Argentodites
Encyclopedia
Argentodites is a possible multituberculate mammal from the Cretaceous
of Argentina. The single species, Argentodites coloniensis, is known from a single blade-like fourth lower premolar
(p4) from the La Colonia Formation
, which is mostly or entirely Maastrichtian
(latest Cretaceous) in age. The p4 is 4.15 mm long and bears eight cusps on its upper margin and long associated ridges on both sides. The enamel
consists of prisms that are completely or partly surrounded by a sheath and that are on average 6.57 μm
apart. Zofia Kielan-Jaworowska
, who described and named the fossil in 2007, regarded it as a multituberculate, perhaps a cimolodonta
n—and thus, a member of a mostly Laurasia
n (northern) group and an immigrant to Argentina from North America—on the basis of the shape of the tooth and features of its enamel. In 2009, however, two teams argued that Argentodites may in fact be close to or identical with Ferugliotherium
, a member of the small Gondwana
n (southern) group Gondwanatheria
; although their relationships are disputed, gondwanatheres may themselves be multituberculates.
tooth, MPEF 604, in the collections of the Museo Paleontológico "Egidio Feruglio" in Trelew
, Argentina. It is from the middle part of the La Colonia Formation
of Chubut Province
, Argentina, which is Late Cretaceous
(Maastrichtian
and perhaps partly Campanian
) in age. The premolar was described in 2007 by Zofia Kielan-Jaworowska
and colleagues as a new genus
and species
, Argentodites coloniensis. The generic name, Argentodites, combines "Argentina" with the Ancient Greek
hodites "traveler", in reference to the animal's presumed migration from North America to Argentina, and the specific name, coloniensis, refers to the La Colonia Formation.
The single known example of Argentodites is a blade-like fourth lower premolar (p4). It has a length of 4.15 mm, height of 2.10 mm, and width of 1.35 mm. The crown is nearly complete, but the roots are largely missing. Kielan-Jaworowska considered two possible orientations of the tooth—one with the back margin nearly vertically, and the other with the margin inclined backwards—but preferred the former, which made for a more natural placement of the roots. Although the left and right sides of the tooth are almost identical, they believed the tooth is most likely a left p4, as this would make the lingual (inner) side the more convex one, as is usual in the p4 of cimolodonta
n multituberculates with a large p4.
The front root is larger than the back one. In side view, the upper and back margins are straight, but the front margin is convex. There are eight cusps arranged in a row on the upper margin, the first of which is located about one third of the tooth's length from the front margin. Only the last is slightly worn, indicating that the tooth is from a young animal. Long ridges extend from the cusps diagonally toward the front on both the lingual and labial (outer) sides of the tooth. The first seven ridges on both sides are connected to the respective cusps, but the eighth ridges do not quite reach their cusp. On both sides of the tooth, there is also a small ridge behind the eighth ridge that extends to the back margin; these ridges are called the posterolabial and posterolingual ridge. An even smaller ridge is located below the ridge on the lingual side.
The tooth enamel
is well-preserved over most of the tooth. It consists of prisms—bundles of hydroxyapatite crystalls—with an average diameter of 3.8 μm
. Most are entirely surrounded by a sheath, but in some the sheath is open. The prisms are slightly curved toward the outer surface of the tooth. Between the prisms, and oriented at an angle of about 45° to them, are crystals of interprismatic material. On average, the prisms are 6.57 μm apart, so that there are about 27,247 per mm2.
) that is also known from a few questionable or fragmentary records from the southern continents (Gondwana
). They tentatively allocated it to the multituberculate subgroup Cimolodonta on the basis of its enamel microstructure, which particularly recalls Ptilodontoidea
(one of the subgroups of Cimolodonta), and the convex front margin of the tooth. On the other hand, the straight back margin resembles the condition in the other major subgroup of multituberculates, the "plagiaulacida
ns", and it does not have the highly vaulted upper margin of p4 that is characteristic of Ptilodontoidea. They regarded Argentodites as distinct from MACN-RN 975, a fragmentary fossil mandible
(lower jaw) with p4 from the Late Cretaceous Los Alamitos Formation
of Argentina, which they identified as a "plagiaulacidan" multituberculate, because the p4 of MACN-RN 975 is rectangular in shape and has fewer cusps. They believed Argentodites to represent an immigrant from North America, but could not determine precisely in which part of the Cretaceous it reached South America.
