Pennatomys
Encyclopedia
Pennatomys nivalis is an extinct oryzomyine
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...

 rodent from the islands of Sint Eustatius, Saint Kitts
Saint Kitts
Saint Kitts Saint Kitts Saint Kitts (also known more formally as Saint Christopher Island (Saint-Christophe in French) is an island in the West Indies. The west side of the island borders the Caribbean Sea, and the eastern coast faces the Atlantic Ocean...

, and Nevis
Nevis
Nevis is an island in the Caribbean Sea, located near the northern end of the Lesser Antilles archipelago, about 350 km east-southeast of Puerto Rico and 80 km west of Antigua. The 93 km² island is part of the inner arc of the Leeward Islands chain of the West Indies...

 in the Lesser Antilles
Lesser Antilles
The Lesser Antilles are a long, partly volcanic island arc in the Western Hemisphere. Most of its islands form the eastern boundary of the Caribbean Sea with the Atlantic Ocean, with the remainder located in the southern Caribbean just north of South America...

. 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.

Pennatomys nivalis was a medium-sized species without many distinctive adaptations. The nasal bone
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....

s were short and blunt-ended. 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 bony plate at the side of the skull, was broad. The bony 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...

 was long and flat. The root 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:...

 was housed in a bony protuberance, 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...

. 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"....

 were low-crowned and possess accessory crests such as mesolophs. The upper molars all had three roots.

Taxonomy

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...

, also known as rice rats, is a diverse grouping of North, Central, and South American rodents within 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...

. Remains of extinct rice rats are known throughout the Lesser Antilles, but the systematic relationships among those animals are poorly understood, and many species remain unnamed. Rice rat fossils were first recorded from Saint Kitts
Saint Kitts
Saint Kitts Saint Kitts Saint Kitts (also known more formally as Saint Christopher Island (Saint-Christophe in French) is an island in the West Indies. The west side of the island borders the Caribbean Sea, and the eastern coast faces the Atlantic Ocean...

 in 1907 by archeologist C.W. Branch and were later found in abundance in Amerindian archeological sites on nearby Nevis
Nevis
Nevis is an island in the Caribbean Sea, located near the northern end of the Lesser Antilles archipelago, about 350 km east-southeast of Puerto Rico and 80 km west of Antigua. The 93 km² island is part of the inner arc of the Leeward Islands chain of the West Indies...

 and Sint Eustatius. The rice rat of these islands was formally described and named as Pennatomys nivalis in a 2010 article by zoologist Samuel Turvey and coworkers. The generic name, Pennatomys, combines the Latin pennatus "winged" with -mys "mouse", a standard element in the names of rodent genera, and honors archeologist Elizabeth Wing. The specific name, nivalis, is Latin for "snowy" and refers to Nevis. This island's name derives from the Spanish Nuestra Señora de las Nieves "Our Lady of the Snows", a reference to the clouds (mistaken for snow) that surround the island's central peak.

Cladistic
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...

 analysis of morphological characters suggest that Pennatomys is most closely related to a 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...

, the Nectomys subclade, that includes members of Aegialomys
Aegialomys
Aegialomys is a genus of oryzomyine rodents from the lowlands and mountains of western Peru and Ecuador, including the Galápagos Islands. The species in this genus have historically been placed in Oryzomys, but according to cladistic research, the genus is more closely related to a group...

, Amphinectomys, Nectomys
Nectomys
Nectomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. It is closely related to Amphinectomys and was formerly considered congeneric with Sigmodontomys...

, Sigmodontomys
Sigmodontomys
Sigmodontomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. It is related to Nectomys and Melanomys and was previously included in Nectomys. It includes two species, Sigmodontomys alfari and the much rarer Sigmodontomys aphrastus, but whether these are indeed each other's...

, Melanomys
Melanomys
Melanomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae, which is distributed in northern South America and adjacent Central America. It contains three species, two of which—Melanomys robustulus and Melanomys zunigae—have limited distributions...

, Megalomys
Megalomys
Megalomys is a genus of rodent in the family Cricetidae, part of the tribe Oryzomyini. The genus contains four large rodents from various Caribbean islands, all of which are now extinct. The last species to survive was M...

