Vespucci's Rodent
Encyclopedia
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.
Noronhomys vespuccii was a fairly large rodent, larger than the black rat
(Rattus rattus). A member of the family Cricetidae
and subfamily Sigmodontinae
, it shares several distinctive characters with Holochilus and related genera within the tribe Oryzomyini
, including high-crowned molars with simplified crown features and the presence of several ridges on the skull which help anchor the chewing muscles. Although a suite of traits suggest that Holochilus is its closest relative, it is distinctive in many ways and is therefore classified in a separate genus
, Noronhomys. Its close relatives, including Holochilus and Lundomys, are adapted to a semiaquatic lifestyle, spending much of their time in the water, but features of the Noronhomys bones suggest that it lost its semiaquatic lifestyle after arrival at its remote island.
may have seen this animal on his fourth voyage, which took him to Brazil; the Lettera di Amerigo Vespucci delle Isole Nuovamente in Quattro Suoi Viaggi recorded that he visited an island just south of the equator on August 10, 1503. On this island, identified as Fernando de Noronha, he saw "very big rats and lizards with two tails, and some snakes". The Lettera purports to be an account of Vespucci's voyages, but it is unlikely that he produced it himself and, additionally, his fourth voyage may never have actually taken place. The biological details given in the Letteras account of Fernando de Noronha agree with what is known of the natural history of the island, lending weight to the view that it derives from an actual visit, whether by Vespucci himself or by another explorer. The lizard is probably Trachylepis atlantica and the record of snakes most likely refers to Amphisbaena ridleyi
, which is actually an amphisbaenia
n instead of a snake.
During excavations conducted in 1973, American ornithologist Storrs L. Olson
found fossil
s of a moderately large rat on Fernando de Noronha, which were described as a new genus and species in a 1999 publication by Olson and his colleague, mammalogist Michael D. Carleton. The material is now in the United States National Museum of Natural History
in Washington, D.C., and in the museum of the Pontifícia Universidade Católica do Rio Grande do Sul
in Porto Alegre
, Rio Grande do Sul
. The generic name, Noronhomys, combines the name of the island of Fernando de Noronha with the Ancient Greek mys "mouse" and the specific name, vespuccii, honors Amerigo Vespucci. Noronhomys would have been larger than the black rat
(Rattus rattus), which was common on ships and which Vespucci would have been familiar with, consistent with his description of "very large rats".
Noronhomys is a member of the tribe Oryzomyini
, which includes 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 vole
s, lemming
s, hamster
s, and deermice
, all mainly from Eurasia and North America.
Carleton and Olson performed a detailed comparison of Noronhomys to members of the mainland genera Holochilus
and Lundomys on the basis of both general morphology
and morphometrical
data, concluding that the Fernando de Noronha rat is distinct from both other animals.
They used a cladistic analysis
to examine its relationships within Oryzomyini, also including two species of Holochilus, Lundomys, and five other oryzomyines. They found that Noronhomys appeared closest to Holochilus, with Lundomys more distantly related. Eighteen shared characters (synapomorphies
) supported the grouping of Noronhomys with Holochilus. Another form described as a species of Holochilus, Holochilus primigenus
, may also be related, but is likely to fall outside the Holochilus–Noronhomys clade
.
In 1998, a fragmentary fossil of another species of this same group of oryzomyines was found in eastern Argentina. It was initially identified as a possible second species of Noronhomys on the basis of the presence of a crest on the upper first molar, the mesoloph, but the specimen is different from Noronhomys vespuccii in other respects, and in 2008 it was described as a new genus and species, Carletonomys cailoi
, related to Noronhomys and associated genera.
s, damaged to various degrees, and many isolated jaws and other bones. This material documents that, with a skull of about 4 cm (1.6 in) (occipitonasal length), Noronhomys was a moderately large oryzomyine, smaller than Lundomys but well within the range of Holochilus. It shares a number of the features that characterize the group of Holochilus and related genera, including a reduction in the complexity of the chewing surface of the molars
, simple posterolateral palatal pits
(perforations of the palate
near the third molar), and a similarly shaped interorbital region
of the skull. Noronhomys is distinctive, among other characters, in its lack of a spinous process
on the zygomatic plate
, the flattened front portion of the zygomatic arch
(cheekbone); the short palate, which does not extend behind the third molars; and the presence of an accessory crest, the mesoloph, on the upper molars.
