An illustration of a Gorgosaurus using its serrated teeth to rip apart its meal, a young Corythosaurus in Alberta, 75 million years ago. 
 
 Secret structures hidden within the serrated teeth of Tyrannosaurus rex and other theropods helped the fearsome dinosaurs tear apart their prey without chipping their pearly whites, a new study finds. 
 
 Researchers looked at the teeth of theropods — a group of bipedal, largely carnivorous dinosaurs that includes T. rex and Velociraptor — to study the mysterious structures that looked like cracks within each tooth. 
 
 The investigation showed that these structures weren't cracks at all, but deep folds within the tooth that strengthened each individual serration and helped prevent breakage when the dinosaur pierced through its prey, said study lead researcher Kirstin Brink, a postdoctoral researcher of biology at the University of Toronto Mississauga. [Image Gallery: The Life of T. Rex] 
 
 The new study upends one from the early 1990s, Brink said. Researchers first noticed these cryptic cracks on the tooth of a T. rex cousin named Albertosaurus about two decades ago. 
 
 Initially, the researchers thought the cracks were signs of damage, likely acquired when the dinosaur ate a hearty meal. But the new analysis finds that isn't the case, Brink said. 
 
 "I sectioned teeth from eight other theropods besides Albertosaurus, and found that the structure is actually in all theropods, and it's not actually a crack," she told Live Science. 
 
 This illustration shows a section of a tooth of the large theropod Gorgosaurus, from Alberta. Credit: Skull drawing by Danielle Default 
 
 Serrated teeth 
 
 The study actually began with a Dimetrodon, a Paleozoic animal with serrated teeth that lived before the time of the dinosaurs. When Brink sliced the Dimetrodon tooth in half and compared it with the serrated teeth of dinosaurs, she found they had different internal structures. 
 
 "They look very similar on the outside," Brink said. "It's only when you cut them open [that you see] that they're completely different." 
 
 Curious, she obtained two to three teeth from eight different theropods species, including T. rex, Coelophysis bauri and Carcharodontosaurus saharicus. She also looked at specimens of theropod teeth that had not yet fully matured and erupted past the gum line, meaning, "they had not been used for feeding," Brink said. 
 
 An analysis using a scanning electron microscope and a synchrotron (a microscope that helps determine the chemical composition of a substance) showed that each tooth, even the ones that had not yet erupted, had these cracklike structures next to each serration, she said. This debunked the idea that the cracks were artifacts of eating a meaty meal, she said. 
 
 Kirstin Brink, a postdoctoral researcher of biology at the University of Toronto Mississauga, shows a theropod tooth next to a cross section of a tooth belonging to the theropod Carcharodontosaurus. Credit: Image courtesy Kirstin Brink 
 
 Furthermore, each structure has a few extra layers of calcified tissue, called dentine, under the tooth's outer enamel coating, making it tough and hard. 
 
 "We proposed a developmental hypothesis that these are structures created when the tooth is first forming," Brink said. "It actually helps to deepen the serration within the tooth and strengthen each serration and the tooth overall." 
 
 Serrated teeth help animals pierce through flesh and hold onto chunks of meat. The formations, which the researchers call "deep interdental folds," strengthen the serrations. In fact, they likely helped theropods survive as top predators for about 165 million years, Brink said. 
 
 Serrated teeth still exist today in Komodo dragons. However, Komodo dragon teeth don't have deep interdental folds, nor do they have the extra layers of dentine that would strengthen their bite, Brink added. 
 
 She called the toothy finding fascinating and "unexpected." 
 
 "It's really cool that such a small, little change in the tooth structure, a small arrangement of the dental tissues, could completely change the ways these animals are living," she said. 
 
 The study was published online today (July 28) in the journal Scientific Reports. 
 
 Follow Laura Geggel on Twitter @LauraGeggel. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science. ||||| 
 
 Gorgosaurus -- one of the T. rex relatives studied -- is shown using its specialized teeth for feeding on a young Corythosaurus in Alberta, Canada, 75 million years ago. (Danielle Dufault) 
 
 As if Tyrannosaurus rex needed to get any cooler, new research suggests that the famous dinosaur had teeth that were serrated like a steak knife. These days, just one living terrestrial animal can boast such a magnificent mouth -- the komodo dragon. 
 
 But according to the new research published Tuesday in Scientific Reports, T. rex teeth stood in a class of their own. While lots of other dinosaurs (and the living komodo dragon) had teeth that seem similar to those in the jaw of a T. rex, researchers found that they were only superficially related. 
 
 [Dinosaurs aren’t really extinct] 
 
 The teeth of T. rex and its close relatives, it seems, were formed by a particularly complex structure of tissues. The building blocks that made their teeth and those of other dinosaurs were the same, but it appears that T. rex's kin, the theropods, had a better way of putting those blocks together. 
 
