Rosa Rubicondior: Refuting Creationism - What T. Rex's Ancestors Were Doing More Than 70 Million Years Before 'Creation Week'.

T. rex’s direct ancestor crossed from Asia to North America | UCL News - UCL – University College London

This artwork illustrates the disparity of the northern and southern hemisphere’s evolution of terrestrial Cretaceous faunas after the Cretaceous Thermal Maximum. On the left, End Cretaceous Southern Hemisphere (Western Gondwana) became dominated by megaraptorid theropods and titanosaur sauropods. The centre of the piece summarises the extinction event of terrestrial fauna at the Cretaceous Thermal Maximum, where the apex predators the carcharodontosaurids and allosaurs went extinct and tyrannosauroids (including megaraptoran and the ancestors of Tyrannosaurus rex) were small. On the right, the end Cretaceous northern hemisphere fauna dominated by tyrannosaurids (such as Tyrannosaurus rex), hadrosaurs and ceratopsian ornithischian dinosaurs. The environment also became more mesic compared to the more semi-arid seasonal environment earlier in the Cretaceous.

Credit: Pedro Salas and Sergey Krasovskiy.

One of the major challenges for creationism is how to ignore the overwhelming volume of evidence that contradicts it—especially from the vast span of Earth’s pre-'Creation Week' history, during which 99.9975% of geological time unfolded. Even allowing for their standard claim that scientists fake their dates and Earth is really only a few thousand years old, there is a vast amount of history to compress into so short a timeline.

During that immense period, something remarkable was happening: a distant ancestor of Tyrannosaurus rex, destined to become one of the most formidable land predators the planet has ever seen, was making its way across a land bridge from Asia into North America.

That’s the conclusion of a new study led by researchers at University College London (UCL), recently published in Royal Society Open Science. The team found that this transcontinental migration—via the Beringian land bridge over 70 million years ago—marked a key moment in the evolution of tyrannosaurids. They also noted a rapid increase in body size that appears to have coincided with a global cooling event following a climatic peak around 92 million years ago. The study was a collaboration between scientists from UCL and the universities of Oxford, Pittsburgh, Aberdeen, Arizona, Anglia Ruskin, Oklahoma, and Wyoming.

Background: The Evolution of the Tyrannosaurs. Tyrannosaurs were a group of theropod dinosaurs that evolved during the Jurassic period, around 165 million years ago. Early tyrannosaurs were small, fast, and lightly built—far from the towering predators that would appear later. Fossil evidence places their origins in what is now Asia, and they remained relatively minor predators for tens of millions of years.

It wasn’t until the Late Cretaceous—roughly 80 to 66 million years ago—that tyrannosaurs began to diversify and dominate. By this time, they had evolved into massive apex predators with powerful jaws, keen senses, and strong hind limbs. Their tiny but famously robust forelimbs remain a subject of debate, but the rest of their anatomy was finely tuned for pursuit and power.

The most famous member of this group, Tyrannosaurus rex, lived in North America about 68 to 66 million years ago. Its ancestors, as the latest research suggests, migrated from Asia across the Beringian land bridge during the Late Cretaceous, adapting to new climates and ecological niches on their journey.

Tyrannosaurs went extinct during the Cretaceous–Paleogene extinction event 66 million years ago, along with the majority of non-avian dinosaurs.

The findings are also summarised in a UCL news release.

T. rex’s direct ancestor crossed from Asia to North America
Tyrannosaurus rex evolved in North America, but its direct ancestor came from Asia, crossing a land bridge connecting the continents more than 70 million years ago, according to a new study led by UCL researchers.
The study, published in Royal Society Open Science, also found that the rapid growth in size of tyrannosaurids (the group that included the T. rex) as well as a closely related group called megaraptors coincided with a cooling of the global climate following a peak in temperatures 92 million years ago.

This suggests T. rex and its cousins might have been better suited to cooler climates than other dinosaur groups at the time, perhaps due to having feathers or a more warm-blooded physiology.

The international team involved researchers from the universities of Oxford, Pittsburgh, Aberdeen, Arizona, Anglia Ruskin, Oklahoma and Wyoming.

