Locomotive versatility helped dinosaurs adapt and survive

Researchers from the University of Bristol have unveiled new insights into the locomotive versatility of dinosaurs, attributing their adaptability as a key factor to their dominance on Earth for 160 million years. 

This study, published in the journal Royal Society Open Science, demonstrates that the earliest dinosaurs possessed superior speed and dynamism compared to their contemporaries, which significantly contributed to their evolutionary success.

Locomotion styles 

By analyzing limb proportions of various reptiles from the Triassic period (252 to 201 million years ago) – the era marking the emergence and ascendancy of dinosaurs – the team was able to discern the locomotion styles of these ancient creatures. 

They distinguished between quadrupedal (four-footed) and bipedal (two-footed) species, additionally evaluating their cursoriality index, indicative of their running capabilities.

Evolutionary advantage 

The findings revealed that dinosaurs and their close relatives were inherently bipedal and cursorial, meaning their limbs were evolutionarily fashioned for running. This adaptability allowed them a broader spectrum of running styles than their rivals, the Pseudosuchia, which included the progenitors of today’s crocodiles.

“When the crunch came, 233 million years ago, dinosaurs won out,” said lead author Amy Shipley, an MSc Palaeobiology student at Bristol. “At that time, climates shifted from wet to dry, intensifying the competition for food. Despite being relatively few in number for 20 million years, dinosaurs managed to flourish while the pseudosuchians faltered.”

Survival and expansion

The study suggests that dinosaurs’ capability for water conservation, akin to many of today’s reptiles and birds, alongside their versatile mobility, were crucial to their survival and expansion, especially following the mass extinction at the Triassic’s close. 

“After the end of the Triassic, when there was a mass extinction, the dinosaurs expanded again,” said study senior author Mike Benton, a professor of Paleontology at the same university. 

“Most of the pseudosuchians were wiped out by the mass extinction, except for the ancestors of crocodiles, and we found that these surviving dinosaurs expanded their range of locomotion again, taking over many of the empty niches.”

New insights

Contrary to expectations, the research, co-authored by Dr Armin Elsler, found that dinosaurs did not evolve at exceptionally rapid rates. 

“This was a surprise because we expected to see fast evolution in avemetatarsalians and slower evolution in pseudosuchians. What this means is that the locomotion style of dinosaurs was advantageous to them, but it was not an engine of intense evolutionary selection. In other words, when crises happened, they were well placed to take advantage of opportunities after the crisis,” Elsler explained.

Immensely adaptable 

Dr Tom Stubbs, another collaborator, highlighted the misconception of dinosaurs as solely massive, slow-moving creatures, pointing out their origins as agile, bipedal insect-eaters. This agility and varied leg posture enabled their ancestors to swiftly navigate their environments, capturing prey while evading larger predators.

“And of course, their diversity of posture and focus on fast running meant that dinosaurs could diversify when they had the chance. After the end-Triassic mass extinction, we get truly huge dinosaurs, over ten meters long, some with armor, many quadrupedal, but many still bipedal like their ancestors,” said co-author Suresh Singh. “The diversity of their posture and gait meant they were immensely adaptable, and this ensured strong success on Earth for so long.” 

The study not only sheds light on the evolutionary prowess of dinosaurs but also underscores the significance of adaptability in the face of changing environmental conditions and crises.

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