Analysis of morphometrical data from the known material of Noronhomys suggests that growth continued in adults—the older the animal, the larger the depth of the mandible
and the size of the lower incisor
—and does not provide evidence for a difference in size
between males and females. Skull shape is strikingly different from both Holochilus and Lundomys, resulting in a clear separation from both of these taxa in statistical analyses of measurement data. In three individuals measured, the occipitonasal length, a measure of skull length, varies from 38.0 to 39.2 mm (1.50 to 1.54 in), averaging 38.5 mm (1.52 in). The width of the braincase is 13.4 to 14.8 mm (0.53 to 0.58 in), averaging 14.1 mm (0.56 in). Between the first molars, the width of the palate is 8.1 to 8.9 mm (0.32 to 0.35 in) in four specimens, averaging 8.4 mm (0.33 in). The lower molars have a total length of 7.57 to 8.29 mm (0.298 to 0.326 in), averaging 8.00 mm (0.315 in), in 39 specimens with intact molar rows. The femur
(upper leg bone) is 32.5 to 41.0 mm (1.28 to 1.61 in) in length in nine specimens, averaging 36.5 mm (1.44 in). Carleton and Olson estimated that body mass in Noronhomys was similar to that of some populations of living Holochilus sciureus at about 200 to 250 g (7 to 9 oz).
The skull is flattened in general shape. The front part is short and broad. The broad interorbital region
(located between the eyes) is hourglass-shaped, with squared edges and weakly developed beading. A postorbital ridge is present, obscuring the suture (joint) between the frontal
and squamosal
bones, a feature shared only with Holochilus among oryzomyines. The braincase is squarish. The interparietal bone is wide, but does not reach the squamosals on the sides. The zygomatic arches, which are well-developed, are furthest apart at the back and converge toward the front. The jugal
bone is small.
The back margin of the zygomatic plate is located close to the front of the upper first molar. The incisive foramina
do not extend between the molars. Unlike in both Holochilus and Lundomys, the palate is flat, lacking a distinct ridge at the midline. The parapterygoid fossae, which are located behind the palate at the level of the molars, are excavated somewhat above the level of the palate. A strut of the alisphenoid bone
is present, separating two openings in the skull, the masticatory–buccinator foramen and the foramen ovale accessorius. The subsquamosal fenestra
, an opening at the back of the skull determined by the shape of the squamosal, is present but small. The squamosal probably lacks a suspensory process that contacts the tegmen tympani, the roof of the tympanic cavity
, a defining character of oryzomyines.
The mandible (lower jaw) is robust. The two masseteric ridges, which anchor some of the chewing muscles, are joined together as a single crest for a portion of their length and extend forward to a point below the first molar. The capsular process
, a raising of the mandibular bone at the back end of the lower incisor, is well developed.
of the lower incisor was reported in a 2005 study. The inner portion (portio interna, PI) is much thicker than the outer portion (portio externa, PE). The PI consists of Hunter-Schreger band
s, which are uniserial (consisting of a single enamel prism), as in all myomorph
rodents. The PE consists of radial enamel, with flattened prisms that are almost parallel to the junction between the enamel and the dentine. The microstructure is similar to that of Holochilus brasiliensis and displays several characters seen only in Myomorpha.
