Mesozoic mammals of Madagascar
Encyclopedia
Several mammal
s are known from the Mesozoic
of Madagascar
. The Bathonian
(middle Jurassic
) Ambondro
, known from a piece of jaw with three teeth, is the earliest known mammal with molars
showing the modern, tribosphenic pattern that is characteristic of marsupial
and placental mammals. Interpretations of its affinities have differed; one proposal places it in a group known as Australosphenida
with other Mesozoic tribosphenic mammals from the southern continents (Gondwana
) as well as the monotreme
s, while others favor closer affinities with northern (Laurasia
n) tribosphenic mammals or specifically with placentals. At least five species are known from the Maastrichtian
(late Cretaceous
), including a yet undescribed species known from a nearly complete skeleton that may represent a completely new group of mammals. The gondwanathere Lavanify
, known from two teeth, is most closely related to other gondwanatheres found in India and Argentina. Two other teeth may represent another gondwanathere or a different kind of mammal. One molar
fragment is one of the few known remains of a multituberculate mammal from Gondwana and another (UA 8699
) has been interpreted as either a marsupial or a placental.
(Bathonian
, about 167 million years ago) of northwestern Madagascar in 1999. It is known from a single lower jaw fragment with three teeth, probably the last premolar
and first two molars
. The molars have been interpreted as showing the tribosphenic pattern that is characteristic of modern mammals; Ambondro is the oldest known mammal with such a pattern. This led its discoverers to propose that the ancestors of tribosphenic mammals arose in the south (Gondwana
), not, as generally assumed, in the north (Laurasia
). In 2001, however, paleontologist Zhe-Xi Luo and colleagues alternatively proposed that Ambondro was part of a clade
with Ausktribosphenos
from the Cretaceous of Australia and the monotreme
s that developed tribosphenicity independently from other mammals (Boreosphenida). This clade, dubbed Australosphenida
, has since been expanded with more recently discovered species from Argentina (Asfaltomylos
and Henosferus
) and Australia (Bishops). Other paleontologists have disagreed with this interpretation and proposed different models; for example, in 2001 Denise Sigogneau-Russell and colleagues proposed that although Ausktribosphenos and monotremes were related, Ambondro was not and was in fact more similar to boreosphenidans, and in 2003 Michael Woodburne and colleagues excluded monotremes from Australosphenida and placed the remaining australosphenidans close to placentals. The deposits that produced Ambondro have yielded some reptiles, but no other mammals.
fauna, including various dinosaur
s and crocodyliforms as well as mammals, found by the team of David Krause since 1993. Many of these taxa show affinities with similarly aged South American and Indian animals, also parts of Gondwana. The mammalian fauna consists of several taxa known only by isolated teeth and a single reasonably complete skeleton, none of which can be plausibly related to the Recent Madagascar fauna (see list of mammals of Madagascar). The fossils come from the Maastrichtian
(latest Cretaceous) of the Anembalembo Member of the Maevarano Formation
.
Two teeth, one complete and one damaged, form the known material of the gondwanathere Lavanify
, first described in 1997. The teeth are high-crowned and curved; one contains a deep cementum
-filled furrow and the other at least one deep pit (infundibulum). Lavanify appears to be most closely related to the Indian gondwanathere Bharattherium
and more distantly to the other gondwanatheres, which are known from Argentina. Two other teeth, not yet fully described, may represent different tooth positions of another gondwanathere. One, a fragmentary molariform (molar or molar-like premolar—the identities of gondwanathere tooth are poorly understood) is larger and lower-crowned than the Lavanify teeth and the other, which is complete and unworn, is yet lower-crowned and has the surface obliquely oriented. Its crown consists of a W-shaped ridge with the parts separated by deep infundibula. This second tooth may also represent a completely different, yet unknown mammalian group.
A fragmentary molar, preserving two cusps, is identified as from a multituberculate. Although multituberculates are common in nearly contemporaneous deposits in Laurasia, this tooth is one of the few records from Gondwana; a few fragmentary remains, the multituberculate affinities of some of which are disputed, are also known from South America (Argentodites
), Africa (Hahnodon
), and Australia (Corriebaatar
). Another fragmentary tooth, UA 8699
, is recognizable as a tribosphenic lower molar. Krause identified it in 2001 as a marsupial, but in 2003 a group led by Alexander Averianov instead argued that the tooth was placental and related to zhelestids (a primitive group possibly related to ungulate
s). Both placentals and marsupials are mostly known from Laurasia during the Cretaceous.