(another Antillean rice rat), and possibly Nesoryzomys
Nesoryzomys
Nesoryzomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae, endemic to the Galápagos Islands. Other rodents restricted to the Galápagos include Megaoryzomys curioi and Aegialomys galapagoensis.-References:...

. However, the exact position of Pennatomys was poorly resolved because of missing data. Turvey and colleagues placed P. nivalis as the only member of its own genus because of its distinctive characters and the absence of evidence for close relationships with any other oryzomyine genus. Pennatomys probably belongs to a subgroup of Oryzomyini known as "clade D". This clade contains a number of species only occurring on islands—including members of Aegialomys, Megalomys, Nesoryzomys, Noronhomys, 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...

, and Pennatomys. Turvey and colleagues suggested that this is related to the high proportion of semiaquatic species in clade D—most other oryzomyines are forest dwellers. As a whole, Oryzomyini includes over a hundred species in about thirty genera. It is one of several tribes within the subfamily Sigmodontinae 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...

, which encompasses hundreds of other species of mainly small rodents, distributed chiefly in Eurasia and the Americas.

Description

A medium-sized oryzomyine, Pennatomys is known from a number of skeletal remains, many of which are fragmentary. Both skull and postcranial bones are represented. Although there are no unusual adaptations in the known material, the animal possesses a combination of characteristics that distinguish it from all other known oryzomyines. The skull is known only from fragments. The nasal bone
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....

s extend back to a point before or slightly behind the point where the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...

ry, 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 lacrimal bone
Lacrimal bone
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...

s meet, and have a blunt back margin. The nasals extend slightly further back than the premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....

ries. The lacrimals articulate with both the frontals and the maxillaries, a trait that distinguishes Pennatomys from its closest relatives (which have lacrimals articulating mainly with the frontals). The 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 bears weak crests at its sides. 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 bony plate at the side of the skull, is broad and its back margin is located in front of the first upper 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"....

 (M1). The incisive foramina, openings in the bony 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 back to a point next to the front root of M1. The palate itself is long and flat, extending beyond the third upper molars (M3). In the mandible (lower jaw), there is a 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 protuberance at the back of the jawbone that houses the root 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:...

. Below the molars, the upper and lower masseteric ridges (crests which support some of the chewing muscles) are sometimes conjoined towards the front, and they extend forward to a point below the first lower molar (m1). The conjoined crests are one of the synapomorphic (shared-derived) characters of the Nectomys subclade.

The maxillary toothrows are parallel to each other. The molars are bunodont (with the cusps higher than the connecting crests) and brachyodont (low-crowned) and have the inter-cusp valleys on the labial (outer) sides closed by a 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...

 (shelf). The valleys on the labial and lingual (inner) sides of the molars meet at the midlines. Each of the upper molars has three roots—unlike in most of the closest relatives of Pennatomys, there is no additional labial root on M1. The m1 has four roots—two large roots at the front and back and two smaller ones in the middle. There are three roots under m2, two at the front and one at the back, and two under m3, at the front and back. Upper toothrow length ranges from 5.6 to 6.7 mm and lower toothrow length is 5.9 to 7.4 mm.

On M1, the anterocone (the cusp at the front of the tooth) is not divided into smaller cuspules. The connection between the protocone
Protocone
thumb|500px|right|Right upper molar showing the four main upper molars cusps.The protocone is a cusp of the molars of the upper dentition in Placental and Marsupial vertebrates .It is found at the mesiolingual area of the tooth...

 and the paracone
Paracone
An atmospheric reentry or spaceflight mission abort concept using an inflatable cone.A notable feature of the paracone concept is that it facilitates an abort throughout the entire flight profile....

, the major cusps immediately after the anterocone, is located relatively far toward the front. Behind the paracone, the mesoloph accessory crest is present. On M2, there is no protoflexus (an indentation in front of the protocone, which on this tooth is the frontmost cusp) and the valley between the paracone and the mesoloph, the mesoflexus, is not divided into two pieces by a paracone–mesoloph connection. These traits are both characteristic of the Nectomys subclade. The mesoloph is present on M3, but the posteroloph, a crest at the back of the tooth, is absent or vestigial, as is the hypoflexus (the valley between the protocone and the cusp behind it, the hypocone
Hypocone
The hypocone is the name for a main cusp found on the molars of the upper dentition of hominids. It is found on the distal lingual side of the tooth. It fits into the grooves of the lower dentition and is an adaptation for the overall grinding and tearing of foods using the occlusal of the tooth...

