Tag Archives: Mammals

Another Mid Jurassic Mystery Mammal Solved!

A Jurassic mammaliaform and the earliest mammalian evolutionary adaptations

Chang-Fu Zhou, Shaoyuan Wu, Thomas Martin & Zhe-Xi Luo

–Nature: Vol. 500, #7461, pp. 163-167 [doi: 10.1038/nature12429]

http://www.nature.com/nature/journal/v500/n7461/full/nature12429.html

The earliest evolution of mammals and origins of mammalian features can be traced to the mammaliaforms of the Triassic and Jurassic periods that are extinct relatives to living mammals. Here we describe a new fossil from the Middle Jurassic that has a mandibular middle ear, a gradational transition of thoracolumbar vertebrae and primitive ankle features, but highly derived molars with a high crown and multiple roots that are partially fused. The upper molars have longitudinal cusp rows that occlude alternately with those of the lower molars. This specialization for masticating plants indicates that herbivory evolved among mammaliaforms, before the rise of crown mammals. The new species shares the distinctive dental features of the eleutherodontid clade, previously represented only by isolated teeth despite its extensive geographic distribution during the Jurassic.  This eleutherodontid was terrestrial and had ambulatory gaits, analogous to extant terrestrial mammals such as armadillos or rock hyrax. Its fur corroborates that mammalian integument had originated well before the common ancestor of living mammals.

– Ian

 

Guest lecture, Mammals from the Age of Dinosaurs, 8.2.2012 16.00

Dear All,

The Björn Kurtén Club is hosting a guest lecture

Mammals from the Age of Dinosaurs by

Thomas Martin

Steinmann-Institut für Geologie, Mineralogie und Paläontologie, Universität Bonn, Nussallee 8, 53115 Bonn, Germany

Mammals are the dominant vertebrates on land, having colonized almost all kinds of environments. The great mammalian radiation began after the extinction of the dinosaurs about 65 million years ago, and subsequently the modern diversity arose. However, the history of mammals started much earlier, some 200 million years ago in the Late Triassic, meaning two thirds of mammalian evolutionary history occurred in the Mesozoic, alongside the dinosaurs. The Jurassic is particularly important for mammalian evolution, with important key characters of modern mammals having evolved. Mammals are characterized by two highly complex sets of features which can be studied in both living and fossil species; tribosphenic molar teeth, with a grinding function in addition to the primitive piercing and cutting; and the inner ear, with a coiled cochlea and three middle ear bones. Recent work and new fossils have thrown up surprises in the evolution of both these features.
For a long time, Mesozoic mammals were regarded as small insectivorous animals without any particular specializations. Spectacularly preserved new fossil discoveries of basal/primitive mammals in the Jurassic have revealed striking body plans and lifestyles that were inconceivable a decade ago for early mammals. Castorocauda from Mongolia reveals the oldest fossilised fur and was perfectly adapted for swimming with a beaver-like, flattened tail covered by small horny scales and webbed hind feet. Volaticotherium was a climber with a gliding membrane like the modern sugar glider. Fruitafossor, from the U.S.A., was a burrower and had enamel-less peglike teeth, like those of living armadillos that feed on ants/termites. These highly specialized Jurassic mammals lived and became extinct during the Mesozoic. In contrast the direct ancestors of modern mammals, such as Henkelotherium from the Jurassic of Portugal, were more generalized. They survived extinction at the end of the Cretaceous and evolved into the spaces left by the dinosaurs.
Professor Thomas Martin’s lecture will explore this fascinating Jurassic mammalian world, weaving these new fossil discoveries with his work on the body plans and lifestyles, teeth, and inner ears of Jurassic mammals, and stories from his fieldwork across the globe. The exciting new fossils may be just a glimpse of what is to come, demonstrating that we stand at the threshold of a dramatic change in the picture of early mammalian evolutionary history.

Time and location:
8.2.2012 (Wed.), 16.00, E204, Physicum, Kumpula Campus

Welcome,
Aleksis Karme

A new Mesozoic mammal from South America

All,

Say hello to _Cronopio dentiacutus_

Rougier, G. W., Apesteguia, S. & Gaetano, L. C., 2011: Highly specialized
mammalian skulls from the Late Cretaceous of South America.
–Nature: Vol. 479, #7371, pp. 98-102 [doi: 10.1038/nature10591]

http://www.nature.com/nature/journal/v479/n7371/abs/nature10591.html
http://www.nature.com/nature/journal/v479/n7371/abs/nature10591.html#supplem
entary-information