The molars are high-crowned (hypsodont
) and planar, with the main cusps as high as the crests connecting them, a configuration shared only with Holochilus and Carletonomys among oryzomyines. The first molars are the longest and the third molars are longer but narrower than the second molars. The molars lack many accessory ridges, including the anteroloph on the first upper molar, the posteroloph on the first and second upper molar, and the anterolophid and mesolophid on all lower molars. The first and second upper molar have a short mesoloph and the front cusp of the first lower molar, the anteroconid, encloses a large internal pit. Most of the folds between the cusps and crests are open at the margins of the molars, but two—the posteroflexid on the lower second molar and the entoflexid on the lower third molar—are closed by a wall, or cingulum
, at the inner margin of the tooth. As in most oryzomyines, the upper molars all have one root on the inner (lingual) side and two on the outer (labial) side and the lower molars have a single root at the front and back of each molar; in addition, the first upper molar has another labial root and the first lower molar has a small labial and usually also a small lingual root located between the main roots.
is absent, as in all members of the Sigmodontinae; if present, as in some other rodents, this foramen
(opening) perforates the distal (far) end of the humerus
(upper arm bone). The pelvis
and the bones of the hindlimbs are heavily built. The femoral tubercle of the acetabulum
(part of the pelvis), which anchors the rectum femoris muscle, is reduced relative to Holochilus and Lundomys.
, a small archipelago of volcanic origin off northeastern Brazil, consisting of a main island and several associated smaller islands. The formation of the archipelago, which has never been connected to the mainland, began about 11 million years ago; active vulcanism
ceased about 2 million years ago. Remains of Noronhomys were found in association with remains of various reptiles, birds, and snails, several of which are also restricted to the archipelago, in sand dunes near the northeastern tip of the main island. The age of the deposits is unknown, but is likely late Holocene
, at most a few thousand years old.
The ancestor of Noronhomys may have been a semiaquatic animal, similar to living Holochilus or Lundomys, that arrived on Fernando de Noronha by chance on a floating log. The morphology of the limb bones in Noronhomys suggests that the animal was not semiaquatic like its relatives, but terrestrial, consistent with its occurrence on a small island, where streams and pools are rare or absent.
black rat and house mouse
(Mus musculus), which became very common on the island, may have driven it to extinction by directly competing for food, preying on young Noronhomys, or transmitting diseases. Other factors that may have played a role include modification of its habitat, introduction of predators such as cat
s (Felis catus), and predation by visiting sailors. These extinction mechanisms are common for island endemic species. In 1888, Henry Nicholas Ridley
already suggested that the rat Vespucci had seen had been driven to extinction by the introduced black rat. The International Union for Conservation of Nature lists it as "extinct".
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
rat species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
from the islands of Fernando de Noronha
Fernando de Noronha
Fernando de Noronha is an archipelago of 21 islands and islets in the Atlantic Ocean, offshore from the Brazilian coast. The main island has an area of and had a population of 3,012 in the year 2010...
off northeastern Brazil. Italian explorer Amerigo Vespucci
Amerigo Vespucci
Amerigo Vespucci was an Italian explorer, financier, navigator and cartographer. The Americas are generally believed to have derived their name from the feminized Latin version of his first name.-Expeditions:...
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
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
age, were discovered in 1973 and described in 1999.
Noronhomys vespuccii was a fairly large rodent, larger than the black rat
Black Rat
The black rat is a common long-tailed rodent of the genus Rattus in the subfamily Murinae . The species originated in tropical Asia and spread through the Near East in Roman times before reaching Europe by the 1st century and spreading with Europeans across the world.-Taxonomy:The black rat was...
(Rattus rattus). A member of the family Cricetidae
Cricetidae
The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...
and 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...
, it shares several distinctive characters with Holochilus and related genera within the tribe Oryzomyini
Oryzomyini
Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of 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...
, including high-crowned molars with simplified crown features and the presence of several ridges on the skull which help anchor the chewing muscles. Although a suite of traits suggest that Holochilus is its closest relative, it is distinctive in many ways and is therefore classified in a separate genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
, Noronhomys. Its close relatives, including Holochilus and Lundomys, are adapted to a semiaquatic lifestyle, spending much of their time in the water, but features of the Noronhomys bones suggest that it lost its semiaquatic lifestyle after arrival at its remote island.
