Lagrivea
Encyclopedia
Lagrivea is a fossil
genus
of squirrel
from the Middle Miocene
of France
. The single species, L. vireti, is known from three mandible
s (lower jaws) and two isolated teeth. All come from the fissure filling (a fossil deposit formed when a rock fissure filled with sediment) of La Grive L5, part of the La Grive-Saint-Alban complex in Saint-Alban-de-Roche
, southeastern France. Lagrivea was a large tree squirrel
with flat lower incisor
s and a large, triangular fourth lower premolar
(p4). Each of the four cheekteeth (p4 and three molar
s, m1 through m3) bears a deep basin in the middle of the crown. The m3 is about rectangular in shape, but rounded at the back. Although m1 and m2 have two roots, m3 has three.
fossil sites of La Grive-Saint-Alban in southeastern France. They suggested that it was probably a tree squirrel
and related to the Sciurini
. Lagrivea belongs to the squirrel
family (Sciuridae), which first appears in the Late Eocene of North America and Early Oligocene of Europe. The specific name, vireti, honors Jean Viret for his work on the mammals of La Grive-Saint-Alban.
Lagrivea is known from three mandible
s (lower jaws)—one, the holotype
, with the fourth premolar
(p4) and all three molars
(m1–3) preserved; one with the incisor
and m2; and one with the incisor, p4, m1, and m2—an isolated lower incisor, and an isolated m2. It was large for a squirrel, and can be distinguished from the fossil squirrels Palaeosciurus, Aliveria, and Ratufa obtusidens by its larger size.
In the mandible, the diastema
(gap) between the incisors and the cheekteeth (premolars and molars) is relatively deep. The mental foramen
(an opening in the bone) is located relatively high and before the p4. The upper and lower masseteric ridges, which are located on the outer side of the jaw and anchor some of the chewing muscles, meet at the m1. The surfaces of the incisor are very flat, but there are small, irregular striations in the enamel
along the length of the tooth.
The cheekteeth increase regularly in size from front to back. They all consist of a large central basin surrounded by cusp
s and crests. The basins are deeper than in Palaeosciurus and Ratufa obtusidens and lack crenulations in the enamel, which distinguishes them from another fossil squirrel, Albanensia. The first cheekteeth, p4, is large and about triangular in form, short and quite broad at the back. The two cusps at the front, the protoconid and metaconid, are isolated from each other. In front of the metaconid, there is a small cuspule, an anteroconid, at the lingual side of the tooth (the side of the tongue). The central basin of the tooth is relatively deep. At the back of the tooth, the entoconid cusp is connected to the posterolophid, a crest that forms the back margin. Of the two roots, the one at the front is round and the one at the back is broad.
Although m1 is nearly rectangular, the width at the front is still smaller than the width at the back. There is a strong anteroconid. A crest, the metalophid, reaches from the protoconid nearly to the metaconid. A small cusp, the mesostylid, is connected to the metaconid in front of it, unlike in Miopetaurista and Aliveria. There are two broad roots. The next tooth, m2, is similar to m1 in most respects, but the width at the front is virtually equal to the width at the back, so that the tooth is about rectangular. The back of m3 is rounded, but the tooth is still nearly rectangular. There is a long anteroconid, with is mainly connected to the metaconid. There is no metalophid. This tooth has three roots: two at the front and a larger one at the back.
, department of Isère
, southeastern France. La Grive L5 is one of several fissure filling sites in the area, collectively known as La Grive-Saint-Alban, which have yielded rich fossil faunas. Another site, La Grive M, is the reference locality for the MN zone
MN 7/8, about 13 to 11 million years ago. La Grive L5 is one of the younger sites of La Grive, and Mein and Ginsburg proposed placing it in a separate zone MN 8. Other squirrels at La Grive-Saint-Alban include species of Heteroxerus, Spermophilinus, Palaeosciurus, and chipmunk
s, and flying squirrel
s in the genera Albanensia, Miopetaurista, Forsythia, Hylopetes
, and Blackia. Miopetaurista neogrivensis, Spermophilinus bredai, and Heteroxerus huerzeleri are also known from La Grive L5.
