Oryzomys anoblepas
Encyclopedia
Juliomys anoblepas is a rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
in the genus Juliomys
Juliomys
Juliomys is a genus of South American rodents of the family Cricetidae. Four species are known, all found in Argentina and Brazil. They are as follows:* Juliomys anoblepas * Juliomys ossitenuis*Juliomys pictipes...
of the subfamily Sigmodontinae
Sigmodontinae
The subfamily Sigmodontinae is one of the most diverse groups of mammals. It includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the species count...
known from a single broken skull. The specimen was collected by Peter Wilhelm Lund
Peter Wilhelm Lund
Peter Wilhelm Lund was a Danish paleontologist, zoologist, archeologist and who spent most of his life working and living in Brazil...
in the caves of Lagoa Santa
Lagoa Santa
For Lagoa Santa, a municipality in Goiás see Lagoa Santa, GoiásLagoa Santa is a municipality and region in the state of Minas Gerais, Brazil...
in Minas Gerais
Minas Gerais
Minas Gerais is one of the 26 states of Brazil, of which it is the second most populous, the third richest, and the fourth largest in area. Minas Gerais is the Brazilian state with the largest number of Presidents of Brazil, the current one, Dilma Rousseff, being one of them. The capital is the...
, Brazil, in the first half of the 19th century and described by Herluf Winge
Herluf Winge
Adolf Herluf Winge was a Danish zoologist.-Biography:As a young student, Winge was interested in small mammals, particularly moles, shrews and insectivora. He studied mammalian dentition and produced a comparison of cusp similarities...
in 1887 as Calomys anoblepas. The species remained unstudied and its affinities unclear until 2011, when it was recognized as a member of the genus Juliomys, which includes three other species from southern Brazil and nearby Argentina and Paraguay. J. anoblepas is probably a distinctive extinct species of the genus, which is no longer found in Lagoa Santa.
Juliomys anoblepas is similar to the other members of its genus in the configuration of its zygomatic plate
Zygomatic plate
In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch . At the back, it connects to the front root of the zygomatic arch, and at the top it is connected to the rest of the skull via the antorbital bridge. It is part of the maxillary...
(a bony plate on the side of the skull). It hardly extends forward in front of the connection between the plate and the main body of the skull, and that connection is relatively low on the skull. Furthermore, the incisive foramina, openings in the front part of the palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
, extend to a point between the first molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
s, and the palate is short, with its back margin between the third molars. The living species of Juliomys differ from J. anoblepas in various characters, including shorter incisive foramina in two species and the shape of the zygomatic arch
Zygomatic arch
The zygomatic arch or cheek bone is formed by the zygomatic process of temporal bone and the temporal process of the zygomatic bone , the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process...
(cheekbone) in J. anoblepas. The upper molar row is 4.13 mm long, which makes J. anoblepas the largest known species of Juliomys.
Taxonomy
Between 1835 and 1849, Danish zoologist Peter Wilhelm LundPeter Wilhelm Lund
Peter Wilhelm Lund was a Danish paleontologist, zoologist, archeologist and who spent most of his life working and living in Brazil...
collected abundant remains of mammals around the village of Lagoa Santa
Lagoa Santa
For Lagoa Santa, a municipality in Goiás see Lagoa Santa, GoiásLagoa Santa is a municipality and region in the state of Minas Gerais, Brazil...
in Brazil. After his death, his fellow Dane Herluf Winge
Herluf Winge
Adolf Herluf Winge was a Danish zoologist.-Biography:As a young student, Winge was interested in small mammals, particularly moles, shrews and insectivora. He studied mammalian dentition and produced a comparison of cusp similarities...
described Lund's collections in detail, among many others publishing a monograph about the rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s of the collection in 1887. Winge described numerous new species, many of which received little attention from systematists afterward, and among these is the species he named Calomys anoblepas. The specific name, anoblepas, comes from the Greek ἄνω ano "upwards" and βλέπω blepo "to look", meaning "looking upward", and although Winge did not explain the name, it most likely refers to the zygomatic plate
Zygomatic plate
In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch . At the back, it connects to the front root of the zygomatic arch, and at the top it is connected to the rest of the skull via the antorbital bridge. It is part of the maxillary...
(a bone plate at the side of the skull), which is bended outward. Winge understood the genus Calomys in a sense very different from that used today, including in it the species Calomys longicaudatus (currently Oligoryzomys nigripes
Oligoryzomys nigripes
Oligoryzomys nigripes, also known as the Black-footed Colilargo or the Black-footed Pygmy Rice Rat, is a rodent in the genus Oligoryzomys of family Cricetidae. It is found from Pernambuco in northeastern Brazil through the Atlantic Forest and Cerrado into Paraguay, Uruguay, and Argentina, where it...
), Calomys coronatus (currently Euryoryzomys russatus), Calomys rex (currently Sooretamys angouya), Calomys laticeps (currently Cerradomys subflavus), Calomys saltator (currently Hylaeamys laticeps
Hylaeamys laticeps
Hylaeamys laticeps, also known as the Atlantic Forest Oryzomys or Large-headed Rice Rat, is a species of rodent in the genus Hylaeamys of family Cricetidae. It occurs in the Atlantic Forest region of southeastern Brazil...
