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SMITHSONIAN MISCELLANEOUS COLLECTIONSVOLUME 139, NUMBER 4
A REVIEW OF THE GENUS HOPLOMYS(THICK-SPINED RATS), WITH DESCRIP-TION OF A NEW FORM FROM ISLAESCUDO DE VERAGUAS, PANAMA
ByCHARLES O. HANDLEY, JR.Associate Curator, Division of MammalsUnited States National MuseumSmithsonian Institution
(Publication 4380)
CITY OF WASHINGTONPUBLISHED BY THE SMITHSONIAN INSTITUTIONJULY 3, 1959
THE LORD BALTIMORE PRESS, INC.BALTIMORE, MD., U. S. A.
A REVIEW OF THE GENUS HOPLOMYS (THICK-SPINED RATS), WITH DESCRIPTION OF ANEW FORM FROM ISLA ESCUDODE VERAGUAS, PANAMABy CHARLES O. HANDLEY, JR.Associate Curator, Division of MammalsUnited States National MuseumSmithsonian InstitutionA specimen of the thick-spined rat, Hoplomys gymnurus Thomas,that Alexander Wetmore shot in a thicket on Isla Escudo deVeraguas on the morning of March I, 1958, is probably the only-mammal from this Caribbean island that is preserved in a museum.Other rats that Wetmore saw in coconut palms on the same dayapparently were of another genus. No other mammals have beenreported from this locality except feral hogs. Although Indians oncelived on the island, human beings are now only transients there.Escudo de Veraguas is a low island, about 1 mile wide and2.5 miles long, in the Caribbean Sea, 11 miles off the base of theValiente Peninsula, Province of Bocas del Toro, north coast of theRepublic of Panama. Wetmore (Smithsonian Misc. Coll., vol. 139,No. 2, 1959) has given a detailed account of the history, geography,and zoological position of the island.Other echimyid genera, Diplomys and Proechimys, are known tooccur on certain islands in the Gulf of Panama and elsewhere, but noinsular populations of Hoplomys have been reported. The Escudo deVeraguas Hoplomys differs in so many respects from other knownpopulations of the thick-spined rat that it has prompted a brief reviewof the genus.Many of the National Museum (US) specimens reported here werecollected in cooperation with the Gorgas Memorial Laboratory,Panama. I express my thanks to Carl Johnson, director, and othermembers of the laboratory staff for numerous courtesies and assistancein fieldwork. Some of the specimens were collected by C. M. Keenanof the Army Preventive Medicine Survey Detachment, Ft. Clayton,Canal Zone. Richard Van Gelder kindly permitted the study of speci-mens in the American Museum of Natural History (AMNH), NewYork. SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 139, NO. 4
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2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 139Genus HOPLOMYS J. A. Allen1908. Hoplomys J. A. Allen, Bull. Amer. Mus. Nat. Hist., vol. 24, p. 649.Genotype.—Hoplomys truei J. A. Allen.Distribution.—The genus has a limited distribution in CentralAmerica and northwestern South America. It is monotypic. Publishedrecords of collecting localities are mapped in figure 1. Hoplomys isknown to occur at medium elevations (800-3,100 ft.) on the Caribbeanslope of the highlands of Nicaragua and Costa Rica ; near sea levelon the Caribbean coast of Panama; at medium elevations (600-4,000ft.) on the Pacific slope of eastern Panama, Colombia, and Ecuador;and near sea level in extreme southwestern Colombia and north-western Ecuador. The distribution of Hoplomys in South Americaappears to be limited by the Western Andes. J. A. Allen's record forPuerto Valdivia on the Rio Cauca (Bull. Amer. Mus. Nat. Hist.,vol. 35, p. 207, 1916) is erroneous (the specimen is a Proechimys).Proechimys cayennensis hoplomyoides Tate (Bull. Amer. Mus. Nat.Hist., vol. j6, p. 179, 1939) from Mt. Roraima, Venezuela, appearsnot to be a Hoplomys, although a relationship has been suggested(Moojen, Univ. Kansas Publ., Mus. Nat. Hist., vol. i, p. 324, 1948).In the Caribbean lowlands of Panama, where Proechimys is abun-dant and Hoplomys seemingly rare, I have trapped individuals ofboth genera under the same log on successive nights. At medium alti-tudes in the mountains of Panama where Hoplomys is fairly common,Proechimys apparently does not occur.All the Hoplomys that I have collected in Panama were caught inbanana-baited live traps under large decaying logs—in fairly openmature rain forest, in grassy clearings and adjacent streamsidethickets, and in dense, hillside Heliconia thickets. Goldman (Smith-sonian Misc. Coll., vol. 69, No. 5, p. 124, 1920) found Hoplomysassociated with fallen trees and rocks in Panamanian forests.Diagnosis.