[Paleontology • 2025] Nanotyrannus and Tyrannosaurus coexisted at the close of the Cretaceous

Nanotyrannus   

in Zanno et Napoli, 2025.

 DOI: doi.org/10.1038/s41586-025-09801-6 

Artwork: Anthony Hutchings

 x.com/JGN_Paleo

Tyrannosaurus rex ranks among the most comprehensively studied extinct vertebrates1 and a model system for dinosaur paleobiology. As one of the last surviving non-avian dinosaurs, Tyrannosaurus is a crucial datum for assessing terrestrial biodiversity, ecosystem structure, and biogeographic exchange immediately preceding the end-Cretaceous mass extinction —one of Earth’s greatest biological catastrophes. Paleobiological studies of Tyrannosaurus, including ontogenetic niche partitioning, feeding, locomotor biomechanics, and life history have drawn upon an expanding skeletal sample comprising multiple hypothesized growth stages—and yet the Tyrannosaurus hypodigm remains controversial. A key outstanding question relates to specimens considered to exemplify immature Tyrannosaurus, which have been argued to represent the distinct taxon Nanotyrannus. Here, we describe an exceptionally well-preserved, near somatically mature tyrannosaur skeleton (NCSM 40000) from the Hell Creek Formation that shares autapomorphies with the holotype specimen of N. lancensis. We couple comparative anatomy, longitudinal growth models, observations on ontogenetic character invariance, and a novel phylogenetic dataset to test the validity of Nanotyrannus, demonstrating conclusively that this taxon is distinguishable from Tyrannosaurus, sits outside Tyrannosauridae, and unexpectedly contains two species—N. lancensis and Nanotyrannus lethaeus, sp. nov. Our results prompt a re-evaluation of dozens of existing hypotheses based on currently indefensible ontogenetic trajectories. Finally, we document at least two co-occurring, ecomorphologically distinct genera in the Maastrichtian of North America, demonstrating that tyrannosauroid alpha diversity was thriving within one million years of the end-Cretaceous extinction.

A pack of Nanotyrannus attacks a juvenile Tyrannosaurus rex.

Artwork: Anthony Hutchings

  Lindsay E. Zanno and James G. Napoli. 2025. Nanotyrannus and Tyrannosaurus coexisted at the close of the Cretaceous. Nature.  DOI: doi.org/10.1038/s41586-025-09801-6  [30 October 2025]

http://x.com/JGN_Paleo/status/1983926921898660347

[Paleontology • 2025] Khankhuuluu mongoliensis • A new Mongolian tyrannosauroid and the Evolution of Eutyrannosauria

Khankhuuluu mongoliensis 

Voris, Zelenitsky, Kobayashi, Modesto, Therrien, Tsutsumi, Chinzorig & Tsogtbaatar, 2025

DOI: doi.org/10.1038/s41586-025-08964-6

Abstract

Eutyrannosaurians were large predatory dinosaurs that dominated Asian and North American terrestrial faunas in latest Cretaceous times. These apex predators arose from smaller-bodied tyrannosauroids during the ‘middle’ Cretaceous that are poorly known owing to the paucity of fossil material. Here we report on a new tyrannosauroid, Khankhuuluu mongoliensis gen. et sp. nov., from lower Upper Cretaceous deposits of Mongolia that provides a new perspective on eutyrannosaurian origins and evolution. Phylogenetic analyses recover Khankhuuluu immediately outside Eutyrannosauria and recover the massive, deep-snouted Tyrannosaurini and the smaller, gracile, shallow-snouted Alioramini as highly derived eutyrannosaurian sister clades. Khankhuuluu and the late-diverging Alioramini independently share features related to a shallow skull and gracile build with juvenile eutyrannosaurians, reinforcing the key role heterochrony had in eutyrannosaurian evolution. Although eutyrannosaurians were mainly influenced by peramorphosis or accelerated growth, Alioramini is revealed as a derived lineage that retained immature features through paedomorphosis and is not a more basal lineage as widely accepted. Our results reveal that Asian tyrannosauroids (similar to Khankhuuluu) dispersed to North America, giving rise to Eutyrannosauria in the mid-Late Cretaceous. Eutyrannosauria diversified and remained exclusively in North America until a single dispersal to Asia in the latest Cretaceous that established Alioramini and Tyrannosaurini. Stark morphological differences between Alioramini and Tyrannosaurini probably evolved due to divergent heterochronic trends—paedomorphosis versus peramorphosis, respectively—allowing them to coexist in Asia and occupy different ecological niches.