Discovery and taxonomy
Italian explorer Amerigo VespucciAmerigo Vespucci
Amerigo Vespucci was an Italian explorer, financier, navigator and cartographer. The Americas are generally believed to have derived their name from the feminized Latin version of his first name.-Expeditions:...
may have seen this animal on his fourth voyage, which took him to Brazil; the Lettera di Amerigo Vespucci delle Isole Nuovamente in Quattro Suoi Viaggi recorded that he visited an island just south of the equator on August 10, 1503. On this island, identified as Fernando de Noronha, he saw "very big rats and lizards with two tails, and some snakes". The Lettera purports to be an account of Vespucci's voyages, but it is unlikely that he produced it himself and, additionally, his fourth voyage may never have actually taken place. The biological details given in the Letteras account of Fernando de Noronha agree with what is known of the natural history of the island, lending weight to the view that it derives from an actual visit, whether by Vespucci himself or by another explorer. The lizard is probably Trachylepis atlantica and the record of snakes most likely refers to Amphisbaena ridleyi
Amphisbaena ridleyi
Amphisbaena ridleyi, known by the common names Ridley's worm lizard or the Noronha worm lizard, is a species of amphisbaenian in the genus Amphisbaena that is endemic to the island of Fernando de Noronha off the coast of Brazil...
, which is actually an amphisbaenia
Amphisbaenia
The Amphisbaenia are a usually legless suborder of squamates closely related to lizards and snakes. As many species possess a pink body coloration and scales arranged in rings, they have a superficial resemblance to earthworms. They are very poorly understood, due to their burrowing lifestyle...
n instead of a snake.
During excavations conducted in 1973, American ornithologist Storrs L. Olson
Storrs L. Olson
Storrs Lovejoy Olson is an American biologist and ornithologist from the Smithsonian Institution. He is one of the world's foremost avian paleontologists....
found fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s of a moderately large rat on Fernando de Noronha, which were described as a new genus and species in a 1999 publication by Olson and his colleague, mammalogist Michael D. Carleton. The material is now in the United States National Museum of Natural History
National Museum of Natural History
The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. Admission is free and the museum is open 364 days a year....
in Washington, D.C., and in the museum of the Pontifícia Universidade Católica do Rio Grande do Sul
Pontifícia Universidade Católica do Rio Grande do Sul
The Pontifícia Universidade Católica do Rio Grande do Sul is a private non-profit Catholic university, with three campuses, in the Brazilian cities of Porto Alegre, Uruguaiana, and Viamão...
in Porto Alegre
Porto Alegre
Porto Alegre is the tenth most populous municipality in Brazil, with 1,409,939 inhabitants, and the centre of Brazil's fourth largest metropolitan area . It is also the capital city of the southernmost Brazilian state of Rio Grande do Sul. The city is the southernmost capital city of a Brazilian...
, Rio Grande do Sul
Rio Grande do Sul
Rio Grande do Sul is the southernmost state in Brazil, and the state with the fifth highest Human Development Index in the country. In this state is located the southernmost city in the country, Chuí, on the border with Uruguay. In the region of Bento Gonçalves and Caxias do Sul, the largest wine...
. The generic name, Noronhomys, combines the name of the island of Fernando de Noronha with the Ancient Greek mys "mouse" and the specific name, vespuccii, honors Amerigo Vespucci. Noronhomys would have been larger than the black rat
Black Rat
The black rat is a common long-tailed rodent of the genus Rattus in the subfamily Murinae . The species originated in tropical Asia and spread through the Near East in Roman times before reaching Europe by the 1st century and spreading with Europeans across the world.-Taxonomy:The black rat was...
(Rattus rattus), which was common on ships and which Vespucci would have been familiar with, consistent with his description of "very large rats".
Noronhomys is a member of the tribe Oryzomyini
Oryzomyini
Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of 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...
