Research: Just how big could dinosaurs get?

By Dr. Tim Sandle
July 27, 2024
DIGITAL JOURNAL

Tyrannosaurus rex holotype specimen at the Carnegie Museum of Natural History, Pittsburgh. — ScottRobertAnselmo — CC BY-SA 3.0

Scientists have assessed just how large dinosaurs could really get. The answer is much bigger than we had previously realised. The inquiry finds, as an example, that the maximum size of T. rex is estimated to be 70% heavier than current values.

The focus of the research from the Canadian Museum of Nature is with the maximum possible sizes of dinosaurs, using the carnivore Tyrannosaurus rex, as an example. Using computer modelling, scientists produced new estimates that T. rex might have been 70 percent heavier than what previous assessment based on the fossil evidence had suggested.

The research was led by Dr. Jordan Mallon of the Canadian Museum of Nature and Dr. David Hone of Queen Mary University of London. The problem they faced exists because most dinosaur species are known from only one or a handful of specimens.

Current research suggests that previous assessments were under-estimates. Hence, the question remains: how big were the largest individuals, and are we likely to find them?

To address this question, Mallon and Hone used computer modelling to assess a population of T. rex. They factored in variables such as population size, growth rate, lifespan, the incompleteness of the fossil record, and other measures.

The dinosaur T. rex was chosen for the model because it is a familiar dinosaur for which many of these details are already well estimated.

Body-size variance at adulthood, which is still poorly known in T. rex, was modelled with and without sex differences, and is based on examples of living alligators, chosen for their large size and close kinship with the dinosaurs.

The palaeontologists found that the largest known T. rex fossils probably fall in the 99th percentile, representing the top 1 percent of body size. However, to find an animal in the top 99.99 percent (a one-in-ten-thousand individual) scientists would need to excavate fossils at the current rate for another 1,000 years.

To overcome this, computer models can provide the necessary data. The computer models suggest that the largest individual that could have existed (one in 2.5 billion animals) may have been 70 percent more massive than the current largest-known T. rex specimens (an estimated 15 tonnes vs 8.8 tonnes) and 25 percent longer (15 metres vs 12 metres).

The values are estimates based on the model, but patterns of discovery of giants of modern species tell us there must have been larger dinosaurs out there that have not yet been found.

This study adds to the debates about the largest fossil animals. Many of the largest dinosaurs in various groups are known from a single good specimen, so remains impossible to know if that one animal was a big or small example of the species.

An apparently large species might be based on a single giant individual, and a small species based on a particularly tiny individual — neither of which reflect the average size of their respective species.

The research appears in the journal Ecology and Evolution, titled “Estimation of maximum body size in fossil species: A case study using Tyrannosaurus rex.”