In addition to these fragmentary teeth, the Maevarano Formation has also yielded a nearly complete, articulated skeleton of an immature, cat-sized mammal that has not yet been fully described. It is the most complete mammal known from the Mesozoic of Gondwana. Its skull is damaged, but its unusual dentition is preserved. The incisor
s (two on each side of the upper and one on each side of the lower jaw) project forwards and are separated from the three or four cheektooth in each side of the lower and upper jaws by a large diastema
(gap). It shows primitive features, such as the presence of epipubic bones (in the pelvis
), a septomaxilla (a small bone placed between the premaxilla
and the maxilla
in the upper jaw), and a deep zygomatic arch
(cheekbone). On the other hand, it has derived
traits like the presence of a well-developed trochlea
on the distal (far) end of the humerus
(upper arm bone), the absence of a rim at the dorsal (upper) margin of the acetabulum
(the opening in the pelvis which receives the head of the femur), a small lesser trochanter
of the femur
(upper leg bone), reduced contact between the fibula (the smaller of the two lower leg bones) and the calcaneum (heel bone), and the dentition. In a 2000 abstract, Krause identified it as a theria
n (a member of the group that includes marsupials, placentals, and their closest extinct relatives) more derived than the early Cretaceous Vincelestes
of Argentina, but in 2006 he and colleagues instead refused to place it in any existing higher-order mammalian group and claimed that "it represents a major new nontherian clade".
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...
s are known from the Mesozoic
Mesozoic
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 Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
. The Bathonian
Bathonian
In the geologic timescale the Bathonian is an age or stage of the Middle Jurassic. It lasted from approximately 167.7 Ma to around 164.7 Ma...
(middle Jurassic
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
) 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...
, known from a piece of jaw with three teeth, is the earliest known mammal with 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"....
showing the modern, tribosphenic pattern that is characteristic of 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...
and placental mammals. Interpretations of its affinities have differed; one proposal places it in a group known as Australosphenida
Australosphenida
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...
with other Mesozoic tribosphenic mammals 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,...
) as well as the monotreme
Monotreme
Monotremes are mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals...
s, while others favor closer affinities with northern (Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
n) tribosphenic mammals or specifically with placentals. At least five species are known 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...
(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...
), including a yet undescribed species known from a nearly complete skeleton that may represent a completely new group of mammals. The gondwanathere 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...
, known from two teeth, is most closely related to other gondwanatheres found in India and Argentina. Two other teeth may represent another gondwanathere or a different kind of mammal. One 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"....
fragment is one of the few known remains of a multituberculate mammal from Gondwana and another (UA 8699
UA 8699
UA 8699 is a fossil mammalian tooth from the Cretaceous of Madagascar. A broken lower molar about 3.5 mm long, it is from the Maastrichtian of the Maevarano Formation in northwestern Madagascar...
) has been interpreted as either a marsupial or a placental.
Jurassic
Ambondro mahabo was described from the middle JurassicMiddle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
(Bathonian
Bathonian
In the geologic timescale the Bathonian is an age or stage of the Middle Jurassic. It lasted from approximately 167.7 Ma to around 164.7 Ma...
, about 167 million years ago) of northwestern Madagascar in 1999. It is known from a single lower jaw fragment with three teeth, probably the last 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...
and first two 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"....
. The molars have been interpreted as showing the tribosphenic pattern that is characteristic of modern mammals; Ambondro is the oldest known mammal with such a pattern. This led its discoverers to propose that the ancestors of tribosphenic mammals arose in the south (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,...
), not, as generally assumed, in the north (Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
). In 2001, however, paleontologist Zhe-Xi Luo and colleagues alternatively proposed that Ambondro was part of 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...
with Ausktribosphenos
Ausktribosphenos
Ausktribosphenos is an extinct genus of Australosphenida from Early Cretaceous of Australia. The only recorded species, Ausktribosphenos nyktos, was found on Flat Rocks, Victoria.-References:...
from the Cretaceous of Australia and the monotreme
Monotreme
Monotremes are mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals...
s that developed tribosphenicity independently from other mammals (Boreosphenida). This clade, dubbed Australosphenida
Australosphenida
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...
