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Arboroharimiya and Megaconus, new Jurassic mammals from China

From: Ben Creisler

New in Nature:

Richard L. Cifelli & Brian M. Davis (2013)
Palaeontology: Jurassic fossils and mammalian antiquity.
Nature 500 (7461): 160--161

Two new Jurassic fossils yield conflicting reconstructions of the
mammalian tree. These divergent genealogies have profoundly different
implications for the origin and early diversification of mammals.



Chang-Fu Zhou, Shaoyuan Wu, Thomas Martin & Zhe-Xi Luo (2013)
A Jurassic mammaliaform and the earliest mammalian evolutionary adaptations.
Nature 500 (7461): 163--167

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.



Xiaoting Zheng, Shundong Bi, Xiaoli Wang & Jin Meng (2013)
A new arboreal haramiyid shows the diversity of crown mammals in the
Jurassic period.
Nature 500 (7461): 199--202

A major unsolved problem in mammalian evolution is the origin of
Allotheria, including Multituberculata and Haramiyida.
Multituberculates are the most diverse and best known Mesozoic era
mammals and ecologically resemble rodents, but haramiyids are known
mainly from isolated teeth, hampering our search for their
phylogenetic relationships. Here we report a new haramiyid from the
Jurassic period of China, which is, to our knowledge the largest
reported so far. It has a novel dentition, a mandible resembling
advanced multituberculates and postcranial features adapted for
arboreal life. Our phylogenetic analysis places Haramiyida within
crown Mammalia, suggesting the origin of crown Mammalia in the Late
Triassic period and diversification in the Jurassic, which contrasts
other estimated divergence times of crown Mammalia. The new haramiyid
reveals additional mammalian features of the group, helps to identify
other haramiyids represented by isolated teeth, and shows again that,
regardless of various phylogenetic scenarios, a complex pattern of
evolution involving many convergences and/or reversals existed in
Mesozoic mammals.

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