Slower Growth, Longer Life: The Woodward Study and the New T. rex

1. Introduction: The Evolution of T. rex, as an Paleontological Icon

In the pantheon of extinct organisms, Tyrannosaurus rex occupies a singular position. Since its initial description by Henry Fairfield Osborn in 1905, based on fossils recovered from the Hell Creek Formation of Montana, this theropod has served as the de facto ambassador of the Dinosauria.¹ For over a century, the scientific understanding of T. rex has undergone radical transformations that mirror the broader evolution of paleobiology itself. Initially reconstructed as a lumbering, tail-dragging, cold-blooded reptile—a "land crocodile" reliant on scavenging—the image of the Tyrant King was rehabilitated during the "Dinosaur Renaissance" of the late 20th century. This paradigm shift, driven by the work of researchers such as John Ostrom and Robert Bakker, reimagined dinosaurs as active, metabolically dynamic, and socially complex animals, more akin to birds than to lizards.

Central to this modern understanding was the question of growth. How did a hatchling, likely weighing no more than a few kilograms, transform into an 8,000-kilogram apex predator? For decades, this question remained a matter of speculation, inferred from scaling relationships with extant reptiles. However, the application of paleohistology—the study of fossil bone microstructure—in the late 1990s and early 2000s provided the first empirical window into the life history of these giants.

The prevailing consensus for the past two decades was established by a landmark 2004 study led by Gregory Erickson. By counting growth lines in the bones of seven specimens, Erickson and colleagues proposed that T. rex achieved its massive size through an explosive adolescent growth spurt. Their model depicted a biological rocket launch: a teenage T. rex would gain up to 2.1 kilograms per day, effectively quadrupling its size in a mere handful of years, and reaching skeletal maturity by age 20.¹ This "live fast, die young" hypothesis suggested a creature operating at the physiological limits of growth, with a lifespan capped at roughly 30 years.

However, science is iterative. In January 2026, a team of researchers led by Dr. Holly Woodward of Oklahoma State University, alongside mathematician Nathan Myhrvold and paleontologist Jack Horner, published a study in PeerJ that fundamentally challenges this established narrative.¹ Leveraging the largest histological dataset of Tyrannosaurus ever assembled and utilizing advanced imaging techniques that revealed previously invisible data, the 2026 study posits a radically different life history. Their findings suggest that T. rex grew more slowly, matured much later (between 35 and 40 years of age), and lived significantly longer than previously thought.¹

This report provides an exhaustive analysis of these new findings. It explores the methodological innovations of cross-polarized light microscopy that allowed researchers to "read" the hidden years in the fossil record. It examines the profound implications of this slower growth curve for the validity of the controversial taxon Nanotyrannus lancensis. Finally, it reconstructs the ecology of Late Cretaceous North America, visualizing a predator that dominated the landscape not just through adult brute force, but through a prolonged, agile subadult phase that effectively crowded out all competitors.

2. The Science of Skeletochronology: Reading the Rings of Deep Time

To appreciate the magnitude of the 2026 revision, one must first understand the "black box" of dinosaur growth: the internal microstructure of fossilized bone. Skeletochronology is the discipline of estimating the age of an individual organism by counting cyclical growth marks recorded in skeletal tissues. This method is analogous to dendrochronology (tree-ring dating), but the biological reality of vertebrate bone is far more dynamic and destructive than the inert cellulose of a tree trunk.

2.1 The Deposition of Growth Marks

In many extant vertebrates, particularly those in temperate climates with distinct seasons, bone growth is not continuous. It is cyclical. During favorable periods—typically the warm, wet seasons—metabolic resources are abundant, and the animal grows rapidly. The bone tissue deposited during this phase is often "woven-fibered" or highly vascularized, characterized by a disorganized matrix of collagen fibers laid down quickly to accommodate rapid expansion.⁵

Conversely, during unfavorable periods—such as the cold, resource-poor winter months or dry seasons—growth slows down or ceases entirely. This physiological throttle leaves a permanent record in the bone cortex.