), and Calomys plebejus (currently Delomys
Delomys
Delomys is a genus of South American rodents in the tribe Thomasomyini of family Cricetidae. Three species are known, all found in Argentina and Brazil. They are as follows:* Montane Atlantic Forest Rat...
, species uncertain). He wrote that C. anoblepas was the most divergent of the species of Calomys, but that it was most similar to C. longicaudatus.
Winge's concept of the genus Calomys essentially included unspecialized species with pentalophodont molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
s, which are characterized by the presence of a crest known as the mesoloph on the upper and mesolophid on the lower molars, and excluded species now placed in Calomys, which he placed in Hesperomys instead. Since 1898, authors have placed Winge's Calomys species in Oryzomys
Oryzomys
Oryzomys is a genus of semiaquatic rodents in the tribe Oryzomyini living in southern North America and far northern South America. It includes eight species, two of which—the marsh rice rat of the United States and O. couesi of Mexico and Central America—are widespread; the six others have...
, conforming to the more conventional taxonomic arrangement; after that, the species was referred to as Oryzomys anoblepas. Over many decades, the identity of most of Winge's species remained uncertain, and in many cases it was not until the 1990s that the original material was restudied to provide a definitive identification of the material. In a 2002 review of the fossil sigmodontine
Sigmodontinae
The subfamily Sigmodontinae is one of the most diverse groups of mammals. It includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the species count...
rodents of South America, Argentinean zoologist Ulyses Pardiñas and his coworkers wrote that the animal was "possibly an Oecomys", but this claim was based only on a cursory investigation.
In 2011, Pardiñas and Pablo Teta published another paper on "Calomys anoblepas" after re-examining the only known specimen in Copenhagen, concluding that the animal was instead related to the living genus Juliomys
Juliomys
Juliomys is a genus of South American rodents of the family Cricetidae. Four species are known, all found in Argentina and Brazil. They are as follows:* Juliomys anoblepas * Juliomys ossitenuis*Juliomys pictipes...
, which currently includes three living species from southern Brazil and nearby Paraguay and Argentina. They recognized some features by which J. anoblepas differs from the living species, and consequently kept it as a distinct, extinct species. Juliomys is a genus of unclear relations within the subfamily Sigmodontinae
Sigmodontinae
The subfamily Sigmodontinae is one of the most diverse groups of mammals. It includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the species count...
, which is widespread and very diverse in South America and southern North America.
Description
Juliomys anoblepas is known only from the front half of a skull that was found in a cave known as "Lapa da Serra das Abelhas". Compared to other species of Juliomys, it is large and has a more robust skull and teeth. Its rostrum (the front part) is broad and short and the interorbital regionInterorbital region
The interorbital region of the skull is located between the eyes, anterior to the braincase. The form of the interorbital region may exhibit significant variation between taxonomic groups....
(between the skull) is hourglass-shaped, with squared margins. The thomasomyine rodent Rhipidomys
Rhipidomys
Rhipidomys is a genus of rodents in the family Cricetidae, comprising at least 18 species of climbing mouse:* Southern Climbing Mouse * Cariri Climbing Mouse...
and the oryzomyine Oecomys, both of which also occur in eastern Brazil, both have a broader interorbital region with better-developed ridges at the margins. One of three living species of Juliomys, Juliomys pictipes, also has a broader interorbital region. Behind the position of the nasals (which are missing in the only known skull) is an interlacrymal depression, a lowered portion of the skull; the suture (connection) between the two frontal bone
Frontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
s is incompletely closed there. This interfrontal fontanella
Fontanella
-Places:Austria*Fontanella, AustriaItaly*Fontanella, Lombardy, a comune in the Province of Bergamo*Fontanelle cemetery, a cemetery in the City of Naples, Campania-People:*Francesc Fontanella , a Catalan poet, dramatist, and priest...
is shared with Juliomys rimofrons, but not with Juliomys pictipes, nor with most specimens of Juliomys ossitenuis. In Wilfredomys, a Brazilian rodent with some similarities to J. anoblepas, the premaxillary bone forms a narrow projection towards the frontals, which is absent in J. anoblepas and other Juliomys species.
The zygomatic plates are almost completely vertical. As Winge already noted, the front margin of the zygomatic plate hardly extends forward before the antorbital bridge, which connects the plate to the body of the skull. This feature distinguishes J. anoblepas from Wilfredomys and many oryzomyines, but the zygomatic plate of living Juliomys species closely resembles that of J. anoblepas. In addition, the connection between the zygomatic plate and the antorbital bridge is inserted higher on the rostrum in Wilfredomys. The zygomatic arch
Zygomatic arch
The zygomatic arch or cheek bone is formed by the zygomatic process of temporal bone and the temporal process of the zygomatic bone , the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process...
es (cheekbones) spread broadly. More than in other Juliomys species, the front part of the zygomatic arches is bended forward and the zygomatic plates are bended outward. In addition, the zygomatic notch, the notch between the zygomatic plate and arch, is deep, not shallow as in J. ossitenuis and J. rimofrons.
