Herbivores diversified quickly after mass extinctions to eat different kinds of plants

The evolution of herbivores is linked to the plants that survived and adapted after the ‘great dying’ when over 90% of the world’s species were wiped out 252 million years ago.

The Triassic (252–201 Ma) marked significant punctuation in Earth history when ecosystems rebuilt themselves following the devastating Permian-Triassic mass extinction. During this period, herbivory evolved several times independently, and many new kinds of plants and animals emerged.

A new study by scientists from the University of Bristol focuses on the plant-eaters, including some of the first dinosaurs. Herbivores are the animals in any ecosystem.

Scientists found that herbivores showed remarkable evidence of specialization in the turbulent times after the great mass extinction.

During the great mass extinction, over 90% of the world’s species were wiped out. And the evolution of herbivores is linked to the plants that survived and adapted after the ‘great dying.’

Herbivores were found to be diversified quickly after mass extinctions to explore and” eat different kinds of plants.

Triassic herbivores illustration
Triassic herbivores illustration Image: James Ormiston

Dr. Tom Stubbs, a collaborator, said, “We were surprised to be able to identify definite specializations among the herbivores. We call these groups the ingestion generalists, prehension specialists, durophagous specialists, shearing pulpers, and heavy oral processors; these names reflect the power of their jaws, their teeth, and the kinds of plants they would likely have been eating.”

Professor Emily Rayfield, who also co-led the project, said, “It might seem to be a speculative enterprise to identify the diets of animals that died over 200 million years ago. But we measured hundreds of fossil jaws and compared their shapes with living animals. We estimated key functional values from the fossil jaws such as mechanical advantage and bite force, measuring the leverage of the jaws and how fast or forcefully they could shut.”

Dr. Armin Elsler, collaborator, said, “We were able to map the evolution of all the functional characters relating to feeding across the evolutionary tree and through time. We found to our surprise that, during this time, several new groups diversified as herbivores, and they seemed to take over their roles by pushing potential competitors aside, not necessarily by wiping them out.”

Dr. Singh said, “Some of the evolution of herbivores relates to the availability of new kinds of plant food. One key thing was the expansion of groups that we’re able to handle tough plant material, with powerful jaws for chopping and chomping.”

“This reflected the drying conditions especially in the Late Triassic when many softer plant groups became less common, and dry-adapted conifers, for example, spread worldwide. These changes combined with strictly enforced niche separation drove patterns of extinction as the generalist, hardy herbivores thrived, as other herbivores died out.”

Professor Mike Benton, who co-led the study, said, “This kind of macroecological analysis represents a huge amount of work. But it sheds real light on key processes at an ecological level and helps explain why some groups died out and were replaced by others, such as the first dinosaurs. We can be reasonably certain of the results because we have excellent data on the geological ages of the specimens, their relationships to each other, and the key features of their jaws and teeth that correspond to their ancient diets. What was once quite a speculative kind of project has now become much more analytical and testable.”

Journal Reference:
  1. Singh, S.A., Elsler, A., Stubbs, T.L. et al. Niche partitioning shaped herbivore macroevolution through the early Mesozoic. Nat Commun 12, 2796 (2021). DOI: 10.1038/s41467-021-23169-x

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