The geographic origin of T. rex is the subject of fierce debate. Palaeontologists have been divided over whether its ancestor came from Asia or North America. Our modelling suggests the ‘grandparents’ of T. rex likely came to North America from Asia, crossing the Bering Strait between what is now Siberia and Alaska.

This is in line with past research finding that the T. rex was more closely related to Asian cousins such as the Tarbosaurus than to North American relatives such as Daspletosaurus. Dozens of T. rex fossils have been unearthed in North America but our findings indicate that the fossils of T. rex’s direct ancestor may lie undiscovered still in Asia.

Cassius Morrison, lead author Department of Earth Sciences
University College London, London, UK.

The research team concluded that T rex. itself evolved in North America, specifically in Laramidia, the western half of the continent, where it was widely distributed.

They disagreed with conclusions published last year that a T. rex relative, Tyrannosaurus mcraeensis, found in New Mexico, predated T. rex by three to five million years – a finding that pointed to T. rex having North American ancestry. The team argued that this T. mcraeensis fossil was not reliably dated.

For the new study, the researchers explored how tyrannosaurids and their cousins the megaraptors moved around the globe. They used mathematical models drawing on fossils, dinosaurs’ evolutionary trees and the geography and climate of the time. Importantly, the models account for gaps in the fossil record, incorporating uncertainty into the calculations.

Megaraptors are regarded as the most mysterious of the large, meat-eating dinosaurs, as few megaraptor fossils have been found. In contrast to the T. rex, they evolved slender heads and arms as long as a person is tall, with claws up to 35cm (14in) long.

The researchers concluded that megaraptors were more widely distributed across the globe than previously thought, likely originating in Asia about 120 million years ago and spreading to Europe and then throughout the large southern landmass of Gondwana (including present-day Africa, South America and Antarctica).

This would mean megaraptors lived in parts of the world (Europe and Africa) where no megaraptor fossils have been found so far.

It may be that they evolved differently from their tyrannosaurid cousins, with killing claws rather than a powerful bite, because they hunted different prey. In southern Gondwana, they may have preyed on (juvenile) sauropods, whereas T. rex hunted Laramidian species such as Triceratops, Edmontosaurus and Ankylosaurus.

Both tyrannosaurids and megaraptors grew to gigantic sizes at broadly the same time, as the climate cooled following a peak in global temperatures known as the Cretaceous Thermal Maximum 92 million years ago. This rapid growth followed the extinction of other giant meat-eaters, carcharodontosaurids, which left a vacuum at the top of the food chain.

The researchers suggested that tyrannosaurs – both tyrannosaurids and megaraptors – may have been able to better exploit cooler temperatures than rival dinosaur groups.

At the end of the age of the dinosaurs, T. rex weighed up to nine tonnes (about the same as a very large African elephant or a light tank), while megaraptors reached lengths of 10 metres.

Our findings have shined a light on how the largest tyrannosaurs appeared in North and South America during the Cretaceous and how and why they grew so large by the end of the age of dinosaurs. They likely grew to such gigantic sizes to replace the equally giant carcharodontosaurid theropods that went extinct about 90 million years ago. This extinction likely removed the ecological barrier that prevented tyrannosaurs from growing to such sizes.

Charlie Roger Scherer, co-author Department of Earth Sciences
University College London, London, UK.

At the beginning of their evolutionary history, around 120 million years ago, megaraptors were part of a widespread and diverse dinosaur fauna. As the Cretaceous period progressed and the continents that once formed Gondwana began to drift apart, these predators became increasingly specialised. This evolutionary shift led them to inhabit more specific environments. While in regions like Asia megaraptors were eventually replaced by tyrannosaurs, in areas such as Australia and Patagonia they evolved to become apex predators, dominating their ecosystems.

Dr Mauro Aranciaga Rolando, co-author
Museo Argentino de Ciencias Naturales Bernardino Rivadavia
Buenos Aires, Argentina.

