Megalomys audreyae Temporal range: Quaternary | |
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Holotype mandible (lower jaw) of Megalomys audreyae, seen from the right (lingual view) above and from the left (labial view) below. [1] | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Rodentia |
Family: | Cricetidae |
Subfamily: | Sigmodontinae |
Genus: | † Megalomys |
Species: | †M. audreyae |
Binomial name | |
†Megalomys audreyae Hopwood, 1926 [2] | |
Synonyms | |
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Megalomys audreyae, known as the Barbudan (?) muskrat [3] or the Barbuda giant rice rat, [4] is an extinct oryzomyine rodent from Barbuda in the Lesser Antilles. Described on the basis of a single mandible (lower jaw) with the first molar missing and an isolated upper incisor, both of uncertain but Quaternary age, it is one of the smaller members of the genus Megalomys . Little is known about the animal, and its provenance and distinction from " Ekbletomys hypenemus ", an even larger extinct oryzomyine that also occurred on Barbuda, have been called into question. The toothrow in the lower jaw has a length of 8.7 mm at the alveoli. The third molar is relatively narrow and both the second and third molars have a wide valley between their outer cusps.
Remains of Megalomys audreyae were found by John Walter Gregory among cave breccia on Barbuda around 1900. The exact locality is unknown. In his 1901 description of Oryzomys luciae , Charles Immanuel Forsyth Major mentioned the Barbuda animal as another member of the Megalomys group, but he never published a description of the latter. Édouard Louis Trouessart gave the name Oryzomys (Megalomys) majori to it in his Catalogus Mammalium, but he did not describe it and therefore the name is a nomen nudum . In 1926, Arthur Hopwood finally described it and named it Megalomys audreyae after Gregory's wife Audrey, following Major's intention. [5]
The oryzomyines of the Caribbean were revised in 1962 by Clayton Ray, who examined the specimens Gregory had found and redescribed them. [6] He suggested that M. audreyae may in fact have come from Barbados instead of similarly named Barbuda, citing the occurrence of a different oryzomyine ("Ekbletomys hypenemus") in other cave deposits on Barbuda, circumstantial evidence for the occurrence of a native rodent on Barbados, uncertainty whether Gregory ever visited Barbuda, and biogeographical considerations. [7]
In the subsequent literature, M. audreyae has seldom been mentioned and never been further described. In a 1999 review of recent extinctions in mammals, Ross MacPhee and C. Flemming reported that M. audreyae had been recovered from a locality on Barbuda known as Darby Sink, which had been radiocarbon dated to around 1200 BCE. They also stated that M. audreyae and "Ekbletomys" may in fact be identical. [8] However, in 2009 Samuel Turvey suggested that two different rice rats were in fact present in material from Barbuda, which would imply that M. audreyae is a valid species. [9]
The only remains of Megalomys audreyae that have been described in the literature are the original two specimens Gregory found, a left upper incisor and a left mandible (lower jaw). The upper incisor is not grooved and its diameter has a length of 2.6 mm and width of 1.5 mm, but exhibits no other significant characters. [10]
The mandible, which is severely damaged and lacks the condyloid, coronoid, and angular processes at the back of the bone, contains the second and third molar and part of the lower incisor, but the first molar is missing. [11] The capsular process of the lower incisor, a slight raising of the mandibular bone at the back end of the incisor, is small. The preserved alveoli, the impressions left by the roots, show that the first molar was supported by large roots at the front and back and a smaller root in between these. The second molar is about square and shows the four main cusps commonly present in rodents: the protoconid, metaconid, hypoconid, and entoconid. A strongly developed mesolophid (a crest) is also present, as in most oryzomyines. The main valley between the cusps, the hypoflexid, is broad and V-shaped. The third molar is as long as the second, but it is narrower and the entoconid is poorly developed. Again, the hypoflexid is broad and V-shaped. [12] The length of the toothrow at the alveoli is 8.7 mm. The length of the second molar is 2.5 mm and the width is 2.2 mm. The third molar has a length of 2.5 mm and width of 1.8 mm. [13]
When Clayton Ray described "Ekbletomys hypenemus" on the basis of abundant skeletal remains from both Barbuda and Antigua, he carefully distinguished it from M. audreyae, the only other native rodent recorded from those islands. [14] M. audreyae is much smaller than "Ekbletomys"; for example, 72 specimens of the latter had the alveolar length of the lower molars ranging from 10.3 to 12.6 mm (mean 11.6 mm, standard deviation 0.49 mm; compare 8.7 mm for M. audreyae). [15] In addition, the V-shaped hypoflexids and narrow third molar of M. audreyae contrast with the narrow, parallel-sided hypoflexids and broad third molar of "Ekbletomys". These characters, and others observable in species of Megalomys represented by more complete material, convinced Ray that M. audreyae and "Ekbletomys" are not only distinct species, but indeed share no close relationship. [16] Instead, he proposed that the combination of large size, occurrence in the Lesser Antilles, and similarity in molar morphology indicated a relationship between M. audreyae and other species of Megalomys, and he suggested that the similarly sized M. curazensis from Curaçao, off Venezuela, may be most closely related to M. audreyae. [17]
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.
