Early Mesozoic mammal Arboroharamiya (Haramiyida) compared with Megaconus

[Ben Creisler <bcreisler@gmail.com>]

Ben Creisler
bcreisler@gmail.com

New in PLoS ONE:


Jin Meng, Shundong Bi, Yuanqing Wang, Xiaoting Zheng & Xiaoli Wang (2014)
Dental and Mandibular Morphologies of Arboroharamiya (Haramiyida,
Mammalia): A Comparison with Other Haramiyidans and Megaconus and
Implications for Mammalian Evolution.
PLoS ONE 9(12): e113847.
doi:10.1371/journal.pone.0113847
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0113847

Background

Two recent studies published in the same issue of Nature reached
conflicting conclusions regarding the phylogeny of early mammals: One
places the clade containing haramiyidans and multituberculates within
the Mammalia and the other separates haramiyidans from
multituberculates and places the former outside of the Mammalia. These
two contrasting results require that the minimally oldest divergence
time of the Mammalia was within the Late Triassic or the Middle
Jurassic, respectively. Morphological descriptions of the species
named in the two papers were brief, and no comparisons between the
newly named species were possible.

Principal Findings

Here we present a detailed description of the dentary bone, teeth,
occlusal and wear patterns of the haramiyidan Arboroharamiya and
compare it with other haramiyidans and Megaconus. Using this new
information, we suggest that tooth identifications and orientations of
several previously described haramiyidan species are incorrect, and
that previous interpretations of haramiyidan occlusal pattern are
problematic. We propose that the published upper tooth orientation of
Megaconus was problematic and question the number of upper molars, the
length of dentition and mandible, and presence of the mandibular
middle ear in Megaconus.

Conclusions

The additional morphological descriptions and comparisons presented
here further support the view that Arboroharamiya, as a derived
haramiyidan, shows similarity to multituberculates in tooth and
mandible morphologies. Our comparison also suggests that Megaconus
lacks many diagnostic features for the family Eleutherodontidae and
that its close affinity with multituberculates cannot be ruled out.
The detailed morphological data demonstrate that haramiyidans are more
similar to multituberculates than to any other mammaliaforms.