''Morganucodon'' ("
Glamorgan
, HQ = Cardiff
, Government = Glamorgan County Council (1889–1974)
, Origin=
, Code = GLA
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* West Glamorgan
* Mid Glamorgan
* South Glamorgan
, Motto ...
tooth") is an early
mammaliaform genus that lived from the
Late Triassic to the
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...
. It first appeared about 205 million years ago. Unlike many other early mammaliaforms, ''Morganucodon'' is well represented by abundant and well preserved (though in the vast majority of cases disarticulated) material. Most of this comes from
Glamorgan
, HQ = Cardiff
, Government = Glamorgan County Council (1889–1974)
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, Code = GLA
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* West Glamorgan
* Mid Glamorgan
* South Glamorgan
, Motto ...
in
Wales (''Morganucodon watsoni''), but fossils have also been found in
Yunnan Province in
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
(''Morganucodon oehleri'') and various parts of Europe and North America. Some closely related animals (''
Megazostrodon'') are known from exquisite fossils from
South Africa.
The name comes from a Latinization of ''Morganuc'', the name for South
Glamorgan
, HQ = Cardiff
, Government = Glamorgan County Council (1889–1974)
, Origin=
, Code = GLA
, CodeName = Chapman code
, Replace =
* West Glamorgan
* Mid Glamorgan
* South Glamorgan
, Motto ...
in the
Domesday Book, the county of
Wales where it was discovered by
Walter Georg Kühne,
[Walter G. Kühne, "On a Triconodont tooth of a new pattern from a Fissure-filling in South Glamorgan", ''Proceedings of the Zoological Society of London'', volume 119 (1949–1950) pages 345–350] giving the meaning "Glamorgan tooth".
History of discovery
In the summer of 1947, fieldwork was done at Duchy Quarry in
Glamorgan
, HQ = Cardiff
, Government = Glamorgan County Council (1889–1974)
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, Code = GLA
, CodeName = Chapman code
, Replace =
* West Glamorgan
* Mid Glamorgan
* South Glamorgan
, Motto ...
in southern Wales. Grey
conglomerate
Conglomerate or conglomeration may refer to:
* Conglomerate (company)
* Conglomerate (geology)
* Conglomerate (mathematics)
In popular culture:
* The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes
** Co ...
that formed fissure fill deposits within
karst
Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ro ...
ic voids in
Carboniferous limestone was extracted. In 1949,
Walter Georg Kühne noted the lower cheek tooth of a primitive mammal while examining samples of the rock. He named it ''Morganucodon watsoni,'' with the genus name being derived from Morganuc, which Kühne stated was the name of South
Glamorgan
, HQ = Cardiff
, Government = Glamorgan County Council (1889–1974)
, Origin=
, Code = GLA
, CodeName = Chapman code
, Replace =
* West Glamorgan
* Mid Glamorgan
* South Glamorgan
, Motto ...
in the
Domesday Book, with the species name being in honour of
D. M. S. Watson.
Additional remains of ''M. watsoni'' were described by Kühne in 1958. Also in 1958,
Kenneth Kermack
Kenneth A. Kermack (1919 – 2000) was a British palaeontologist at University College London most notable for his work on early mammals with his wife, Doris Mary Kermack.
Among Kermack's other significant contributions was the observation ...
and Frances Mussett described additional remains from Pant Quarry, about a mile from Duchy Quarry, that had been collected in 1956.
In August 1948, an expedition to
Lufeng in
Yunnan, China yielded a 1 in (2.5 cm) long skull. It was shortly sent to Beijing (then Peking) and then eventually sent out of China, and deposited with Kenneth Kermack at
University College London in 1960. The specimen was preliminarily described in 1963 by Harold W. Rigney, who noted the similarity to ''Morganucodon'' from Britain, and considered it cogeneric, naming the new species ''Morganucodon oehleri'' in honor of the reverend Edgar T. Oehler, who had originally collected the specimen. In 1978
C. C. Young described ''
Eozostrodon heikuopengensis'' from the Hei Koa Peng locality near Lufeng, based on an associated skull and dentary, as well as a right maxilla and associated dentary. A revision by
William A. Clemens
William Alvin Clemens Jr. (May 15, 1932 — November 17, 2020) was a paleontologist at the University of California at Berkeley. He was faculty of the Department of Paleontology from 1967, then the Department of Integrative Biology from 1994 to h ...
in 1979 assigned this species to ''Morganucodon,'' based on its close similarity to the two previously named species.''
'' In 1980 Clemens named the species ''Morganucodon peyeri'', from isolated teeth found in Late Triassic (
Rhaetian
The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age ...
) deposits near
Hallau, Switzerland, with the species being named after paleontologist
Bernhard Peyer. In 1981, Kermack, Mussett and Rigney published an extensive monograph on the skull of ''Morganucodon''. In 2016
Percy Butler and
Denise Sigogneau-Russell named the species ''Morganucodon tardus'' from an upper right molar (M34984) collected from the Watton Cliff locality near
Eype in
Dorset, England, dating to the late
Bathonian stage of the
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...
. The species being named after the Latin ''tardus'', late, in reference to it being the youngest member of the genus.
