Carletonomys

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Carletonomys
Temporal range: Mid Pleistocene (Ensenadan)
~1.2–0.8  Ma
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Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Cricetidae
Subfamily: Sigmodontinae
Genus:† Carletonomys
Pardiñas, 2008
Species:
†C. cailoi
Binomial name
†Carletonomys cailoi
Pardiñas, 2008
Carletonomys distribution.png

Carletonomys cailoi is an extinct rodent from the Pleistocene (Ensenadan) of Buenos Aires Province, Argentina. Although known only from a single maxilla (upper jaw) with the first molar, its features are so distinctive that it is placed in its own genus, Carletonomys. Discovered in 1998 and formally described in 2008, it is part of a well-defined group of oryzomyine rodents that also includes Holochilus , Noronhomys , Lundomys , and Pseudoryzomys . This group is characterized by progressive semiaquatic specializations and a reduction in the complexity of molar morphology.

Contents

The single known molar is high-crowned (hypsodont) and flat-crowned (planar) and is distinctive in lacking the ridge that connects the front to the middle part of the molar, the anterior mure, and in the configuration of another ridge, the mesoloph. Carletonomys was probably herbivorous and lived in a wet habitat.

Taxonomy

Carletonomys cailoi was discovered in 1998 in a silt deposit in San Cayetano Partido, southeastern Buenos Aires Province. The stratigraphic context suggests this locality is slightly over 1 million years old (Ensenadan South American Land Mammal Age), making Carletonomys the oldest known oryzomyine. [1] The single known specimen is now in the collections of the Museo de La Plata. It was initially referred to the genus Noronhomys , which is currently known only from the island of Fernando de Noronha off northeastern Brazil, but in 2008 Argentinean mammalogist Ulyses Pardiñas established it as the holotype of a new genus and species of rodent in a publication in the Journal of Mammalogy . The generic name, Carletonomys, combines the name of American mammalogist Michael Carleton with the Ancient Greek μυς mys "mouse" [2] and the specific name, cailoi, honors Argentinean biologist Carlos "Cailo" Galliari. [3]

The fossil has a number of features that suggest a relation to a group of oryzomyine rodents that includes the South American marsh rat Holochilus , its living relatives Lundomys and Pseudoryzomys , and the extinct Noronhomys and Holochilus primigenus . [4] They share high-crowned (hypsodont) molars and several simplifications of molar morphology, [5] as well as other features that cannot be assessed in Carletonomys, which indicate specializations towards a semiaquatic lifestyle. [6] It shows the most similarity to Noronhomys and Holochilus, so much so that Pardiñas considered placing it in either of these two genera, but its distinctive morphological features justify placement in a separate genus. [7]

This group of genera encompasses only a small part of the diversity of the tribe Oryzomyini, a group of over a hundred species distributed mainly in South America, including nearby islands such as the Galápagos Islands and some of the Antilles. Oryzomyini is one of several tribes recognized within the subfamily Sigmodontinae, which encompasses hundreds of species found across South America and into southern North America. Sigmodontinae itself is the largest subfamily of the family Cricetidae, other members of which include voles, lemmings, hamsters, and deermice, all mainly from Eurasia and North America. [8]

Description

Skull of Lundomys molitor, a living rodent closely related to Carletonomys, with a mandible of a different species. Lundomys molitor type.png
Skull of Lundomys molitor , a living rodent closely related to Carletonomys, with a mandible of a different species.

The holotype is a right maxilla (upper jaw) with the upper first molar (M1) in it. It is broken off behind the M1, but much of the front part is preserved, including the zygomatic plate, the flattened front portion of the zygomatic arch (cheekbone). The M1 is moderately worn, indicating that it is from an adult individual. [2] With an M1 length of 3.59 mm and width of 2.53 mm, C. cailoi was one of the largest oryzomyines known, rivaled only by Lundomys and the extinct Antillean Megalomys and " Ekbletomys ". [10] The height of the M1 is 1.37 mm and it has four roots, including a large one in front, another large one on the inner (lingual) side, and two smaller ones on the outer (labial) side. The presence of a second labial root is a variable character among oryzomyines, occurring among others in Holochilus and Pseudoryzomys but not in Lundomys. The maxilla itself shows few significant characters. The back margin of the incisive foramen, which perforates the palate between the upper incisors and the molars, is not visible, suggesting that the foramen was short, as in Holochilus. The configuration of the zygomatic plate shows features that distinguish C. cailoi from some of its relatives. [11]

The molar is plane and hypsodont: the crowns are relatively high and the main cusps are about as high as the other parts of the crown, [3] as they are in Holochilus. Most other oryzomyines have bunodont and brachydont molars, in which the crowns are lower and the cusps are higher than the rest of the crown. [12] As in closely related species, the front part of the molar is relatively simple, lacking an anteroloph, an additional ridge that is well-developed in most oryzomyines. [13] A shallow anteromedian flexus is present, superficially dividing the front cusp (anterocone). [3] Uniquely, the anterior mure, which connects the anterocone to the rest of the crown, is absent; although this structure is sometimes missing in young individuals of other oryzomyines, it usually develops as a result of wear in adults. [14] The two cusps on the middle part of the molar, the paracone and the protocone, are broadly connected. The median mure, which connects the middle to the back pair of cusps, is attached to the back of the paracone. A complete mesoloph is present, descending from the median mure slightly behind the paracone. [3] The configuration of the paracone–median mure–mesoloph complex is unique to Carletonomys. [11] The two posterior cusps, the hypocone and the metacone, are connected at the back margin of the molar. Unlike in most oryzomyines, no posteroflexus is present, so that the metacone is situated directly at the back margin. [15]