, has since been expanded with more recently discovered species from Argentina (Asfaltomylos
Asfaltomylos
Asfaltomylos is an extinct genus of Australosphenida from the middle Jurassic of Argentina. Only one species is recorded, Asfaltomylos patagonicus, from the Cañadon Asfalto Formation, Chubut Province, Patagonia.-References:...
and Henosferus
Henosferus
Henosferus is an extinct genus of Australosphenida from Middle Jurassic of Argentina. The only recorded species, Henosferus molus, was found on Cañadón Asfalto Formation, Chubut Province, Patagonia.-References:...
) and Australia (Bishops). Other paleontologists have disagreed with this interpretation and proposed different models; for example, in 2001 Denise Sigogneau-Russell and colleagues proposed that although Ausktribosphenos and monotremes were related, Ambondro was not and was in fact more similar to boreosphenidans, and in 2003 Michael Woodburne and colleagues excluded monotremes from Australosphenida and placed the remaining australosphenidans close to placentals. The deposits that produced Ambondro have yielded some reptiles, but no other mammals.
Cretaceous
The Mahajanga Basin of northwestern Madagascar has produced a rich late CretaceousLate 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...
fauna, including various dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s and crocodyliforms as well as mammals, found by the team of David Krause since 1993. Many of these taxa show affinities with similarly aged South American and Indian animals, also parts of Gondwana. The mammalian fauna consists of several taxa known only by isolated teeth and a single reasonably complete skeleton, none of which can be plausibly related to the Recent Madagascar fauna (see list of mammals of Madagascar). The fossils come 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...
(latest Cretaceous) of the Anembalembo 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...
.
Two teeth, one complete and one damaged, form the known material of the gondwanathere 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...
, first described in 1997. The teeth are high-crowned and curved; one contains a deep cementum
Cementum
Cementum is a specialized calcified substance covering the root of a tooth. Cementum is excreted by cells called cementoblasts within the root of the tooth and is thickest at the root apex. These cementoblasts develop from undifferentiated mesenchymal cells in the connective tissue of the dental...
-filled furrow and the other at least one deep pit (infundibulum). Lavanify appears to be most closely related to the Indian gondwanathere Bharattherium
Bharattherium
Bharattherium is a mammal that lived in India during the Maastrichtian . The genus has a single species, Bharattherium bonapartei. It is part of the gondwanathere family Sudamericidae, which is also found in Madagascar and South America during the latest Cretaceous...
and more distantly to the other gondwanatheres, which are known from Argentina. Two other teeth, not yet fully described, may represent different tooth positions of another gondwanathere. One, a fragmentary molariform (molar or molar-like premolar—the identities of gondwanathere tooth are poorly understood) is larger and lower-crowned than the Lavanify teeth and the other, which is complete and unworn, is yet lower-crowned and has the surface obliquely oriented. Its crown consists of a W-shaped ridge with the parts separated by deep infundibula. This second tooth may also represent a completely different, yet unknown mammalian group.
A fragmentary molar, preserving two cusps, is identified as from a multituberculate. Although multituberculates are common in nearly contemporaneous deposits in Laurasia, this tooth is one of the few records from Gondwana; a few fragmentary remains, the multituberculate affinities of some of which are disputed, are also known from South America (Argentodites
Argentodites
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 from the La Colonia Formation, which is mostly or entirely Maastrichtian in age...
), Africa (Hahnodon
Hahnodon
Hahnodon is a genus of extinct mammal of the Lower Cretaceous. It was a relatively early member of the also extinct order Multituberculata...
), and Australia (Corriebaatar
Corriebaatar
Corriebaatar is the type and only genus of Corriebaataridae, a family of multituberculate mammals. It contains the single species Corriebaatar marywaltersae and represents the first evidence of Australian multituberculates Fossils date back to the Aptian stage of the Early Cretaceous....
). Another fragmentary tooth, UA 8699
UA 8699
UA 8699 is a fossil mammalian tooth from the Cretaceous of Madagascar. A broken lower molar about 3.5 mm long, it is from the Maastrichtian of the Maevarano Formation in northwestern Madagascar...
, is recognizable as a tribosphenic lower molar. Krause identified it in 2001 as a marsupial, but in 2003 a group led by Alexander Averianov instead argued that the tooth was placental and related to zhelestids (a primitive group possibly related to ungulate
Ungulate
Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...
s). Both placentals and marsupials are mostly known from Laurasia during the Cretaceous.
