João Moojen

“ Absolute size of head and body, tail, hind-foot and ear are useful in distinguishing subgenera and subspecies and to some extent in differentiating species.
The length of head and body is large to medium in Proechimys and medium to small in Trinomys. The tail is long to medium in Trinomys and short in Proechimys. The longest tail, 242 mm, is found in P. i. denigratus, and the shortest tail, 123 mm, in P. g. steerei. The relative length of tail also provides gradients or clines.
In every species, males surpass females in average size. Nevertheless, the largest animals are usually females. ”

“ Sometimes it is convenient to recognize species-groups, a systematic category without nomenclatural status, intermediate between the species and the subgenus. When there are two groups of species not sharply separated, including one species whose characters overlap those of each of the two groups, it would seem most appropriate to recognize only species-groups instead of subgenera. ”

“ Some of the counterfolds are especially shallow and tend to disappear in an early stage of wear, and adult individuals may have these folds completely worn away. Advanced wear usually develops a cuplike occlusal surface with only the remains of the main fold and also remains of one or more counterfolds represented by small enamel islands (Figs. 2 to 17) . In the form Proechimys iheringi iheringi, for example, every tooth shows three counterfolds in the upper molariform teeth of individuals in which the wear is not advanced. ”

“ Shelter is usually procured under boulders, stumps or masses of roots. The reproductive rate is low; on the average, there are only two young per litter and only two litters per year.
Sixty-odd names have been given to species and subspecies of Proechimys in the last hundred and fifty years and no serious revision of the taxonomy of the genus was undertaken in the last century. The purpose of the present work is to provide means of understanding species and subspecies within the genus and to describe the different kinds known to occur within the confines of Brazil. ”

“ The absolute size of the skull is proportionate to bulk of the body. The supraorbital and parietal ridges are especially developed in the P. semispinosus group, where they extend across the parietals to the interparietals. In all members of the subgenus Proechimys, these ridges extend onto the parietal region. In Trinomys, however, they do not extend so far posteriorly as the parietal, but only onto the squamosal. ”

“ The intermediate nature of hoplomyoides argues for including the genus Hoplomys as a subgenus of Proechimys.
Species with narrow aristiforms have a rather soft and flexible pelage, while those with wide aristiforms have harsh, spiny pelage. The aristiforms vary in width from 0.45 to 1.3 mm, depending upon the species or subspecies.
Animals with narrow aristiforms tend to have a more or less uniform coloration throughout the dorsal parts. The blackish distal parts of the aristiforms regularly interline the ground color made by the subapical zone of the setiforms. ”

“ Once isolated geographically, the species probably differentiated at an accelerated rate.
The fact that a much larger number of subspecies occupies the larger geographic range of the subgenus Proechimys would not be sufficient to prove that this subgenus, Proechimys, is nearer to the primitive group than Trinomys, the subgenus occupying the smaller range with fewer subspecies. The paleontological evolution of the rodents, however, consistently points to teeth with a larger number of counterfolds (as seen in Proechimys) as the primitive condition. ”

“ Proechimys semispinosus has its wide range in the mountainous, western area of South America, the headwaters of the Amazon drainage and northward in Central America and the nearby Pacific Islands. In these populations a gradient may exist in the number of counterfolds which is varied in every population. The highest number seems to occur in the populations from northern Peru and Ecuador, decreasing from there in all directions, except in the Panamanian and Columbian islands. In gross examination, it seems that the size of the animals increases to the northwards. ”

“ In the one species, Proechimys albispinus, which has the widest distribution of aristiforms on the body of any species in the genus, some of the aristiforms are clavate. Clavate aristiforms occur in the most spiny species of the related genus Echimys.
4. In subspecies of any one full species the incisive foramen is larger in animals which inhabit arid areas than in those which inhabit humid areas. Possibly increased area of moist mucosa associated with Jacobson's organ is required in arid areas for maintenance of the necessary keenness of smell. ”

“ His conclusion seems to be correct, but actually other species of Proechimys (subgenus Trinomys) , for example, P. dimidiatus, have four or more crests in each cheektooth, and, therefore, may be considered as more closely related to Cercomys than is P. setosus. If a large number of crests indicates primitiveness, P. dimidiatus, always with four, is more primitive than any other species in the subgenus Trinomys. Also, the large skull, long hind foot, short tail and thin aristiforms of P. dimidiatus, in my opinion, are primitive characters. ”

“ The recently named subspecies Proechimys cayennensis hoplomyoides Tate, 1939, shows an extraordinary development of the [Pg 325] aristiforms on the back and sides such as occurs in the genus Hoplomys. Actually the small bulla, wide basisphenoid and tooth structure add to the possibility of hoplomyoides being a true Hoplomys, and worn teeth might have been responsible for the difficulty which Tate had in allocating the form to the proper genus. However, the narrow braincase is more nearly like that of Proechimys than that of Hoplomys. ”

“ Proechimys guyannensis appears to be more plastic than any other species. In size of animal, width of aristiforms, color and number of counterfolds in the cheekteeth, it shows marked response to variations in geographic conditions. Proechimys longicaudatus is apparently less plastic; only the number of counterfolds shows marked variation. Proechimys semispinosus varies much within its range. Proechimys goeldii seems to be relatively uniform. Proechimys canicollis shows relatively little variation throughout its range but probably is divisible into two or more subspecies. ”

“ Apparently a small population restricted to a small island tends to revert to the primitive type. The homozygous condition will tend toward a generalized genotype and the disappearance of secondary biotypes. P. i. iheringi on the Island of São Sebastião averages larger, has thinner aristiforms, and a stronger skull than the same subspecies on the mainland, and the cheekteeth usually have two and three counterfolds. The same subspecies on the mainland has no more than two counterfolds. ”