In a 2009 paper on the affinities of Gondwanatheria, Yamila Gurovich and Robin Beck argue that the difference in shape between MACN-RN 975 and Argentodites is due to extensive wear on the former specimen; they write that the parts of the p4 that are not worn are virtually identical to the equivalents parts of the Argentodites p4. In addition, MACN-RN 975 is said to have as many ridges as Argentodites and to be of approximately similar size—about 15% larger. They allocate MACN-RN 975 to the gondwanathere Ferugliotherium
and consequently, they argue that Argentodites most likely represents either Ferugliotherium or some related species. In the same year, Guillermo Rougier and colleagues also suggested ferugliotherian affinities of Argentodites in a paper on the mammals of the Allen Formation
, another Cretaceous rock unit of Argentina. Ferugliotherium is a gondwanathere from Late Cretaceous Argentinean deposits. Gondwanatheres are a small and enigmatic group from the late Cretaceous and Paleogene
of South America, Antarctica, Madagascar, India, and perhaps Tanzania. Although the evolutionary affinities of gondwanatheres are controversial, both teams that identified Argentodites as gondwanathere believe gondwanatheres are likely themselves multituberculates or closely related to them.
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
of Argentina. The single species, Argentodites coloniensis, is known from a single blade-like 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) from the La Colonia Formation
La Colonia Formation
The La Colonia Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation....
, which is mostly or entirely Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
(latest Cretaceous) in age. The p4 is 4.15 mm long and bears eight cusps on its upper margin and long associated ridges on both sides. 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...
consists of prisms that are completely or partly surrounded by a sheath and that are on average 6.57 μm
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
apart. Zofia Kielan-Jaworowska
Zofia Kielan-Jaworowska
Zofia Kielan-Jaworowska is a Polish paleobiologist. In the mid-1960s Kielan-Jaworowska led a series of Polish-Mongolian paleontological expeditions to the Gobi Desert...
, who described and named the fossil in 2007, regarded it as a multituberculate, perhaps a cimolodonta
Cimolodonta
The Cimolodonta are a taxon of extinct mammals that lived from the Cretaceous to the Eocene. They were some of the more derived members of the extinct order Multituberculata. They probably lived something of a rodent-like existence until their ecological niche was assumed by true rodents...
n—and thus, a member of a mostly Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
n (northern) group and an immigrant to Argentina from North America—on the basis of the shape of the tooth and features of its enamel. In 2009, however, two teams argued that Argentodites may in fact be close to or identical with Ferugliotherium
Ferugliotherium
Ferugliotherium is a fossil mammal from the Campanian and/or Maastrichtian of Argentina in the family Ferugliotheriidae. The genus contains a single species, Ferugliotherium windhauseni, which was first described in 1986...
, a member of the small Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
n (southern) group Gondwanatheria
Gondwanatheria
Gondwanatheria is an extinct group of mammals that lived during the Upper Cretaceous through the Eocene in the Southern Hemisphere, including Antarctica...
; although their relationships are disputed, gondwanatheres may themselves be multituberculates.
Discovery and context
Argentodites is known from a single premolarPremolar
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...
tooth, MPEF 604, in the collections of the Museo Paleontológico "Egidio Feruglio" in Trelew
Trelew
-References:La Pasión según Trelew, Espejo de la Argentina, 1997, Editorial Planeta Argentina S.A.I.C.; Third Edition: April 2000, Buenos Aires, ISBN 950-742-859-3-External links:* * * *...
, Argentina. It is from the middle part of the La Colonia Formation
La Colonia Formation
The La Colonia Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation....
of Chubut Province
Chubut Province
Chubut a province in the southern part of Argentina situated between the 42nd parallel south and the 46th parallel south , the Andes range separating Argentina from Chile, and the Atlantic ocean...
, Argentina, which is Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
(Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
and perhaps partly Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
) in age. The premolar was described in 2007 by Zofia Kielan-Jaworowska
Zofia Kielan-Jaworowska
Zofia Kielan-Jaworowska is a Polish paleobiologist. In the mid-1960s Kielan-Jaworowska led a series of Polish-Mongolian paleontological expeditions to the Gobi Desert...
and colleagues as a new 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...
and 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...
, Argentodites coloniensis. The generic name, Argentodites, combines "Argentina" with the Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
hodites "traveler", in reference to the animal's presumed migration from North America to Argentina, and the specific name, coloniensis, refers to the La Colonia Formation.
Description
Cimolodonta
The Cimolodonta are a taxon of extinct mammals that lived from the Cretaceous to the Eocene. They were some of the more derived members of the extinct order Multituberculata. They probably lived something of a rodent-like existence until their ecological niche was assumed by true rodents...
n multituberculates with a large p4.
The front root is larger than the back one. In side view, the upper and back margins are straight, but the front margin is convex. There are eight cusps arranged in a row on the upper margin, the first of which is located about one third of the tooth's length from the front margin. Only the last is slightly worn, indicating that the tooth is from a young animal. Long ridges extend from the cusps diagonally toward the front on both the lingual and labial (outer) sides of the tooth. The first seven ridges on both sides are connected to the respective cusps, but the eighth ridges do not quite reach their cusp. On both sides of the tooth, there is also a small ridge behind the eighth ridge that extends to the back margin; these ridges are called the posterolabial and posterolingual ridge. An even smaller ridge is located below the ridge on the lingual side.