). The absence or near-absence of the posteroloph is a distinctive trait that differentiates Pennatomys from related oryzomyines.

The anteroconid on m1 (the frontmost cusp, corresponding to the anterocone) contains an internal hollow, an anteromedian fossettid. There is an ectolophid, an accessory crest in the valley between the protoconid (the cusp on the labial side, behind the anteroconid) and the hypoconid (the cusp behind the protoconid, at the back labial corner of the tooth). On the other side of the tooth, the mesolophid (another accessory crest) is also present. On each of the lower molars, an anterolabial cingulum (a shelf on the front labial corner) is present. On m2 and m3, an anterolophid is present—a crest in front of the metaconid (the cusp on the front lingual corner of the tooth).

Range and history

Remains of Pennatomys nivalis come from several Amerindian archeological sites on each of the three islands where it has been found; it was eaten by the native Amerindian population. The oldest site is Hichmans' Shell Heap on Nevis, which is from the Archaic age and is dated to 790 to 520 BCE. The youngest, Sulphur Ghaut (900–1200 CE), is also on Nevis, and is from the post-Saladoid
Saladoid
Saladoid culture is a pre-columbian indigenous culture of Venezuela and the Caribbean that flourished from 500 BCE to 545 CE.-Name:They have been given the name of the sites where their unique pottery styles were first recognised. The suffix "oid" has been added in this cultural classification...

 period. Other sites on Nevis include Hichmans (Saladoid, 100 BCE – 600 CE), Indian Castle (post-Saladoid, 650–880 CE), and Coconut Walk (post-Saladoid, no absolute dates known). The only site on Sint Eustatius is the Saladoid and post-Saladoid site Golden Rock (80 BCE – 980 CE). Each of the three sites yielding Pennatomys on Saint Kitts is from the post-Saladoid period: Sugar Factory (700–1000 CE), Bloody Point
Bloody Point
Bloody Point is a headland in Trinity Parish, Saint Kitts. The Stone Fort or Bloody River runs towards Bloody Point. In 1626, English and French settlers killed most of the Carib population at Bloody point....

 (660–1115 CE), and Cayon
Cayon
Cayon is a town on the northeast coast of Saint Kitts in the Caribbean. It is the capital of Saint Mary Cayon Parish. The 2010 estimated population was 805.Cayon is home to the campus of Windsor University School of Medicine.- References :...

 (undated).

Unambiguous historical records of Pennatomys are lacking, but there are some references to Saint Kitts and Nevis rodents that may relate to it. George Percy
George Percy
George Percy was an English explorer, author, and early Colonial Governor of Virginia.-Early life:George Percy was born in England, the youngest son of Henry Percy, 2nd/8th Earl of Northumberland and Lady Catherine Neville. He was sickly for much of his life, possibly suffering from epilepsy or...

 reported on the presence of "great store of Conies" on Nevis around 1606, probably a reference to the agoutis (Dasyprocta) that have been introduced
Introduced 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...

 throughout the Lesser Antilles. There are references from 1631 and 1720 to people eating rats on Saint Kitts and Nevis, respectively, but these may well have been introduced 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...

s (Rattus rattus), not Pennatomys. There are anecdotal records of unusual rats on Nevis up to recent times; these were reportedly eaten by the islanders until the 1930s. Surveys on Nevis in 2009 found no evidence for the survival of Pennatomys. The extinction of the Antillean rice rats, including Pennatomys, may have resulted from the introduction of exotic animals such as the black rat and the small Asian mongoose (Herpestes auropunctatus) to the Lesser Antilles.

There are no known morphological differences between the three island populations, but Turvey and colleagues found that animals from Nevis were slightly smaller than those from the two other islands. Such a difference in size might be related to the fact that Saint Kitts is larger than Nevis, in accordance with the trend that animals become larger on larger islands. However, Turvey and colleagues also observed that their Saint Kitts material consisted of older individuals than those from Nevis; thus, the size difference may result from differences in the mode of exploitation by Amerindians.

Literature cited

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