A transitional species of <i>Daspletosaurus</i> Russell, 1970 from the Judith River Formation of eastern Montana

Warshaw, Elías A.; Fowler, Denver W.

doi:10.7717/peerj.14461

Cited by 8 publications

(3 citation statements)

References 41 publications

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“…However, many ceratopsid taxa are known from single specimens, and are often poorly constrained stratigraphically. Previous work inferring anagenesis in dinosaurs of the WIB ( e.g ., Freedman-Fowler & Horner, 2015 ; Fowler, 2017 ; Carr et al, 2017 ; Fowler & Freedman-Fowler, 2020 ; Wilson, Ryan & Evans, 2020 ; Warshaw & Fowler, 2022 ), rely heavily on stratigraphic position of singleton specimens to construct ‘connect-the-dots’ ancestor-descendant sequences. This approach ignores the fact that few of the employed taxonomic units have any actual stratigraphic ranges (as opposed to a point occurrence).…”

Section: Discussionmentioning

confidence: 99%

Lokiceratops rangiformis gen. et sp. nov. (Ceratopsidae: Centrosaurinae) from the Campanian Judith River Formation of Montana reveals rapid regional radiations and extreme endemism within centrosaurine dinosaurs

Loewen,

Sertich,

Sampson

et al. 2024

PeerJ

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The Late Cretaceous of western North America supported diverse dinosaur assemblages, though understanding patterns of dinosaur diversity, evolution, and extinction has been historically limited by unequal geographic and temporal sampling. In particular, the existence and extent of faunal endemism along the eastern coastal plain of Laramidia continues to generate debate, and finer scale regional patterns remain elusive. Here, we report a new centrosaurine ceratopsid, Lokiceratops rangiformis, from the lower portion of the McClelland Ferry Member of the Judith River Formation in the Kennedy Coulee region along the Canada-USA border. Dinosaurs from the same small geographic region, and from nearby, stratigraphically equivalent horizons of the lower Oldman Formation in Canada, reveal unprecedented ceratopsid richness, with four sympatric centrosaurine taxa and one chasmosaurine taxon. Phylogenetic results show that Lokiceratops, together with Albertaceratops and Medusaceratops, was part of a clade restricted to a small portion of northern Laramidia approximately 78 million years ago. This group, Albertaceratopsini, was one of multiple centrosaurine clades to undergo geographically restricted radiations, with Nasutuceratopsini restricted to the south and Centrosaurini and Pachyrostra restricted to the north. High regional endemism in centrosaurs is associated with, and may have been driven by, high speciation rates and diversity, with competition between dinosaurs limiting their geographic range. High speciation rates may in turn have been driven in part by sexual selection or latitudinally uneven climatic and floral gradients. The high endemism seen in centrosaurines and other dinosaurs implies that dinosaur diversity is underestimated and contrasts with the large geographic ranges seen in most extant mammalian megafauna.

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Section: Discussionmentioning

confidence: 99%

Lokiceratops rangiformis gen. et sp. nov. (Ceratopsidae: Centrosaurinae) from the Campanian Judith River Formation of Montana reveals rapid regional radiations and extreme endemism within centrosaurine dinosaurs

Loewen,

Sertich,

Sampson

et al. 2024

PeerJ

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“…Tyrannosaurs were diverse in the Late Cretaceous of Laurasia [4,39,52,[56][57][58][59][60][61][62]. Small tyrannosaurs of the Cenomanian [63] and Turonian [64,65] were replaced by large-bodied tyrannosaurs by the Campanian [52,57].…”

Section: Diversity Patterns Of Tyrannosaurs and Apex Predatorsmentioning

confidence: 99%

Taxonomic Status of Nanotyrannus lancensis (Dinosauria: Tyrannosauroidea)—A Distinct Taxon of Small-Bodied Tyrannosaur

Longrich,

Saitta

2024

Fossil Studies

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Tyrannosaurs are among the most intensively studied and best-known dinosaurs. Despite this, their relationships and systematics are highly controversial. An ongoing debate concerns the validity of Nanotyrannus lancensis, interpreted either as a distinct genus of small-bodied tyrannosaur or a juvenile of Tyrannosaurus rex. We examine multiple lines of evidence and show that the evidence strongly supports recognition of Nanotyrannus as a distinct species for the following reasons: 1. High diversity of tyrannosaurs and predatory dinosaurs supports the idea that multiple tyrannosaurids inhabited the late Maastrichtian of Laramidia; 2. Nanotyrannus lacks characters supporting referral to Tyrannosaurus or Tyrannosaurinae but differs from T. rex in >150 morphological characters, while intermediate forms combining the features of Nanotyrannus and T. rex are unknown; 3. Histology shows specimens of Nanotyrannus showing (i) skeletal fusions, (ii) mature skull bone textures, (iii) slow growth rates relative to T. rex, (iv) decelerating growth in their final years of life, and (v) growth curves predicting adult masses of ~1500 kg or less, showing these animals are subadults and young adults, not juvenile Tyrannosaurus; 4. growth series of other tyrannosaurids, including Tarbosaurus and Gorgosaurus, do not show morphological changes proposed for a Nanotyrannus–Tyrannosaurus growth series, and deriving Tyrannosaurus from Nanotyrannus requires several changes inconsistent with known patterns of dinosaur development; 5. Juvenile T. rex exist, showing diagnostic features of Tyrannosaurus; 6. Phylogenetic analysis suggests that Nanotyrannus may lie outside Tyrannosauridae. Tyrannosaur diversity before the K-Pg extinction is higher than previously appreciated. The challenges inherent in diagnosing species based on fossils mean paleontologists may be systematically underestimating the diversity of ancient ecosystems.

