec.
It is highly desirable that the phosphate and "oolite" deposits of Bonaire and
Curaçao, and other similar deposits known to be present in the Caribbean islands, should be searched for animal remains. The finds in the reported upon present paper lead to believe in these remains of ani- one that, deposits, many more interesting mals, either no longer living on the islands or entirely extinct, await discovery and identification.
Hydrochoerus hydrochaeris (L.) from Curaçao
The fossil remains dealt with below were found in a reddish- brown phosphatic "oolite" collected at the Tafelberg Santa Bar- bara, eastern Curaçao, at a height of about 160 m above sea-level.
The matrix was less workable by the acid method than that of
Duivelsklip, and the specimens had to be prepared mechanically.
Remains three teeth the of are available, for greater part still embedded in the matrix, viz., an M 3 dext., aP4 sin., and an M3 dext. In addition, a number of incisor fragments have been found.
The specimens, being softer than the surrounding matrix, have suffered badly from the mechanical treatment, but they are readily identifiable: they belong to the living species of Hydrochoerus,
H. hydrochaeris (L.).
The best available is last the tooth of the series specimen an upper molar, largest
(E 3413). The occlusal surface, seen in profile in the matrix, is perfectly flat and
to entire from front back : the tooth was evidently embedded whole. At the anterior end the V-shaped lobe with the deep outer fold is well exposed. The V-shaped lobe at the posterior end, with the fold internally, is also seen. Between the two terminal lobes there are ten transverse plates, and the overall length of the crown is 27 mm.
The width of the cannot be because of the state of crown given poor preservation of the specimen.
The left lower premolar shown in another fragment of the matrix (E 3414)
with inner lobe consists of three lobes, each an fold; the anterior is incomplete
in front. The junction of the anterior wing of the posterior lobe to the posterior 22
wing of the middle lobe is just external to the median line of the crown, and the
anterior wing of the middle lobe is joined internally to the posterior wing of the
anterior lobe. the anterior of the front is Unfortunately, loop wing gone.
The right lower last molar (E 3415) is likewise incompletely preserved, but the occlusal surface partially exposed shows the posterior lobe, which consists of two narrow transverse plates joined internally; two more plates somewhat thicker
and the anterior the front of which anteroposteriorly ; lobe, plate is, again, narrow.
The of the two anterior is not exact of junction plates shown; the length the worn surface cannot be given.
of molars also embedded the rock and Several portions are in (E3416-E3418
E their 3423), but these are too small for serial position to be determined. There are a number of fragments of incisors (E 3419-E 3422) ; one of them, which is exposed for a length of 4 cm and, judging by its slight curvature, is evidently from
7 and 6 the lower jaw, left side, measures mm transversely, mm anteroposteriorly in cross section. The cross section is triangular with rounded angles; only the front surface is coated with enamel, and it is ungrooved.
Bone fragments abound in places throughout the matrix, but, except for parts of with an ilium and of an astragalus, nothing can be identified certainty
(E 3424-E 3440, E 4330).
I have compared the above-mentioned remains with twenty skulls of Hydro-
choerus hydrochaeris (L.) in the Leiden Museum. If the series is arranged according to increasing basilar length (basion-prosthion), it also shows an increase in length
of the occlusal surfaces of the teeth. The diameters of the extremely hypsodont premolars and molars increase slowly to their bases, enabling the occlusal surfaces to with the skull It should be that P4 keep pace growing (table 10). emphasized
in in all examined. and M3 are place, and use, in the skulls The smallest skull of my
with MÙLLER series corresponds in size a juvenileskull figuredby (1933, figs. 6d, 8d) ; the of neonatus basilar length a skull (MÙLLER, I.e., figs. 6b, 8b) is ca. 55 mm.
M3 varies in lengthfrom 18 to 43 mm; the number of plates between the terminal
is M3 in that the two lobes 9 or 10. The posterior end of varies somewhat plates constituting the hind lobe may not be connected externally, and in the width of the
TABLE 10
Measurements of skulls of recent Hydrochoerus
Leiden Museum, Basilar Leiden Museum, Basilar 3 3 Length M Length M nos. reg. nos. length reg. length
2516 93 18 2215 176 35
cat. f ca. 105 20 3812 178 34
10905 124 27 3467 182 35
2224 128 24 cat. b 182 38
cat. a 134 27 1317 196 37
3479 150 28 2276 200 38
2041 158 32 cat. 212 42 g
3744 172 33 cat. c 215 43
1704 173 34 cat. d 216 39
cat. e ca. 175 36 803 219 41 23
which but is hindmost wing, may be incipient to full-sized, generally distinctly narrower than the anterior wing of the hind lobe.
The fossil specimen of M3 corresponds in size with that shown in recent skulls
of with a basilar length around 130 mm, a stage of growthin which the skull is only
the surfaces of molars about two-thirds as largein linear dimensions, and crown the
in are about one-half as large, as they are full-grown animals.
well in the Both the P4 and the M3, though incompleteanteriorly, compare very matter of size and proportions with their homologuesin the small skulls (especially
in the the fourth and fifth of the series), and evidently belonged to individuals same
of that of the M3 The incisor also in size with the lower I stage growth as . agrees in the small skulls in question, which measure 6.7-7.0 mm transversely, and
5.4-5.9 in section. The median is mm anteroposteriorly, longitudinal groove only
marked in the front surface ofthe incisor as has been said above, very slightly young ; it in the fossil but of this small is apparently absent specimen, specimen only a very portion of the front surface is exposed.
the of other remains In absence that can definitely be ascribed
that what have to Hydrochoerus hydrochaeris *), it seems likely we found in the block of "oolite" from the Tafelberg Santa Barbara
the basilar are the remains of a single individual, an individual
about length of whose skull was 130 mm.