The incisive foramina
Incisive foramen
The fossa incisiva is an opening in the bone of the oral hard palate where blood vessels and nerves may pass. There are four of these openings in the incisive fossa.-Formation:...
(openings in the palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
between the incisors and the molars
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
) are broad and long, extending to the front margins of the first upper molar (M1). Wilfredomys has even longer incisive foramina, extending between the molars, but the foramina are shorter in J. ossitenuis and J. pictipes. The palate itself is wide and short, with its back margin between the M3s. Oryzomyines like Oecomys and Oligoryzomys
Oligoryzomys
Oligoryzomys is a genus of rodents in the tribe Oryzomyini of family Cricetidae. Many species are known as pygmy rice rats or colilargos...
have longer palates, extending beyond the third molars. Fine openings (foramina) are present on the palate. The back margin of the palate is squared; J. anoblepas lacks a spine in the middle of the back margin, as is present in Rhipidomys. Wilfredomys has the back margin U-shaped instead and has a longer palate, with the back margin behind the M3s.
The well-developed upper incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
s have orange enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
at their front surfaces and are slightly opisthodont (with their cutting edge behind the vertical plane of the incisors). The molars are brachyodont (low-crowned) and bear crests and cusps
Cusp (dentistry)
A cusp is an occlusal or incisal eminence on a tooth.Canine teeth, otherwise known as cuspids, each possess a single cusp, while premolars, otherwise known as bicuspids, possess two each. Molars normally possess either four or five cusps...
arranged in pairs opposite each other. The front cusp of M1, the anterocone, is divided into two smaller cusps on each side of the tooth by a valley, the anteromedian flexus. Both M1 and the second molar (M2) have a well-developed mesoloph (a crest near the middle of the tooth). Although M3 is relatively large, its back part is reduced.
The interorbital region is 4.14 mm long and the zygomatic plate is 2.38 mm. The diastema
Diastema (dentistry)
Diastema is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars.-In humans:...
(gap) between the incisors and molars is 6.39 mm long. The incisive foramina are 5.25 mm long and 1.77 mm broad. The palatal bridge (the portion of the palate between the incisive foramina and the mesopterygoid fossa behind the back end of the palate) is 4.29 mm long and 2.75 mm broad at the first molars. The upper molar row is 4.13 mm long and M1 is 1.19 mm broad.
Distribution and habitat
Juliomys anoblepas is known only from Lagoa Santa, where the genus no longer occurs; the nearest records are about 70 km (43.5 mi) to the southeast. It is one of several Lagoa Santa fossil rodents that no longer occur in the area. Although the precise environmental background of the Lagoa Santa fossil assemblage remains unclear, they may have been deposited in a period of climatic cooling that led to higher local diversity.Literature cited
- Hershkovitz, P. 1962. Evolution of Neotropical cricetine rodents (Muridae) with special reference to the phyllotine group. Fieldiana Zoology 46:1–524.
- Musser, G.G. and Carleton, M.D. 2005. Superfamily Muroidea. Pp. 894–1531 in Wilson, D.E. and Reeder, D.M. (eds.). Mammal Species of the World: a taxonomic and geographic reference. 3rd ed. Baltimore: The Johns Hopkins University Press, 2 vols., 2142 pp. ISBN 978-0-8018-8221-0
- Pardiñas, U.F.J., D'Elía, G. and Ortiz, P.E. 2002. Sigmodontinos fósiles (Rodentia, Muroidea, Sigmodontinae) de América del sur: Estado actual de su conocimiento y prospectiva. Mastozoología Neotropical 9(2):209–252 (in Spanish).
- Pardiñas, U.F.J. and Teta, P. 2011. On the taxonomic status of the Brazilian mouse Calomys anoblepas Winge, 1887 (Mammalia, Rodentia, Cricetidae). Zootaxa 2788:38–44.
- Trouessart, E.L. 1898. Catalogus mammalium tam viventium quam fossilium. Tomus 2. Berlin: R. Friedländer and Sohn, 1469 pp. (in Latin).
- Voss, R.S. and Myers, P. 1991. Pseudoryzomys simplex (Rodentia: Muridae) and the significance of Lund's collections from the caves of Lagoa Santa, Brazil. Bulletin of the American Museum of Natural History 206:414–432.
- Weksler, M. and Bonvicino, C.R. 2005. Taxonomy of pygmy rice rats genus Oligoryzomys Bangs, 1900 (Rodentia, Sigmodontinae) of the Brazilian Cerrado, with the description of two new species. Arquivos do Museu Nacional 63(1):113–130.
- Weksler, M., Percequillo, A.R. and Voss, R.S. 2006. Ten new genera of oryzomyine rodents (Cricetidae: Sigmodontinae). American Museum Novitates 3537:1–29.
- Winge, H. 1887. Jordfundne og nulevende Gnavere (Rodentia) fra Lagoa Santa, Minas Geraes, Brasilien. E Museo Lundii 1(3):1–200 (in Danish).