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“…All else being equal, we should expect more than one tyrannosaur to exist in the latest Maastrichtian of North America, and arguments for the existence of a distinct taxon should therefore be considered seriously rather than dismissed out of hand. Tyrannosaurs were diverse in the Late Cretaceous of Laurasia (Currie 2003, Holtz 2004, Carr and Williamson 2010, Carr, Williamson et al 2011, Loewen, Irmis et al 2013, Carr, Varricchio et al 2017, Voris, Therrien et al 2020, Warshaw and Fowler 2022 (Molnar 1974). Small tyrannosaurs of the Cenomanian (Zanno, Tucker et al 2019) and Turonian (Brusatte, Averianov et al 2016, Nesbitt, Denton Jr et al 2019 were replaced by large-bodied tyrannosaurs by the Campanian.…”

Section: Diversity Of Tyrannosaurs and Apex Predatorsmentioning

confidence: 99%

Taxonomic status of Nanotyrannus lancensis (Dinosauria: Tyrannosauroidea) — a distinct taxon of small-bodied tyrannosaur

Longrich,

Saitta

2023

Preprint

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Tyrannosaurs, giant predatory dinosaurs from the end of the Cretaceous, are among the most intensively researched and best-known groups of dinosaurs. Despite this, their relationships and systematics are highly controversial, and the number of tyrannosaur species occurring in the latest Cretaceous in North America is debated. An ongoing debate concerns the status of Nanotyrannus lancensis, which has variously been interpreted as a distinct taxon of small-bodied tyrannosaur or a juvenile of the coeval Tyrannosaurus rex. Here, we review multiple lines of evidence and show that the totality of evidence strongly supports recognition of Nanotyrannus as a distinct species: 1. The high diversity of Late Cretaceous tyrannosaurs and predatory dinosaurs in general is consistent with the idea that more than one species lived in the late Maastrichtian of Western North America; 2. Nanotyrannus shows few if any diagnostic characters allowing referral specifically to Tyrannosaurus or even Tyrannosaurinae, but is differentiated from T. rex by at least 77 morphological characters, while intermediate forms, combining characteristics of Nanotyrannus and T. rex, remain unknown; 3. Histological evidence shows that individuals previously referred to Nanotyrannus lancensis show (i) skeletal fusions consistent with maturity, (ii) skull bone textures consistent with maturity, (iii) slow growth rates relative to T. rex, (iv) decelerating growth in their final years of life, and (v) growth curves predicting adult body sizes of ~1500 kg or less, implying that these animals are young adults, not juveniles of Tyrannosaurus; 4. Juveniles of other tyrannosaurids, including Gorgosaurus and Tarbosaurus, do not show the kinds of changes proposed for a Nanotyrannus-Tyrannosaurus growth series, suggesting the Nanotyrannus morphology cannot simply be explained as the result of immaturity; 5. Small T. rex exist, comparable in size to Nanotyrannus, which exhibit diagnostic features of Tyrannosaurus, and which differ from Nanotyrannus; 6. Phylogenetic analysis suggests that Nanotyrannus is not a tyrannosaurid. Taken together, the totality of the evidence rejects referral of Nanotyrannus to T. rex. Phylogenetic analysis tentatively supports placement of Nanotyrannus outside of Tyrannosauridae as a non-tyrannosaurid member of Tyrannosauroidea. Tyrannosaur diversity appears to have been higher than previously appreciated in the latest Cretaceous before the K-Pg extinction. The difficulties in recognizing species based on fossils alone mean that paleontologists may be systematically biased towards underestimating the species diversity of ancient ecosystems.

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A transitional species of Daspletosaurus Russell, 1970 from the Judith River Formation of eastern Montana

Cited by 8 publications

References 41 publications

Lokiceratops rangiformis gen. et sp. nov. (Ceratopsidae: Centrosaurinae) from the Campanian Judith River Formation of Montana reveals rapid regional radiations and extreme endemism within centrosaurine dinosaurs

Lokiceratops rangiformis gen. et sp. nov. (Ceratopsidae: Centrosaurinae) from the Campanian Judith River Formation of Montana reveals rapid regional radiations and extreme endemism within centrosaurine dinosaurs

Taxonomic Status of Nanotyrannus lancensis (Dinosauria: Tyrannosauroidea)—A Distinct Taxon of Small-Bodied Tyrannosaur

Taxonomic status of Nanotyrannus lancensis (Dinosauria: Tyrannosauroidea) — a distinct taxon of small-bodied tyrannosaur

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