• Lines of Arrested Growth (LAGs): When growth stops completely, a thin, dark line of hyper-mineralized tissue is deposited. In cross-section, these appear as distinct rings.⁵

• Annuli: When growth slows significantly but does not stop, the bone texture shifts from the chaotic woven pattern to a more organized "parallel-fibered" or "lamellar" bone. These bands, known as annuli, represent periods of lethargy or resource scarcity.¹

By sectioning a limb bone and counting these LAGs and annuli, paleontologists can infer the chronological age of the animal at death. However, Tyrannosaurus rex presents a unique histological challenge: massive internal remodeling.

2.2 The Challenge of Remodeling and Retrocalculation

As a theropod dinosaur grows, its bones do not simply accrue layers on the outside; they change shape and structure internally to support increasing weight. The medullary cavity—the hollow, marrow-filled center of the bone—expands outward as the animal matures. This expansion is destructive. It erodes the innermost layers of the cortical bone, effectively erasing the growth record of the animal's juvenile years.¹

In a massive adult specimen like "Sue" (FMNH PR 2081), the first 10 to 15 years of growth rings may be completely obliterated by the medullary cavity or obscured by secondary remodeling (the formation of dense Haversian bone). To overcome this, researchers use a mathematical technique called "retrocalculation".¹⁰ This involves superimposing the growth records of smaller, younger specimens (whose early rings are still intact) onto the cross-sections of adults. By "stitching" these records together, scientists can estimate the number of missing rings in the adult's hollow center.¹

2.3 Methodological Limitations of the 2004 Model

The Erickson et al. (2004) study was a pioneering effort that established the first quantitative baseline for tyrannosaur growth. However, the 2026 retrospective identifies several critical limitations in that early methodology:

1. Element Selection: The 2004 study utilized a mixture of skeletal elements, including ribs, gastralia (belly ribs), and fibulae.³ While these bones are easier to sample than a massive femur, they are non-weight-bearing or functionally distinct elements that may record growth differently. Ribs, for instance, remodel at different rates than limb bones. The 2026 Woodward study restricted its analysis exclusively to the major weight-bearing bones—femora and tibiae—to ensure a consistent record of body mass support.¹

2. Visualization Techniques: The earlier study relied primarily on standard transmitted light microscopy. Under normal light, distinct LAGs are visible, but faint annuli—zones of slow but continuous growth—can be difficult to distinguish from the surrounding fast-growing tissue. If these faint bands are missed, the observer counts fewer years, leading to an underestimation of age and an overestimation of growth rate.⁴

3. The 2026 Innovation: Illuminating the Invisible

The core breakthrough of the Woodward, Myhrvold, and Horner study lies in the rigorous application of cross-polarized light (CPL) microscopy. This technique exploits the optical properties of collagen, the primary structural protein in bone.

3.1 The Physics of Birefringence in Bone

Collagen fibers are anisotropic and birefringent. Birefringence refers to the property of a material to refract light into two distinct rays (the ordinary and extraordinary rays) depending on the polarization and propagation direction of the light.¹³ The refractive index of collagen depends on its orientation.

• Woven Bone (Fast Growth): In rapidly deposited bone, collagen fibers are loosely packed and randomly oriented. When viewed under cross-polarized light, this disorganization results in a generally dark or isotropic appearance because there is no uniform alignment to refract the light coherently.⁶

• Lamellar/Parallel-Fibered Bone (Slow Growth/Annuli): During periods of slow growth, the body lays down collagen in highly organized, parallel sheets. This alignment creates strong birefringence. When polarized light passes through these organized bands, it is rotated, causing the bands to "light up" or appear bright against the dark background of the woven bone.¹³

3.2 Finding the "Lost Years"

By analyzing thin sections of T. rex femora under CPL, Woodward’s team discovered numerous "faint annuli" that were invisible under standard light. These bands represented years where the animal’s growth slowed down but did not stop completely.1

Previous studies, lacking the sensitivity of CPL to detect these subtle structural changes, had likely interpreted these zones as continuous periods of rapid growth. The 2026 analysis revealed that what looked like a single year of massive growth might actually be two or three years of moderate growth interspersed with these faint slowdowns.

