In a study published in the journal Papers in Palaeontology, paleontologists from the State Museum of Natural History Stuttgart investigated growth rates of Macrospondylus bollensis, a speices of teleosauroid crocodyliform from the Jurassic of Europe.
A Macrospondylus bollensis mother keeps a watchful eye on her young. Image credit: Henry Sutherland Sharpe.
Macrospondylus bollensis lived in what is now Europe during the Early Jurassic epoch, between 183 and 182 million years ago.
The reptile’s length was estimated at 5.5 m (18 feet), making it the largest known Early Jurassic crocodylomorph.
Also known as Steneosaurus bollensis, the species is particularly abundant in the Posidonienschiefer Formation (Posidonia Shale) of southwestern Germany.
“Multiple well-preserved specimens have been found, ranging in body size from less than 1 m to c. 5 m,” said lead author Dr. Michela Johnson and her colleagues from the State Museum of Natural History Stuttgart.
“This massive range in size makes Macrospondylus bollensis an ideal species for growth rate studies.”
In the study, the researchers performed statistical analyses on 16 juvenile, 7 subadult, and 39 adult specimens of Macrospondylus bollensis from the Posidonienschiefer Formation.
They found that much of the body in these crocodyliforms grew isometrically.
This means that in Macrospondylus bollensis, many parts of the body show a near-uniform growth in all age stages in relation to the total growth. This is very unusual in vertebrates.
“The most important finding of our study is that juvenile, subadult and adult individuals show nearly equal growth in many areas of the body,” Dr. Johnson said.
“We also call this isometric growth, which is unusual in vertebrates.”
“But that’s why Macrospondylus bollensis juveniles look quite similar to adults.”
“In many vertebrates, individual body parts, such as the legs, grow either faster or slower than other parts of the body,” the scientists explained.
“Our analyses show that the scaling of the limbs in Macrospondylus bollensis is different from that of modern alligators and crocodiles, but comparable to that of the now critically endangered Indian gavial (Gavialis gangeticus).”
“Why isometric growth was present in Macrospondylus bollensis is still unclear.”
“Our study raises new questions about the ecology and lifestyle of these animals, which we hope to clarify with further research.”
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Michela M. Johnson et al. 2023. Evaluating growth in Macrospondylus bollensis (Crocodylomorpha, Teleosauroidea) in the Toarcian Posidonia Shale, Germany. Papers in Palaeontology 9 (5): e1529; doi: 10.1002/spp2.1529
