Note: This is an AI-assisted English translation of the original Portuguese post published on 4 May 2012 at Ciência ao Natural. The original text was written by Luís Azevedo Rodrigues and is reproduced here for archival and educational purposes.
This text was written following contact from journalist Marco Túlio Pires of the Brazilian magazine Veja, who wanted my comment on an article published in Nature Communications about dinosaur morphology. The article in question was by Roger Benson and colleagues, and it addressed a question that is both scientifically fascinating and surprisingly underexplored: what is the relationship between morphological disparity and species diversity in dinosaurs?
Two Ways of Measuring Diversity
When we talk about the "diversity" of a group of organisms, we can mean two quite different things.
Biodiversity — in its most common usage — refers to the number of species: how many distinct species belong to a given group at a given time. This is the metric that most people have in mind when they talk about the diversity of dinosaurs.
Morphological disparity, on the other hand, refers to the variety of body plans, shapes and sizes within a group. A group can have many species but relatively little morphological disparity (if all the species look broadly similar), or it can have few species but enormous morphological disparity (if the species are radically different from one another in their anatomy).
What the Study Found
Benson and colleagues analysed a large dataset of dinosaur specimens, coding hundreds of anatomical characters for each, and used this data to quantify both the species diversity and the morphological disparity of different dinosaur groups through time.
Their key finding was that morphological disparity and species diversity did not always track each other in the history of the dinosaurs. In some groups and at some times, high species diversity was accompanied by high morphological disparity — as one might expect if diversification was driven by ecological opportunity. But in other cases, the two metrics diverged: species diversity could be high while morphological disparity remained relatively low, or vice versa.
This finding has important implications for how we interpret the fossil record. Species counts alone can be misleading as a measure of evolutionary success or ecological diversity. A group with 50 morphologically similar species may be less ecologically diverse — occupying fewer ecological niches, exploiting fewer resources — than a group with 10 morphologically disparate species.
The Broader Significance
The distinction between biodiversity and morphological disparity is not merely an academic one. It has practical implications for conservation biology: a group of organisms with high species diversity but low morphological disparity may be more vulnerable to extinction than its species count would suggest, because the loss of a few key lineages could eliminate a disproportionate amount of morphological and ecological diversity.
It also has implications for how we reconstruct the history of life. The Cambrian explosion — the rapid diversification of animal body plans approximately 540 million years ago — is often described as an explosion of biodiversity, but it is more accurately described as an explosion of morphological disparity: the number of fundamentally different body plans (phyla) that appeared in the Cambrian has never been exceeded, even though species diversity has continued to increase throughout the history of animal life.
Dinosaurs, it turns out, are a useful model system for exploring these questions — not just because they are spectacular and well-known, but because their fossil record is good enough to allow the kind of quantitative analysis that Benson and colleagues have undertaken.
Original post published on 4 May 2012 on the blog Ciência ao Natural.
Written by
Luís Azevedo Rodrigues
Palaeontologist & Science Communicator