In addition to these fragmentary teeth, the Maevarano Formation has also yielded a nearly complete, articulated skeleton of an immature, cat-sized mammal that has not yet been fully described. It is the most complete mammal known from the Mesozoic of Gondwana. Its skull is damaged, but its unusual dentition is preserved. The incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
s (two on each side of the upper and one on each side of the lower jaw) project forwards and are separated from the three or four cheektooth in each side of the lower and upper jaws by a large 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). It shows primitive features, such as the presence of epipubic bones (in the pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
), a septomaxilla (a small bone placed between 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....
and 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...
in the upper jaw), and a deep zygomatic arch
Zygomatic arch
The zygomatic arch or cheek bone is formed by the zygomatic process of temporal bone and the temporal process of the zygomatic bone , the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process...
(cheekbone). On the other hand, it has derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
traits like the presence of a well-developed trochlea
Trochlea of humerus
The medial portion of the articular surface of the humerus is named the trochlea, and presents a deep depression between two well-marked borders; it is convex from before backward, concave from side to side, and occupies the anterior, lower, and posterior parts of the extremity...
on the distal (far) end of the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
(upper arm bone), the absence of a rim at the dorsal (upper) margin of the acetabulum
Acetabulum
The acetabulum is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.-Structure:...
(the opening in the pelvis which receives the head of the femur), a small lesser trochanter
Lesser trochanter
The lesser trochanter of the femur is a conical eminence, which varies in size in different subjects-Anatomy:It projects from the lower and back part of the base of the femur neck.From its apex three well-marked borders extend:...
of the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
(upper leg bone), reduced contact between the fibula (the smaller of the two lower leg bones) and the calcaneum (heel bone), and the dentition. In a 2000 abstract, Krause identified it as a 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 (a member of the group that includes marsupials, placentals, and their closest extinct relatives) more derived than the early Cretaceous Vincelestes
Vincelestes
Vincelestes is an extinct genus of actively mobile mammal, that lived in what would be South America during the Early Cretaceous from 130—112 mya, existing for approximately ....
of Argentina, but in 2006 he and colleagues instead refused to place it in any existing higher-order mammalian group and claimed that "it represents a major new nontherian clade".
Literature cited
- Archibald, J.D. 2003. Timing and biogeography of the eutherian radiation: fossils and molecules compared (subscription required). Molecular Phylogenetics and Evolution 28:350–359.
- 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.
- Flynn, J.J., Parrish, J.M., Rakotosamimanana, B., Simpson, W.F. and Wyss, A.R. 1999. A Middle Jurassic mammal from Madagascar (subscription required). Nature 401:57–60.
- Krause, D.W. 2000. New mammalian specimens from the Late Cretaceous of Madagascar (subscription required). Journal of Vertebrate Paleontology 20:52A–53A.
- Krause, D.W. 2001. Fossil molar from a Madagascar marsupial (subscription required). Nature 412:497–498.
- Krause, D.W. 2003. Discovery of a relatively complete mammalian specimen from the Late Cretaceous of Madagascar (subscription required). Journal of Vertebrate Paleontology 23:69A.
- Krause, D.W. and Grine, F.E. 1996. The first multituberculates from Madagascar: Implications for Cretaceous biogeography (subscription required). Journal of Vertebrate Paleontology 16:46A.
- 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.
- Luo, Z.-X., Cifelli, R.L. and Kielan-Jaworowska, Z. 2001. Dual origin of tribosphenic mammals (subscription required). Nature 409:53–57.
- Luo, Z.-X., Kielan-Jaworowska, Z. and Cifelli, R.L. 2002. In quest for a phylogeny of Mesozoic mammals. Acta Palaeontologica Polonica 47(1):1–78.
- 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., Martinelli, A.G., Forasiepi, A.M. and Novacek, M.J. 2007. New Jurassic mammals from Patagonia, Argentina: A reappraisal of australosphenidan morphology and interrelationships. American Museum Novitates 3566:1–54.
- Sigogneau-Russell, D., Hooker, J.J. and Ensom, P.C. 2001. The oldest tribosphenic mammal from Laurasia (Purbeck Limestone Group, Berriasian, Cretaceous, UK) and its bearing on the 'dual origin' of Tribosphenida (subscription required). Comptes Rendus de l'Académie des Sciences, Series IIA (Earth and Planetary Science) 333(2):141–147.
- Woodburne, M.O. 2003. Monotremes as pretribosphenic mammals (subscription required). Journal of Mammalian Evolution 10(3):195–248.
- Woodburne, M.O., Rich, T.H. and Springer, M.S. 2003. The evolution of tribospheny and the antiquity of mammalian clades (subscription required). Molecular Phylogeny and Evolution 28:360–385.