Abstract
Late Cretaceous Earth was dominated by theropods such as tyrannosauroids and megaraptorans; however, it is unclear how these clades diversified and grew to massive proportions. This study aimed to conduct a biogeographical analysis and test climate as a potential mechanism for the increase in size. We used published phylogenetic matrices with the R package BioGeoBears to test different biogeographical hypotheses for both clades. We mapped body mass (BM) and body length against known climate data to test this potential hypothesis. Continental-scale variance did not drive tyrannosauroid biogeography and instead widespread ancestral populations, sympatric speciation and localized extinctions throughout these clades constricted geographic range. Both patterns were supported by statistical analyses. This biogeographical model also indicates the ancestor of the clade Tarbosaurus and Tyrannosaurus was present in both Asia and Laramidia, and therefore the ancestor of Tyrannosaurus came from Asia. Statistical data illustrated no correlation between Mean Annual Temperature (MAT) and BM but potential climatic shifts may be associated with gigantism in derived megaraptorids and eutyrannosaurians. This biogeographical model implies megaraptorans may have had a cosmopolitan distribution prior to the splitting of Laurasia and Gondwana. Also, gigantism in these clades may be associated with climatic shifts in the Late Cretaceous.

1. Introduction
Despite vast amounts of anatomical and phylogenetic analyses over the past decades, some aspects of the evolutionary history of Megaraptora remain elusive. Megaraptora represents a clade of coelurosaurian theropods characterized by long skulls, recurved and proportionally small teeth, highly pneumatic skeletons and long, powerful arms bearing large and sharp manual claws [1–9]. Megaraptorans evolved from small forms in Laurasia (Barremian) [10–12] to large and highly pneumatic species in Gondwana (Turonian-Maastrichtian) [1,3,5,9]. During the Late Cretaceous, this clade became the apex terrestrial predator of western and southern Gondwana after the Cenomanian-Turonian faunal turnover [7,9,13]. However, it is unclear if there was dispersal from Laurasia to Gondwana or if there was a cosmopolitan distribution of Megaraptora prior to the separation of Laurasia and Gondwana [7]. Therefore, despite a concentrated study, the evolutionary history of this clade remains unresolved.

Multiple competing hypotheses exist for the evolutionary trajectory of Megaraptora in the Cretaceous [5,7,9–11]. These competing hypotheses are informed by a fragmentary fossil record, conflicting phylogenetic relationships and wide biogeographic range achieved over a narrow temporal interval. Specifically, the fragmentary fossil record has averted detailed study of this clade’s phylogenetic relationships and prevents an understanding of the true origins and diversification of megaraptorans. This suggests that megaraptorans could be more diverse and more widespread than previously thought. Secondly, conflicting phylogenetic hypotheses for megaraptorans results in differing reconstructions of the biogeographic history. The wide biogeographic range being achieved over a narrow temporal interval may be a result of the aforementioned factors. These inferences represent discrete arguments evidencing the evolutionary history of Megaraptora. However, these findings are insufficient to identify (i) how this clade became globally distributed and (ii) the climatic regimes under which gigantism evolved within the clade.

Related to this matter, the acquisition of gigantic body masses (BM; >1000 kg [14]) and body lengths (BL) are more sparse within Megaraptora and the origin of the more derived megaraptorid clade is not well understood [3,9], which contrasts with tyrannosaurids where gigantism is well documented and observed rapidly after the extinction of Allosauroidea in Laurasia [15,16]. Tyrannosaurs provide a comparative framework for Megaraptorids due to their likely phylogenetic relationship, similar biogeographical origins but differing dispersal trajectories and anatomical evolution. However, there are also competing hypotheses on the evolutionary history and gigantism of Tyrannosaurus rex. Phylogenetic evidence has been presented for T. rex being derived from an Asian ancestor [17,18]. Meanwhile, Currie et al. [19] and geochronological constraints on a new taxon, T. mcraeensis, provided evidence for generic evolution in North America [20]. These separate pieces of evidence have left the subject open to interpretation.

