Evolutionary Development of the Middle Ear in Mesozoic Therian Mammals

• Published in: Science (American Association for the Advancement of Science) Vol. 326; no. 5950; pp. 278 - 281
• Main Authors: Ji, Qiang, Luo, Zhe-Xi, Zhang, Xingliao, Yuan, Chong-Xi, Xu, Li
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 09.10.2009; The American Association for the Advancement of Science
• Subjects: Animals; Biological Evolution; Cartilage; Cartilage - embryology; Cartilage - physiology; Chondrogenesis; Dentition; Ear Ossicles - anatomy & histology; Ear Ossicles - embryology; Ear, Middle - anatomy & histology; Ear, Middle - embryology; Ears & hearing; Earth sciences; Earth, ocean, space; Embryo, Mammalian - anatomy & histology; Evolution; Evolutionary biology; Exact sciences and technology; Fossils; Gene Expression Regulation, Developmental; Geology; Intercellular Signaling Peptides and Proteins - metabolism; Mammals; Mammals - anatomy & histology; Mammals - classification; Mammals - embryology; Mammals - genetics; Mandible; Mandible - anatomy & histology; Marsupials; Mice; Mice, Mutant Strains; Middle ear; Monotremes; Osteogenesis; Paleontology; Phylogeny; Signal Transduction; Skull; Teeth; Vertebrate paleontology; Mesozoic; development; Chordata; morphology; mandibles; evolution; Vertebrata; Mammalia; Theria; teeth; Phanerozoic; heterochrony; Tetrapoda
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1178501

The definitive mammalian middle ear (DMME) is defined by the loss of embryonic Meckel's cartilage and disconnection of the middle ear from the mandible in adults. It is a major feature distinguishing living mammals from nonmammalian vertebrates. We report a Cretaceous trechnotherian mammal with an ossified Meckel's cartilage in the adult, showing that homoplastic evolution of the DMME occurred in derived therian mammals, besides the known cases of eutriconodonts. The mandible with ossified Meckel's cartilage appears to be paedomorphic. Reabsorption of embryonic Meckel's cartilage to disconnect the ear ossicles from the mandible is patterned by a network of genes and signaling pathways. This fossil suggests that developmental heterochrony and gene patterning are major mechanisms in homplastic evolution of the DMME.