Khankhuuluu mongoliensis gen. et sp. nov.

Jared T. Voris, Darla K. Zelenitsky, Yoshitsugu Kobayashi, Sean P. Modesto, François Therrien, Hiroki Tsutsumi, Tsogtbaatar Chinzorig and Khishigjav Tsogtbaatar. 2025. A new Mongolian tyrannosauroid and the Evolution of Eutyrannosauria. Nature. DOI: doi.org/10.1038/s41586-025-08964-6 [11 June 2025]

[Paleontology • 2025] Rise of the King: Gondwanan Origins and Evolution of Megaraptoran Dinosaurs

Gondwanan Origins and Evolution of Megaraptoran Dinosaurs

in Morrison, Scherer, O’Callaghan, Layton, Boisvert, Rolando, Durrant, Salas, Allain et Gascoigne, 2025. 

DOI: doi.org/10.1098/rsos.242238 

 

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.

Keywords: Biogeography, Late Cretaceous, Megaraptora, Tyrannosauroidea

 

The end Cretaceous Northern Hemisphere fauna was dominated by Tyrannosaurids (such as Tyrannosaurus rex), hadrosaurs and ceratopsian ornithischian dinosaurs.

Artwork by Pedro Salas and Sergey Krasovskiy.

Potential dispersal routes for megaraptorans during the Middle Jurassic–Early Cretaceous (approx. 143 Ma). ...

Cassius Morrison, Charlie Roger Scherer, Ezekiel V. O’Callaghan, Collin Layton, Colin Boisvert, Mauro Aranciaga Rolando, Leroy Durrant, Pedro Salas, Steven J. R. Allain and Samuel J. L. Gascoigne. 2025. Rise of the King: Gondwanan Origins and Evolution of Megaraptoran Dinosaurs. R. Soc. Open Sci. 12: 242238. DOI: doi.org/10.1098/rsos.242238  [07 May 2025] 

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[Paleontology • 2024] Labocania aguillonae • A New Tyrant Dinosaur (Theropoda: Tyrannosauridae) from the Late Campanian of Mexico Reveals a Tribe of Southern Tyrannosaurs

  

 Labocania aguillonae

    Rivera-Sylva & Longrich, 2024

 www.mdpi.com/2813-6284/2/4/12  

facebook.com/NickLongrich

Artwork by Andrey Atuchin.

Abstract

The end of the Cretaceous saw the Western Interior Seaway divide North America into two land masses, Laramidia in the west and Appalachia in the east. Laramidian dinosaurs inhabited a narrow strip of land extending from Mexico to Alaska. Within this geographically restricted area, dinosaurs evolved high diversity and endemism, with distinct species in the north and south. Here, we report a new tyrannosaurid from the Late Campanian-aged Cerro del Pueblo Formation of Coahuila, Mexico, which is part of a tribe of tyrannosaurs originating in southern Laramidia. Phylogenetic analysis recovers the new tyrannosaur as part of a clade including Labocania anomala from the La Bocana Roja Formation of Baja California Norte, Bistahieversor sealeyi from the Kirtland Formation of New Mexico, Teratophoneus curriei from the Kaiparowits Formation in Utah, and Dynamoterror dynastes from the Menefee Formation of New Mexico. Distinct frontal morphology and the younger age (~72.5–73 Ma versus >75.8 Ma for L. anomala) support recognition of the new tyrannosaur as a distinct species of Labocania, Labocania aguillonae. The Labocania clade dominated southern Laramidia at a time when the north was dominated by daspletosaurins and albertosaurines. The high endemism seen in tyrannosaurids is remarkable, given that modern apex predators have large geographic ranges and hints that the diversity of carnivorous dinosaurs has been underestimated.

Keywords: Tyrannosauridae; dinosauria; Campanian; Cretaceous; Laramidia

Skeletal reconstruction of Labocania aguillonae (CPC 2974) showing preserved material. Scale = 1 m.

Systematic paleontology

Dinosauria—Owen 1842  

Theropoda—Marsh, 1881  

Coelurosauria—von Huene 1914  

Tyrannosauridae—Osborn, 1906 

Tyrannosaurinae—Osborn, 1906  

Teratophoneini—Scherer & Voiculescu-Holvad, 2024  

Labocania—Molnar 1974  

Labocania aguillonae sp. nov.

