Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont

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The transference of post-dentary jaw elements to the cranium of mammals as auditory ossicles is one of the central topics in evolutionary biology of vertebrates. Homologies of these bones among jawed vertebrates have long been demonstrated by developmental studies; but fossils illuminating this critical transference are sparse and often ambiguous. Here we report the first unambiguous ectotympanic (angular), malleus (articular and prearticular) and incus (quadrate) of an Early Cretaceous eutriconodont mammal from the Jehol Biota, Liaoning, China. The ectotympanic and malleus have lost their direct contact with the dentary bone but still connect the ossified Meckel’s cartilage (OMC); we hypothesize that the OMC serves as a stabilizing mechanism bridging the dentary and the detached ossicles during mammalian evolution. This transitional mammalian middle ear narrows the morphological gap between the mandibular middle ear in basal mammaliaforms and the definitive mammalian middle ear (DMME) of extant mammals; it reveals complex changes contributing to the detachment of ear ossicles during mammalian evolution.

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Figure 1: The skeleton of the new mammal Liaoconodon hui (dorsal view of the holotype, IVPP V16051, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing).
Figure 2: Skull and ear ossicles of Liaoconodon hui (IVPP V16051).
Figure 3: Morphological transference of mammalian middle ear.
Figure 4: Phylogeny of mammaliaforms (simplified after ref. 18 ) mapping distributions of the post-dentary trough and the Meckelian groove.


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We thank X.-L. Wang of the Institute of Vertebrate Paleontology and Paleoanthropology for collecting the specimen; S.-H. Xie for preparing the specimen; J. Zhang, W. Gao, X. Jin, F.-C. Zhang and S.-B. Wang for photographs; W.-D. Zhang for scanning electron microscope and X-ray images; and E. Allin, G. Rougier and M. Takechi for discussion. The study was supported by the Major Basic Research Project of the Ministry of Science and Technology, China (2006CB806400), the National Science Foundation of China (40121202), the Special Fund for Fossil Excavation and Preparation of the Chinese Academy of Sciences, and the National Science Foundation of USA (EF-0629811 to J.M.).

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J.M. designed the study, performed the comparative and analytical work and wrote the paper. Y.W. and C.L. provided most of the photographs and contributed to the writing and discussion.

Correspondence to Jin Meng.

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Supplementary Information

This file contains Supplementary Sections A-G comprising Systematic Paleontology, Description, Discussion, Supplementary Figures 1-8 with legends, Phylogenetic analyses, Methods and References (see Table of Contents for full list). (PDF 2741 kb)

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Meng, J., Wang, Y. & Li, C. Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont. Nature 472, 181–185 (2011) doi:10.1038/nature09921

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