 
 
 Detail of a thin section through the tooth of a large theropod, Gorgosaurus, from Alberta. (Danielle Default) 
 
 The researchers investigated a small, crack-like feature at the bottom of the serrations -- a feature that can only be found when the tooth is cut open. It's not something you see in other animals with serrated teeth, and one previous study had suggested that the cracks were formed by use. In other words, they were stress cracks that formed when the dinosaurs chomped on hard bone, and their formation kept the whole tooth from shattering. 
 
 [Dinosaurs may have been warm-blooded after all] 
 
 But this new study suggests that theropod teeth had those "cracks" on purpose. By studying teeth that had yet to erupt (dinosaurs shed and produced teeth continuously throughout adulthood) in addition to ones that had been used for eating for awhile, the researchers found evidence that strange structures at the bottom of the serrations were there from the start. 
 
 [Why paleontologists love the noisy, featherless, inaccurate dinosaurs of ‘Jurassic Park’] 
 
 "The strange structure is actually a special arrangement of tooth tissues that increases the size of the serration, strengthening it and preventing it from wearing away quickly," lead study author Kristin Brink of the University of Toronto told The Post. "This means that teeth could last longer in the jaw, preventing gaps from occurring in the tooth row while a new tooth is developing, allowing for a more efficient bite when piercing through the flesh of its meal." 
 
 This hidden complexity, Brink said, no doubt helped the theropods find their success -- to the tune of about 165 million years at the very top of the food chain. 
 
 Read More: 
 
 Four-limbed, long-fingered snake hints at a creepy crawly evolutionary journey 
 
 Before dinosaurs, the giant ‘Carolina Butcher’ was a North American terror 
 
 A crummy dinosaur fossil turns out to hold 75 million-year-old blood and proteins 
 
 First ever evidence of a swimming, shark-eating dinosaur ||||| Erupted teeth 
 
 Erupted homodont maxillary teeth (Fig. 1A) show a level of tissue organization in the serrated cutting edge that is common to archosaurs. Deep folds are present in the dentine at the base of each externally visible interdental sulcus, reminiscent of the dentine folds present in teeth with tightly-folded plicidentine17, effectively increasing the size of the individual denticles inside the tooth on both the mesial and distal carinae (Fig. 1). The denticles in all theropod teeth have similarly sized denticle bases along the length of the carina that are tightly apposed (Fig. 1), but denticle sizes vary in ziphodont teeth in taxa that lack deep folds (Fig. 2). 
 
 Figure 1: Microanatomy of ziphodont archosaur teeth with deep interdental folds. (A) Skull of Gorgosaurus libratus, a tyrannosaurid dinosaur, drawn by Danielle Dufault. (B) Complete tooth (ROM 31535) and sagittal thin sections through distal and mesial carinae of a maxillary cf. Gorgosaurus sp. (ROM 57981) tooth. (C–H), carinae of ziphodont teeth under SEM (left) and in thin section (right). (C), Indeterminate phytosaur, ROM 7981, mesial carina. (D) Coelophysis bauri, CM 76863, distal carina. (E) Allosaurus fragilis, ROM 66106, distal carina. (F) Carcharodontosaurus saharicus, ROM 52017 (left) and ROM 47691 (right), mesial carina. (G) cf. Gorgosaurus libratus, ROM 57981, mesial carina. (H) Tyrannosaurus rex, ROM 66108, mesial carina. Abbreviations: dej, dentine-enamel junction; e, enamel; if, interdental fold; is, interdental sulcus; pd, primary dentine. Full size image (759 KB) Figures index 
 
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 Figure 2: Microanatomy of ziphodont teeth lacking deep interdental folds. (A) Carcharodon megalodon (ROM 30530). (B) Smilodon sp. (ROM 3288) carina, lacking denticles (not a true ziphodont animal as the carina is composed of enamel only). (C) Varanus komodoensis (ROM R7565), distal carina, with unevenly sized denticles. (D) Hadrosaurid (ROM 58205) labial denticles. (E) Sagittal thin section through the distal carina of a maxillary tooth of Dimetrodon grandis (ROM 6039), showing inconsistently-sized denticles. Thin section (top), SEM (bottom). (F) Troodon formosus (ROM 05089), mesial carina. Thin section (top), SEM (bottom). Full size image (741 KB) Previous 
 
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 A number of features were found only in theropod dinosaurs. The mantle dentine immediately surrounding the interdental fold is globular in theropod teeth, and dentine tubules that originate in the fold and curve towards the pulp cavity extend outward from the globular dentine (Fig. 3A). In transverse and sagittal section, the globular dentine and interglobular spaces are visible as dark atubular areas surrounding the interdental fold (Fig. 3A,B). The distribution of globular dentine is unusual, being absent in each denticle, where enamel tufts and spindles are often present near denticle tips (Figs 3B and 4). The enamel tufts and spindles are similar to those observed in ornithischian dinosaurs (Fig. 4A,B). The appearance of globular dentine and interglobular spaces (0–50 μm), visible under SEM (Fig. 3C), are what was previously misinterpreted as the hollow “ampulla”4, 5, 6. 
 
