Reconstruction of Feredocodon chowi (right) and Dianoconodon youngi (left).
© Chuang Zhao
Some 165 million years before their god created the small flat planet with a dome over it that Creationists love hearing about, early mammals were evolving into modern mammals, complete with the tiny bones called ossicles that are essential for hearing. These three small bones transmit sound across the inner ear to the auditory sense organ, the cochlea.
Changes in the mammalian dentition were key to freeing these parts of the jaw joint, according to an analysis of two Jurassic-era mammal fossils which are the subject of articles in Nature. These analyses fill a gap in our understanding of the evolution of mammalian dentition and provide evidence of the transition from part of the jaw to the auditory ossicles - the stapes, malus and incus.
Like almost all of the history of life on earth, this all happened in the very long 'pre-Creation' age when 99.99% of Earth's history happened. The discovery was made by a research team that included Jin Meng of the American Museum of Natural History. Their findings are explained in an American Museum of Natural History press release.
New insights into mammalian tooth, jaw, and ear evolution, gleaned from analyzing fossils of two Jurassic-era mammal species from China, are reshaping how scientists think about early mammals.Sadly, both papers are behind paywalls with only the abstracts freely available:
Two studies in this week’s journal Nature, both led by scientists at the Museum and the Chinese Academy of Sciences, focus on two new species of fossil mammals that offer new evidence about early mammalian evolution.
The first study focuses on two newly discovered fossils of mouse-sized mammals called shuotheriids, which lived between 168–164 million years ago in what is today Inner Mongolia and had molars that are unlike those of any other living mammal. Shuotheriids were previously linked to the group that includes today’s monotremes—mammals that lay eggs, such as the platypus.
Since the 1980s, the perplexing tooth shape seen in shuotheriids has been a barrier to our efforts to understand early mammal evolution. These new specimens have allowed us to solve this longstanding problem.
Jin Meng, co-corresponding author.
Division of Paleontology
American Museum of Natural History, New York, NY, USA.
The new research suggests that shuotheriid molars more closely resembled those of another extinct mammal group, the docodontans. The new species is named Feredocodon chowi.
Feredocodon chowi, along with a second new species, named Dianoconodon youngi, is also the focus of a second study, in which researchers found fossil evidence of the transition from the reptilian to the modern mammalian middle ear.
The modern mammalian middle ear, which gives modern mammals the sharpest hearing on Earth, has three bones. This feature that is unique to mammals; reptiles and birds only have one middle-ear bone. From prior studies and fossil evidence, scientists know that during the early evolution of mammals from the reptilian group that includes lizards, crocodilians, and dinosaurs, bones that formed the joints of the jaw were separated and became associated with hearing.
The transition started from an ancestral animal that had a double jaw joint, a feature with the joint of a mammal on the outside and a reptilian joint on the inside. Analyses of the older fossil, Dianoconodon youngi, which dates back to between 201–184 million years ago, show that one of its two joints, the reptilian one, was starting to lose its ability to handle the forces created by chewing. The more recent specimen, Feredocodon chowi, already had a mammal middle ear, formed and adapted exclusively for hearing.
Scientists have been trying to understand how the mammalian middle ear evolved since Darwin’s time. These new fossils bring to light a critical missing link and enrich our understanding of the gradual evolution of the mammalian middle ear.
Jin Meng.
AbstractThere are so many sources of painful cognitive dissonance for creationists to have to cope with in these two papers which probably explains why they can never be induced to read scientific articles other than those prepared by the creationist frauds who supply them with the disinformation and falsehoods they depend on to confirm their biases.
Shuotheriids are Jurassic mammaliaforms that possess pseudotribosphenic teeth in which a pseudotalonid is anterior to the trigonid in the lower molar, contrasting with the tribosphenic pattern of therian mammals (placentals, marsupials and kin) in which the talonid is posterior to the trigonid1,2,3,4. The origin of the pseudotribosphenic teeth remains unclear, obscuring our perception of shuotheriid affinities and the early evolution of mammaliaforms1,5,6,7,8,9. Here we report a new Jurassic shuotheriid represented by two skeletal specimens. Their complete pseudotribosphenic dentitions allow reidentification of dental structures using serial homology and the tooth occlusal relationship. Contrary to the conventional view1,2,6,10,11, our findings show that dental structures of shuotheriids can be homologized to those of docodontans and partly support homologous statements for some dental structures between docodontans and other mammaliaforms6,12. The phylogenetic analysis based on new evidence removes shuotheriids from the tribosphenic ausktribosphenids (including monotremes) and clusters them with docodontans to form a new clade, Docodontiformes, that is characterized by pseudotribosphenic features. In the phylogeny, docodontiforms and ‘holotherians’ (Kuehneotherium, monotremes and therians)13 evolve independently from a Morganucodon-like ancestor with triconodont molars by labio-lingual widening their posterior teeth for more efficient food processing. The pseudotribosphenic pattern passed a cusp semitriangulation stage9, whereas the tribosphenic pattern and its precursor went through a stage of cusp triangulation. The two different processes resulted in complex tooth structures and occlusal patterns that elucidate the earliest diversification of mammaliaforms.