—Dorsum, flanks, and rump, in both adult and juvenilepelages, with spines 26 to 33 mm. in maximum length and 1.5 to 2.0mm. in maximum diameter, tending to obscure soft fur. Tail shorterthan head and body, scaly, and sparsely haired. Ears scantily haired.Hind feet long and narrow ; fifth toe scarcely longer than first ; clawsrelatively straight, but claw of second toe slightly expanded. Skullprominently ridged, and supraorbital shelf beaded ; rostrum relativelybroad at tip ; auditory bullae relatively small ; and infraorbital foramenwithout subsidiary canal on floor, and with external wall thin inlateral view. Cheek teeth with oblique folds ; counterfold formulanormally 4/4-4/4-4/4-4/4, rarely 4/4-4/3-4/3-4/3.
NO. 4 HOPLOMYS (THICK-SPINED RATS) HANDLEY 3
Variation.—Specimens of Hoplomys have never before been availa-ble in series. Fourteen specimens, seven of which are adult, recently-collected on Cerro Azul, Panama, now permit a fairly good estimate
90° 85° 80°
4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 139
Size, flatness, and ridging of the skull increase with advancing agein Hoplomys and Proechimys. Tooth wear appears to be a reliablecriterion of age. Full adult pelage usually is attained after M3 appearsand before it becomes functional. Only juvenile and adult pelages havebeen distinguished. Specimens in which all cheek teeth are functionalare considered to be adults. Generally, the largest, flattest, mostheavily ridged skulls have the most worn teeth. Apparently theserodents continue to grow after all teeth are functional. Thus, thereis considerable size spread among adult skulls. For this reason onlymaximum and minimum figures are given in the table of measurements(p. 6).Body sizes appear to be uniform throughout the mainland rangeof the species, but larger on Escudo de Veraguas. The skull is narrowin the south—Ecuador, Colombia, and Darien—somewhat broaderin central Panama, Costa Rica, and Nicaragua, and broadest of allon Escudo de Veraguas. Likewise the nasals and cheek teeth aresmaller in the southern populations. Size of the auditory bullaeincreases northward from Ecuador to Nicaragua, but the bullae arelargest and most inflated anterolaterally in the Escudo specimen.Several features of the zygomatic arches vary geographically. Themaxillary roots of the zygomata flare less widely and less perpendicu-larly from the longitudinal axis of the skull (so that the zygomata aremore convergent anteriorly) from the Canal Zone southward thanthey do in the north. From Cerro Azul southward the maxillary rootstend to flare up, away from the ventral plane of the skull, rather thanparalleling that plane as they do in the north. The jugal has a hooklikeposteroventral process in most Canal Zone and Cerru Azul specimens,but not in others. Most of the specimens from Ecuador, Colombia,and Darien, and a smaller percentage of the central Panamanianspecimens have a small conical projection on the dorsal edge of thezygoma at the jugal-squamosal suture. I failed to check this characterin the Costa Rican and Nicaraguan specimens. There is hardly atrace of it in the Escudo individual. The nasals, broad and posteriorlytruncate in the island specimen, are usually narrower and posteriorlyacute in mainland populations.Among mainland populations of Hoplomys flatness and ridging ofthe skulls of mature individuals are similar to these features in matureindividuals of Proechimys semispinosus. None of the availableHoplomys or Proechimys closely approaches the Escudo specimen inflatness or ridging, despite the fact that the island specimen, judgedby tooth wear, is a prime adult, not as old as many individuals with
NO. 4 HOPLOMYS (THICK-SPINED RATS) HANDLEY 5
