Gorgas's oryzomys facts for kids
Quick facts for kids Gorgas's oryzomys |
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Oryzomys
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gorgasi
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| Where Oryzomys gorgasi (blue) and O. couesi (red) live in South America. | |
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The Oryzomys gorgasi, also known as Gorgas's oryzomys or Gorgas's rice rat, is a type of rodent. It belongs to the Oryzomys group, which are often called rice rats. This animal was first found in 1967.
We only know about it from a few places. These include a freshwater swamp in Colombia and a mangrove island in Venezuela. People also believe it used to live on the island of Curaçao. This group from Curaçao is now extinct. Some scientists thought it was a different species, Oryzomys curasoae. But it looks the same as the rats found on the mainland.
Oryzomys gorgasi is a medium-sized rat. It has brownish fur and large feet. These feet are special for living partly in water. Its skull also has features that make it different from other Oryzomys species. This rat eats crustaceans, insects, and plants. The International Union for Conservation of Nature lists it as "Endangered." This means it is in danger of disappearing. Its habitat is being destroyed, and it faces competition from black rats.
Contents
Discovering and Naming the Gorgas's Rice Rat
The first Oryzomys gorgasi was found in 1967. This happened in Antioquia Department, Colombia. An expedition by the U.S. Army Medical Department found it. The Gorgas Memorial Laboratory was also part of this trip.
In 1971, a zoologist named Philip Hershkovitz described this new species. He worked at the Field Museum of Natural History. He named the rat Oryzomys gorgasi. The name honors William Crawford Gorgas, a doctor. The Gorgas Memorial Laboratory was named after him. Hershkovitz thought this new rat was related to the Oryzomys palustris group. This group includes the marsh rice rat.
Scientists did not find this species again until 2001. That year, J. Sánchez H. and his team found 11 more rats. They were in coastal northwestern Venezuela. This was about 700 kilometers (430 miles) from where the first one was found. Their findings confirmed that O. gorgasi is a unique species. It is related to the O. palustris group.
The Curaçao Rice Rat Mystery
In 2001, Donald McFarlane and Adolphe Debrot described a new Oryzomys species. They found it on the island of Curaçao. This island is part of the Kingdom of the Netherlands. They used old skull and jaw bones found in owl pellets. Owl pellets are undigested parts of an owl's meal. They named this new species Oryzomys curasoae. It was also called the "Curaçao Rice Rat."
Later, in 2006, Marcelo Weksler and his team studied Oryzomys species. They kept O. gorgasi and O. curasoae in the same group. They also wondered if O. curasoae was truly different from O. gorgasi.
In 2009, R.S. Voss and Weksler compared the two. They found that they were the same species. They looked at their features and how they were related. They decided that O. curasoae was just another name for O. gorgasi. This means O. gorgasi was named first, so that is the correct name.
Where the Gorgas's Rice Rat Fits In
Oryzomys gorgasi lives in the southeasternmost part of the Oryzomys group's range. This group stretches north into the eastern United States. O. gorgasi is also part of the O. couesi section. This section includes the widespread O. couesi from Central America. It also has six other species that live in smaller, separate areas. Scientists are still learning about these groups. They think there might be even more species than we know now.
Oryzomys belongs to a larger group called Oryzomyini. This group has over a hundred species of American rodents. They are part of the Sigmodontinae family. This family includes hundreds of other small rodents.
What the Gorgas's Rice Rat Looks Like
The Oryzomys gorgasi is a medium-sized rice rat. It has small ears and large feet. It looks a lot like the marsh rice rat. Its fur is long and rough. It is brownish on top and lighter underneath. The top and bottom of its tail are different colors. The tail also has a small tuft of hair at the end.
Its hindfeet are special for living in water. The bottom of its feet are bare. It has small pads on its feet. The hairs at the base of its claws are not very developed. It has some interdigital webbing between its toes. But this webbing covers less than half of the first toe bones.
Size of the Rat
Rats from El Caimito in Venezuela have these average measurements:
- Total length: 259 millimeters (10.2 inches)
- Tail length: 130 millimeters (5.1 inches)
- Hindfoot length: 31 millimeters (1.2 inches)
- Ear length: 16 millimeters (0.6 inches)
- Skull length: 29.6 millimeters (1.17 inches)
The first rat found in Colombia was an old male. It was 240 millimeters (9.4 inches) long. Its tail was 125 millimeters (4.9 inches). Its ear was 19 millimeters (0.7 inches). Its skull was 32.1 millimeters (1.26 inches).
Skull and Teeth Features
The front part of its skull is short. The zygomatic plate (a bone on the side of the skull) has a notch. The area between the eyes is narrowest at the front. The incisive foramina (holes in the roof of the mouth) are narrow and long. The roof of the mouth itself is also long. It extends past the molars.
The lower jaw has masseteric ridges that are close together. The upper incisors are yellowish. They are also angled backward. The molars are small. They have low crowns and rounded bumps. They are similar to those of the marsh rice rat.
Oryzomys gorgasi is different from other Oryzomys species. It has a short snout and unique incisive foramina. It also lacks certain openings in its skull. The rat from Colombia was larger than the Venezuelan ones. But its teeth were smaller. This might be because it was kept in captivity for a while. There are no big differences between the rats from the mainland and those from Curaçao.
Where the Gorgas's Rice Rat Lives and What It Eats
The Oryzomys gorgasi lives in separate areas in northwestern South America. These areas include Colombia, Venezuela, and Curaçao. Some scientists think it might also live in Central America.
The Colombian rat was found in a freshwater swamp. This was near the Río Atrato. Scientists believe it likely lives throughout the swamp forests there. On Curaçao, its bones were found in caves. These bones were found with bones of black rats. This suggests the Gorgas's rice rat lived there until Europeans arrived in 1499.
In Venezuela, it was found on El Caimito. This is a small island near Lake Maracaibo. The island has sand banks with dry plants. It also has marshy areas with mangrove trees. Oryzomys gorgasi was found in all these habitats on the island. But it has not been found in other similar places in Venezuela. In those places, the introduced black rat is the only rodent found.
Scientists looked at the stomach contents of these rats. They found that Oryzomys gorgasi is an omnivore. This means it eats both plants and animals. Its diet includes crustaceans, insects, and plant seeds. The crustaceans might be fiddler crabs or mangrove tree crabs. The insects include flies. The plants include grass seeds.
Two types of parasitic nematodes can infect O. gorgasi. These are Litomosoides sigmodontis and a species of Pterygodermatites.
Protecting the Gorgas's Rice Rat
The Oryzomys gorgasi is listed as "endangered" by the IUCN Red List. This means it is at high risk of extinction. The Curaçao population is "data deficient," meaning we don't have enough information about it.
This species is threatened by two main things. First, its habitat is being destroyed. Second, it faces competition from introduced black rats. Black rats have caused the Gorgas's rice rat to disappear from some areas in Venezuela.
However, O. gorgasi does live in at least one protected area. There are also suitable habitats for it in other parts of Venezuela. More studies are needed to find out if it lives in those areas too. The black rat may also have caused the extinction of the Curaçao population. Black rat bones have been found with Oryzomys bones in old deposits there.
See also
In Spanish: Oryzomys gorgasi para niños
