These long-necked reptiles were decapitated by their predators, fossil evidence confirms

Newswise — During the era of dinosaurs, numerous aquatic reptiles possessed notably elongated necks in contrast to modern reptiles. Despite being an evidently prosperous evolutionary tactic, scientists have harbored suspicions for a considerable period that their lengthy necks rendered them susceptible to predators. Presently, after nearly two centuries of ongoing investigation, tangible fossil evidence substantiates this hypothesis in the most vivid manner conceivable.

In a study published in the journal Current Biology on June 19, scientists examined the distinctive necks of two Tanystropheus species from the Triassic period. Tanystropheus is a reptile species distantly linked to crocodiles, birds, and dinosaurs. These reptiles exhibited peculiar necks comprising 13 remarkably elongated vertebrae and rib-like struts. As a result, it is believed that these marine reptiles had rigid necks and employed an ambush strategy to capture their prey. However, it appears that Tanystropheus's predators also capitalized on the advantages offered by its lengthy neck.

Close scrutiny of fossilized remains has revealed unmistakable bite marks on the severed necks of two distinct species. These specimens, belonging to different species, exhibit clear signs of predation, including a bite mark precisely at the point where one of the necks was fractured. According to the researchers, these findings provide macabre and highly uncommon proof of predator-prey interactions in the fossil record dating back more than 240 million years ago.

Stephan Spiekman from the Staatliches Museum für Naturkunde Stuttgart in Germany remarked, "Paleontologists had previously speculated that the elongated necks of these reptiles presented an obvious vulnerability to predation, as famously depicted in Henry de la Beche's renowned painting from 1830, almost 200 years ago." He further added, "However, prior to our current study on these two Tanystropheus specimens, there was no evidence of decapitation or any other specific attacks targeting the necks in the extensive fossil record of long-necked marine reptiles."

Having conducted his doctoral research at the Paleontological Museum of the University of Zurich, Switzerland, Spiekman possesses intimate knowledge of these reptiles. The specimens in question are housed in the very museum where he studied. Through his investigation, he identified two distinct Tanystropheus species coexisting within the same habitat. The smaller species, measuring approximately one and a half meters in length, likely subsisted on soft-shelled creatures such as shrimp. On the other hand, a considerably larger species, reaching lengths of up to six meters, fed on fish and squid. Moreover, Spiekman's findings indicated clear indications in the skull structure of Tanystropheus, suggesting that it primarily inhabited aquatic environments.

It was widely acknowledged that two specimens of these Tanystropheus species possessed remarkably preserved heads and necks that terminated abruptly. There had been speculations regarding the possibility of these necks being bitten off, but no comprehensive study had been conducted on the matter. In this recent research, Spiekman collaborated with Eudald Mujal, also from the Stuttgart Museum, and a research associate at the Institut Català de Paleontologia Miquel Crusafont in Spain. Mujal is an expert in fossil preservation and the study of predatory interactions in the fossil record, particularly through the examination of bite traces on bones. After devoting an afternoon to examining the two specimens in Zurich, the researchers reached the conclusive determination that the necks had indeed been bitten off.

Mujal highlighted an intriguing observation, stating, "One striking aspect is that the skull and a section of the neck that are preserved show no signs of disturbance, except for some disarticulation resulting from the natural decay of a carcass in a tranquil environment." He further emphasized, "Only the neck and head regions have been preserved, while there is an absence of any evidence pertaining to the remainder of the animals. The abrupt termination of the necks strongly suggests that they were completely severed by another animal during an exceptionally violent event, as indicated by the presence of tooth marks."

Mujal further elaborated, stating, "The remarkably preserved condition of the head and neck implies that when these specimens reached their final resting place, their bones were still enveloped by soft tissues like muscles and skin." He continued, "It is evident that they were not preyed upon by the predator. While this is speculative, it is reasonable to assume that the predators were less interested in the slender neck and small head, instead targeting the more substantial and meatier parts of the body. Considering all these factors, it is highly probable that both individuals were decapitated during the hunt rather than being scavenged, although scavenging cannot be completely ruled out in fossils of such antiquity."

Spiekman noted an intriguing observation, stating, "Interestingly, the same scenario unfolded for both specimens, despite the fact that they represent individuals from two distinct Tanystropheus species, which vary significantly in size and potentially in lifestyle." This suggests that although executed by different predators, the decapitation event occurred similarly for both specimens.

The researchers assert that the recent findings validate previous interpretations regarding the distinctive evolutionary structure of the ancient reptiles' necks. These necks were considerably narrower and more rigid compared to the long necks observed in plesiosaurs. The study further demonstrates that the evolution of a long neck in marine reptiles carried potential disadvantages. However, the researchers acknowledge that despite the drawbacks, elongated necks proved to be an immensely successful evolutionary strategy. They were found in numerous marine reptile species spanning a remarkable duration of 175 million years.

Spiekman highlights the fundamental concept of trade-offs in evolution, stating, "In a broad perspective, our research reaffirms that evolution involves balancing advantages and risks." He further emphasizes that the benefits of possessing a long neck outweighed the vulnerability to predator attacks for an extensive period. Tanystropheus, in particular, achieved considerable success from an evolutionary standpoint, with a lifespan of at least 10 million years and a geographic distribution spanning Europe, the Middle East, China, North America, and potentially South America.

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