UA 8699
Encyclopedia
UA 8699 is a fossil mammal
ian tooth from the Cretaceous
of Madagascar
. A broken lower molar
about 3.5 mm (0.14 in) long, it is from the Maastrichtian
of the Maevarano Formation
in northwestern Madagascar. Details of its crown morphology indicate that it is a boreosphenidan, a member of the group that includes living marsupial
s and placentals. Krause, who first described the tooth in 2001, interpreted it as a marsupial on the basis of five shared characters, but in 2003 Averianov and others noted that all those are shared by zhelestid placentals and favored a close relationship between UA 8699 and the Spanish zhelestid Lainodon. Krause used the tooth as evidence that marsupials were present on the southern continents (Gondwana
) as early as the late Cretaceous and Averianov and colleagues proposed that the tooth represented another example of faunal exchange between Africa and Europe at the time.
(UA) and placed in the collections of the latter as specimen 8699. It was found at a locality named MAD93-95 in the Anembalemba Member of the Maevarano Formation
, which is Maastrichtian
(latest Cretaceous
) in age. The locality is in the Mahajanga Basin of northwestern Madagascar. Several other mammals have been recovered from similarly aged Madagascar deposits, but most are also known from very limited material. These include the gondwanathere
Lavanify
, an indeterminate multituberculate, and a few other indeterminate teeth, as well as a nearly complete skeleton representing an otherwise unknown mammalian lineage. In a 2001 Nature
paper, David Krause announced the discovery of UA 8699 and argued for marsupial
affinities of the specimen. Because the specimen is so fragmentary, he refrained from assigning a new scientific name to the tooth. Two years later, Alexander Averianov, David Archibald, and Thomas Martin favored a placental interpretation in a paper in Acta Palaeontologica Polonica
, noting that the specimen was essentially similar to the zhelestid Lainodon. In a 2006 review of some of the Cretaceous vertebrates of Madagascar, Krause and colleagues continued to consider the specimen as a marsupial and announced that an upcoming paper by Case would make the case for marsupial affinities more fully.
(the proposed clade
uniting monotreme
s and some ancient Gondwana
n mammals, including the Jurassic
Madagascan Ambondro
); thus, it can be identified as representing Boreosphenida, which includes marsupials, placentals, and their extinct relatives.
Krause listed five features that indicate that UA 8699 is a marsupial, not a placental or primitive theria
n. There is a well-developed cingulid at the outer back margin (distobuccally), between the hypoconid (one of the main cusps) and the hypoconulid (a smaller cuspule). The hypoconulid itself is located far lingually, relatively far from the hypoconid. The trigonid and talonid are about as broad, the trigonid is low-crowned, and wear is mainly horizontal, resulting in broad, flat exposed wear facets. Averianov and colleagues noted that zhelestids, a placental group, share all those traits, though to varying degrees, and that the hypoconulid in similarly aged marsupials is even more lingually located, "twinned" to the entoconid (the cusp on the back lingual corner of the tooth). They wrote that the specimen is on the whole more similar to zhelestids than to marsupials.
of any part of Gondwana. Marsupials date back to the Eocene
in Australia and Africa and to the Paleocene
in South America; although Cretaceous marsupials have been recorded there, none of the records are unambiguous. Marsupials were certainly present in the Northern Hemisphere during the late Cretaceous. He interpreted UA 8699 as evidence that marsupials must already have colonized the southern continents by the late Cretaceous, presumably having reached Madagascar through South America and Antarctica. By the late Cretaceous, boreosphenidans must already have been in the process of replacing archaic mammals like gondwanatheres on the southern continents, as suggested by the presence of Deccanolestes
, a placental, in the Cretaceous of India.
Averianov, Archibald, and Martin instead placed UA 8699 in the context of faunal similarity and exchange between the late Cretaceous faunas of Europe and Africa, noting the presence of similar animals, such as snakes (Medtsoia) and sauropods (Lirainosaurus
and Repetosaurus), in the Cretaceous faunas of Madagascar and the Spanish locality Laño
. They proposed the relationship between Lainodon, which is from Laño, and UA 8699 as another example of this relationship and cited a previous prediction by Gheerbrant and Astibia that zhelestids similar to Lainodon would be found in Africa.