The cumulative effect of these discoveries was dramatic. Specimens that were previously aged at 18 or 20 years old were found to be significantly older—perhaps 24 or 26. When the same amount of body mass is accumulated over a longer period of time, the growth rate curve flattens. The "vertical" growth spurt of the 2004 model was replaced by a shallower, steadier incline.⁴

4. The New Growth Curve: The "Mature Monarch" Hypothesis

The results of the 2026 PeerJ study fundamentally rewrite the biography of Tyrannosaurus rex. The data indicates a life history characterized by prolonged development, delayed maturity, and exceptional longevity.

4.1 Delayed Skeletal Maturity

One of the most robust indicators of skeletal maturity in vertebrates is the External Fundamental System (EFS). The EFS is a band of tightly stacked LAGs at the outermost surface of the bone cortex, formed when the animal has effectively stopped growing in size and is only maintaining its skeleton.16

The Erickson (2004) model suggested that T. rex reached this plateau in its early 20s. However, the 2026 study found that an EFS was absent in the majority of specimens, including many large adults. An EFS was only observed in the very oldest and largest individuals, indicating that T. rex continued to grow actively well into its third decade.1

The study concludes that asymptotic body size—the theoretical maximum weight—was not achieved until approximately 35 to 40 years of age.¹ This is a staggering extension of the growth phase, nearly doubling the time to maturity proposed by earlier models. It implies that "Sue," estimated to be around 28–30 years old at death, was not a geriatric animal at the end of its life, but a mature adult that was likely still growing.⁴

4.2 Revised Growth Rates

Because the animal was accumulating its 8,000+ kg mass over 35 years rather than 20, the annual growth rate must be lower. The 2004 model estimated peak growth rates of ~767 kg/year (2.1 kg/day). The 2026 study, using varying statistical models (Variants A, NoM, NoX, NoXM), calculated lower maximum growth rates. The "NoXM" variant, for example, indicated a maximum growth rate of approximately 557.2 kg/year.¹

While gaining half a ton a year is still an impressive biological feat, this reduction in rate has significant physiological implications. A slower, steadier growth trajectory suggests a metabolic strategy that was less energetically volatile. It implies that T. rex may have been better adapted to survive seasonal fluctuations in resource availability, spreading the energetic cost of gigantism over a longer period.⁹

4.3 Statistical "Stitching" of the Curve

To create this new curve, the team employed a sophisticated statistical approach led by Nathan Myhrvold. They utilized a dataset of 17 individuals, ranging from small juveniles to large adults. Rather than treating each specimen as a single point on a graph, they used the histological data to reconstruct the individual growth history of each bone.

Using a "stitching" method, they overlapped the growth trajectories of juveniles (like "Jane") with subadults and adults to create a composite curve. This method allowed for the calculation of simultaneous confidence bands, providing a statistical range of expected size-at-age for the entire species complex.1 This rigorous statistical framework provided the necessary evidence to tackle one of the most controversial topics in paleontology: Nanotyrannus.

5. The Nanotyrannus Divergence: A Distinct Lineage

The debate over Nanotyrannus lancensis has raged since the 1988 redescription of a small tyrannosaur skull (CMNH 7541) originally found in 1942. Critics, notably Thomas Carr and Jack Horner, have long argued that Nanotyrannus is invalid, representing merely the juvenile form of T. rex. They cited the "plasticity" of dinosaur skulls during ontogeny, arguing that the distinct features of "Nano" (narrow snout, more teeth) would morph into the robust T. rex form with age.²

The 2026 PeerJ study, however, provides powerful histological evidence that supports the validity of Nanotyrannus as a distinct species.