Diagnosis: Tyrannosaurine diagnosed by the following character combination (*—autapomorphies): orbit large and circular, with a very strongly convex anteroventral margin of the lacrimal* with a prominent, strongly dorsally extended* subocular process on the lacrimal along the anteroventral margin of the orbit; strong posteroventral extension of the antorbital fossa onto the lacrimal to end below the anterior margin of the orbit; lateral ends of frontals with a very prominent, acutely triangular shape, with strong transversely expanded overlap of frontal onto lacrimal; broad anteromedial extension of supratemporal fossa extending far forward onto frontal*; strong medial projection of postorbitals behind frontals onto dorsolateral surface of postorbital process, such that frontal underlaps the postorbital anteriorly*, lateral teeth with a figure-eight basal cross-section, and deep, prominent grooves or fullers extending from the root up the labial and lingual surfaces of the crown.

 Etymology: The species name honors Martha C. Aguillón, discoverer of the specimen and a long-time career paleontologist of Coahuila.

Conclusions: 

CPC 2974 represents a new species of tyrannosaurid, Labocania aguillonae, closely related to Labocania anomala, Bistahieversor sealeyi, and Teratophoneus curriei. It adds to the diversity of the Cerro del Pueblo Formation and shows that endemicity existed within tyrannosaurs in the Late Campanian, with distinct species and clades inhabiting the northern Great Plains in the north and the American Southwest and Mexico in the south. Given the limited geographic sampling, many tyrannosaur species likely remain undiscovered. Competition between species likely helped to enforce endemism among dinosaurs. Why large dinosaurs seem to have such unusually high levels of endemism compared to modern mammals remains unclear.

 Héctor E. Rivera-Sylva and Nicholas R. Longrich. 2024. A New Tyrant Dinosaur from the Late Campanian of Mexico Reveals a Tribe of Southern Tyrannosaurs. Foss. Stud. 2024, 2(4), 245-272. DOI: doi.org/10.3390/fossils2040012  www.mdpi.com/2813-6284/2/4/12

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[Paleontology • 2024] Asiatyrannus xui • The first deep-snouted tyrannosaur from Upper Cretaceous Ganzhou City of southeastern China

Asiatyrannus xui

 Zheng, Jin, Xie & Du, 2024

 

DOI:  10.1038/s41598-024-66278-5

Abstract

Tyrannosaurids were the most derived group of Tyrannosauroidea and are characterized by having two body plans: gracile, long-snouted and robust, deep-snouted skulls. Both groups lived sympatrically in central Asia. Here, we report a new deep-snouted tyrannosaurid, Asiatyrannus xui gen. et sp. nov., from the Upper Cretaceous of Ganzhou City, southeastern China, which has produced the large-bodied and long-snouted Qianzhousaurus. Based on histological analysis, the holotype of Asiatyrannus xui is not a somatically mature adult, but it already passed through the most rapid growth stages. Asiatyrannus is a small to medium-sized tyrannosaurine, with a skull length of 47.5 cm and an estimated total body length of 3.5–4 m; or around half the size of Qianzhousaurus and other large-bodied tyrannosaurines in similar growth stages. Asiatyrannus and Qianzhousaurus are sympatric tyrannosaurid genera in the Maastrichtian of southeastern China. Asiatyrannus differs from Qianzhousaurus in that it has a proportionally deeper snout, longer premaxilla, deeper maxilla, and deeper dentary, and the cornual process of the lacrimal is inflated without developing a discrete horn. The different skull proportions and body sizes suggest that Asiatyrannus and Qianzhousaurus likely had different feeding strategies and occupied different ecological niches.

 

Keywords: Asiatyrannus xui, Tyrannosauridae, Nanxiong Formation, Upper Cretaceous, China

 

Systematic paleontology

Theropoda Marsh, 1881

Tetanurae Gauthier, 1986

Coelurosauria Huene, 1914

Tyrannosauroidea Osborn, 1905

Tyrannosauridae Osborn, 1905

Tyrannosaurinae Osborn, 1905

Asiatyrannus xui gen. et sp. nov.