The recent capybara is known to occur in the Guiana lowlands wherever there are large enough streams with sufficient succulent
it northward into Panama vegetation (TATE, 1939, p. 186); ranges
(MILLER & KELLOGG, 1955,p.635), and southward to Peru (SANBORN,
and south-eastern Brazil. In the Pleistocene it also 1951, p. 23) occurred in North America, but the Pleistocene forms from Florida,
Texas, and South Carolina (HAY, 1926; SIMPSON, 1928, 1930) are in part considerably larger than the living Hydrochoerus and have been remarked referred to a distinct genus: Neochoerus. As by
KRAGLIEVICH of the fossil North American (1930, p. 246) none forms is directly ancestral to the recent form, which doubtless evolved in South America.
South American fossil hydrochoerines are currently referred to a number of distinct genera reviewed by KRAGLIEVICH (1930). How-
stated RUSCONI the fossil material does ever, as by (1939, p. 233), not permit of a phylogeny to be established ; the available evidence would point to a polyphyletic rise of the carpinchos. However this
x Two enamel-coated about 5.5 in width and 2 ) surfaces, mm only cm long, are too straight for incisors and may have formed part of molars. 24
the fossil remains of from recorded may be, Hydrochoerus Curaçao above are indistinguishable from the living species. This is the first record of the species from the Caribbean islands, no specimens having been reported from either the Greater or the Lesser Antilles.
It should be borne in mind, however, that the remains of Hydro-
derived from choerus hydrochaeris (L.) are most probably a single juvenile individual. Although, as observed by DARWIN (1889,
the islands in the mouth p. 36), capybaras "occasionally frequent
it much of the Plata, where the water is quite salt", seems too to
the animal have is 64 km from suppose to swum across. Curaçao the Peninsula of Paraguanâ. Moreover, the fact that the lower
found close in the block of and the upper teeth were together
militates the matrix against supposition that the carcass floated
all the from the Venezuelan for such way coast, during a long
period in the water the lower jaw would have become detached from
the calvarium, and the teeth would have fallen out. Mr. DE BUI-
in the cliff have been SONJÉ tells me that, any case, may too high
above sea-level for the animal to have been deposited by the ocean
waves even during a storm.
Therefore, if the individual to which the teeth belonged did not
arrive alive natural human is on a raft, transportation by agency
the most probable interpretation. However, we know neither the
time of the first human settlement of Curaçao, nor the time of
formation of the Hydrochoerus-bearing deposit.
If the fossilized Hydrochoerus teeth are accepted as having be-
longed to a single individualthat somehow accidentally got trans-
ported out to sea from the Venezuelan coast, either by flotsam-
methods jetsam or by native boats, we do not have to believe that
the capybara, an animal so partial to water, was able to establish
and there for of time. itself on semi-arid Curaçao persist any length
As further evidence of the former existence of the long as no capy-
bara in is I do think in Curaçao available not we are justified con-
sidering Hydrochoerus hydrochaeris (L.) as belonging to the endemic
fauna of that island. 25
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WOOD, A. E., & WILSON, R. W., 1936. A suggested nomenclature for the cusps of the
cheek teeth of 2 rodents. Journ. Pal. 10, p. 388-391, figs. PLATE I
dext.
1 M
2,
fig. 3187; 15. x E figures (holotype)
dext. 3204.
1-2 E M
1, sin.
1 fig. M 5, views: fig. 3205; crown E sin.
1 Curaçao, M 4,
fig. Duivelsklip, 3188; E
from dext.
1 M—All
spec, 3, fig. nov. 3189; curazensis E Megalomys PLATE II
from views: Figs. 1—9, Megalomys curazensis nov. spec. Duivelsklip, Curaçao, crown 2 E 2 M3 E M3 E fig. 1, M dext. 3221 ; fig. 2, M sin. E 3236 ; fig. 3, dext. 3246 ; fig. 4, dext. 3 sin. E dext. E 3271 E 3247; fig. 5, M 3262; fig. 6, M1 ; fig. 7, M1 sin. 3283; fig. 8,
E — Cave of M1 sin. E3285;fig. 9, M1 sin. 3284. Fig. 10, Oryzomys spec. from Hato,
view. — All Curaçao, M3 sin., crown figures X 15. PLATE III
1—7, curazensis from all, Fig. Megalomys nov. spec, Duivelsklip, Curaçao, except
fig. 5, crown views: fig. 1, M2 dext. E 3289; fig. 2, M2 dext. E 3290; fig. 3, M2 dext. E 3291 ; fig. 4, M3 sin. E 3341 ; fig. 5, M2 dext. E 3293, external view; fig. 6, M2 dext.
E sin. E 3343. — from 3292; fig. 7, M3 Figs. 8—10, Thomasomys spec. Fontein, M 1 E Bonaire, crown views: fig. 8, sin. E 3400; fig. 9, M1 sin. 3402; fig. 10, M1
sin. E 3403. — All figures x 15.