This Fossil Friday we revisit the ancestry of birds, with the featured skeleton of the Late Cretaceous chook Hesperornis gracilis, exhibited on the Natural History Museum in Karlsruhe, Germany. Hesperornis was a flightless and toothed marine chook, considerably just like trendy penguins, and lived contemporaneous with a number of the raptor dinosaurs which are well-known from the Jurassic Park motion pictures.
Few hypotheses in evolutionary biology have turn out to be as well-liked amongst lay individuals because the postulated ancestry of birds from bipedal dinosaurs. Indeed, many a faculty child will let you know proudly that birds merely are surviving dinosaurs. The theropod ancestry of birds has turn out to be an evolutionary dogma that’s almost universally accepted and taught because the consensus view. However, there are a number of dissenters, amongst whom the paleornithologist Alan Feduccia from the University of North Carolina definitely is probably the most outstanding. He famously coined the time period “temporal paradox” for the truth that the fossil file of the assumed theropod stem group of birds tends to be younger than the oldest precise birds. Last week I mentioned new proof that makes this temporal paradox a lot worse (Bechly 2023).
Beyond the Fossil Record
However, Feduccia’s critique of the dinosaur-bird speculation isn’t based mostly simply on issues with the fossil file, but in addition on conflicting proof from comparative anatomy. Now, he presents new proof that also extra sharply contradicts the consensus view. One of the arguments for a dinosaur-bird relationship has been the presence of a so-called “open” acetabulum, which “is a concave pelvic surface formed by the ilium, ischium, and pubis, which accommodates the head of the femur in tetrapods.” Feduccia (2024) studied the acetabulum in early basal birds and located that their acetabulum tends to be partially closed and an antitrochanter (technique of the ischium or iliac) is absent. This casts strongly into doubt one of many key characters for a dinosaur-bird relationship and means that this speculation have to be re-evaluated. The incontrovertible fact that microraptorids and troodontids “also exhibit partial closure of the acetabulum and lack an antitrochanter is a further incongruity in that these taxa should exhibit “typical” theropod pelvic girdle modifications for terrestrial cursoriality.” This may assist the view of a number of consultants (e.g., Martin 2004, and varied research cited by Feduccia), that these maniraptoran taxa characterize secondarily flightless birds moderately than theropod dinosaurs.
Feduccia concluded his new examine with this exceptional assertion:
The speculation that birds are maniraptoran theropod dinosaurs, regardless of the certitude with which it’s proclaimed, continues to endure from unaddressed difficulties … Until issues like these mentioned right here — and plenty of others that proceed to be dismissed both by enchantment to “consensus” or by way of overconfidence within the outcomes of phylogenetic evaluation of morphological knowledge — have satisfactorily been resolved, skepticism towards the present consensus and continued investigation of other hypotheses are needful for the promotion of crucial discourse in vertebrate phylogenetics and evolutionary biology.
Birds and dinosaurs might not characterize arbitrary chunks of an evolutionary grade in spite of everything, however might as a substitute characterize distinct pure varieties. At the very least, the proof appears to be far more ambiguous, weaker, and fewer convincing than most evolutionary biologists like to fake.