Abstract:
“Dryolestoids are an extinct mammalian group belonging to the
lineage leading to modern marsupials and placentals1,2. Dryolestoids
are known by teeth and jaws from the Jurassic period of North
America and Europe2,3, but they thrived in South America up to the
end of the Mesozoic era and survived to the beginnings of the
Cenozoic2,4–7. Isolated teeth and jaws from the latest Cretaceous of
South America provide mounting evidence that, at least in western
Gondwana, dryolestoids developed into strongly endemic groups by
the Late Cretaceous4–9. However, the lack of pre-Late Cretaceous
dryolestoid remains made study of their origin and early diversification
intractable. Here we describe the first mammalian remains
from the early Late Cretaceous of South America, including two
partial skulls and jaws of a derived dryolestoid showing dental
and cranial features unknown among any other group of
Mesozoic mammals, such as single-rooted molars preceded by
double-rooted premolars, combined with a very long muzzle,
exceedingly long canines and evidence of highly specialized
masticatory musculature. On one hand, the new mammal shares
derived features of dryolestoids1–3 with forms from the Jurassic of
Laurasia, whereas on the other hand, it is very specialized and
highlights the endemic, diverse dryolestoid fauna from the
Cretaceous of South America. Our specimens include only the
second mammalian skull known for the Cretaceous of Gondwana,
bridging a previous 60-million-year gap in the fossil record, and
document the whole cranial morphology of a dryolestoid, revealing
an unsuspected morphological and ecological diversity for nontribosphenic
mammals.”

–Mikko

Juramaia, Jurassic eutherian from China

This message was seen in DINOSAUR mailing list… Of all things…

–Mikko

—–Original Message—–

A Mesozoic mammal of interest:

Zhe-Xi Luo, Chong-Xi Yuan, Qing-Jin Meng & Qiang Ji (2011)
Jurassic eutherian mammal and divergence of marsupials and placentals.
Nature 476: 442-445
doi:10.1038/nature10291
http://www.nature.com/nature/journal/v476/n7361/full/nature10291.html

Placentals are the most abundant mammals that have
diversified into every niche for vertebrates and
dominated the world’s terrestrial biotas in the Cenozoic.
A critical event in mammalian history is the divergence
of eutherians, the clade inclusive of all living
placentals, from the metatherian-marsupial clade. Here we
report the discovery of a new eutherian of 160 Myr from
the Jurassic of China, which extends the first appearance
of the eutherian-placental clade by about 35 Myr from the
previous record, reducing and resolving a discrepancy
between the previous fossil record and the molecular
estimate for the placental-marsupial divergence. This
mammal has scansorial forelimb features, and provides the
ancestral condition for dental and other anatomical
features of eutherians.

News Stories:
http://www.carnegiemnh.org/press/11-jul-sep/082511fossil.htm
http://www.eurekalert.org/pub_releases/2011-08/cmon-doa081911.php
http://www.pittsburghlive.com/x/pittsburghtrib/news/pittsburgh/s_753170.html

Diversity of hypsodont teeth in mammalian dentitions

Just in case somebody finds this interesting… 🙂

http://www.schweizerbart.de/papers/pala/detail/294/76206

Diversity of hypsodont teeth in mammalian dentitions – construction and
classification

von Koenigswald, Wighart

Palaeontographica Abteilung A Band 294 Lieferung 1-3 (2011)
p. 63-94, published: 8/22/2011
9 figures 3 tables

Abstract

“Hypsodonty, as used here, describes a specific type of tooth with the crown
elongated parallel to the growing axis, a condition which can occur in any
tooth position. Hypsodonty is interpreted as the elongation of specific
ontogenetic phases during tooth development at the cost of all others in a
heterochronic mode. Three parameters are used for differentiation: the
specific elongated ontogenetic phase or phases; the degree of hypsodonty
(increasing hypsodont and euhypsodont); and the kind of abrasion (balanced
wear by an antagonist or free growth). The first parameter is regarded as
the most important one. Although the separation of the four ontogenetic
phases (I – cusps, II – sidewalls, III – dentine surface, and IV –
differentiated roots) is artificial, it allows characterization of the great
diversity of hypsodont teeth in six categories: 1) multicusped hypsodonty
(extended phase I); 2) unicuspid hypsodonty (confluent phases I+II); 3)
sidewall hypsodonty (extended phase II); 4) enamel band hypsodonty (phases
II+III synchronous); 5) partial hypsodonty (phases II+III+IV synchronous);
and 6) dentine hypsodonty (phase III dominant). A synopsis with previously
defined types of hypsodonty is given. The new classification is
comprehensive, opens the view to the construction of hypsodont teeth, and
allows a comparison under evolutionary aspects.”