, which includes over a hundred species distributed mainly in South America, including nearby islands such as the Galápagos Islands
Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...
and some of the Antilles
Antilles
The Antilles islands form the greater part of the West Indies in the Caribbean Sea. The Antilles are divided into two major groups: the "Greater Antilles" to the north and west, including the larger islands of Cuba, Jamaica, Hispaniola , and Puerto Rico; and the smaller "Lesser Antilles" on the...
. Oryzomyini is one of several tribes recognized 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 encompasses hundreds of species found across South America and into southern North America. Sigmodontinae itself is the largest subfamily of the family Cricetidae
Cricetidae
The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...
, other members of which include vole
Vole
A vole is a small rodent resembling a mouse but with a stouter body, a shorter hairy tail, a slightly rounder head, smaller ears and eyes, and differently formed molars . There are approximately 155 species of voles. They are sometimes known as meadow mice or field mice in North America...
s, lemming
Lemming
Lemmings are small rodents, usually found in or near the Arctic, in tundra biomes. They are subniveal animals, and together with voles and muskrats, they make up the subfamily Arvicolinae , which forms part of the largest mammal radiation by far, the superfamily Muroidea, which also includes rats,...
s, hamster
Hamster
Hamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera....
s, and deermice
Peromyscus
The genus Peromyscus contains the animal species commonly referred to as deer mice. This is a genus of New World mouse only distantly related to the common house mouse and laboratory mouse, Mus musculus...
, all mainly from Eurasia and North America.
Carleton and Olson performed a detailed comparison of Noronhomys to members of the mainland genera Holochilus
Holochilus
Holochilus is a genus of semiaquatic rodents in the tribe Oryzomyini of family Cricetidae, sometimes called marsh rats. It contains three living species, Holochilus brasiliensis, Holochilus chacarius, and Holochilus sciureus, which are widely distributed in South America east of the Andes, and a...
and Lundomys on the basis of both general morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
and morphometrical
Morphometrics
Morphometrics refers to the quantitative analysis of form, a concept that encompasses size and shape. Morphometric analyses are commonly performed on organisms, and are useful in analyzing their fossil record, the impact of mutations on shape, developmental changes in form, covariances between...
data, concluding that the Fernando de Noronha rat is distinct from both other animals.
They used a cladistic analysis
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
to examine its relationships within Oryzomyini, also including two species of Holochilus, Lundomys, and five other oryzomyines. They found that Noronhomys appeared closest to Holochilus, with Lundomys more distantly related. Eighteen shared characters (synapomorphies
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
) supported the grouping of Noronhomys with Holochilus. Another form described as a species of Holochilus, Holochilus primigenus
Holochilus primigenus
Holochilus 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...
, may also be related, but is likely to fall outside the Holochilus–Noronhomys clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
.
In 1998, a fragmentary fossil of another species of this same group of oryzomyines was found in eastern Argentina. It was initially identified as a possible second species of Noronhomys on the basis of the presence of a crest on the upper first molar, the mesoloph, but the specimen is different from Noronhomys vespuccii in other respects, and in 2008 it was described as a new genus and species, Carletonomys cailoi
Carletonomys
Carletonomys cailoi is an extinct rodent from the Pleistocene 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...
, related to Noronhomys and associated genera.
Description
Noronhomys vespuccii is known from a number of bone fragments, including five skullSkull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
s, damaged to various degrees, and many isolated jaws and other bones. This material documents that, with a skull of about 4 cm (1.6 in) (occipitonasal length), Noronhomys was a moderately large oryzomyine, smaller than Lundomys but well within the range of Holochilus. It shares a number of the features that characterize the group of Holochilus and related genera, including a reduction in the complexity of the chewing surface of 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"....
, simple posterolateral palatal pits
Posterolateral palatal pits
In anatomy, posterolateral palatal pits are gaps at the sides of the back of the bony palate, near the last molars. Posterolateral palatal pits are present, in various degrees of development, in several members of the rodent family Cricetidae...