Diagnosis: Asiatyrannus xui is a small to medium-sized tyrannosaurine theropod that differs from other tyrannosauroids in possessing the following autapomorphies: two small, deep fossae located on the lateral surface of the premaxilla just lateral to the anteroventral border of the external naris, a large and sub-rectangular shaped maxillary fenestra, the posterior protuberances of the nasals connect to form two separated medium low ridges, a low ridge-like jugal accessory horn, the ventral margin of the anterior ramus of the jugal curving ventrally anterior to the accessory horn, the lateral surface of the descending process of the postorbital developed the anterodorsally trending fine lineations, the slender, straight, and banded-shaped postorbital bar, with almost straight and parallel anterior and posterior margins in lateral view, and the lateral surangular shelf extends to the posterior end of the surangular.

Type locality: Nanxiong Formation (Upper Cretaceous, Maastrichtian) of Shahe Town, Nankang District, Ganzhou City, Jiangxi Province, China.

The photograph (A) and line drawing (B) of the skull of Asiatyrannus xui (ZMNH M30360) in right lateral view. The inset box in (A) indicates the position of the detailed jugal accessory horn in (C).

 acf accessory fossa of maxilla; ang angular; aof antorbital fenestra; cor cornual process; d dentary; d.t dentary tooth; emf external mandibular fenestra; en external naris; f frontal; gr groove; itf infratemporal fenestra; j jugal; jah jugal accessory horn; L left; la lacrimal; mf maxillary fenestra; mnvf maxillary neurovascular foramina; mx maxilla; nas nasal; nr nasal ridge; orb orbit; par parietal; pal palatine; pmx premaxilla; po postorbital; q quadrate; qj quadratojugal; R right; sa surangular; sf surangular foramen; snf subnarial foramen; sq squamosal; t1–6 maxillary tooth 1–6.

Fossil remains of Asiatyrannus xui (ZMNH M30360).
(A) Skeletal outlines showing recovered elements in yellow color. The skeletal reconstruction is the proportional scaling of Lythronax argestes drawn by Scott Hartman from Loewen et al.23; (B) the skull in right lateral view; (C) the caudal vertebrae in left lateral view; (D) the right femur in posterior view; (E) the right tibia and fibula in posterior view; (F) The distal portion of the right metatarsal III in medial view and metatarsal IV in anterior view; (G) the middle shaft of the left tibia and fibula in anterior view; (H) The middle shaft of the left metatarsals in anterior view. ft the fourth trochanter; ift iliofibularis tubercle; mt metatarsal.

Etymology: The generic name is derived from Asia, and the suffix ‘tyrannus’ is derived from the Latin word for ‘king’ or ‘tyrant’, to emphasize that this is the new tyrannosaur collected in the continent of Asia. The specific name honors Dr. Xing Xu (Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences), a distinguished dinosaurologist who contributed greatly to the study of dinosaurs from China, including the research of several tyrannosaurs: Guanlong, Dilong, and Yutyrannus. Dr. Xing Xu has also been a great supporter of the paleontological research and science popularization work of the Zhejiang Museum of Natural History.

Wenjie Zheng, Xingsheng Jin, Junfang Xie and Tianming Du. 2024. The first deep-snouted tyrannosaur from Upper Cretaceous Ganzhou City of southeastern China. Scientific Reports. 14,  16276. DOI:  doi.org/10.1038/s41598-024-66278-5

[Paleontology • 2024] The First Occurrence of a Basal Tyrannosauroid in Southeast Asia: Dental Evidence from the Upper Jurassic of Northeastern Thailand

Tyrannosauroidea indet.

in Chowchuvech, Manitkoon, Chanthasit et Ketwetsuriya, 2024.

   li01.tci-thaijo.org/index.php/TNH/article/view/261261

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Illustration: Chatcharin Somboon.

Abstract

Isolated theropod teeth are one of the most common vertebrate fossils that have been found in the Khorat Group of Thailand. Furthermore, several isolated teeth have been discovered from the Upper Jurassic Phu Kradung Formation, located in Phu Noi locality of Kalasin Province, Northeastern Thailand. Three of those theropod teeth from the Phu Noi locality show unique dental features that can be distinguished from previous discovered metriacanthosaurid theropod, including the lateral teeth with mesiolingual twisted mesial carinae extending above the cervix line and braided enamel surface texture. Morphological examination with cladistics and morphometric analyses show that these isolated teeth exhibit the synapomorphies of basal tyrannosauroids, closely related to Guanlong wucaii and Proceratosaurus bradleyi from the Jurassic Period. This paper notes the first report of a basal tyrannosauroid in Southeast Asia as well as significantly contributes to our understanding of paleoecology of the Upper Jurassic Phu Kradung Formation and paleobiogeography of Tyrannosauroidea during the Jurassic Period.