Too bad that we don’t have rights to download it…

–Mikko

Fossil Evidence on Origin of the Mammalian Brain

Timothy B. Rowe, Thomas E. Macrini, Zhe-Xi Luo

ABSTRACT

Many hypotheses have been postulated regarding the early evolution of the mammalian brain. Here, x-ray tomography of the Early Jurassic mammaliaforms Morganucodon and Hadrocodium sheds light on this history. We found that relative brain size expanded to mammalian levels, with enlarged olfactory bulbs, neocortex, olfactory (pyriform) cortex, and cerebellum, in two evolutionary pulses. The initial pulse was probably driven by increased resolution in olfaction and improvements in tactile sensitivity (from body hair) and neuromuscular coordination. A second pulse of olfactory enhancement then enlarged the brain to mammalian levels. The origin of crown Mammalia saw a third pulse of olfactory enhancement, with ossified ethmoid turbinals supporting an expansive olfactory epithelium in the nasal cavity, allowing full expression of a huge odorant receptor genome.

Science 20 May 2011: Vol. 332 no. 6032 pp. 955-957 DOI: 10.1126/science.1203117

http://www.sciencemag.org/content/332/6032/955.full

http://beta.news.yahoo.com/ancient-furry-mammals-had-big-brains-smell-191357916.html
__________________________________
Laura

Brain evolution and other Mesozoic mammal stuff

Some new meso-mammal-papers picked up from Dinosaur Discussion List… 🙂

–Mikko H.

Some recent items about Mesozoic mammals.

In the new issue of Science:

R. Glenn Northcutt (2011)
Perspective Paleontology: Evolving Large and Complex Brains.
Science 332 (6032): 926-927 (20 May 2011):
DOI: 10.1126/science.1206915
http://www.sciencemag.org/content/332/6032/926.summary

Summary
During the Mesozoic (∼250 million to 65 million years ago), two
distantly related groups of reptiles-the cynodont (or mammal-like) reptiles
and the coelurosaurian theropod dinosaurs-gave rise to mammals and birds,
respectively. Both mammals and birds evolved brains some 10 times as large,
relative to a given body weight, as those of their ancestors (1). In both
groups, these brains contributed to the evolution of the ability to control
body temperature (endothermy) and complex social interactions, including
parental care and a reliance on learning that even involves tool use (2,
3). The size of most parts of the brain increased in birds and mammals, but
the cerebral hemispheres and cerebellum, both of which are involved in
sensory and motor integration, underwent particularly spectacular
development (see the figure). Although mammals and birds evolved from
distantly related groups of reptiles, the higher integrative centers and
circuitry of their cerebral hemispheres are very similar, and comparative
neurobiologists continue to vigorously debate whether these centers evolved
from the same ancestral neural centers (4, 5) or from different ones (6-8).
Speculation about the evolutionary steps leading to large and complex
mammalian and avian brains is equally contentious and unresolved, in part
because of the rarity of fossil skulls and, until recently, the need to
destroy such skulls in order to expose the endocasts (casts molded by the
cranial cavity). Typically, endocasts are the only record of the brain’s
outward appearance in a transitional form, because brains themselves are
rarely fossilized.

Timothy B. Rowe, Thomas E. Macrini, and Zhe-Xi Luo (2011)
Fossil Evidence on Origin of the Mammalian Brain.
Science 332(6032): 955-957 (20 May 2011):
DOI: 10.1126/science.1203117
http://www.sciencemag.org/content/332/6032/955.abstract

Abstract
Many hypotheses have been postulated regarding the early evolution of the
mammalian brain. Here, x-ray tomography of the Early Jurassic mammaliaforms
Morganucodon and Hadrocodium sheds light on this history. We found that
relative brain size expanded to mammalian levels, with enlarged olfactory
bulbs, neocortex, olfactory (pyriform) cortex, and cerebellum, in two
evolutionary pulses. The initial pulse was probably driven by increased
resolution in olfaction and improvements in tactile sensitivity (from body
hair) and neuromuscular coordination. A second pulse of olfactory
enhancement then enlarged the brain to mammalian levels. The origin of
crown Mammalia saw a third pulse of olfactory enhancement, with ossified
ethmoid turbinals supporting an expansive olfactory epithelium in the nasal
cavity, allowing full expression of a huge odorant receptor genome.