 Figure 3: Microanatomy of interdental folds. (A) Sagittal thin section of an interdental fold below the DEJ in Carcharodontosaurus saharicus (ROM 52037). Carina to the top. (B) Oblique transverse thin section through an interdental fold and denticle in a maxillary tooth of C. saharicus (ROM 52037) under cross-polarized light. Carina to the right, pulp cavity to the left. (C) SEM image of an interdental fold in a cf. Gorgosaurus (ROM 57981) maxillary tooth in coronal section. Abbreviations: dej, dentine-enamel junction; dt, dentine tubules; e, enamel; gd, globular dentine; if, interdental fold; pd, primary dentine; sd, sclerotic dentine. Full size image (2,056 KB) Previous 
 
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 Figure 4: Dentine-Enamel Junction of archosaur teeth. (A) Triceratops sp. (ROM 67669) with enamel spindles and no globular mantle dentine. (B) Hadrosaurid (ROM 58205) with enamel spindles and no globular mantle dentine. (C) Spinosaurus aegyptiacus (ROM 65613) carina with dentine, globular dentine, and enamel ornamentations, but lacking true denticles. (D) Indeterminate phytosaur (ROM 7981) with globular mantle dentine. (E) cf. Gorgosaurus (CMN 2225) unerupted, newly forming tooth with globular mantle dentine, primary dentine, and incompletely mineralized enamel. (F) Cretaceous crocodilian (ROM 67512) with globular mantle dentine. (G) Coelophysis bauri (CM 87671) unerupted tooth, carina to the top right corner, showing a lack of globular dentine within the denticle. The globular dentine can be seen behind the dentine tubules of the denticle in the interdental space. (H) Sagittal thin section of the DEJ at a denticle tip in C. saharicus (ROM 52037), showing enamel spindles. Abbreviations: dt, dentine tubule; e, enamel, es, enamel spindle; gd, globular dentine; pd, primary dentine. Full size image (1,088 KB) Previous 
 
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 Surrounding the interdental fold is an area of clear dentine, originally thought to be a deep layer of enamel encircling the globular dentine4. We interpret this layer as sclerotic dentine, as the dentine tubules are transparent and not visible under SEM (Fig. 3). 
 
 The interdental fold is continuous below each interdental sulcus, forming a 1 μm channel through the enamel (Figs 1 and 3). The channel is identical at each interdental sulcus in an individual tooth, being similar in width, length, and orientation. The channel and interdental folds are present along the majority of the carina, but tend to be absent near the tooth apex where the tooth curves and the enamel is thickened. The structure of the DEJ (Dentine Enamel Junction) usually stops enamel cracks from penetrating into the dentine, thereby preserving the tooth from catastrophic damage18, 19. Therefore, the presence of a channel through the enamel and the DEJ is unusual and unique to theropod dinosaurs. 
 
 Unerupted teeth 
 
 Histological sections of unerupted replacement teeth provide a developmental perspective on the microanatomy of theropod teeth. Unerupted teeth of Allosaurus and Gorgosaurus (Fig. 5) also have deep interdental folds. The folds are similar in shape to those of erupted teeth in being surrounded by globular mantle dentine, and extending to the external enamel surface through a channel in the interdental sulcus. However, the unerupted teeth lack the clear layer of sclerotic dentine that surround the interdental folds of erupted teeth (Fig. 5B). The dentine tubules are visible from the DEJ to the pulp cavity, even in the area of the fold. A comparison of the dentine tubules in the area of the fold shows deposition of thick peritubular dentine around each dentine tubule in erupted teeth only (Fig. 5C–D). Peritubular dentine deposition increases with age, and may be accelerated in response to an external stressor, forming sclerotic dentine18, 20. The absence of sclerotic dentine is also noticeable in transverse section (Fig. 5E). As in erupted teeth, globular dentine is absent in the denticles, but is present directly below the DEJ in the remainder of the unerupted tooth (Fig. 5F). 
 