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
ian tooth from the Cretaceous
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 Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
. A broken lower 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"....
about 3.5 mm (0.14 in) long, it is from the 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...
of the Maevarano Formation
Maevarano Formation
The Maevarano Formation is an Upper Cretaceous sedimentary rock formation found in the Mahajanga Province of northwestern Madagascar. It is most likely Maastrichtian in age, and records a seasonal, semiarid environment with rivers that had greatly varying discharges...
in northwestern Madagascar. Details of its crown morphology indicate that it is a boreosphenidan, a member of the group that includes living marsupial
Marsupial
Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
s and placentals. Krause, who first described the tooth in 2001, interpreted it as a marsupial on the basis of five shared characters, but in 2003 Averianov and others noted that all those are shared by zhelestid placentals and favored a close relationship between UA 8699 and the Spanish zhelestid Lainodon. Krause used the tooth as evidence that marsupials were present on 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,...
) as early as the late Cretaceous and Averianov and colleagues proposed that the tooth represented another example of faunal exchange between Africa and Europe at the time.
Discovery and context
UA 8699 was discovered in a joint study by Stony Brook University and the University of AntananarivoUniversity of Antananarivo
University of Antananarivo is the primary public university of Madagascar, located in the capital Antananarivo.The school traces its founding to 16 December 1955 and the formation of the Institute for Advanced Studies in Antananarivo. It quickly established itself as the main center for higher...
(UA) and placed in the collections of the latter as specimen 8699. It was found at a locality named MAD93-95 in the Anembalemba Member of the Maevarano Formation
Maevarano Formation
The Maevarano Formation is an Upper Cretaceous sedimentary rock formation found in the Mahajanga Province of northwestern Madagascar. It is most likely Maastrichtian in age, and records a seasonal, semiarid environment with rivers that had greatly varying discharges...
, which is 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
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...
) in age. The locality is in the Mahajanga Basin of northwestern Madagascar. Several other mammals have been recovered from similarly aged Madagascar deposits, but most are also known from very limited material. These include the gondwanathere
Gondwanatheria
Gondwanatheria is an extinct group of mammals that lived during the Upper Cretaceous through the Eocene in the Southern Hemisphere, including Antarctica...
Lavanify
Lavanify
Lavanify is a mammalian genus from the late Cretaceous of Madagascar. The only species, L. miolaka, is known from two isolated teeth, one of which is damaged. The teeth were collected in 1995–1996 and described in 1997...
, an indeterminate multituberculate, and a few other indeterminate teeth, as well as a nearly complete skeleton representing an otherwise unknown mammalian lineage. In a 2001 Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...
paper, David Krause announced the discovery of UA 8699 and argued for marsupial
Marsupial
Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
affinities of the specimen. Because the specimen is so fragmentary, he refrained from assigning a new scientific name to the tooth. Two years later, Alexander Averianov, David Archibald, and Thomas Martin favored a placental interpretation in a paper in Acta Palaeontologica Polonica
Acta Palaeontologica Polonica
Acta Palaeontologica Polonica is a peer-reviewed open access journal of paleontology and paleobiology, founded by Roman Kozłowski in 1956. It is published by the Institute of Paleobiology of the Polish Academy of Sciences and edited by Richard L...
, noting that the specimen was essentially similar to the zhelestid Lainodon. In a 2006 review of some of the Cretaceous vertebrates of Madagascar, Krause and colleagues continued to consider the specimen as a marsupial and announced that an upcoming paper by Case would make the case for marsupial affinities more fully.
Description
UA 8699 is a worn and broken left lower molar. Part of the trigonid (the front group of cusps), at the mesiolingual (inner front) corner of the tooth is missing. Krause estimated that the complete tooth would have been 3.5 mm (0.14 in) long and 2.2 mm (0.09 in) wide. The tooth is tribosphenic, like that of modern mammals, as indicated by a number of features, including the broad basin of the talonid (the back group of cusps), and the acute angle (48°) between the cusps of the trigonid. UA 8699 lacks a cingulid (ridge) resembling a shelf on the lingual (inner) side, indicating that is not a member of AustralosphenidaAustralosphenida
The Australosphenida are a clade of mammals. Today, living specimens exist only in Australia and New Guinea with only five surviving species, but fossils have been found in Madagascar and Argentina...