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
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...
of squirrel
Squirrel
Squirrels belong to a large family of small or medium-sized rodents called the Sciuridae. The family includes tree squirrels, ground squirrels, chipmunks, marmots , flying squirrels, and prairie dogs. Squirrels are indigenous to the Americas, Eurasia, and Africa and have been introduced to Australia...
from the Middle Miocene
Middle Miocene
The Middle Miocene is a sub-epoch of the Miocene Epoch made up of two stages: the Langhian and Serravallian stages. The Middle Miocene is preceded by the Early Miocene....
of France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. The single species, L. vireti, is known from three mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
s (lower jaws) and two isolated teeth. All come from the fissure filling (a fossil deposit formed when a rock fissure filled with sediment) of La Grive L5, part of the La Grive-Saint-Alban complex in Saint-Alban-de-Roche
Saint-Alban-de-Roche
Saint-Alban-de-Roche is a commune in the Isère department in south-eastern France.-References:*...
, southeastern France. Lagrivea was a large tree squirrel
Tree squirrel
Tree squirrels include over a hundred species that are found on all continents except Antarctica, and are the members of the squirrel family most commonly referred to as "squirrels"...
with flat lower incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
s and a large, triangular fourth lower premolar
Premolar
The premolar teeth or bicuspids are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered as a 'transitional tooth' during chewing, or...
(p4). Each of the four cheekteeth (p4 and three 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"....
s, m1 through m3) bears a deep basin in the middle of the crown. The m3 is about rectangular in shape, but rounded at the back. Although m1 and m2 have two roots, m3 has three.
Taxonomy
Pierre Mein and Léonard Ginsburg described Lagrivea vireti in 2002 in a review of the ages and faunas of the MioceneMiocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
fossil sites of La Grive-Saint-Alban in southeastern France. They suggested that it was probably a tree squirrel
Tree squirrel
Tree squirrels include over a hundred species that are found on all continents except Antarctica, and are the members of the squirrel family most commonly referred to as "squirrels"...
and related to the Sciurini
Sciurini
Sciurini is a tribe that includes about forty species of squirrels, mostly from the Americas. It includes five living genera—the American dwarf squirrels, Microsciurus; the Bornean Rheithrosciurus; the widespread American and Eurasian tree squirrels of the genus Sciurus, which includes some of the...
. Lagrivea belongs to the squirrel
Squirrel
Squirrels belong to a large family of small or medium-sized rodents called the Sciuridae. The family includes tree squirrels, ground squirrels, chipmunks, marmots , flying squirrels, and prairie dogs. Squirrels are indigenous to the Americas, Eurasia, and Africa and have been introduced to Australia...
family (Sciuridae), which first appears in the Late Eocene of North America and Early Oligocene of Europe. The specific name, vireti, honors Jean Viret for his work on the mammals of La Grive-Saint-Alban.
Description
| Variable | Measurements (in mm) |
|---|---|
| Depth of mandible at m1 | 8.5, 8.7, 9.2 |
| Diastema Diastema (dentistry) Diastema is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars.-In humans:... between incisors and p4 |
6.1, 6.9, 7.6 |
| p4–m3 | 11.1, 12.2, 12.2 |
| Length of p4 | 2.37, 2.42 |
| Width of p4 | 2.45, 2.45 |
| Length of m1 | 2.55, 2.60, 2.66 |
| Width of m1 | 2.68, 2.70, 2.75 |
| Length of m2 | 2.8, 3.03, 3.07 |
| Width of m2 | 2.90, 3.05, 3.18 |
| Length of m3 | 3.22 |
| Width of m3 | 2.75 |
Lagrivea is known from three mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
s (lower jaws)—one, the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
, with the fourth premolar
Premolar
The premolar teeth or bicuspids are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered as a 'transitional tooth' during chewing, or...
(p4) and all three 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"....
(m1–3) preserved; one with the incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
and m2; and one with the incisor, p4, m1, and m2—an isolated lower incisor, and an isolated m2. It was large for a squirrel, and can be distinguished from the fossil squirrels Palaeosciurus, Aliveria, and Ratufa obtusidens by its larger size.
In the mandible, the diastema
Diastema (dentistry)
Diastema is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars.-In humans:...
(gap) between the incisors and the cheekteeth (premolars and molars) is relatively deep. The mental foramen
Mental foramen
The mental foramen is one of two holes located on the anterior surface of the mandible. It permits passage of the mental nerve and vessels. The mental foramen descends slightly in edentulous individuals.- Variations :...
(an opening in the bone) is located relatively high and before the p4. The upper and lower masseteric ridges, which are located on the outer side of the jaw and anchor some of the chewing muscles, meet at the m1. The surfaces of the incisor are very flat, but there are small, irregular striations in the enamel
Tooth 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...
along the length of the tooth.