Ecology

Carletonomys was found in association with remains of several other animals, including fishes, chelid turtles, frogs, birds, armadillos, and several rodents, including Reithrodon auritus , the coypu (Myocastor), both of which still live in the area, the extinct echimyid Dicolpomys , and unidentified caviids and octodontids. C. cailoi probably lived in a wetland habitat under relatively warm and moist climatic conditions. Although the limited material known permits few inferences as to the animal's natural history, it likely fed on hard plant material, as do related, morphologically similar extant species. [1]

Related Research Articles

<i>Oryzomys</i> Genus of semiaquatic rodents

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 (O. palustris) of the United States and O. couesi of Mexico and Central America—are widespread; the six others have more restricted distributions. The species have had eventful taxonomic histories, and most species were at one time included in the marsh rice rat; additional species may be recognized in the future. The name Oryzomys was established in 1857 by Spencer Fullerton Baird for the marsh rice rat and was soon applied to over a hundred species of American rodents. Subsequently, the genus gradually became more narrowly defined until its current contents were established in 2006, when ten new genera were established for species previously placed in Oryzomys.

<i>Lundomys</i> A semiaquatic rat species from southeastern South America.

Lundomys molitor, also known as Lund's amphibious rat or the greater marsh rat, is a semiaquatic rat species from southeastern South America.

<i>Pseudoryzomys</i> Genus of rodent from South America with one species

Pseudoryzomys simplex, also known as the Brazilian false rice rat or false oryzomys, is a species of rodent in the family Cricetidae from south-central South America. It is found in lowland palm savanna and thorn scrub habitats. It is a medium-sized species, weighing about 50 grams (1.8 oz), with gray–brown fur, long and narrow hindfeet, and a tail that is about as long as the head and body. The IUCN has assessed its conservation status as being of least concern, although almost nothing is known about its diet or reproduction.

Microryzomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. It is closely related to Oreoryzomys, Oligoryzomys, and Neacomys. It contains two species, both restricted to the Andes: M. altissimus and M. minutus.

Hammonds rice rat Species of rodent in the family Cricetidae from Ecuador

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<i>Eremoryzomys</i> Rodent species in the family Cricetidae from central Peru

Eremoryzomys polius, also known as the gray rice rat or the Marañon oryzomys, is a rodent species in the tribe Oryzomyini of the family Cricetidae. Discovered in 1912 and first described in 1913 by Wilfred Osgood, it was originally placed in Oryzomys and named Oryzomys polius. In 2006, a cladistic analysis found that it was not closely related to Oryzomys in the strict sense or to any other oryzomyine then known, so that it is now placed in its own genus, Eremoryzomys. The Brazilian genus Drymoreomys, named in 2011, is probably the closest relative of Eremoryzomys. Eremoryzomys has a limited distribution in the dry upper valley of the Marañón River in central Peru, but may yet contain more than one species.

<span class="mw-page-title-main">Oryzomyini</span> Tribe of rodents

Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of the family Cricetidae. It includes about 120 species in about thirty genera, distributed from the eastern United States to the southernmost parts of South America, including many offshore islands. It is part of the clade Oryzomyalia, which includes most of the South American Sigmodontinae.

<i>Noronhomys</i> Extinct rat species from the islands of Fernando de Noronha off northeastern Brazil

Noronhomys vespuccii, also known as Vespucci's rodent, is an extinct rat species from the islands of Fernando de Noronha off northeastern Brazil. Italian explorer Amerigo Vespucci may have seen it on a visit to Fernando de Noronha in 1503, but it subsequently became extinct, perhaps because of the exotic rats and mice introduced by the first explorers of the island. Numerous but fragmentary fossil remains of the animal, of uncertain but probably Holocene age, were discovered in 1973 and described in 1999.

Reigomys primigenus is an extinct oryzomyine rodent known from Pleistocene deposits in Tarija Department, southeastern Bolivia. It is known from a number of isolated jaws and molars which show that its molars were almost identical to those of the living Lundomys. On the other hand, the animal possesses a number of derived traits of the palate which document a closer relationship to living Holochilus, the genus of South American marsh rats, and for this reason it was placed in the genus Holochilus when it was first described in 1996. The subsequent discoveries of Noronhomys and Carletonomys, which may be more closely related to extant Holochilus than H. primigenus is, have cast its placement in Holochilus into doubt, and it was ultimately made the type species of a separate genus, Reigomys.

