Tyrannosaurus rex hatchlings and dinosaur reproductive strategies (free pdf)
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Ben Creisler
Jul 7, 2026, 11:53:32 AM (10 days ago) Jul 7
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Ben Creisler
Free pdf:
Nicholas R. Longrich, Peter J. Makovicky, Tim Tokaryk, David M. L. Cooper, Evan T. Saitta, Gregory M. Erickson, Tamas Szekely and Eric Snively (2026)
Hatchlings of Tyrannosaurus rex and the Evolution of Dinosaur Reproductive Strategies
Biology 15(13): 1090
doi: https://doi.org/10.3390/biology15131090
https://www.mdpi.com/2079-7737/15/13/1090
Simple Summary
Dinosaurs were intermediate between more primitive reptiles and modern birds in their anatomy, and in some aspects of their biology. Their reproductive strategies remain poorly understood because fossils of young dinosaurs and eggs are rare. We report fossils of hatchling T. rex and other tyrannosaurs that help us understand the reproductive strategies of these animals. Tyrannosaurs had relatively small hatchlings compared to modern birds, suggesting they laid large numbers of eggs and provided relatively little care for hatchlings. Dinosaur reproductive strategies were likely intermediate between those of more primitive reptiles, with limited parental investment, and the advanced parental care strategies and intensive investment seen in modern birds.
Abstract
Tyrannosaurs were giant predatory dinosaurs that occupied the apex of Late Cretaceous food chains. Little is known about the early life and reproductive ecology of tyrannosaurs due to the extreme rarity of hatchling and juvenile fossils. We report bones of hatchlings (<1 yr) for Tyrannosaurus rex and Gorgosaurus libratus, weighing ~2.5 kg and ~2.4 kg, respectively, i.e., <0.1% of adult mass. Clutches were likely large. We conservatively estimate ~20 eggs in a small adult T. rex versus ~30 eggs in the largest T. rex, and clutches of ~15 eggs in G. libratus; larger clutches of 50 or even 100 eggs are not impossible. This suggests an r-selected reproductive strategy. Synchrotron scans reveal Haversian bone remodeling, suggesting that tyrannosaurs moved soon after hatching. Hatchling tyrannosaurs’ small size and precociality suggest limited parental care; teeth of hatchlings show wear suggesting that they fed on relatively large vertebrates. Tyrannosaurs had proportionately larger offspring than most reptiles, but relatively smaller hatchlings than Eumaniraptora and birds, suggesting retention of a primitive reproductive strategy intermediate between that of basal diapsids and birds. Multiple dinosaur lineages evolved large eggs independently, suggesting an evolutionary trend towards increased parental investment.
A new paper:
Free pdf:
Nicholas R. Longrich, Peter J. Makovicky, Tim Tokaryk, David M. L. Cooper, Evan T. Saitta, Gregory M. Erickson, Tamas Szekely and Eric Snively (2026)
Hatchlings of Tyrannosaurus rex and the Evolution of Dinosaur Reproductive Strategies
Biology 15(13): 1090
doi: https://doi.org/10.3390/biology15131090
https://www.mdpi.com/2079-7737/15/13/1090
Simple Summary
Dinosaurs were intermediate between more primitive reptiles and modern birds in their anatomy, and in some aspects of their biology. Their reproductive strategies remain poorly understood because fossils of young dinosaurs and eggs are rare. We report fossils of hatchling T. rex and other tyrannosaurs that help us understand the reproductive strategies of these animals. Tyrannosaurs had relatively small hatchlings compared to modern birds, suggesting they laid large numbers of eggs and provided relatively little care for hatchlings. Dinosaur reproductive strategies were likely intermediate between those of more primitive reptiles, with limited parental investment, and the advanced parental care strategies and intensive investment seen in modern birds.
Abstract
Tyrannosaurs were giant predatory dinosaurs that occupied the apex of Late Cretaceous food chains. Little is known about the early life and reproductive ecology of tyrannosaurs due to the extreme rarity of hatchling and juvenile fossils. We report bones of hatchlings (<1 yr) for Tyrannosaurus rex and Gorgosaurus libratus, weighing ~2.5 kg and ~2.4 kg, respectively, i.e., <0.1% of adult mass. Clutches were likely large. We conservatively estimate ~20 eggs in a small adult T. rex versus ~30 eggs in the largest T. rex, and clutches of ~15 eggs in G. libratus; larger clutches of 50 or even 100 eggs are not impossible. This suggests an r-selected reproductive strategy. Synchrotron scans reveal Haversian bone remodeling, suggesting that tyrannosaurs moved soon after hatching. Hatchling tyrannosaurs’ small size and precociality suggest limited parental care; teeth of hatchlings show wear suggesting that they fed on relatively large vertebrates. Tyrannosaurs had proportionately larger offspring than most reptiles, but relatively smaller hatchlings than Eumaniraptora and birds, suggesting retention of a primitive reproductive strategy intermediate between that of basal diapsids and birds. Multiple dinosaur lineages evolved large eggs independently, suggesting an evolutionary trend towards increased parental investment.
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Ben Creisler
Jul 7, 2026, 2:44:20 PM (10 days ago) Jul 7
to DinosaurMa...@googlegroups.com
A video:
Baby T. rex and the Evolution of Vertebrate Parental Care
Nick Longrich Evolution and Paleontology (video)
66 min.
https://www.youtube.com/watch?v=zd0dR2n9hLA
Nick Longrich Evolution and Paleontology (video)
66 min.
https://www.youtube.com/watch?v=zd0dR2n9hLA
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