which it was compared. The degree of reduction of dorsal doming andventral depression of the brain case of the Escudo specimen is reflectedin the convergence of greatest and condylobasal lengths of the skull,and in the more posteriorly oriented (as opposed to ventrallyoriented) foramen magnum.The thick spines that distinguish Hoplomys are longest andstrongest just behind the shoulders on the upper midback, fromwhich point they diminish in size in all directions. The spines possiblyvary geographically in size. They appear to be longer and strongertoward the southern part of the range of Hoplomys. The Escudospecimen, although it is larger than any other, has the smallest andweakest spines. Maximum spine length varies as follows (mean,followed by extremes) : 6 Ecuador 29 mm. (28-31), 4 Darien 30( 2&-33)> XI Cerro Azul 28 (26-29), 5 Canal Zone 28 (27-30),1 Escudo de Veraguas 26.Coloration of the spines is individually variable. All specimenshave all spines proximally white and distally colored. The tips of thoseof the dorsum are always black, but the flank spines usually are tingedwith orange or banded with orange and black distally. Occasionallythe flank spines are colored like the dorsal spines.Coloration of the soft hairs of the dorsum is geographically variable.At the southern extreme they are reddish orange, especially on theshoulders. The soft hairs of the Escudo specimen are similar butdarker and brighter. Costa Rican and Nicaraguan examples have thehairs more orange, and those from Panama and northern Colombiaare more yellowish on the average. The presence or absence of blackocular and crown areas appears to be individually variable throughoutthe range of Hoplomys, but only the Escudo specimen has the softhairs blackened to form a distinct middorsal stripe from snout to baseof tail.All populations have the underparts dominantly white, and all havesome individuals that show encroachment of agouti hairs of the sideneck onto the throat, suggesting an incipient collar. This is wellmarked in the Escudo specimen; one from Rio Indio, Canal Zone,has a complete collar. Nine of the 14 Cerro Azul specimens haveclear orange collars, and several of them have a band of clear orangehairs separating the agouti hairs of the flanks from the white hair ofthe belly. Neither of these features is seen in samples of other popu-lations. Coloration of the forefeet (usually white on the inner side,colored on the outer, occasionally colored throughout), and colorationof the cheeks (clear orange, buff, gray, or agouti) are individuallyvariable.
SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 139
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8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 39The large size of the Escudo specimen, the massiveness, broadness,and heavy ridging of its skull, the inflation of its auditory bullae,and its distinctive coloration all seem to be beyond the possibility ofindividual variation. This suggests that the Escudo animal is taxo-nomically distinct from mainland populations. That it is conspecificwith them is indicated by its alignment with some of the morphologi-cal clines observed in the mainland populations. Wetmore {op. cit.)has named three birds (a wren, a manakin, and a tanager) collectedon Escudo de Veraguas that differ from their mainland counterpartsin greater size, in addition to differences in color.Classification.—The genus Hoplomys is represented by one species,which includes four subspecies
:
HOPLOMYS GYMNURUS GOETHALSI Goldman1912. Hoplomys gocthalsi Goldman, Smithsonian Misc. Coll., vol. 56, No. 36,p. 10 (Rio Indio, near Gatun, Canal Zone, Panama).Characters.—Size medium ; skull of medium width and ridged
;