(the proposed 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...
uniting monotreme
Monotreme
Monotremes are mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals...
s and some ancient 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 mammals, including the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
Madagascan Ambondro
Ambondro (genus)
Ambondro is a genus of mammal from the middle Jurassic of Madagascar. The single species, A. mahabo, is known from a fragmentary lower jaw with three teeth, interpreted as the last premolar and the first two molars...
); thus, it can be identified as representing Boreosphenida, which includes marsupials, placentals, and their extinct relatives.
Krause listed five features that indicate that UA 8699 is a marsupial, not a placental or primitive theria
Theria
Theria is a subclass of mammals that give birth to live young without using a shelled egg, including both eutherians and metatherians . The only omitted extant mammal group is the egg-laying monotremes....
n. There is a well-developed cingulid at the outer back margin (distobuccally), between the hypoconid (one of the main cusps) and the hypoconulid (a smaller cuspule). The hypoconulid itself is located far lingually, relatively far from the hypoconid. The trigonid and talonid are about as broad, the trigonid is low-crowned, and wear is mainly horizontal, resulting in broad, flat exposed wear facets. Averianov and colleagues noted that zhelestids, a placental group, share all those traits, though to varying degrees, and that the hypoconulid in similarly aged marsupials is even more lingually located, "twinned" to the entoconid (the cusp on the back lingual corner of the tooth). They wrote that the specimen is on the whole more similar to zhelestids than to marsupials.
Interpretations
Krause wrote that UA 8699 was the first marsupial to be identified from Madagascar and the first from the MesozoicMesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
of any part of Gondwana. Marsupials date back to the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
in Australia and Africa and to the Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
in South America; although Cretaceous marsupials have been recorded there, none of the records are unambiguous. Marsupials were certainly present in the Northern Hemisphere during the late Cretaceous. He interpreted UA 8699 as evidence that marsupials must already have colonized the southern continents by the late Cretaceous, presumably having reached Madagascar through South America and Antarctica. By the late Cretaceous, boreosphenidans must already have been in the process of replacing archaic mammals like gondwanatheres on the southern continents, as suggested by the presence of Deccanolestes
Deccanolestes
Deccanolestes is a scansorial, basal Euarchontan from the Late Cretaceous Intertrappean Beds of Andhra Pradesh, India. It may be closely related to Sahnitherium...
, a placental, in the Cretaceous of India.
Averianov, Archibald, and Martin instead placed UA 8699 in the context of faunal similarity and exchange between the late Cretaceous faunas of Europe and Africa, noting the presence of similar animals, such as snakes (Medtsoia) and sauropods (Lirainosaurus
Lirainosaurus
Lirainosaurus is the name given to a genus of dinosaur from the Late Cretaceous. It was a titanosaurid sauropod which lived in what is now Spain. The type species, Lirainosaurus astibiae, was described by Sanz, Powell, Le Loeuff, Martinez, and Pereda-Suberbiola in 1999.-References:J. L. Sanz, J. E....
and Repetosaurus), in the Cretaceous faunas of Madagascar and the Spanish locality Laño
Lano
Lano is a leading brand of soap in Norway. It comes in varieties of shower gels and liquid hand wash as well as the original soap bar. Lano is produced by Lilleborg Commodities, a hygiene product manufacturer owned in turn by the Orkla Group.-History:...
. They proposed the relationship between Lainodon, which is from Laño, and UA 8699 as another example of this relationship and cited a previous prediction by Gheerbrant and Astibia that zhelestids similar to Lainodon would be found in Africa.
Literature cited
- Averianov, A.O., Archibald, J.D. and Martin, T. 2003. Placental nature of the alleged marsupial from the Cretaceous of Madagascar. Acta Palaeontologica Polonica 48(1):149–151.
- Krause, D.W. 2001. Fossil molar from a Madagascar marsupial (subscription required). Nature 412:497–498.
- Krause, D.W., O'Connor, P.M., Rogers, K.C., Sampson, S.D., Buckley, G.A. and Rogers, R.R. 2006. Late Cretaceous terrestrial vertebrates from Madagascar: Implications for Latin American biogeography (subscription required). Annals of the Missouri Botanical Garden 93(2):178–208.