5.1 The "Jane" and "Petey" Problem

Central to this analysis were two specimens housed at the Burpee Museum of Natural History: BMRP 2002.4.1 ("Jane") and BMRP 2006.4.4 ("Petey"). These specimens have historically been pivotal to the "juvenile T. rex" argument. In fact, a 2020 study also led by Woodward initially interpreted them as juveniles based on the absence of an EFS.²⁰

However, the 2026 re-analysis, equipped with the new, robust T. rex growth curve, yielded a different result. When the size-at-age data for "Jane" and "Petey" were plotted against the composite T. rex curve, they did not fit. They fell outside the 95% confidence intervals of the model.¹

• The Mismatch: If "Jane" were a juvenile T. rex, her growth trajectory should align with the early phase of the T. rex curve. Instead, the data showed that she was growing at a fundamentally different rate—too slow to ever catch up to the "Sue" trajectory within a normal lifespan.

• Statistical Incompatibility: The authors note that the growth patterns of these two specimens are "not statistically compatible" with the rest of the T. rex dataset.¹ While they acknowledge that pathological stunting is a theoretical possibility, the consistency between the two specimens suggests a taxonomic distinction.

5.2 Convergence with Morphological Evidence

This histological divergence aligns perfectly with recent morphological studies. A 2024 paper by Nicholas Longrich and Evan Saitta presented a comprehensive analysis of over 150 anatomical characters separating Nanotyrannus from T. rex. Their study highlighted differences in skull architecture, arm length, and tooth count that are not seen in the developmental series of other tyrannosaurs like Tarbosaurus or Gorgosaurus.²¹

Furthermore, Longrich and Saitta identified a frontal bone from a true juvenile T. rex that looked radically different from the Nanotyrannus skulls. The T. rex juvenile frontal showed the beginnings of the broad, robust structure typical of adults, whereas the Nanotyrannus skulls retained a sleek, distinct morphology even in larger specimens.²² The convergence of the 2026 histological data (different growth rates) and the 2024 morphological data (different anatomy) builds a formidable case that Nanotyrannus was a valid, distinct species sharing the Hell Creek landscape with its larger cousin.

6. Ecological Implications: The Tyrant's Grip on the Guild

The realization that T. rex grew slowly and occupied a "subadult" size range for over a decade has profound implications for our understanding of the Late Cretaceous ecosystem. It provides the mechanism for a phenomenon known as Ontogenetic Niche Partitioning.

6.1 The "Missing Middle" Mystery

The Hell Creek Formation exhibits a peculiar predator guild structure. In most ecosystems, carnivores are distributed across a size spectrum: small, medium, and large. However, in Hell Creek, there is a massive gap.

• Small Predators: Acheroraptor (~5–10 kg), Dakotaraptor (~300 kg, though rare).

• Apex Predator: Adult T. rex (~8,000+ kg).

• The Void: There are virtually no distinct species of medium-sized carnivores (500–2,000 kg) identified in the formation—unless one counts Nanotyrannus (approx. 900–1,500 kg) and subadult T. rex.

The "Slow Growth" model explains this void. Tyrannosaurus rex did not simply jump from hatchling to giant; it loitered in the medium-sized niche for 15 to 20 years.¹ A population of 15-year-old T. rex, weighing between 1,000 and 3,000 kg, would have functioned as the ecosystem's "lions," while the 40-year-old adults acted as the "elephants" (if elephants were carnivorous). This single species effectively monopolized multiple niches, competitively excluding any other medium-sized theropod lineage from evolving or migrating into the area.¹

6.2 Dietary Shifts and the Gorgosaurus Evidence

This niche partitioning was not just about size; it was about diet. Direct fossil evidence for tyrannosaur diet is rare, but a pivotal discovery involving Gorgosaurus (a close relative of T. rex) illuminates this ontogenetic shift.

Researchers Darla Zelenitsky and colleagues described a juvenile Gorgosaurus specimen with the fossilized remains of two small, bird-like dinosaurs (Citipes elegans) preserved in its stomach.24

• Precision Feeding: The juvenile predator had dismembered the prey, swallowing the meaty hind legs whole. This suggests a lifestyle of agility and precision—chasing down fast, small game.