Keywords: Dinosauria, Theropod, isolated teeth, Phu Kradung Formation, Mesozoic Era

Paleoenvironmental reconstruction of the Late Jurassic Phu Kradung Formation of Northeastern Thailand.

Illustrated by Chatcharin Somboon.

Wongwech Chowchuvech, Sita Manitkoon, Phornphen Chanthasit and Chatchalerm Ketwetsuriya. 2024. The First Occurrence of a Basal Tyrannosauroid in Southeast Asia: Dental Evidence from the Upper Jurassic of Northeastern Thailand. Tropical Natural History. 24(1); 84–95.   li01.tci-thaijo.org/index.php/tnh/article/view/261261

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Researchgate.net/publication/376029479_The_First_Occurrence_of_Tyrannosauroid_Dinosaur_in_Southeast_Asia

ค้นพบ ฟันไดโนเสาร์ไทแรนโนซอรอยด์ ญาติเก่าแก่ของ T. rex ยุคจูแรสซิกในประเทศไทย 🦖

...  ซากดึกดำบรรพ์ฟันไดโนเสาร์ไทแรนโนซอรอยด์แรกเริ่ม จากหมวดหินภูกระดึงตอนล่าง ยุคจูแรสซิกตอนปลาย ในแหล่งซากดึกดำบรรพ์ภูน้อย อำเภอคำม่วง จังหวัดกาฬสินธ์ุ ซึ่งเป็นหนึ่งในญาติเก่าแก่ของไดโนเสาร์กินเนื้อขนาดใหญ่ชื่อดังอย่างไทแรนโนซอรัส เร็กซ์ หรือ ที. เร็กซ์ ในยุคครีเทเชียสตอนปลาย ทวีปอเมริกาเหนือ ...

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[Paleontology • 2024] Tyrannosaurus mcraeensis • A Giant tyrannosaur from the Campanian–Maastrichtian of southern North America and the Evolution of tyrannosaurid gigantism

Tyrannosaurus mcraeensis 

Dalman, Loewen, Pyron, Jasinski, Malinzak, Lucas, Fiorillo, Currie & Longrich, 2024

 

DOI: 10.1038/s41598-023-47011-0

Artwork by Sergei Krasinski.

Abstract

Tyrannosaurid dinosaurs dominated as predators in the Late Cretaceous of Laurasia, culminating in the evolution of the giant Tyrannosaurus rex, both the last and largest tyrannosaurid. Where and when Tyrannosaurini (T. rex and kin) originated remains unclear. Competing hypotheses place tyrannosaurin origins in Asia, or western North America (Laramidia). We report a new tyrannosaurin, Tyrannosaurus mcraeensis, from the Campanian–Maastrichtian Hall Lake Formation of New Mexico, based on a fossil previously referred to T. rex. T. mcraeensis predates T. rex by ~ 6–7 million years, yet rivaled it in size. Phylogenetic analysis recovers T. mcraeensis as sister to T. rex and suggests Tyrannosaurini originated in southern Laramidia. Evolution of giant tyrannosaurs in southern North America, alongside giant ceratopsians, hadrosaurs, and titanosaurs suggests large-bodied dinosaurs evolved at low latitudes in North America.

Locality and stratigraphy of Tyrannosaurus mcraeensis sp. nov., NMMNH P-3698.
(A), type locality in Sierra County, New Mexico; (B), stratigraphy of fossil and the Hall Lake Formation (C), recovered skull elements. Scale = 10 cm. Map by Ron Blakey.

Mandibular elements of Tyrannosaurus mcraeensis sp. nov. (NMMNH P-3698).
 Left dentary in (A), medial view; (B), lateral view; (C), dorsal view; (D), right splenial, medial view; (E), right angular, medial view; (F), right prearticular, medial view. ang angular contact, de shelf for dentary, mec Meckelian canal, pre prearticular facet, a1, a5, a15 alveoli 1, 5, and 15, sp splenial, sym symphysis. Scale = 20 cm.

Dinosauria Owen, 1842.

Theropoda Marsh, 1881.

Tetanurae Gauthier, 1986.

Coelurosauria von Huene, 1914.

Tyrannosauridae Osborn, 1905.