The cheekteeth increase regularly in size from front to back. They all consist of a large central basin surrounded by cusp
Cusp (dentistry)
A cusp is an occlusal or incisal eminence on a tooth.Canine teeth, otherwise known as cuspids, each possess a single cusp, while premolars, otherwise known as bicuspids, possess two each. Molars normally possess either four or five cusps...
s and crests. The basins are deeper than in Palaeosciurus and Ratufa obtusidens and lack crenulations in the enamel, which distinguishes them from another fossil squirrel, Albanensia. The first cheekteeth, p4, is large and about triangular in form, short and quite broad at the back. The two cusps at the front, the protoconid and metaconid, are isolated from each other. In front of the metaconid, there is a small cuspule, an anteroconid, at the lingual side of the tooth (the side of the tongue). The central basin of the tooth is relatively deep. At the back of the tooth, the entoconid cusp is connected to the posterolophid, a crest that forms the back margin. Of the two roots, the one at the front is round and the one at the back is broad.
Although m1 is nearly rectangular, the width at the front is still smaller than the width at the back. There is a strong anteroconid. A crest, the metalophid, reaches from the protoconid nearly to the metaconid. A small cusp, the mesostylid, is connected to the metaconid in front of it, unlike in Miopetaurista and Aliveria. There are two broad roots. The next tooth, m2, is similar to m1 in most respects, but the width at the front is virtually equal to the width at the back, so that the tooth is about rectangular. The back of m3 is rounded, but the tooth is still nearly rectangular. There is a long anteroconid, with is mainly connected to the metaconid. There is no metalophid. This tooth has three roots: two at the front and a larger one at the back.
Range and context
The remains of Lagrivea were probably collected by Viret at the site La Grive L5 in the village of Saint-Alban-de-RocheSaint-Alban-de-Roche
Saint-Alban-de-Roche is a commune in the Isère department in south-eastern France.-References:*...
, department of Isère
Isère
Isère is a department in the Rhône-Alpes region in the east of France named after the river Isère.- History :Isère is one of the original 83 departments created during the French Revolution on March 4, 1790. It was created from part of the former province of Dauphiné...
, southeastern France. La Grive L5 is one of several fissure filling sites in the area, collectively known as La Grive-Saint-Alban, which have yielded rich fossil faunas. Another site, La Grive M, is the reference locality for the MN zone
MN zonation
The MN zonation is a system used to correlate mammal-bearing fossil localities in the Miocene and Pliocene of Europe. It consists of sixteen consecutive zones defined through reference faunas, well-known sites that other localities can be correlated with.The zones are as follows:*MN 1*MN 2*MN 3*MN...
MN 7/8, about 13 to 11 million years ago. La Grive L5 is one of the younger sites of La Grive, and Mein and Ginsburg proposed placing it in a separate zone MN 8. Other squirrels at La Grive-Saint-Alban include species of Heteroxerus, Spermophilinus, Palaeosciurus, and chipmunk
Chipmunk
Chipmunks are small striped squirrels native to North America and Asia. They are usually classed either as a single genus with three subgenera, or as three genera.-Etymology and taxonomy:...
s, and flying squirrel
Flying squirrel
Flying squirrels, scientifically known as Pteromyini or Petauristini, are a tribe of 44 species of squirrels .- Description :...
s in the genera Albanensia, Miopetaurista, Forsythia, Hylopetes
Hylopetes
Hylopetes is a genus of flying squirrels.-Species:*Particolored Flying Squirrel Hylopetes alboniger *Afghan Flying Squirrel Hylopetes baberi *Bartel's Flying Squirrel Hylopetes bartelsi Chasen, 1939...
, and Blackia. Miopetaurista neogrivensis, Spermophilinus bredai, and Heteroxerus huerzeleri are also known from La Grive L5.
Literature cited
- McKenna, M.C. and Bell, S.K. 1997. Classification of Mammals: Above the species level. New York: Columbia University Press, 631 pp. ISBN 978-0-231-11013-6
- Mein, P. and Ginsburg, L. 2002. Sur l'âge relatif des différents karstiques miocènes de La Grive-Saint-Alban (Isère). Cahiers scientifiques, Muséum d'Histoire naturelle, Lyon 2:7–47 (in French).
- Steininger, F. 1999. Chronostratigraphy, geochronology and biochronology of the Miocene "European Land Mammal Mega-Zones (ELMMZ)" and the Miocene "Mammal Zones (MN-Zones)". Pp. 9–24 in Rössner, G.E. and Heissig, K. (eds.). The Miocene Land Mammals of Europe. Munich: Verlag Dr. Friedrich Pfeil, 515 pp.