brain case domed and slightly depressed ; foramen magnum ventrallyoriented ; cheek teeth large ; auditory bullae medium ; zygomata con-verging conspicuously anteriorly, and maxillary root tending to flareup slightly from ventral plane of skull ; jugal with hooklike postero-ventral process and small conical posterodorsal projection ; nasals long,narrow, and posteriorly acute ; dorsal spines long and strong ; softhairs of dorsum appear uniform yellowish orange in mass effect.Specimens examined.—Panama : Cana, 2,000 ft., 5 US ; CerroAzul, 2,100 ft., 14 US ; Ft. Sherman, 4 US ; Gatun, 3 (2 AMNH,1 US) ; Cerro Tacarcuna, 2,650 ft., 6 AMNH ; Rio Cangandi, 200 ft.,1 US ; Rio Indio, 2 US. Colombia: Alto Bonito, Antioquia, 1,500 ft.,1 AMNH ; Bagado, Choco, 600 ft., 2 AMNH.Additional published records.—Colombia : Rio Tamana, branch ofthe Rio San Juan, Choco (J. A. Allen, Bull. Amer. Mus. Nat. Hist.,vol. 35, p. 207, 1916).HOPLOMYS GYMNURUS GYMNURUS Thomas1897. Echimys gymnurus Thomas, Ann. Mag. Nat. Hist., ser. 6, vol. 20, p. 550(Cachabi, N. Ecuador, alt. 560 ft.).Characters.—Size medium or small ; skull narrow and ridged ; braincase domed and slightly depressed ; foramen magnum ventrallyoriented ; cheek teeth small ; auditory bullae small ; zygomata con-verging conspicuously anteriorly, and maxillary root flaring up fromventral plane of skull; jugal lacking posteroventral process, but with
NO. 4 HOPLOMYS (THICK-SPINED RATS) HANDLEY 9prominent conical posterodorsal projection ; nasals short, narrow,and posteriorly acute ; dorsal spines long and strong ; soft hairs ofdorsum giving reddish-orange mass effect, slightly darkened onshoulders.Specimens examined.—Colombia: Barbacoas, Narifio [75 ft.],8 AMNH ; Buenavista, Narifio [1,200 ft], 1 AMNH ; La Guayacana,Narifio, 800 ft., 2 US. Ecuador: Mindo, Rio Blanco [4,000 ft.],1 AMNH ; San Javier, 60 ft., 7 (1 AMNH, 6 US).Additional published records.—Ecuador: Cachabi, 560 ft. (Thomas,op. cit., p. 551).HOPLOMYS GYMNURUS TRUEI J. A. Allen1896. Echimys semispinosus Alfaro (not Tomes, i860, Proc. Zool. Soc. Lon-don, p. 265), Primera Exposition Centroamericana de Guatemala, MuseoNacional, San Jose, p. 41 (Suerre, Costa Rica).1908. Hoplomys truei J. A. Allen, Bull. Amer. Mus. Nat. Hist., vol. 24, p. 650(Savala, Matagalpa Prov., Nicaragua).Characters.—Size medium ; skull of medium width and ridged
;
brain case domed and slightly depressed ; foramen magnum ventrallyoriented ; cheek teeth large ; auditory bullae large ; zygomata con-verging less anteriorly than in goethalsi, and maxillary root in planeof ventral surface of skull ; jugal without hooklike posteroventralprocess ; nasals long, narrow, and posteriorly acute ; dorsal spinesrelatively short and weak; soft hairs of dorsum giving uniform darkorange mass effect.Specimens examined.—Nicaragua : Lavala [ = Savala, 800 ft., alongthe inner border of the low east coast region], 2 AMNH ; Rio Coco[800 ft.], 2 AMNH ; Vijagua [ = Bijagua, probably 1,500 to 2,000 ft.,on eastern slope of highlands in Matagalpa Prov.], 3 AMNH. CostaRica: Santa Teresa Peralta [3,100 ft.], 1 AMNH; Suerre, 1,500 ft.[near Jimenez], 1 AMNH.Additional published records.—Tate (Bull. Amer. Mus. Nat. Hist.,vol. 68, p. 401, 1935) supposed that True's record (Proc. U. S. Nat.Mus., vol. 11, p. 467, 1889) of Echinomys semispinosus in Nicaraguawas the first published reference to a Hoplomys. The specimens,still in the U. S. National Museum, however, are Proechimys.HOPLOMYS GYMNURUS WETMOREI subsp. nov.Holotypc.—U.S.N.M. No. 307057 ; adult male, skin and skullcollected March 1, 1958, by Alexander Wetmore ; Isla Escudo deVeraguas, Prov. Bocas del Toro, Panama; original No. 1479.
IO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 139Characters.—Size large ; skull broad and heavily ridged ; braincase flattened dorsally and ventrally ; foramen magnum posteriorlyoriented ; cheek teeth large ; auditory bullae large and inflated antero-lateral^ ; zygomata converging less anteriorly than in goethalsi, andmaxillary root in plane of ventral surface of skull ; jugal without hook-like posteroventral process, or conical posterodorsal projection ; nasalslong, broad, and posteriorly truncate; dorsal spines relatively shortand weak ; and soft hairs of dorsum giving dark reddish-orange masseffect (between Burnt Sienna and Sanford's Brown of Ridgway, 1912,Color Standards and Color Nomenclature), with black middorsalstripe from snout to base of tail. For measurements see table I.Specimen examined.—The holotype.