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For decades, many palaeontologists have regarded several small-bodied, gracile tyrannosaur-like specimens—such as CMNH 7541, BMRP 2002.4.1, and KUVP 156375—as juvenile individuals of Tyrannosaurus rex . Under this interpretation, T. rex  would have undergone extreme ontogenetic transformations, shifting from a slender, cursorial juvenile form to a massive apex predator in adulthood. However, a recent study re-examines this hypothesis using exceptionally complete skeletal mate

From the Cambrian to the Ordovician, many animal phyla first appeared and diversified rapidly, and the phylum Echinodermata eventually became one of the major groups of marine animals that continues to thrive today. The ancestors of modern echinoderms—such as sea stars, sea urchins, and sea cucumbers—can largely be traced back to the early Paleozoic. During that time, echinoderms evolved at a remarkable pace. Within only a few tens of millions of years, they underwent extensi

（Stocktrek Images via Getty Images） In 1955, an American amateur fossil collector, Francis Tully, obtained a peculiar fossil from the Mazon Creek fossil beds in Illinois. Intrigued by its unusual form, he brought the specimen to the Field Museum of Natural History for identification. The paleontologists there were immediately puzzled. The fossil preserved an organism with a cigar-shaped body, a triangular tail fin, and a pair of eyes mounted on a long horizontal stalk. Most b

Anyone who has watched Game of Thrones  will remember the enormous wolf-like animals raised by members of House Stark. These creatures, known as “direwolves” in the story, were inspired by a real prehistoric animal: the dire wolf. Ecological reconstruction of the habitat where dire wolves lived, with the dire wolf shown in the lower left（圖片來源： National Park Service ， CC0 1.0  公共領域。） Like the fictional ice wolves, dire wolves were noticeably larger than the modern grey wolf. Y

Reconstruction of Scleromochlus taylori （感謝Gabriel Ugueto提供） Pterosaurs were the first vertebrates to take to the skies. From the Late Triassic until the end of the Cretaceous, they occupied the air for more than 150 million years. Anyone fascinated by prehistoric life is familiar with these flying reptiles, yet the earliest stages of their evolution have long remained obscure. The fossil record reveals a considerable anatomical and temporal gap between fully developed pteros

Fossil locality of Ajnabia Geological age of Ajnabia （白稜製作） During the Late Cretaceous, dinosaur faunas in the northern hemisphere (Laurasia) and the southern hemisphere (Gondwana) differed markedly. In Laurasia, herbivorous dinosaurs were dominated by ornithischians such as hadrosaurids and ceratopsians, while tyrannosaurids served as the apex predators. In contrast, Gondwanan ecosystems were characterized by titanosaurian sauropods as the primary herbivores and abelisaurids

Model of the tail based on Apatosaurus  specimens used in this study（手手蟲/呂淳濤提供） Sauropod dinosaurs are famous for their enormous body size and their remarkably long necks and tails. Among them, diplodocids possessed some of the most extreme tail elongation known in vertebrate animals, a feature that has long intrigued researchers and prompted numerous hypotheses about the function of these tails. The diplodocid tail consisted of roughly eighty caudal vertebrae. Their morpholo

Illustration of Saichania  and Pinacosaurus （圖片來源：ABelov2014，採用  CC BY 3.0  授權） When people imagine the sound of dinosaurs, the thunderous roars popularized by films such as Jurassic Park  often come to mind. However, a recent study focusing on an ornithischian dinosaur suggests that this image may not reflect reality. Instead of roaring like giant reptiles, some dinosaurs may have produced sounds more reminiscent of bird calls.

Reconstruction of Yuanchuavis kompsosoura （圖片來源：Luxquine，採用  CC BY-SA 4.0  授權） Many birds display bright colors or exaggerated ornamental features that appear to offer little advantage for survival. Vivid plumage can make individuals easier for predators to detect, and elongated feathers may hinder rapid escape. Yet such traits are widespread among modern birds. At first glance, one might expect natural selection to eliminate these seemingly disadvantageous characteristics, b

Hupehsuchus filter-feeding reconstruction（感謝Shunyi Shu & Long Cheng, Wuhan Center of China Geological Survey提供） Among modern marine giants, several animals obtain food by filtering tiny organisms from seawater. Baleen whales and whale sharks are two well-known examples, yet they rely on very different anatomical solutions. Baleen whales possess baleen plates derived from specialized skin tissues of the upper jaw. These structures are made of keratin, the same material that fo