Fig. 1: Type specimens of F. chowi.Fig. 2: Right dentition and dental morphology of F. chowi (holotype, IMMNH-009166).Fig. 3: Tooth occlusion and competing hypotheses for tooth cusp homology of Feredocodon.Fig. 4: Primary tooth patterns of mammaliaforms in the phylogenetic frame.Mao, F., Li, Z., Wang, Z. et al.
Jurassic shuotheriids show earliest dental diversification of mammaliaforms.
Nature (2024). https://doi.org/10.1038/s41586-024-07258-7
© 2024 Springer Nature Ltd.
Reprinted under the terms of s60 of the Copyright, Designs and Patents Act 1988.
Abstract
The dual jaw joint of Morganucodon1.1,2.1 consists of the dentary–squamosal joint laterally and the articular–quadrate one medially. The articular–quadrate joint and its associated post-dentary bones constitute the precursor of the mammalian middle ear. Fossils documenting the transition from such a precursor to the mammalian middle ear are poor, resulting in inconsistent interpretations of this hallmark apparatus in the earliest stage of mammaliaform evolution1.1,2.1,3.1,4.1,5.1 . Here we report mandibular middle ears from two Jurassic mammaliaforms: a new morganucodontan-like species and a pseudotribosphenic shuotheriid species6.1. The morganucodontan-like species shows many previously unknown post-dentary bone morphologies1.1,2.1 and exhibits features that suggest a loss of load-bearing function in its articular–quadrate joint. The middle ear of the shuotheriid approaches the mammalian condition in that it has features that are suitable for an exclusively auditory function, although the post-dentary bones are still attached to the dentary. With size reduction of the jaw-joint bones, the quadrate shifts medially at different degrees in relation to the articular in the two mammaliaforms. These changes provide evidence of a gradual loss of load-bearing function in the articular–quadrate jaw joint—a prerequisite for the detachment of the post-dentary bones from the dentary7.1,8.1,9.1,10.1,11.1,12.1 and the eventual breakdown of the Meckel’s cartilage13.1,14.1,15.1 during the evolution of mammaliaforms.
Fig. 1: CT images of the holotype of Dianoconodon youngi (IVPP V4257).Fig. 2: Lower jaw and mandibular middle ear of Dianoconodon youngi (IVPP V4257).Fig. 3: Mandibular middle ear of the shuotheriid docodontiform Feredocodon chowi.Fig. 4: Mandibular middle ears and transformation of the articular–quadrate joints in mammaliaforms.Mao, F., Zhang, C., Ren, J. et al.
Fossils document evolutionary changes of jaw joint to mammalian middle ear.
Nature (2024). https://doi.org/10.1038/s41586-024-07235-0
© 2024 Springer Nature Ltd.
Reprinted under the terms of s60 of the Copyright, Designs and Patents Act 1988.
Apart from the fact that this all happened about 165 million years before they believe Earth was created, the first paper fills one of their beloved gaps in which they try to force fit their magic invisible friend. The gap was in our understanding of the origins of mammalian dentition and how this diversified from our reptilian ancestors.
The second paper provides an example of transition - that thing creationists are required to believe doesn't exist in the fossil record. This fossil shows the transition from part of the reptilian jaw to the auditory ossicles, as parts of the jaw became redundant due to the reorganized dentition explained in the first paper and were exapted for a new function.
This neatly illustrates how an evolutionary change in one part, in this case the dentition, can produce opportunities for further evolution in another, so improved dentition in mammalian ancestors led to improved hearing and the appearance of what creationist frauds will try to misrepresent as irreducible complexity and thus 'proof' of design by an unproven magic supernatural entity, and so, by the circular reasoning which appeals to their dupes, 'proof' that the magic supernatural entity is real, so you need to give money to the church.
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