Photo credit: Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons.
Fossil Friday: New Fossil Evidence Challenges Another Icon of Evolution
This Fossil Friday features the skull of Syngnathus currents, a mammal-like reptile from the Middle Triassic of the Southern Hemisphere landmasses that had formed the ancient supercontinent Gondwana. It belongs to a group called Cydonia. The recent analysis of the jaw anatomy of fossil remains from South America challenged some longstanding evolutionary ideas.
When evolutionists are asked what in their view represents the best evidence for the Darwinian story of common descent with modification, they will refer to the fossil record and especially to supposed transitional series like those of horses, elephants, whales, hominids, fish to tetrapods, Minos to birds, and most of all the transition from reptiles to mammals. The latter allegedly shows an unambiguous transformation of the jaw articulation from a primitive reptilian state to the derived mammalian condition, correlated with a reduction in bone number and the incorporation of the original jaw articulation into the mammalian ear as auditory ossicles (Rather-Gap theory).
A More Complicated Picture
However, a closer look at the fossil evidence reveals a much more complex picture involving multiple independent origins of anatomical similarities. In a seminal study on the evolution of the mammalian middle ear, the authors admitted that “current hypotheses on the convergent evolution of middle ear bones are complex and controversial, partly because of a lack of phylogenetic resolution and partly because the interpretation of the fossil evidence is difficult” (Ramírez-Chaves et al. 2016). They concluded that “the departure of postdental bones from the denary to form a partial mammalian middle ear (MME); … occurred convergently in the Northern Hemisphere ancestors of Athenians and the Southern Hemisphere ancestors of monochromes … the transition from a PM ME to a definite mammalian middle ear (MME) occurred [sic] multiple times, including at least three cases of independent evolution within extant mammals (in monochromes, metatherian, and eutherians).”
Now, a new study complicated this scenario even more: The scientists studied the well-preserved fossil remains of three key species of probainognathian bunodont, viz. Basildon quadrangular is and Rio Grande goodness from the Late Triassic of Brazil, as well as Oleographs major from the Early Jurassic of Great Britain. They used CT scanning to digitally reconstruct the jaw joints of these animals and found something unexpected (Luo 2024). The jaw joint anatomy of the two Brazilian species differed markedly, with the Rio Grande joint being more mammal-like than that of Basildondenary-squamosal, even though the latter genus is considered more closely related to modern mammals. Furthermore, ground was dated to be about 17 million years older than any other previously known mammal-like reptile with such an advanced jaw articulation. The authors concluded that “the denary-squamosal contact, which is traditionally considered to be a typical mammalian feature, therefore evolved more than once and is more evolutionary labile than previously considered.”
Interesting News About a Departed Colleague
The press release unashamedly speaks about “rewriting our understanding of mammal evolution” (News his indicates that the defining mammalian jaw feature evolved multiple times in different groups of creatures, earlier than expected. The findings suggest that mammalian ancestors experimented with varying functions of jaw, leading to the evolution of mammalian traits independently across lineages. The early evolution of mammals, it turns out, was far more complex and varied than previously understood.
The author of the new study, Dr. James Lawson from the University of Bristol, said
What these new Brazilian fossils have shown is that different cynodont groups were experimenting with various jaw joint types, and that some features once considered uniquely mammalian developed numerous times in other lineages as well.
Dr. Zhu Xi Luo, one of the world’s leading experts on mammalian origins and not involved in the new study, commented that this is “a jaw-dropping discovery about early mammals” (Luo 2024). It certainly is, and it definitely looks like we are witnessing the beginning of the dismantling of yet another icon of evolution, which would have been very interesting news to my recently deceased friend and colleague, Jonathan Wells, who had described many such cases in his ground-breaking books.