“ In all forms of southeastern Brazil the premolars are larger than the first molars, the first molars are larger than the second molars, and the second molars are larger than the third molars. The forms from central and northern Bahia, Brazil, have the molariform teeth more or less the same size. The forms from the remaining part of the area occupied by the genus have premolars smaller than the first molars, the first molars smaller than the second molars, but the second molars larger than third ones. ”

“ Dr. Remington Kellogg, Curator of Mammals in the United States National Museum, and the late Dr. Wilfred H. Osgood, formerly Curator Emeritus of the Department of Zoölogy in the Chicago Natural History Museum, generously permitted me to use their private lists of South American mammals. These lists contain much unpublished data, as for example, proof, in Kellogg's list, that Proechimys guyannensis (E. Geoffroy Saint-Hilaire, 1803) antedates P. cayennensis (Desmarest, 1817) . ”

“ Proechimys semispinosus gorgonae and Proechimys semispinosus ignotus, living on Gorgona and San José islands, respectively, are both characterized by large size, short tails, strong and conspicuously ridged skulls, and cheekteeth frequently with four and five counterfolds. On the mainland, closely related subspecies, like P. s. panamensis, chiriquinus and gularis, far [Pg 317] less frequently have four counterfolds in more than one or two teeth. More striking still is the population-sample of gularis from the island of Llunchi, in the Rio Napo, eastern Ecuador. ”

“ P. i. panema, occurring approximately 100 kilometers to the northward of P. i. gratiosus (lowland form) , has one counterfold in M3 in only 20 per cent of the specimens but the lower third molar has only one counterfold in 80 per cent of the specimens. In P. i. denigratus, from about 3 degrees north of the range of P. i. panema, the reduction is proportionately greater: P4 now is the only upper cheektooth with two counterfolds in every specimen; all molars tend to have only one; p4 has also two counterfolds but all lower molars have only one. ”

“ Adjacent counterfolds may appear to be coalesced in many instances. Coalescence is more likely to be seen in species where a wider variation in the number of the counterfolds is involved and it appears as a gradient in the reduction of the number of counterfolds. ”

“ P. longicaudatus roberti, belonging in the other subgenus, showed no susceptibility at all.
At Teresópolis, Estado do Rio de Janeiro, the two species were found in two different forests, only a few kilometers apart, but dimidiatus lived at a higher elevation, where the humidity was remarkably higher. Naturally the plant associations were different in the two forests. This seeming ecological adaptation of the two kinds of Proechimys may explain why P. iheringi ranges farther north; the forests to the northward are less humid. ”

“ P. setosus is poorly represented, both of the available skins being faded. Furthermore, no type locality is known for the subspecies P. s. setosus.
P. albispinus has only two known subspecies: P. a. albispinus, living in a region of higher humidity, is slightly the darker and has subapical zones of the setiforms on the sides Ochraceous-Tawny; P. a. sertonius, living in a much drier region, has the same subapical zone Ochraceous-Buff. The number of specimens of P. a. sertonius is so few that no gradient can be detected, even if one exists. ”

“ Trinomys—main fold deep: aristiforms well-developed on the rump and outer thighs; tail no less than 75 per cent of length of head and body; skull without ridges across the parietals; no conspicuous groove for transmission of nerve inside infraorbital foramen; molariform teeth decreasing in size from premolar to third molar; 1 to 3 counterfolds in the molariform teeth.
Proechimys—main fold shallow: aristiforms not developed on rump and outer thighs; tail less than 75 per cent of length of head and body; groove for transmission of nerve present in infraorbital foramen of several subspecies ”

“ In these, and other alleged instances of two or more kinds occurring together, detailed study of the specimens concerned was necessary to learn the true facts. Also with the opportunity to compare collections from several different places, new facts emerged. P. longicaudatus, as it was conceived of by Allen, was a composite species, but in one locality, Utiarití, Ribeiro and Allen actually were dealing with two distinct species.
The species, or subspecies belonging to different species, living together are: goeldii and hyleae, at Fazenda Paraiso; goeldii and riparum in Manaus ”

“ General characters.—Size large; tail short and hairy; aristiforms wide and stiff, especially well-developed on back; general color on upper parts some shade of ochraceous, usually much darker on back and forming a conspicuous dorsal band; feet dark; ventral surfaces and inner sides of legs white; skull elongate and strong with ridges well developed; incisive foramen long and narrow; bullae large; usually four counterfolds in M3 and M2; usually three but sometimes four counterfolds in M1 and even P4; lower premolar with four and lower molars with three counterfolds. ”

“ Color.—Upper parts vary from Buckthorn Brown to Ochraceous-Buff. Dark color ordinarily is correlated with an environment of higher degree of humidity and light color with lower humidity. However, species may be found in similar conditions of humidity but differing in color. Proechimys albispinus albispinus, for example, a light-colored form, is found in areas where the rainfall averages 1,000 to 1,500 mm of annual precipitation, in the isohygra of 80 per cent relative humidity. ”

“ When differences in the structure of the animal are known, a person is led to speculate on the factors which could cause them. For one thing, does the observed degree of difference tend to isolate animals possessing the "new" character from the other animals? ”

“ The development of the main fold varies in two different ways: in all samples from southeastern and eastern Brazil it is strongly developed, deeply grooves the tooth through its crown and, in younger individuals, completely divides the occlusal surface of the tooth. ”

“ No more than two adult animals (male and female) were captured in the same shelter, and only a few times were young captured in the same place with adults. Nesting places were located also at the bases of trees and near fallen logs where litter accumulates.
Records of animals kept in captivity show that the species dimidiatus survives more than two years. Specimen MN no. 5448 [M] was adult when captured by the Serviços de Estudos e Pesquisas sobre a Febre Amarela on December 5, 1938, and died on January 17, 1942. ”