(perforations 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...
near the third molar), and a similarly shaped interorbital region
Interorbital 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....
of the skull. Noronhomys is distinctive, among other characters, in its lack of a spinous process
Process (anatomy)
In anatomy, a process is a projection or outgrowth of tissue from a larger body. The vertebra has several kinds of processes,such as: transverse process, prezygapophysis, postzygapophysis.-Examples:Examples of processes include:...
on 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...
, the flattened front portion 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); the short palate, which does not extend behind the third molars; and the presence of an accessory crest, the mesoloph, on the upper molars.
Analysis of morphometrical data from the known material of Noronhomys suggests that growth continued in adults—the older the animal, the larger the depth of the mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
and the size of the lower incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
—and does not provide evidence for a difference in size
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
between males and females. Skull shape is strikingly different from both Holochilus and Lundomys, resulting in a clear separation from both of these taxa in statistical analyses of measurement data. In three individuals measured, the occipitonasal length, a measure of skull length, varies from 38.0 to 39.2 mm (1.50 to 1.54 in), averaging 38.5 mm (1.52 in). The width of the braincase is 13.4 to 14.8 mm (0.53 to 0.58 in), averaging 14.1 mm (0.56 in). Between the first molars, the width of the palate is 8.1 to 8.9 mm (0.32 to 0.35 in) in four specimens, averaging 8.4 mm (0.33 in). The lower molars have a total length of 7.57 to 8.29 mm (0.298 to 0.326 in), averaging 8.00 mm (0.315 in), in 39 specimens with intact molar rows. The femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
(upper leg bone) is 32.5 to 41.0 mm (1.28 to 1.61 in) in length in nine specimens, averaging 36.5 mm (1.44 in). Carleton and Olson estimated that body mass in Noronhomys was similar to that of some populations of living Holochilus sciureus at about 200 to 250 g (7 to 9 oz).
Skull
Interorbital 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....
(located between the eyes) is hourglass-shaped, with squared edges and weakly developed beading. A postorbital ridge is present, obscuring the suture (joint) between the frontal
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....
and squamosal
Squamosal
The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex,...
bones, a feature shared only with Holochilus among oryzomyines. The braincase is squarish. The interparietal bone is wide, but does not reach the squamosals on the sides. The zygomatic arches, which are well-developed, are furthest apart at the back and converge toward the front. The jugal
Jugal
The jugal is a skull bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the malar or Zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species....
bone is small.
The back margin of the zygomatic plate is located close to the front of the upper first molar. 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:...
do not extend between the molars. Unlike in both Holochilus and Lundomys, the palate is flat, lacking a distinct ridge at the midline. The parapterygoid fossae, which are located behind the palate at the level of the molars, are excavated somewhat above the level of the palate. A strut of the alisphenoid bone
Alisphenoid strut
In some rodents, the alisphenoid strut is an extension of the alisphenoid bone that separates two foramina in the skull, the masticatory–buccinator foramen and the foramen ovale accessorius...
is present, separating two openings in the skull, the masticatory–buccinator foramen and the foramen ovale accessorius. The subsquamosal fenestra
Subsquamosal fenestra
In some rodents, the subsquamosal fenestra is an opening between two parts of the squamosal bone, at the back of the skull. It can be seen in lateral view. Most Oryzomyini have the fenestra, but some species, including those in the genera Nectomys, Sigmodontomys, and Melanomys among others, lack...
, an opening at the back of the skull determined by the shape of the squamosal, is present but small. The squamosal probably lacks a suspensory process that contacts the tegmen tympani, the roof of the tympanic cavity
Tympanic cavity
The tympanic cavity is a small cavity surrounding the bones of the middle ear.It is formed from the tubotympanic recess, an expansion of the first pharyngeal pouch....
, a defining character of oryzomyines.
The mandible (lower jaw) is robust. The two masseteric ridges, which anchor some of the chewing muscles, are joined together as a single crest for a portion of their length and extend forward to a point below the first molar. The capsular process
Capsular process
In rodents, the capsular process or projection is a bony capsule that contains the root of the lower incisor. It is visible on the labial side of the mandible as a raising in the bone...
, a raising of the mandibular bone at the back end of the lower incisor, is well developed.
