or rows, from a triconodont-like tooth pattern or even from a tooth pattern
with an initially reversed triangular cusp arrangement.It was noted that
in lateral view the teeth of Haramiyavia are more similar to those of
Sinoconodon and Morganucodon than to those of multituberculates
We note, however, that the tooth pattern of Haramiyavia is also similar
to that of Woutersia, which co-existed with Theroteinus, another Late
. The tooth morphology and occlusionof euha-
ramiyidans indicate that, if the allotherian tooth pattern was derived
from a triconodont tooth pattern, the secondary cusp row has to be added
on the buccal side in the lower teeth. In the conventional view, how-
ever, development of extra cusps on the lingual cingula is common, but
buccal cingula are rare on lower molars
, although exceptions exist, such
. Nonetheless, the orientation of an isolated tooth
in early mammals is not always certain, as demonstrated in the case of
(this study). There is no convincing evidence to rule
out the possibility that additional cusps could be added on the buccal
side of the tooth in early mammals. Better material with teeth in situ
from each taxon of interest, such as Woutersia, is needed to test this
Interpretations of character evolution in early mammals depends
on their phylogeny. If ‘haramiyidans’ were separated from multituber-
culatesand placed outside mammals, while multituberculatesfell within
, then numerous similar craniodental and postcranial fea-
tures, particularly the molar pattern with two cusp rows and bilateral
occlusion, must have evolvedindependently in ‘haramiyidans’ andmul-
tituberculates during different periods of time. In addition, detachment
of the postdentary bones from the dentary would have evolved at least
four times independently in ‘haramiyidans’, multitubuculates, mono-
tremes andtherians. However, our phylogeny (Fig. 4 and Extended Data
Figs 9 and 10) indicates that Euharamiyida and Multituberculata were
probably derived from a Haramiyavia-like commonancestor at a min-
imum oldest age (according to current fossil records; future finds may
reveal an earlier ancestor)in the Late Triassic and diversified thereafter
during the Jurassic epoch, with known euharamiyidans adapting to a
scansorial and/or arboreal lifestyle which may explain their rare fossil
record. In contrast to interpreting numerous parallelisms in ‘harami-
yidans’ and multituberculates
, our hypothesis favours homologous
acquisition of many similar craniodental and postcranial features in
euharamiyidans and multituberculates, such as reduction of teeth, enlarge-
mentof the lower incisors,possessing only twomolars in each side of the
upper and lower jaws, and a palinal chewing motion. Moreover, euhar-
amiyidans are similar to multituberculates in lacking the postdentary
trough and Meckelian groove, indicating the presence of the definitive
mammalian middle ear
. If the reinterpretation is correct—that the den-
tary of Haramiyavia has only the Meckelian groove (see Supplemen-
tary Information, section F)—then the clade containing Eutricondonta,
Allotheria and Trechnotheria
(Fig. 4 and Extended Data Fig.9) would
have evolved from a common ancestor that had a transitional mamma-
lian middle ear
. This clade and the geological and geographic occur-
rences of its earliest known members are consistent with accumulating
evidence fromGondwana landmassesthat shows a cosmopolitandistri-
bution ofmembers in the clade
and suggest a Laurasianorigin of mam-
mals. Finally, by reinterpretating Hadrocodium as having postdentary
bones (see Supplementary Information, section G), our phylogeny sug-
gests that detachment of the postdentary bones evolved twice indepen-
dently during the early evolution of mammals, once in the clade leading
to monotremes and once towards the clade containing Eutricondonta,
Allotheria and Trechnotheria.
Online Content Methods, along with any additional Extended Data display items
and SourceData, are available in theonline version of the paper;references unique
to these sections appear only in the online paper.
Received 11 April; accepted 25 July 2014.
Published online 10 September 2014.
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