• Osteophagy in Adults: In contrast, coprolites (fossilized feces) and bite marks attributed to adult T. rex show evidence of "osteophagy"—the consumption and pulverization of bone. Adults, with their massive, reinforced skulls and banana-shaped teeth, hunted megaherbivores like Triceratops and Edmontosaurus, crunching through bone to access marrow.²⁶

A juvenile T. rex lacked the bite force to crush a Triceratops femur. It was biomechanically engineered for a different food source. The 2026 study's confirmation of a prolonged subadult phase suggests that for nearly half its life, T. rex was a pursuit predator of small-to-medium ornithischians (Thescelosaurus, Pachycephalosaurus, ornithomimids), only graduating to the "bone-crusher" niche in its third decade.²⁷

7. Comparative Physiology and Life History Strategies

The findings of Woodward et al. (2026) invite a reassessment of T. rex physiology in the context of extant vertebrates.

7.1 The "Inflection Point" and Sexual Maturity

In many growth models, the inflection point of the sigmoidal curve (where growth is fastest) is correlated with sexual maturity. The 2004 model placed this around age 14, suggesting T. rex reproduced as a rapidly growing teenager.

The 2026 study, however, found "no strong link from extant vertebrates" to support this correlation in dinosaurs.1 This ambiguity suggests that T. rex might have followed a reptilian strategy of reaching sexual maturity well before reaching maximum size. If T. rex became sexually mature at age 15 but continued growing until age 40, the breeding population would have been incredibly diverse in size. This "size-assortative mating" or complex social hierarchy would have been necessary to manage interactions between a 2,000 kg suitor and an 8,000 kg potential mate.

7.2 Metabolic Implications

The shift from an "explosive" 20-year growth curve to a "gradual" 40-year curve might seemingly challenge the hypothesis of dinosaur endothermy (warm-bloodedness). High growth rates are typically linked to high metabolic rates.

However, even the "slow" rate of ~557 kg/year is vastly higher than that of any extant ectotherm.1 A crocodile of similar size would take a century or more to reach such mass. T. rex was almost certainly endothermic or mesothermic (maintaining an elevated body temperature).

The extended growth period may represent an adaptation for metabolic efficiency. By spreading the cost of growth over a longer timeframe, T. rex reduced its daily caloric obligation. In an environment like the Hell Creek—which experienced seasonal variations and potential resource bottlenecks—a lower daily energy requirement (relative to the "explosive" model) would have increased the animal's resilience to starvation.9

7.3 Longevity and the "Grandmother Hypothesis"?

The confirmation that T. rex lived into its 40s (and possibly older) suggests a population structure with overlapping generations. While there is no direct evidence for parental care in T. rex specifically, the presence of long-lived adults raises the possibility of complex social structures. In many long-lived birds and mammals, older individuals play roles in territory defense or knowledge transfer. The "Subadult Loiter" phase means that siblings or cohorts might have remained together for years, potentially hunting cooperatively to secure the elusive mid-sized prey that the solitary adults ignored.²⁹

8. Conclusion: The King Reimagined

The 2026 PeerJ study stands as a watershed moment in dinosaur paleobiology. By integrating the largest histological dataset to date with the precise optics of cross-polarized light, Woodward, Myhrvold, and Horner have deconstructed the "rockstar" image of T. rex—the live-fast, die-young teenage giant—and replaced it with something far more complex.

We now see a Mature Monarch: an animal that grew with relentless persistence over four decades. We see a predator that was effectively a shapeshifter, occupying distinct ecological niches as a juvenile, a subadult, and an elder, thereby exerting a totalitarian grip on the food web. We see a biodiversity in the Hell Creek Formation that includes not just the King, but likely the distinct, smaller tyrant Nanotyrannus, validated by the very growth curves that define T. rex.

This study underscores the dynamic nature of the fossil record. The bones in our museums are not static statues; they are data repositories waiting for the right key to unlock them. As techniques like synchrotron scanning and chemical isotope analysis continue to advance, the story of Tyrannosaurus rex will undoubtedly continue to evolve. But for now, the King stands taller, older, and more enduring than ever before.