Teeth
In the upper incisors, the chewing edges are located behind the vertical plane of the incisors; thus, they are opisthodont. The microstructure of the enamelTooth 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...
of the lower incisor was reported in a 2005 study. The inner portion (portio interna, PI) is much thicker than the outer portion (portio externa, PE). The PI consists of Hunter-Schreger band
Hunter-Schreger band
Hunter-Schreger bands, commonly abbreviated as HSB, are features of the enamel of the teeth in mammals, mostly placentals. In HSB, enamel prisms are arranged in layers of varying thickness at about right angles to each other...
s, which are uniserial (consisting of a single enamel prism), as in all myomorph
Myomorpha
Suborder Myomorpha contains 1,137 species of mouse-like rodents, nearly a quarter of all mammal species. Included are mice, rats, gerbils, hamsters, lemmings and voles. They are grouped according to the structure of the jaw and the structure of the molar teeth. Both their medial and lateral...
rodents. The PE consists of radial enamel, with flattened prisms that are almost parallel to the junction between the enamel and the dentine. The microstructure is similar to that of Holochilus brasiliensis and displays several characters seen only in Myomorpha.
The molars are high-crowned (hypsodont
Hypsodont
Hypsodont dentition is characterized by high-crowned teeth and enamel which extends past the gum line. This provides extra material for wear and tear. Some examples of animals with hypsodont dentition are cows, horses and deer; all animals that feed on gritty, fibrous material. The opposite...
) and planar, with the main cusps as high as the crests connecting them, a configuration shared only with Holochilus and Carletonomys among oryzomyines. The first molars are the longest and the third molars are longer but narrower than the second molars. The molars lack many accessory ridges, including the anteroloph on the first upper molar, the posteroloph on the first and second upper molar, and the anterolophid and mesolophid on all lower molars. The first and second upper molar have a short mesoloph and the front cusp of the first lower molar, the anteroconid, encloses a large internal pit. Most of the folds between the cusps and crests are open at the margins of the molars, but two—the posteroflexid on the lower second molar and the entoflexid on the lower third molar—are closed by a wall, or cingulum
Cingulum (tooth)
In dentistry, cingulum refers to an anatomical feature of the anterior teeth . It refers to the portion of the teeth, occurring on the lingual or palatal aspects, that forms a convex protuberance at the cervical third of the anatomic crown. It represents the lingual or palatal developmental lobe...
, at the inner margin of the tooth. As in most oryzomyines, the upper molars all have one root on the inner (lingual) side and two on the outer (labial) side and the lower molars have a single root at the front and back of each molar; in addition, the first upper molar has another labial root and the first lower molar has a small labial and usually also a small lingual root located between the main roots.
Postcranial skeleton
The entepicondylar foramenEntepicondylar foramen
The entepicondylar foramen is an opening in the distal end of the humerus present in some mammals. It is often present in primitive placentals, such as the enigmatic Madagascan Plesiorycteropus...
is absent, as in all members of the Sigmodontinae; if present, as in some other rodents, this foramen
Foramen
In anatomy, a foramen is any opening. Foramina inside the body of humans and other animals typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body with another.-Skull:...
(opening) perforates the distal (far) end of the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
(upper arm bone). The pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
and the bones of the hindlimbs are heavily built. The femoral tubercle of the acetabulum
Acetabulum
The acetabulum is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.-Structure:...
(part of the pelvis), which anchors the rectum femoris muscle, is reduced relative to Holochilus and Lundomys.
Distribution and origin
Noronhomys is known only from Fernando de NoronhaFernando de Noronha
Fernando de Noronha is an archipelago of 21 islands and islets in the Atlantic Ocean, offshore from the Brazilian coast. The main island has an area of and had a population of 3,012 in the year 2010...