Tyrannosaurinae Currie, 2003.

Tyrannosaurini Olshevsky, 1995.

(Tyrannosaurini is here defined as the last common ancestor of Tarbosaurus baatar and Tyrannosaurus rex and all its descendants).

Tyrannosaurus mcraeensis sp. nov.

Diagnosis: Large tyrannosaurin distinguished from Tyrannosaurus rex (Fig. 4; SI) by the following characters (*autapomorphies): postorbital with low, posteriorly positioned cornual process; postorbital with anteriorly projecting prefrontal/frontal articular surfaces; squamosal with ventrally projecting quadratojugal process; squamosal with a concave medial margin; strong ridge bounding the anterior margin of the squamosal ventral pneumatic fossa; dentary very shallow posteriorly and with a convex posteroventral margin*; splenial with anteriorly positioned apex*; splenial with shelf-like dentary overlap*, splenial with deep, posteriorly directed angular process; prearticular weakly bowed*; small ventral prearticular-angular contact; articular T-shaped in dorsal/ventral view; retroarticular process deep and quadrangular in posterior view.

Holotype: NMMNH P-3698, partial skull including right postorbital and squamosal (Fig. 2), left palatine, fragment of maxilla, and lower jaws (Fig. 3) including left dentary, right splenial, prearticular, angular and articular, isolated teeth and associated chevrons.

 

Horizon and locality: Uppermost Campanian or lower Maastrichtian of the Hall Lake Formation, McRae Group, NMMNH locality 343, near Kettle Top Butte, Sierra County, New Mexico21 (Fig. 1A). The site lies 43 m above the base of the Hall Lake Formation. A tuff 33 m below the tyrannosaur site has a U/Pb age of 73.2 ± 0.7 Ma22 (Fig. 1B).

Etymology: The species name, mcraeensis, refers to the McRae Group of western New Mexico.

 

Reconstruction of Tyrannosaurus mcraeensis.

Artwork by Sergei Krasinski.

 

Sebastian G. Dalman, Mark A. Loewen, R. Alexander Pyron, Steven E. Jasinski, D. Edward Malinzak, Spencer G. Lucas, Anthony R. Fiorillo, Philip J. Currie and Nicholas R. Longrich. 2024. A Giant tyrannosaur from the Campanian–Maastrichtian of southern North America and the Evolution of tyrannosaurid gigantism. Scientific Reports. 13: 22124. DOI: 10.1038/s41598-023-47011-0

[Paleontology • 2023] Exceptionally preserved Stomach Contents of A Young tyrannosaurid reveal An Ontogenetic Dietary Shift in an iconic Extinct Predator

Gorgosaurus libratus feeding on Citipes elegans.

in Therrien, Zelenitsky, Tanaka, Voris, ... et Kobayashi, 2023.

 DOI: 10.1126/sciadv.adi0505

Illustration by Julius Csotonyi 

RoyalTyrrellMuseum.wpcomstaging.com

 

Abstract

Tyrannosaurids were large carnivorous dinosaurs that underwent major changes in skull robusticity and body proportions as they grew, suggesting that they occupied different ecological niches during their life span. Although adults commonly fed on dinosaurian megaherbivores, the diet of juvenile tyrannosaurids is largely unknown. Here, we describe a remarkable specimen of a juvenile Gorgosaurus libratus that preserves the articulated hindlimbs of two yearling caenagnathid dinosaurs inside its abdominal cavity. The prey were selectively dismembered and consumed in two separate feeding events. This predator-prey association provides direct evidence of an ontogenetic dietary shift in tyrannosaurids. Juvenile individuals may have hunted small and young dinosaurs until they reached a size when, to satisfy energy requirements, they transitioned to feeding on dinosaurian megaherbivores. Tyrannosaurids occupied both mesopredator and apex predator roles during their life span, a factor that may have been key to their evolutionary success.

Juvenile Gorgosaurus TMP 2009.12.14 preserving stomach contents.
Photographs of specimen in (A) right lateral view and (B) left anterolateral view. (C) Interpretive illustration of specimen in right lateral view. Skeleton consists of a nearly complete skull, the left side of the body and limbs, and a nearly complete pelvis. Red rectangle delineates location of stomach contents. (D) Histological photomicrograph of tibia showing the presence of five lines of arrested growths and two annuli (marked by asterisks), indicating that the individual was between 5 and 7 years old.