Table 2: Key Statistical & Biological Metrics from the 2026 Study

Metric	Previous Consensus (Erickson 2004)	Revised Model (Woodward et al. 2026)
Sample Size	7 Individuals	17 Individuals
Primary Method	Transmitted Light Histology	Cross-Polarized Light (CPL) Histology
Skeletal Maturity (Age)	~20–25 Years	~35–40 Years
Max Growth Rate	~767 kg/year (2.1 kg/day)	~557 kg/year (Variant NoXM)
Asymptotic Mass	Reached at ~20 years	Reached at ~35+ years
"Jane" & "Petey" Status	Juvenile T. rex (Fits curve)	Distinct Taxon (Outliers to curve)
Ecological Role	Rapid ascent to apex niche	Prolonged "Mesopredator" phase (15+ yrs)

Table 3: The Predator Guild of Hell Creek (Revised)

Predator Size Class	Estimated Mass	Representative Taxa
Small	< 50 kg	Acheroraptor, T. rex hatchlings
Small-Medium	50 – 400 kg	Dakotaraptor, Juvenile T. rex
Medium (The "Gap")	500 – 1,500 kg	Subadult T. rex, Nanotyrannus
Large	2,000 – 5,000 kg	Young Adult T. rex
Mega/Apex	> 8,000 kg	Mature Adult T. rex

This revised guild structure illustrates the dominance of Tyrannosaurus across multiple trophic levels, a strategy that ensured its reign until the very end of the Cretaceous.

Works cited

1. Prolonged growth and extended subadult development in the ..., accessed January 14, 2026, https://peerj.com/articles/20469/

2. The growth of Tyrannosaurus rex | Letters from Gondwana. - WordPress.com, accessed January 14, 2026, https://paleonerdish.wordpress.com/2020/06/05/the-growth-of-tyrannosaurus-rex/

3. Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs - PubMed, accessed January 14, 2026, https://pubmed.ncbi.nlm.nih.gov/15306807/

4. T. Rex Was Still Growing At 40, Taking A Slower Path To Adulthood Than Previously Thought - IFLScience, accessed January 14, 2026, https://www.iflscience.com/t-rex-was-still-growing-at-40-taking-a-slower-path-to-adulthood-than-previously-thought-82211

5. GROUNDWORK: - Geological Society of America, accessed January 14, 2026, https://www.geosociety.org/gsatoday/archive/17/1/pdf/i1052-5173-17-1-45.pdf

6. Bone Histology of Fossil Tetrapods - ResearchGate, accessed January 14, 2026, https://www.researchgate.net/profile/Sarah-Werning/publication/286324592_Selection_Of_Specimens/links/57715d3508ae6219474a493c/Selection-Of-Specimens.pdf

7. A Protocol for Aging Anurans Using Skeletochronology - USGS Publications Warehouse, accessed January 14, 2026, https://pubs.usgs.gov/of/2008/1209/pdf/ofr20081209.pdf

8. Bone Histology in Dysalotosaurus lettowvorbecki (Ornithischia: Iguanodontia) – Variation, Growth, and Implications | PLOS One - Research journals, accessed January 14, 2026, https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0029958

9. Tyrannosaurus Rex Grew Until 40, Study Shows - Mirage News, accessed January 14, 2026, https://www.miragenews.com/tyrannosaurus-rex-grew-until-40-study-shows-1601859/

10. Age determination in dinosaurs - Wikipedia, accessed January 14, 2026, https://en.wikipedia.org/wiki/Age_determination_in_dinosaurs

11. Histological variability in the limb bones of the Asiatic wild ass and its significance for life history inferences - PeerJ, accessed January 14, 2026, https://peerj.com/articles/2580.pdf

12. Growing up Tyrannosaurus rex: Osteohistology refutes the pygmy “Nanotyrannus” and supports ontogenetic niche partitioning in juvenile Tyrannosaurus - PMC - NIH, accessed January 14, 2026, https://pmc.ncbi.nlm.nih.gov/articles/PMC6938697/