, a small archipelago of volcanic origin off northeastern Brazil, consisting of a main island and several associated smaller islands. The formation of the archipelago, which has never been connected to the mainland, began about 11 million years ago; active vulcanism
Vulcanism
Vulcanism may refer to* Volcanism or volcanic activity.* Plutonism, a scientific theory of the Earth....
ceased about 2 million years ago. Remains of Noronhomys were found in association with remains of various reptiles, birds, and snails, several of which are also restricted to the archipelago, in sand dunes near the northeastern tip of the main island. The age of the deposits is unknown, but is likely late Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
, at most a few thousand years old.
The ancestor of Noronhomys may have been a semiaquatic animal, similar to living Holochilus or Lundomys, that arrived on Fernando de Noronha by chance on a floating log. The morphology of the limb bones in Noronhomys suggests that the animal was not semiaquatic like its relatives, but terrestrial, consistent with its occurrence on a small island, where streams and pools are rare or absent.
Extinction
Vespucci's account suggests that Noronhomys was common when the island was first visited, but was not encountered by the first biological explorers of the island, who conducted their research in the late 19th century. The introducedIntroduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
black rat and house mouse
House mouse
The house mouse is a small rodent, a mouse, one of the most numerous species of the genus Mus.As a wild animal the house mouse mainly lives associated with humans, causing damage to crops and stored food....
(Mus musculus), which became very common on the island, may have driven it to extinction by directly competing for food, preying on young Noronhomys, or transmitting diseases. Other factors that may have played a role include modification of its habitat, introduction of predators such as cat
Cat
The cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...
s (Felis catus), and predation by visiting sailors. These extinction mechanisms are common for island endemic species. In 1888, Henry Nicholas Ridley
Henry Nicholas Ridley
Henry Nicholas Ridley CMG , MA , FRS, FLS, F.R.H.S. was an English botanist and geologist.Born at West Harling Hall, Norfolk, England...
already suggested that the rat Vespucci had seen had been driven to extinction by the introduced black rat. The International Union for Conservation of Nature lists it as "extinct".
Literature cited
- Carleton, M.D. and Olson, S.L. 1999. Amerigo Vespucci and the rat of Fernando de Noronha: a new genus and species of Rodentia (Muridae, Sigmodontinae) from a volcanic island off Brazil's continental shelf. American Museum Novitates 3256:1–59.
- Kalthoff, D.C. 2000. Die Schmelzmikrostruktur in den Incisiven der hamsterartigen Nagetiere und anderer Myomorpha (Rodentia, Mammalia). Palaeontographica (A)259(1–6):1–193 (in German).
- Miralles, A., Chaparro, J.C. and Harvey, M.B. 2009. Three rare and enigmatic South American skinks. Zootaxa 2012:47–68.
- 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, ISBN 978-0-8018-8221-0
- Pardiñas, U.F.J. 2008. A new genus of oryzomyine rodent (Cricetidae: Sigmodontinae) from the Pleistocene of Argentina (subscription required). Journal of Mammalogy 89(5):1270–1278.
- Ridley, H.N. 1888. Notes on the zoology of Fernando Noronha. Journal of the Linnean Society: Zoology 20:473–570.
- Voss, R.S. and Carleton, M.D. 1993. A new genus for Hesperomys molitor Winge and Holochilus magnus Hershkovitz (Mammalia, Muridae) with an analysis of its phylogenetic relationships. American Museum Novitates 3085:1–39.
- Weksler, M. 2006. Phylogenetic relationships of oryzomyine rodents (Muroidea: Sigmodontinae): separate and combined analyses of morphological and molecular data. Bulletin of the American Museum of Natural History 296:1–149.
- Weiss, F.E. and Malabarba, M.C. 2005. Dental enamel microstructure in three rodents (Mammalia: Rodentia): Noronhomys vespuccii Carleton & Olson, 1999, Myocastor coypus Kerr, 1792 and Hydrochaeris hydrochaeris Linnaeus, 1766. Comunicações do Museu de Ciências e Tecnologia da PUCRS, Série Zoologia, Porto Alegre 18(2):151–160.
- Weksler, M. and Costa, L. 2008. . In IUCN. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Retrieved on November 14, 2009.