Here, we tested two specific hypotheses: (H1) that megaraptorans were widely dispersed prior to the breakup of Laurasia and Gondwana. This hypothesis is supported by multiple fossil records originating from Early Cretaceous Eurasia and Eastern Gondwana [3,9,11]. Secondly, we hypothesized (H2) tyrannosauroid gigantism evolved multiple times in conjunction with temperate climates. This evolutionary trajectory is supported by fossils such as Yutyrannus and other tyrannosaurs, such as T. rex, being found in cooler climates [21–23]. In other words, the global cooling trend after the Cretaceous Thermal Maximum (CTM) [24] and the extinction of the other apex non-coelurosaurian theropods may have allowed for the evolution of gigantism in megaraptorans and tyrannosauroids. We also hypothesized (H3) that T. rex evolved from direct Asian ancestors. This hypothesized descendance is based on the phylogenetic placement of T. rex in a clade with other Asian tyrannosaurs [17,18]. Regarding these clades, the origins and dispersal of the tyrannosaurids and megaraptorids have important implications for understanding dinosaurian ecosystem evolution by the end of the Cretaceous.

Figure 1. Biogeographic history of Megaraptora with ancestral area reconstructions positioned at each node, highlighting the widespread distribution during early megaraptoran evolution and the rapid evolution of South American Megaraptoridae after the extinction of carcharodontosaurids in the Turonian. Ancestral areas are those estimated by the BAYAREALIKE + J model.

Figure 2. Potential dispersal routes for megaraptorans during the Middle Jurassic–Early Cretaceous (approx. 143 Ma). The dispersal routes were devised using the ancestral area reconstructions in figure 1 and plotting them on a base map redrawn from Scotese [26]. Here, megaraptoran populations disperse via the most-connected regions of geographical areas (i.e. geodispersal). Abbreviations: ANT.: Antarctica; AUS.: Australia. Silhouettes by ‘the funk monk’ and ‘jagged fang designs’ and available from Phylopic.org under a Creative Commons license.

Figure 3. The evolution of body mass (A), body length (B) and habitat mean annual temperature (MAT) (C) across Tyrannosauroidea during the late Early to end-Cretaceous. Body size proxies vary independent of habitat MAT, although both proxies in eutyrannosaurians and megaraptorids show a qualitatively correlated increase after a temperature spike during the Turonian.

Morrison, Cassius; Scherer, Charlie Roger; O’Callaghan, Ezekiel V.; Layton, Collin; Boisvert, Colin; Rolando, Mauro Aranciaga; Durrant, Leroy; Salas, Pedro; Allain, Steven J. R.; Gascoigne, Samuel J. L.
Rise of the king: Gondwanan origins and evolution of megaraptoran dinosaurs
Royal Society Open Science 12(5) 242238; DOI: 10.1098/rsos.242238

Copyright: © 2025 The authors.
Published by The Royal Society. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

This new study presents yet another major problem for creationists, particularly for those who claim that evolutionary biology is somehow crumbling under the weight of its own contradictions. On the contrary, the research on tyrannosaur migration and evolution showcases exactly the kind of robust, evidence-driven work that continues to strengthen evolutionary theory. The idea that T. rex evolved from smaller, earlier tyrannosaurs in Asia before migrating to North America fits perfectly into the evolutionary framework of common descent, gradual change, and adaptation to shifting environments over immense timescales.

Creationist models, by contrast, rely on a fixed and recent origin of species—typically within the last 6,000 to 10,000 years—often invoking a global flood or sudden acts of special creation. These views cannot begin to account for the detailed fossil record, the clear transitional forms, or the geographical patterns that emerge from studies like this one. The idea of a species line evolving and spreading across continents over tens of millions of years is not only foreign to creationist thinking—it directly contradicts it.

And yet, some creationists persist in claiming that mainstream science is abandoning evolution. If that were true, we would expect to see studies like this one promoting supernatural explanations or denying deep time. Instead, what we see is a growing, self-correcting body of knowledge based on testable hypotheses and physical evidence. Far from retreating, evolutionary science is continually advancing—while creationism remains stuck, unable to explain even the most basic facts of natural history.

This research is a textbook example of evolutionary theory in action. From anatomical changes and climate-linked size increases to intercontinental migration through now-vanished land bridges, it all points to a deep, dynamic, and ancient history of life that no literal reading of Genesis can accommodate.

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