13. Histovariability in human clavicular cortical bone microstructure and its mechanical implications - NIH, accessed January 14, 2026, https://pmc.ncbi.nlm.nih.gov/articles/PMC6794202/

14. Polarized Microscopy and What It Can Teach Us About the Materials That Make Up Our Skeletal Tissue, accessed January 14, 2026, https://evidentscientific.com/en/applications/polarized-microscopy-and-what-it-can-teach-us-about-the-materials-that-make-up-our-skeletal-tissue

15. BONE HISTOLOGY OF THE SAUROPOD DINOSAUR Alamosaurus sanjuanensis FROM THE JAVELINA FORMATION, BIG BEND, accessed January 14, 2026, https://ttu-ir.tdl.org/bitstreams/3ee06b4a-b9cd-4c67-aced-deeccdf73801/download

16. Osteohistological variation in growth marks and osteocyte lacunar density in a theropod dinosaur (Coelurosauria: Ornithomimidae) - PMC - PubMed Central, accessed January 14, 2026, https://pmc.ncbi.nlm.nih.gov/articles/PMC4269922/

17. Determinate growth is predominant and likely ancestral in squamate reptiles, accessed January 14, 2026, https://royalsocietypublishing.org/rspb/article/287/1941/20202737/85917/Determinate-growth-is-predominant-and-likely

18. Tyrannosaurus - Wikipedia, accessed January 14, 2026, https://en.wikipedia.org/wiki/Tyrannosaurus

19. A high-resolution growth series of Tyrannosaurus rex obtained from multiple lines of evidence - PeerJ, accessed January 14, 2026, https://peerj.com/articles/9192/

20. New evidence that Nanotyrannus was a juvenile T. rex - NetMassimo Blog, accessed January 14, 2026, https://english.netmassimo.com/2020/01/04/new-evidence-that-nanotyrannus-was-a-juvenile-t-rex/

21. Taxonomic status of Nanotyrannus lancensis (Dinosauria: Tyrannosauroidea) — a distinct taxon of small-bodied tyrannosaur - the University of Bath's research portal, accessed January 14, 2026, https://researchportal.bath.ac.uk/en/publications/taxonomic-status-of-nanotyrannus-lancensis-dinosauria-tyrannosaur/

22. Nanotyrannus lancensis a Valid Taxon According to New Study - Everything Dinosaur Blog, accessed January 14, 2026, https://blog.everythingdinosaur.com/blog/_archives/2024/01/03/nanotyrannus-is-a-valid-taxon.html

23. Growing up Tyrannosaurus rex - Dinodata, accessed January 14, 2026, https://dinodata.de/bibliothek/pdf_g/2020/eaax6250.full.pdf

24. Dino nuggets ... for dinosaurs? A young tyrannosaur's last meal gives new insight, accessed January 14, 2026, https://www.nationalgeographic.com/science/article/young-tyrannosaurs-last-meal-gives-new-insight-dinosaur-gut-contents

25. Exceptionally preserved stomach contents of a young tyrannosaurid reveal an ontogenetic dietary shift in an iconic extinct predator - NIH, accessed January 14, 2026, https://pmc.ncbi.nlm.nih.gov/articles/PMC10846869/

26. Fossilized Scat Provides Clues About T. rex's Diet | AMNH, accessed January 14, 2026, https://www.amnh.org/explore/news-blogs/fossilized-scat-t-rex-diet

27. Bite force estimates in juvenile Tyrannosaurus rex based on simulated puncture marks, accessed January 14, 2026, https://peerj.com/articles/11450/

28. Dinosaur Census Reveals Abundant Tyrannosaurus and Rare Ontogenetic Stages in the Upper Cretaceous Hell Creek Formation (Maastrichtian), Montana, USA - NIH, accessed January 14, 2026, https://pmc.ncbi.nlm.nih.gov/articles/PMC3036655/

29. Are there any good examples of niche partitioning between age groups in a mammal species? - Reddit, accessed January 14, 2026, https://www.reddit.com/r/Paleontology/comments/18g3z4w/are_there_any_good_examples_of_niche_partitioning/