{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,7]],"date-time":"2026-07-07T12:22:02Z","timestamp":1783426922479,"version":"3.54.6"},"reference-count":148,"publisher":"MDPI AG","issue":"13","license":[{"start":{"date-parts":[[2026,7,7]],"date-time":"2026-07-07T00:00:00Z","timestamp":1783382400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Biology"],"abstract":"<jats:p>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 (&lt;1 yr) for Tyrannosaurus rex and Gorgosaurus libratus, weighing ~2.5 kg and ~2.4 kg, respectively, i.e., &lt;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\u2019 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.<\/jats:p>","DOI":"10.3390\/biology15131090","type":"journal-article","created":{"date-parts":[[2026,7,7]],"date-time":"2026-07-07T09:53:46Z","timestamp":1783418026000},"page":"1090","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Hatchlings of Tyrannosaurus rex and the Evolution of Dinosaur Reproductive Strategies"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9586-8907","authenticated-orcid":false,"given":"Nicholas R.","family":"Longrich","sequence":"first","affiliation":[{"name":"Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9307-9982","authenticated-orcid":false,"given":"Peter J.","family":"Makovicky","sequence":"additional","affiliation":[{"name":"Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN 55455, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tim","family":"Tokaryk","sequence":"additional","affiliation":[{"name":"Department of Earth Sciences, University of Regina, Regina, SK S4S 0A2, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"David M. L.","family":"Cooper","sequence":"additional","affiliation":[{"name":"Department of Anatomy, Physiology and Pharmacology, University of Saskatchewan, Saskatoon, SK S7N 5SA2, Canada"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9306-9060","authenticated-orcid":false,"given":"Evan T.","family":"Saitta","sequence":"additional","affiliation":[{"name":"Field Museum of Natural History, Integrative Research Center, Life Sciences Section, Chicago, IL 60605, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gregory M.","family":"Erickson","sequence":"additional","affiliation":[{"name":"Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tamas","family":"Szekely","sequence":"additional","affiliation":[{"name":"Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4046-0282","authenticated-orcid":false,"given":"Eric","family":"Snively","sequence":"additional","affiliation":[{"name":"Oklahoma State University College of Osteopathic Medicine at the Cherokee Nation, Tahlequah, OK 74464, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,7,7]]},"reference":[{"key":"ref_1","unstructured":"Weishampel, D.B., Dodson, P., and Osmolska, H. 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