Scale bars, 50 cm (A) to (C) and 1 mm (D).

  

Juvenile Citipes remains preserved as stomach contents.
(A) Diagram illustrating relative body sizes of predator and prey and skeletal elements preserved in TMP 2009.12.14. Scale bar, 50 cm.
Histological photomicrographs of (B) posterior Citipes individual (metatarsal II) and (C) anterior Citipes individual (tibia), showing highly vascularized woven bone with reticular and longitudinally oriented vascular canals and lacking growth lines, indicative of young individuals that are less than 1 year old. Scale bars, 500 μm.

Gorgosaurus libratus feeding on Citipes elegans.

Illustration by Julius Csotonyi 

RoyalTyrrellMuseum.wpcomstaging.com 

 Francois Therrien, Darla K. Zelenitsky, Kohei Tanaka, Jared T. Voris, Gregory M. Erickson, Philip J. Currie, Christopher L. Debuhr, and Yoshitsugu Kobayashi. 2023. Exceptionally preserved Stomach Contents of A Young tyrannosaurid reveal An Ontogenetic Dietary Shift in an iconic Extinct Predator. SCIENCE ADVANCES. 9, 49. DOI: 10.1126/sciadv.adi0505

 ucalgary.ca/news/whats-dinner-ucalgary-paleontologist-finds-out-through-remarkable-specimen

 RoyalTyrrellMuseum.wpcomstaging.com/2023/12/08/a-young-tyrannosaurs-last-meal

 

[Paleontology • 2022] Daspletosaurus wilsoni • A Transitional Species of Daspletosaurus Russell, 1970 (Theropoda: Tyrannosauridae) from the Judith River Formation of eastern Montana, USA

Daspletosaurus wilsoni

 Warshaw​ & Fowler, 2022 

DOI:  10.7717/peerj.14461 

 twitter.com/DF9465 

Illustration: Andrey Atuchin & Badlands Dinosaur Museum

Abstract 

Here we describe a new derived tyrannosaurine, Daspletosaurus wilsoni sp. nov., from Judithian strata (~76.5 Ma) intermediate in age between either of the previously described species of this genus. D. wilsoni displays a unique combination of ancestral and derived characteristics, including a cornual process of the lacrimal reduced in height relative to D. torosus and more basal tyrannosaurines, and a prefrontal with a long axis oriented more rostrally than in D. horneri and more derived tyrannosaurines. The description of this taxon provides insight into evolutionary mode in Tyrannosaurinae, lending strength to previous hypotheses of anagenesis within Daspletosaurus and increasing the resolution with which the evolution of this lineage can be reconstructed. Cladistic phylogenetic methods, stratigraphy, and qualitative analysis of the morphology of relevant taxa supports an anagenetic model for the origin of morphological novelty in this genus, highlighting the predominance of anagenetic evolution among contemporary dinosaur lineages.

The new species (Daspletosaurus wilsoni, 76.5 Ma) is transitional in form and age between D. torosus (77 Ma) and D. horneri (75.6 Ma). This suggests that Daspletosaurus underwent linear evolution - where one form evolves into the next without splitting or branching.

by Dickinson Museum Center

The new specimen, "Sisyphus", is one of four tyrannosaur skeletons recently collected by Badlands Dinosaur Museum. Here the four tyrannosaurs dispute ownership of the fresh carcass of a Centrosaurus.

by Rudolf Hima & Badlands Dinosaur Museum.

Tyrannosaurinae Matthew & Brown, 1922 (sensu Sereno, McAllister & Brusatte, 2005)

Daspletosaurus Russell, 1970

Daspletosaurus wilsoni sp. nov.

Diagnosis: D. wilsoni can be assigned to Daspletosaurus based on the following characteristics: extremely coarse subcutaneous surface of the maxilla with no elevated ridges or corresponding fossae (Carr et al., 2017; Voris et al., 2020); cornual process of the postorbital approaching the laterotemporal fenestra (Carr et al., 2017); dorsal postorbital process of the squamosal terminating caudal to the rostral margin of the laterotemporal fenestra (Carr et al., 2017; Voris et al., 2019); and extremely coarse symphyseal surface of the dentary (Voris et al., 2020).

...

Etymology: wilsoni, Latinization of “Wilson,” after John Wilson, the discoverer of the holotype specimen.