<i>Juliomys anoblepas</i> Species of rodent

Juliomys anoblepas is a rodent in the genus Juliomys of the subfamily Sigmodontinae known from a single broken skull. The specimen was collected by Peter Wilhelm Lund in the caves of Lagoa Santa, Minas Gerais, Brazil, in the first half of the 19th century and described by Herluf Winge in 1888 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 separate extinct species of the genus, which is no longer found at Lagoa Santa.

<i>Transandinomys</i> Genus of small rodents from Central and South America

Transandinomys is a genus of rodents in the tribe Oryzomyini of family Cricetidae. It includes two species—T. bolivaris and T. talamancae—found in forests from Honduras in Central America south and east to southwestern Ecuador and northwestern Venezuela in northern South America. Until 2006, its members were included in the genus Oryzomys, but phylogenetic analysis showed that they are not closely related to the type species of that genus, and they have therefore been placed in a new genus. They may be most closely related to genera like Hylaeamys and Euryoryzomys, which contain very similar species. Both species of Transandinomys have had eventful taxonomic histories.

<i>Nephelomys</i> Genus of rodents

Nephelomys is a genus of South American oryzomyine rodents found in the Andes from Bolivia to Venezuela, with a westward extension into the mountains of Costa Rica. Its generic name is derived from the Ancient Greek word nephelê "mist", referring to the cloud forest habitat of the members of the genus.

<i>Oecomys sydandersoni</i> Species of rodent

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<span class="mw-page-title-main">Zygomatic plate</span> Bony plate in rodent anatomy

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Natatory fringes are rows of stiff hairs that occur along the margins of the hindfeet in some rodents. They occur along the plantar margins and in some cases also between the toes. Among sigmodontines, a mostly South American groups, natatory fringes are present in Ichthyomyini and some Oryzomyini. Among ichthyomyines, the fringes are poorly developed in Neusticomys but well-developed in other genera, and in Rheomys mexicanus the hairs of the fringes may exceed 3 millimetres (0.12 in) in length. Amphinectomys, Holochilus, Lundomys, and Nectomys are the only oryzomyines with natatory fringes, but have them only weakly developed; one study also records them in Oryzomys. In oryzomyines, the fringes are an adaptation for a semiaquatic lifestyle that appeared convergently in the Holochilus-Lundomys and Nectomys-Amphinectomys lineages. The term was introduced in 1993 by Voss and Carleton in describing Lundomys.

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Agathaeromys is an extinct genus of oryzomyine rodents from the Pleistocene of Bonaire, Netherlands Antilles. Two species are known, which differ in size and some details of tooth morphology. The larger A. donovani, the type species, is known from hundreds of teeth that are probably 900,000 to 540,000 years old, found in four localities. A. praeuniversitatis, the smaller species, is known from 35 teeth found in a single fossil site, which is probably 540,000 to 230,000 years old.

<i>Pennatomys</i> Extinct oryzomyine rodent in the Lesser Antilles

Pennatomys nivalis is an extinct oryzomyine rodent from the islands of Sint Eustatius, Saint Kitts, and Nevis in the Lesser Antilles. The only species in the genus Pennatomys, it is known from skeletal remains found in Amerindian archeological sites on all three islands, with dates ranging from 790–520 BCE to 900–1200 CE. No live specimens are known, but there are several historical records of rodents from Saint Kitts and Nevis that could conceivably refer to Pennatomys. The animal apparently belongs to a group within the tribe Oryzomyini that includes many other island-dwelling species.

<i>Drymoreomys</i> A rodent genus with one species in the family Cricetidae from the Atlantic Forest of Brazil.

Drymoreomys is a rodent genus in the tribe Oryzomyini that lives in the Atlantic Forest of Brazil. The single species, D. albimaculatus, is known only from the states of São Paulo and Santa Catarina and was not named until 2011. It lives in the humid forest on the eastern slopes of the Serra do Mar and perhaps reproduces year-round. Although its range is relatively large and includes some protected areas, it is patchy and threatened, and the discoverers recommend that the animal be considered "Near Threatened" on the IUCN Red List. Within Oryzomyini, Drymoreomys appears to be most closely related to Eremoryzomys from the Andes of Peru, a biogeographically unusual relationship, in that the two populations are widely separated and each is adapted to an arid or a moist environment.

References

  1. 1 2 Pardiñas, 2008, p. 1276
  2. 1 2 Pardiñas, 2008, p. 1271
  3. 1 2 3 4 Pardiñas, 2008, p. 1272
  4. ↑ Pardiñas, 2008, p. 1275
  5. ↑ Pardiñas, 2008, pp. 1273–1274; Weksler, 2006, p. 131
  6. ↑ Weksler, 2006, p. 131
  7. ↑ Pardiñas, 2008, pp. 1274–1275
  8. ↑ Musser and Carleton, 2005
  9. ↑ Voss and Carleton, 1993, p. 6
  10. ↑ Pardiñas, 2008, table 1; Ray, 1962
  11. 1 2 Pardiñas, 2008, p. 1273
  12. ↑ Weksler, 2006, p. 44
  13. ↑ Pardiñas, 2008, fig. 1; Weksler, 2006, p. 45
  14. ↑ Pardiñas, 2008, pp. 1272–1273
  15. ↑ Pardiñas, 2008, fig. 1; p. 1273

Bibliography

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