Biology
''Morganucodon'' was a small,
plantigrade
151px, Portion of a human skeleton, showing plantigrade habit
In terrestrial animals, plantigrade locomotion means walking with the toes and metatarsals flat on the ground. It is one of three forms of locomotion adopted by terrestrial mammals. T ...
animal. The tail was moderately long. According to Kemp (2005), "the skull was 2–3 cm in length and a presacral body length of about 10 cm
inches In general appearance, it would have looked like a shrew or mouse". There is evidence that it had specialized glands used for grooming, which may indicate that, like present day mammals, it had fur.
Like present day mammals of similar size and presumed habit, ''Morganucodon'' was likely nocturnal and spent the day in a burrow. There is no direct fossil evidence, but several lines of evidence point to a
nocturnal bottleneck
The nocturnal bottleneck hypothesis is a hypothesis to explain several mammalian traits. In 1942, Gordon Lynn Walls described this concept which states that placental mammals were mainly or even exclusively nocturnal through most of their evolu ...
in the evolution of the mammal class, and almost all modern mammals of similar size to ''Morganucodon'' are still nocturnal. Likewise, burrowing was widespread both in non-mammalian
cynodont
The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...
s and in primitive mammals. The logics of
phylogenetic bracketing would make ''Morganucodon'' nocturnal and burrowing too. Plant material from the conifer ''
Hirmeriella
''Hirmeriella'' is a genus of fossil tree, a conifer that was widespread in Late Triassic and Early Jurassic of Germany, the UK, and Poland.BARBACKA M., ZIAJA J., WCISŁO-LURANIEC E. 200Hirmeriella muensteri (Schenk) Jung from Odrowąż (Poland ...
'' was also found in the fissure fills, indicating ''Morganucudon'' lived in, or near, a forested area.
The diet appears to have been insects and other small animals, with a preference for hard prey such as beetles. Like most modern mammal insectivores, it grew fairly quickly to adult size. Its eggs were probably small and leathery, a condition still found in monotremes.
The teeth grew in mammalian fashion, with
deciduous teeth
Deciduous teeth or primary teeth, also informally known as baby teeth, milk teeth, or temporary teeth,Illustrated Dental Embryology, Histology, and Anatomy, Bath-Balogh and Fehrenbach, Elsevier, 2011, page 255 are the first set of teeth in the ...
being replaced by permanent teeth that were retained throughout the rest of the animal's life.
[Alexander F. H. van Nievelt and Kathleen K. Smith, "To replace or not to replace: the significance of reduced functional tooth replacement in marsupial and placental mammals", ''Paleobiology'', Volume 31, Issue 2 (June 2005) pages 324–346] The combination of rapid growth in juveniles and a toothless stage at infancy strongly suggests that ''Morganucodon'' raised its young by
lactation; indeed, it may have been among the first animals to do so. The molars in the adult had a series of raised humps and edges that fit into each other, allowing for efficient chewing. However, unlike the situation in most later mammals, the upper and lower molars did not occlude properly when they first met; as they wore against each other, however, their shapes were modified by wear to produce a precise fit.
A 2020 study suggests that the metabolism of ''Morganucodon'' was significantly slower than that of comparably sized modern mammals, and that it had a life-span more similar to that of reptiles, with the oldest specimen having a lifespan of 14 years. Thus it likely did not possess the fully
endothermic metabolism seen in current mammals.
Species
Classification
''Morganucodon'' is the
type genus for the order
Morganucodonta
Morganucodonta ("Glamorgan teeth") is an extinct order of basal Mammaliaformes, a group including crown-group mammals (Mammalia) and their close relatives. Their remains have been found in Southern Africa, Western Europe, North America, India an ...
, a group of generally similar mammaliaforms known from the
Late Triassic to
Late Jurassic epochs, with one possible member (''
Purbeckodon'') dating to the
Early Cretaceous
The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma.
Geology
Pro ...
. All were small and likely insectivorous. ''Morganucodon'' is the best preserved and best understood member of Morganucodonta.
There is currently controversy about whether or not to classify ''Morganucodon'' as a mammal or as a non-mammalian
mammaliaform. Some researchers limit the term "mammal" to the
crown group
In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...
mammals, which would not include ''Morganucodon'' and its relatives. Others, however, define "mammals", as a group, by the possession of a special, secondarily evolved jaw joint between the dentary and the squamosal bones, which has replaced the primitive one between the
articular and
quadrate bones in all modern mammalian groups. Under this definition, ''Morganucodon'' would be a mammal. Nevertheless, its lower jaw retains some of the bones found in its non-mammalian ancestors in a very reduced form rather than being composed solely of the dentary. Furthermore, the primitive reptile-like jaw joint between the articular and quadrate bones, which in modern mammals has moved into the middle ear and become part of the ear ossicles as malleus and incus, is still to be found in ''Morganucodon''. ''Morganucodon'' also suckled (it may have been the earliest animal to do so), had only two sets of teeth and grew rapidly to adult size and stopped growing thereafter, all typical mammalian traits.
[Mammals of the Mesozoic: The least mammal-like mammals]
/ref>
;Phylogeny
See also
* Evolution of mammals
References
{{Taxonbar, from=Q131813
Morganucodonts
Prehistoric cynodont genera
Late Triassic synapsids
Triassic synapsids of Europe
Jurassic synapsids
Transitional fossils
Rhaetian first appearances
Middle Jurassic extinctions
Fossil taxa described in 1949
Taxa named by Walter Georg Kühne