Lundomys molitor, also known as Lund's amphibious rat or the greater marsh rat, is a semiaquatic rat species from southeastern South America.
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.
Oligoryzomys victus, also known as the St. Vincent colilargo or St. Vincent pygmy rice rat, is a species of rodent in the genus Oligoryzomys of the oryzomyine tribe. Only one specimen is known, which was collected on Saint Vincent in the Lesser Antilles in about 1892, and it is now presumed extinct.
Oryzomys gorgasi, also known as Gorgas's oryzomys or Gorgas's rice rat, is a rodent in the genus Oryzomys of family Cricetidae. First recorded in 1967, it is known from only a few localities, including a freshwater swamp in the lowlands of northwestern Colombia and a mangrove islet in northwestern Venezuela. It reportedly formerly occurred on the island of Curaçao off northwestern Venezuela; this extinct population has been described as a separate species, Oryzomys curasoae, but does not differ morphologically from mainland populations.
Mindomys hammondi, also known as Hammond's rice rat or Hammond's oryzomys, is an endangered species of rodent in the tribe Oryzomyini of family Cricetidae. Formerly considered to be related with Nectomys, Sigmodontomys, Megalomys, or Oryzomys, it is now placed in then genus Mindomys, but its relationships remain obscure; some evidence supports a placement near Oecomys or as a basal member of Oryzomyini.
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.
Transandinomys talamancae is a rodent in the family Cricetidae that occurs from Costa Rica to southwestern Ecuador and northern Venezuela. Its habitat consists of lowland forests up to 1,500 m (5,000 ft) above sea level. With a body mass of 38 to 74 g, it is a medium-sized rice rat. The fur is soft and is reddish to brownish on the upperparts and white to buff on the underparts. The tail is dark brown above and lighter below and the ears and feet are long. The vibrissae (whiskers) are very long. In the skull, the rostrum is long and the braincase is low. The number of chromosomes varies from 34 to 54.
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.
Carletonomys cailoi is an extinct rodent from the Pleistocene (Ensenadan) of Buenos Aires Province, Argentina. Although known only from a single maxilla 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.
"Ekbletomys hypenemus" is an extinct oryzomyine rodent from the islands of Antigua and Barbuda, Lesser Antilles. It was described as the only species of the subgenus "Ekbletomys" of genus Oryzomys in a 1962 Ph.D. thesis, but that name is not available under the International Code of Zoological Nomenclature and the species remains formally unnamed. It is currently referred to as "Ekbletomys hypenemus" in the absence of a formally available name. The species is now thought to be extinct, but association with introduced Rattus indicates that it survived until before 1500 BCE on Antigua.
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.
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.
?Oryzomys pliocaenicus is a fossil rodent from the Hemphillian of Kansas, central United States. It is known from a single mandible with the back part missing. All three molars are present, but very worn. Together, the molars are 3.6 mm long. The fossil was discovered in 1935 and described in 1939 as a possible species of Oryzomys. Later authors doubted this allocation and suggested that it may instead belong in Bensonomys or Jacobsomys, but the material may not allow a definite identification.
Microgale macpheei is an extinct shrew tenrec from southeastern Madagascar. It is known only from two partial skulls found in Andrahomana cave, which radiocarbon dating of associated rodent remains suggests are about 3000 years old. It is the only known recently extinct tenrec. First described in 2007, it is most similar to the smaller Microgale brevicaudata of northern and western Madagascar. M. macpheei has a broad rostrum and, like M. brevicaudata, lacks a diastema (gap) between the premolars. A number of details of tooth morphology are characteristic of M. macpheei.
Nesomys narindaensis is an extinct rodent that lived in northwestern Madagascar. It is known from subfossil skull bones and isolated molars found in several sites during field work that started in 2001. First described in 2010, it is placed in the genus Nesomys together with three smaller living species, which may differ in some details of molar morphology. The presence of N. narindaensis, a rare element in the local rodent fauna, suggests that the region was previously more humid.
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.
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.
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.