Reconstruction of a katydid in its ecological environment (楊定華繪製提供) Sound transmission is one of the most widely used forms of communication among animals today. For many species, the ability to send and receive signals through sound is essential for survival. Animals that rely on acoustic communication occur broadly among both insects and vertebrates. Their signals serve a wide range of functions, including attracting mates, issuing warnings, and sharing the location of reso

The sabertooth cat subfamily Machairodontinae represents an extinct lineage of felids that once occupied most continental regions of the world, with the exception of places such as Australia and Antarctica. These predators persisted for more than sixteen million years before finally disappearing around ten thousand years ago. As one of the most recognizable groups of prehistoric mammals, sabertooth cats have long attracted scientific attention, particularly regarding their ec

Location where Tyrannomimus  was discovered Geological age of Tyrannomimus （白稜製作） Ornithomimosaurs are a distinctive group of theropod dinosaurs. They typically possessed relatively small heads and long necks, and their overall body form resembled a long-tailed ostrich. Many members of this lineage also show anatomical features associated with herbivorous diets. During the Cretaceous period these dinosaurs achieved remarkable diversity, yet the early stages of their evolution

Reconstruction of Tyrannosaurus mcraeensis (圖片來源：Sergei Krasinski，採用  CC BY 4.0  授權) Tyrannosaurus is the largest terrestrial predator ever discovered. Its ferocious appearance and immense power have left a lasting impression on the public imagination. As the dominant predator of North America during the final stage of the Cretaceous, Tyrannosaurus  has attracted enormous scientific attention. Compared with many other non-avian dinosaurs, its fossil record is relatively abun

Reconstruction of Cabrières Biota（圖片來源：Christian McCall ，採用  CC BY 4.0  授權） Lagerstätten are sedimentary deposits that preserve unusually rich fossil assemblages, often including delicate soft tissues that rarely survive the fossilization process. Because these deposits capture such a wide array of organisms, they provide an exceptional window into the ecological structure of ancient environments. Most Lagerstätten known from the Cambrian and Ordovician periods come from regi

Cambrian Explosion（圖片來源：Smithsonian Institution， CC0 1.0  公共領域） In the history of animal evolution, the Cambrian Explosion stands as one of the most important and fascinating episodes. Its recognition arose from early studies of stratigraphic fossils. Researchers were struck by the observation that Cambrian rock layers suddenly contained an abundant and diverse array of animal fossils. Compared with the strata from the preceding period, this represented a dramatic transformat

Reconstruction of Nanotyrannus lancensis (圖片來源：Nobu Tamura，採用  CC BY-SA 4.0  授權) Nanotyrannus lancensis , named in 1988, is a tyrannosauroid that appears noticeably smaller than Tyrannosaurus . This size difference is the reason for the name “dwarf tyrant.” Its body length is estimated at slightly over five meters, with a body mass roughly between one and two tonnes. Despite clear differences in size and certain anatomical details between Nanotyrannus  and Tyrannosaurus , th

Sanfordiacaulis densifolia （圖片來源：Tim Stonesifer/Gastaldo RA et al，採用  CC BY 4.0  授權） The earliest vascular plants appeared in the late Silurian, around 420 million years ago. Trees with true woody structures evolved later, emerging during the middle to late Devonian roughly 380 million years ago. During that period, several ancient plant groups already formed tall tree-like organisms. Examples include Wattieza , Archaeopteris , and Calamophyton . These plants could reach heig

（圖片感謝John Sibbick提供） As early as the late nineteenth century, scientists had already begun searching for evidence of life in the Precambrian, the vast span of time preceding the Cambrian Period. Fossils that would later be recognized as belonging to the Ediacaran biota were described during this early period of investigation, yet these discoveries attracted little attention at the time. Many paleontologists were reluctant to accept the possibility that large, macroscopic orga

The dolphin lineage Delphinida  represents the most diverse group within the infraorder Cetacea , which includes all whales and dolphins alive today. Among living cetaceans, dolphins alone account for nearly half of all species. Based on my own tally—excluding forms whose taxonomic status remains uncertain—44 of the approximately 90 recognized living cetacean species belong to this dolphin lineage. The extraordinary success of dolphins may be closely linked to one of their ea