 Figure 5: Microanatomy of unerupted cf. Gorgosaurus sp. teeth. (A) Distal carina of CMN 2225 showing the deep folds at the base of each interdental sulcus. (B) Detail of interdental fold from (A) showing absence of sclerotic dentine. (C) Dentine tubules in an erupted tooth (ROM 57981) showing peritubular dentine in each hollow tubule. (D) Dentine tubules in an unerupted tooth (CMN 2225) showing less peritubular dentine when compared to erupted tooth in (C). (E) Transverse section between two neighbouring denticles (CMN 2225), carina to the top. (F) Transverse section through a denticle showing absence of globular dentine in the denticle tip. Carina to the right. (G) Unerupted tooth of cf. Gorgosaurus libratus (RTMP 2012.012.0029), with interdental folds. (H) Unerupted tooth of Allosaurus fragilis (UMNH.VP 23761), with interdental folds. Abbreviations: dt, dentine tubule; e, enamel; gd, globular dentine; if, interdental fold; is, interdental sulcus; pd, primary dentine. Full size image (1,142 KB) Previous 
 
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 SR-FTIR spectroscopic analyses 
 
 SR-FTIR results support the interpretations made through SEM and histology (Fig. 6). The spectral assignment of type A and type B carbonate of carbonated hydroxylapatite (cHAP), being resolved after deconvolution of FTIR spectra, was in agreement with the results of previous investigations21, 22, 23. cHAP type A (Fig. 6D), considered to be invasive to the tooth, was found in the interglobular spaces around the interdental fold, and cHAP type B (Fig. 6E), considered to be native to the tooth, was found in the globular dentin. A noticeable organic signal within the primary dentine of the tooth was recovered, but no signal from the globular dentine (Fig. 6F,G). These findings were consistent with the results of previous investigations which indicated that the type A carbonate of cHAP was more energetically feasible and more thermodynamically stable than the type B carbonate of cHAP24, 25. Thus, we propose that it was highly likely that carbonate from groundwater was substituted for the hydroxyl group of cHAP within the enamel to form type A carbonate, not affecting the dentine. The absence of an organic signal in the area of the interdental fold suggests that the interdental sulcus was likely not used to house bacteria for a septic bite in carnivorous dinosaurs4. 
 
 Figure 6: SR-FTIR spectra of enamel and dentine of a cf.Gorgosaurus tooth, ROM 30582. (A–F), region of interdental fold, (A) optical image, (B) reflectance image, (C) CO 2 at 2345 cm−1 present in enamel and interdental fold. (D) cHAP-A at 879 cm−1 in the globular dentine of the interdental fold. (E) cHAP-B at 867 cm−1 in the globular dentine of the interdental fold. (F) Alkyl at 3000-2800 cm−1, representing organic material. Colour bar at the far right with blue as the lowest and red as the highest concentration. (G) FT-IR spectra and assignments. (H) FT-IR spectrum of enamel. (I) FT-IR spectrum of dentine. (J) Deconvolution of cHAP Type A and Type B of enamel. (K) Deconvolution of -CH 3 and -CH 2 of preserved organics in dentine. Full size image (396 KB) Previous 
 
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 High levels of physisorbed CO 2 (at 3574 cm−1 (combination band n3+2n2) and 2345 cm−1 (asymmetric stretching ν 3 )) were recorded within the globular dentine and the type A carbonate of the enamel, but not within the primary dentine (Fig. 6C). Also, the typical broad absorption band of chemisorbed CO 2 was observed in the range of 1723-1586 cm-1, and its intensity was strongly related to the intensity of physisorbed CO 2 within the tooth, consistent with previous studies25, 26. We consider that CO 2 was rarely produced from dissociation of carbonates of cHAP within the whole tooth because only the enamel layer presented the intense infrared absorption of physisorbed and chemisorbed CO 2 . Groundwater CO 2 partial pressure is typically ~10–100 times higher than that of the atmosphere25, and higher levels of atmospheric CO 2 have been suggested for the Mesozoic26. We therefore propose that the relatively higher level of CO 2 was likely dissolved in the groundwater and infiltrated into the tooth for further reaction with the hydroxyl group of cHAP within the tooth tissues during fossilization.
– The Komodo dragon is the only known creature on the planet today to boast teeth that are serrated, like a jagged-edged steak knife. But now researchers have discovered that the mighty T. rex not only sported serrated teeth, but also secret folds hidden toward the bottom of those teeth that both increased the size and strength of the serration and allowed the beast to shred the flesh of its prey, reports the Washington Post. "This means that teeth could last longer in the jaw, preventing gaps from occurring in the tooth row while a new tooth is developing, allowing for a more efficient bite when piercing through the flesh of its meal," says the lead author of the study, which appears this week in the journal Scientific Reports. Her team investigated the teeth of theropods, a group of primarily carnivorous and bipedal dinosaurs like T. rex and Velociraptor, to sort out why they were cracked at the bottom. It turns out the mysterious structures were deep folds that helped the mighty beasts tear apart their prey. (Previous theories suggested these structures were signs of wear and tear.) "The structure is actually in all theropods, and it's not actually a crack," the lead researcher tells LiveScience. "It's really cool that such a small, little change in the tooth structure, a small arrangement of the dental tissues, could completely change the ways these animals are living." (As if the teeth weren't enough, the T. rex's bite was likely the equivalent of this huge animal sitting on you.)