Conclusions: 

D. wilsoni sp. nov., a stratigraphic and morphological intermediate between D. torosus and D. horneri, is hypothesized to represent a transitional form along an anagenetic lineage linking both previously named species of Daspletosaurus. This finding, in concert with previous identifications of anagenesis in contemporary dinosaur lineages, emphasizes the explanatory power of anagenesis in the production of evolutionary trends among dinosaurs of the Late Cretaceous Western Interior (Scannella et al., 2014; Freedman Fowler & Horner, 2015; Fowler & Fowler, 2020; Wilson, Ryan & Evans, 2020). Indeed, as anagenesis continues to be identified among fossil lineages, the predominant relative frequency of strictly cladogenetic evolutionary models (e.g., punctuated equilibria; Eldredge & Gould, 1972) must eventually come under scrutiny. Future explorations of evolutionary mode in fossil taxa, including further tests of the hypotheses presented here, will be important in this regard, and have the potential to refine understanding of the pattern and process of dinosaur evolution.

 

 

Elías A. Warshaw​ and Denver W. Fowler. 2022. A Transitional Species of Daspletosaurus Russell, 1970 from the Judith River Formation of eastern Montana.  PeerJ. 10:e14461. DOI:  10.7717/peerj.14461

  twitter.com/DF9465/status/1596149970779897862

 phys.org/news/2022-11-species-tyrannosaur-daspletosaurus-wilsoni-hints.html

[Paleontology • 2021] Intraspecific Facial Bite Marks in Tyrannosaurids provide insight into Sexual Maturity and Evolution of Bird-like Intersexual Display

Artistic reconstructions of hypothesized face-biting behaviour in Tyrannosauridae.

Left, two Gorgosaurus individuals aggressively square off.

Right, the aftermath of face-biting behaviour, 

showing recent wounds and older scars. 

in Brown, Currie & Therrien, 2021.

DOI: 10.1017/pab.2021.29

  RoyalTyrrellMuseum.wpcomstaging.com

Image © Royal Tyrrell Museum, illustration by Julius Csotonyi.

Abstract

Intraspecific aggression, or agonism, is a widespread intrasexual selective behavior important to understanding animal behavioral ecology and reproductive systems. Such behavior can be studied either by direct observation or inferred from wound/scar frequency in extant species but is difficult to document in extinct taxa, limiting understanding of its evolution. Among extant archosaurs, crocodylians display extensive intrasexual aggression, whereas birds show extreme visual/vocal intersexual display. The evolutionary origin of this behavioral divergence, and pattern in non-avian dinosaurs, is unknown. Here we document the morphology, frequency, and ontogeny of intraspecific facial bite lesions (324 lesions) in a large sample of tyrannosaurids (202 specimens, 528 elements) to infer patterns of intraspecific aggression in non-avian theropods. Facial scars are consistent in position and orientation across tyrannosaurid species, suggesting bites were inflicted due to repeated/postured behavior. Facial scars are absent in young tyrannosaurids, first appear in immature animals (~50% adult skull length), are present in ~60% of the adult-sized specimens, and show aggressor:victim size isometry. The ontogenetic distribution of bite scars suggests agonistic behavior is associated with the onset of sexual maturity, and scar presence in approximately half the specimens may relate to a sexual pattern. Considered in a phylogenetic context, intraspecific bite marks are consistent and widely distributed in fossil and extant crocodyliforms and non-maniraptoriform theropods, suggesting a potential plesiomorphic behavior in archosaurs. Their absence in maniraptoriform theropods, including birds, may reflect a transition from boney cranial ornamentation and crocodylian-like intrasexual aggression to avian-like intersexual display with the evolution of pennaceous feathers.

Skull bones with tooth-strike scars across tyrannosaur specimens of increasing sizes.

    

Presence of facial tooth marks, ornamentation of the skull, and presence of feathered forelimbs, across various members of Theropoda.

Caleb M. Brown, Philip J. Currie and François Therrien. 2021. Intraspecific Facial Bite Marks in Tyrannosaurids provide insight into Sexual Maturity and Evolution of Bird-like Intersexual Display. Paleobiology. FirstView. pp. 1 - 32. DOI: 10.1017/pab.2021.29

Clash of the Titans: Facial Scars as Indicators of Aggressive Behaviour and Sexual Maturity in Tyrannosaurs

 RoyalTyrrellMuseum.wpcomstaging.com/2021/09/07/tyrannosaur-facial-scars/