J. David Archibald, Yue Zhang, Tony Harper and Richard L. Cifelli (2011)
Protungulatum, Confirmed Cretaceous Occurrence of an Otherwise Paleocene
Eutherian (Placental?) Mammal.
Journal of Mammalian Evolution (advance online publication)
DOI: 10.1007/s10914-011-9162-1
http://www.springerlink.com/content/n661405803q511n8/

Neither pre-Cenozoic crown eutherian mammals (placentals) nor archaic
ungulates (“condylarths”) are known with certainty based on the fossil
record. Herein we report a new species of the Paleocene archaic ungulate
(“condylarth”) Protungulatum from undisputed Late Cretaceous aged rocks in
Montana USA based on an isolated last upper premolar, indicating rare
representatives of these common early Tertiary mammals appeared in North
America a minimum of 300 k  years before the extinction of non-avian
dinosaurs. The other 1200 mammal specimens from the locality are
characteristic Late Cretaceous taxa. This discovery overturns the current
hypothesis that archaic ungulates did not appear in North America until
after the Cretaceous/Tertiary (K/T) boundary and also suggests that other
reports of North American Late Cretaceous archaic ungulates may be correct.
Recent studies, including ours, cannot determine whether Protungulatum does
or does not belong to the crown clade Placentalia.

A few months old but its free–pdf of short survey article about Chinese
Mesozoic mammals:
http://english.ivpp.cas.cn/rh/as/201012/P020101207396650166902.pdf

A. O. Averianov and A. V. Lopatin (2011)
Phylogeny of triconodonts and symmetrodonts and the origin of extant
mammals.
Doklady Biological Sciences 436(1): 32-35,
DOI: 10.1134/S0012496611010042
http://www.springerlink.com/content/3x027744038g6866/
(no abstract)

Definitive* proof of multiple origins of Definitive Mammalian Middle Ear (DMME)

A very nice paper and ‘News and Views’ on the discovery of yet another incredibly well preserved early mammal from Liaoning, China. This one preserved both ossified Meckels cartilage (OMC, already known from close relatives) AND attached to this are ALL of the middle ear bones! These are adrift of the dentary where they are thought to have moved from into the ear of mammals, yet they are still attached to it via this OMC. As the new beastie is found ‘higher’ up the phylogenetic tree than monotremes and multituberculates, both known to have the DMME, and plenty of close and distant relatives have either the OMC or a groove where it is thought the OMC lies, it indicates that the DMME, once thought to indicate the origin of mammalia, has likely evolved multiple times independently:

http://www.nature.com/nature/journal/v472/n7342/full/nature09921.html

and News and Views on the paper:

http://www.nature.com/nature/journal/v472/n7342/full/472174a.html

* This is ‘definitive’ if you accept a) the phylogeny presented and b) that this is not simply a reversal (though the presence of the ossified meckels cartilage in multiple taxa indicates this is unlikely). The phylogeny is open to discussion however, as it is partly based on the hypothesis that tribosphenic teeth also evolved independently at least twice, and there is evidence both for and against this. If you accept both of these, it’s homoplasy a go go in the two key mammalian morphological key innovations!

-Ian

Newsflash: Diversity and evolution of Hunter-Schreger Band configuration in tooth enamel of perissodactyl mammals

Diversity and evolution of Hunter-Schreger Band configuration in tooth enamel of perissodactyl mammals

Wighart Von Koenigswald, Luke T. Holbrook, and Kenneth D. Rose

Acta Palaeontologica Polonica 56 (1), 2011: 11-32 doi:10.4202/app.2010.0021

Four different Hunter−Schreger Band (HSB) configurations were observed in the teeth of fossil and extant Perissodactyla. This variability exceeds that observed in Artiodactyla or Proboscidea. The four HSB configurations represent two different evolutionary pathways. Transverse HSB found in many mammalian taxa outside the Perissodactyla represents the most primitive HSB configuration. It occurs in several primitive perissodactyl families and is retained in Palaeotheriidae and extant Equidae. Curved HSB evolved from transverse HSB and occurs in Tapiridae, Helaletidae, and Lophiodontidae, as well as in Ancylopoda and Titanotheriomorpha. This likely indicates independent evolution of curved HSB in two or more lineages, but the number of instances of parallelism of this configuration is obscured by uncertainty in the relationships among these taxa and by a lack of data for some important basal taxa. A second evolutionary pathway leads from transverse HSB via compound HSB to vertical HSB. Compound HSB were detected in Hyrachyidae, Deperetellidae, and the early rhinocerotid Uintaceras. Vertical HSB configuration characterizes the molar dentition of other Rhinocerotidae, Hyracodontidae, Indricotheriidae, andAmynodontidae. Often, the incisors of rhinocerotids retain traces of compound HSB. Thus theHSB configuration reflects phylogenetic relationships to some degree. The selective value of themodified HSB configurations is interpreted functionally as amechanismto reduce abrasion duringmastication, assuming that the perpendicular intersection of prismswith the actual grinding surfaces resists wear better than prisms running parallel to the occlusal surface.

-Mikko