The tooth 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...
is well-preserved over most of the tooth. It consists of prisms—bundles of hydroxyapatite crystalls—with an average diameter of 3.8 μm
Micrometer
A micrometer , sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier,...
. Most are entirely surrounded by a sheath, but in some the sheath is open. The prisms are slightly curved toward the outer surface of the tooth. Between the prisms, and oriented at an angle of about 45° to them, are crystals of interprismatic material. On average, the prisms are 6.57 μm apart, so that there are about 27,247 per mm2.
Identity
Kielan-Jaworowska and colleagues identified Argentodites as a multituberculate, a diverse fossil group from the northern continents (LaurasiaLaurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
) that is also known from a few questionable or fragmentary records from the southern continents (Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
). They tentatively allocated it to the multituberculate subgroup Cimolodonta on the basis of its enamel microstructure, which particularly recalls Ptilodontoidea
Ptilodontoidea
Ptilodontoidea is a group of extinct mammals from the Northern Hemisphere.They were generally small, somewhat rodent-like creatures of the extinct order Multituberculata.Some of these genera boast a great many species, though remains are generally sparse....
(one of the subgroups of Cimolodonta), and the convex front margin of the tooth. On the other hand, the straight back margin resembles the condition in the other major subgroup of multituberculates, the "plagiaulacida
Plagiaulacida
Plagiaulacida is a group of extinct multituberculate mammals. Multituberculates were among the most common mammals of the Mesozoic, "the age of the dinosaurs"...
ns", and it does not have the highly vaulted upper margin of p4 that is characteristic of Ptilodontoidea. They regarded Argentodites as distinct from MACN-RN 975, a fragmentary fossil mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
(lower jaw) with p4 from the Late Cretaceous Los Alamitos Formation
Los Alamitos Formation
The Los Alamitos Formation is a geological formation in Rio Negro, Argentina whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.-Dinosaurs:-Mammaliaforms:-References:...
of Argentina, which they identified as a "plagiaulacidan" multituberculate, because the p4 of MACN-RN 975 is rectangular in shape and has fewer cusps. They believed Argentodites to represent an immigrant from North America, but could not determine precisely in which part of the Cretaceous it reached South America.
In a 2009 paper on the affinities of Gondwanatheria, Yamila Gurovich and Robin Beck argue that the difference in shape between MACN-RN 975 and Argentodites is due to extensive wear on the former specimen; they write that the parts of the p4 that are not worn are virtually identical to the equivalents parts of the Argentodites p4. In addition, MACN-RN 975 is said to have as many ridges as Argentodites and to be of approximately similar size—about 15% larger. They allocate MACN-RN 975 to the gondwanathere Ferugliotherium
Ferugliotherium
Ferugliotherium is a fossil mammal from the Campanian and/or Maastrichtian of Argentina in the family Ferugliotheriidae. The genus contains a single species, Ferugliotherium windhauseni, which was first described in 1986...
and consequently, they argue that Argentodites most likely represents either Ferugliotherium or some related species. In the same year, Guillermo Rougier and colleagues also suggested ferugliotherian affinities of Argentodites in a paper on the mammals of the Allen Formation
Allen Formation
The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous The Allen Formation is a geological formation in Argentina whose strata date back to the...
, another Cretaceous rock unit of Argentina. Ferugliotherium is a gondwanathere from Late Cretaceous Argentinean deposits. Gondwanatheres are a small and enigmatic group from the late Cretaceous and Paleogene
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...
of South America, Antarctica, Madagascar, India, and perhaps Tanzania. Although the evolutionary affinities of gondwanatheres are controversial, both teams that identified Argentodites as gondwanathere believe gondwanatheres are likely themselves multituberculates or closely related to them.
Literature cited
- Gurovich, Y. and Beck, R. 2009. The phylogenetic affinities of the enigmatic mammalian clade Gondwanatheria (subscription required). Journal of Mammalian Evolution 16:25–49.
- 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).
- Kielan-Jaworowska, Z., Ortiz-Jaureguizar, E., Vieytes, C., Pascual, R. and Goin, F.J. 2007. First ?cimolodontan multituberculate mammal from South America. Acta Palaeontologica Polonica 52(2):257–262.
- Rich, T.H., Vickers-Rich, P., Flannery, T.F., Kear, B.P., Cantrill, D.J., Komarower, P., Kool, L., Pickering, D., Trusler, P., Morton, S., Klaveren, N. van and Fitzgerald E.M.G. 2009. An Australian multituberculate and its palaeobiogeographic implications. Acta Palaeolontologica Polonica 54(1):1–6.
- Rougier, G.W., Chornogubsky, L., Casadio, S., Paéz Arango, N. and Giallombardo, A. 2009. Mammals from the Allen Formation, Late Cretaceous, Argentina (subscription required). Cretaceous Research 30:233–238.