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Fossil Friday: Rapid Elongation of Plesiosaur Necks Points to Intelligent Design

October 13, 2023, 6:49 AM
Photo credit: Ninjatacoshell, CC BY-SA 3.0 , via Wikimedia Commons.

Apart from ichthyosaurs, plesiosaurs likely represent the best-known group of Mesozoic marine reptiles. This may partly be related to the fact that they were discussed as potential identification for the Loch Ness monster by cryptozoologists, which of course is total nonsense. The distinctive body plan of plesiosaurs has been compared to a hybrid of a sea snake with a sea turtle. Studies suggest that they had a unique mode of swimming, with two pairs of flippers (Muscutt et al. 2017), but it has been a matter of considerable debate and speculation “whether both flipper pairs were moved up and down in synchrony or in some sort of alternating or asymmetrical gait” (Naish 2017). The most striking trait of plesiosaurs is their extremely elongated neck, which may have been very useful for catching fish. This elongated neck is already present in the older pachypleurosaurs, nothosaurs, and pistosaurs, which represent the assumed stem group from which plesiosaurs are thought to have evolved. They all belong to the 15 groups of marine reptiles that abruptly appeared in the Early Triassic after the Great Dying at the end of the Permian period (Bechly 2023).

Just Allometric Growth?

A new study by Liu et al. (2023), recently published in the journal BMC Ecology and Evolution, found that the neck length of plesiosaur-related pachypleurosaurs increased dramatically and doubled in length within only 5 million years in the Early Triassic (Freedman 2023). At first glance, it may seem that such an elongation of the neck is just allometric growth and therefore not out of the reach of unguided Darwinian mechanisms, but not so fast: indeed the neck of these marine reptiles was not just growing in length, as in giraffes which retain the normal number of vertebrae, but by an extreme multiplication of neck (cervical) vertebrae to as many as 72. This is a very unusual phenomenon and not easy to achieve for mutations without fatal consequences for the organism.

A study on abnormal numbers of cervical vertebrae in humans by Varela-Lasheras et al. (2011) showed that such deviations are generally deleterious. It might be objected that this is only true in mammals, where the number of cervical vertebrae is strictly constrained to seven (the only exceptions are manatees, sloths, lorises, and pottos, where homeotic mutations were responsible; Galis 1999, Böhmer et al. 2018, Galis et al. 2021), but maybe less so in reptiles, where the number of cervical vertebrae is less conserved. However, even in lizards deviations from the usual number of eight cervical vertebrae are extremely rare compared to the considerable individual variability for many other osteological traits (Barbadillo & Barahona 1994). Likewise, the usual number of nine cervical vertebrae in crocodilians was not broken even in the extinct, highly aberrant giant caiman Purussaurus (Scheyer et al. 2019). Obviously, the number of cervical vertebrae is highly conserved in reptiles as well and usually numbers around seven to nine.

Hard to Reconcile with Darwinian Evolution

Consequently, the breaking of the conserved number of cervical vertebrae is hard to reconcile with an unguided evolutionary mechanism, and better explained by intelligent design, which could coordinate changes and avoid deleterious consequences. Also, the very fast growth rate of the neck length exceeds the limitations of population genetics for the accumulation of mutations in a population of marine reptiles within the available window of time of less than 5 million years, which is about the average longevity of a single vertebrate species. This rather suggests coordinated non-random adaptive macromutations as a better explanation, which is my preferred model of the ID mechanism.

What is the evolutionary explanation suggested by the authors of the new study? They simply postulate an extremely rapid rate of change in the time of crisis after the end-Permian mass extinction (Freedman 2023), as if the opening of new niches by itself could create the genetic information required for biological novelty to emerge.

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