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The sparse dinosaur record of eastern North America has rendered the dinosaurs of the Late Cretaceous landmass of Appalachia obscure. Appalachia may have been a refugium for dinosaur species that would be replaced on Appalachia's western contemporary, Laramidia, from which the former landmass was isolated by the Western Interior Seaway. Among the theropods of the landmass, Appalachian tyrannosaurs are only represented currently by the two valid taxa Dryptosaurus aquilunguis and Appalachiosaurus montgomeriensis, a distinct but indeterminate taxon from the Campanian of Delaware, and indeterminate skeletons and isolated elements. New Jersey in particular has rendered many bones assignable to tyrannosauroids, contributing much to the study of members of this clade from Appalachia. Here, the partial tibia of a tyrannosauroid is described from the Maastrichtian Navesink Formation of Monmouth County, New Jersey. The specimen, originally described by paleontologists Edward Drinker Cope and Joseph Leidy, is important for revealing further the theropod fauna of the Navesink Formation of New Jersey and being the second definite occurrence of a tyrannosauroid in eastern North America during the Maastrichtian, thus illuminating the group's ecology and biogeography during that stage of the Cretaceous. Phylogenetic analysis plots the Navesink specimen as the sister taxon to Bistahieversor in a larger polytomy of all tyrannosauroids more derived than Eotyrannus, suggesting that the Navesink bone may represent either another “intermediate”-grade tyrannosauroid from Appalachia or a relative of B. sealeyi that migrated to eastern North America after the regression of the Western Interior Seaway.

The Barremian through Turonian record of tyrannosauroids in North America is sparse, and neither the western nor eastern portions of the continent have produced substantial material of early tyrant dinosaurs. This is unfortunate, as the discovery and description of several new tyrannosauroid genera from this temporal interval in recent years has shown that this period of time was likely when the tyrannosauroids evolved many of the signature features of the large- bodied genera that famously roamed the planet during the latest Cretaceous. One particular trait of the younger tyrant dinosaur genera that seems to have evolved during the aforementioned temporal interval was that of large body size. Here, I describe the metatarsal II of an indeterminate tyrannosauroid from the Cenomanian Potomac Formation of New Jersey. The metatarsal II is significant for several reasons. It is the only definite occurrence of a tyrannosauroid in eastern North America (Appalachia) before the Coniacian and Santonian and indicates an animal in the size range of tyrannosauroids from the Santonian to Maastrichtian of the Cretaceous. The New Jersey specimen thus differs from other, mostly small and gracile, known tyrannosaur genera of the mid-Cretaceous, suggesting that the evolution of large size among tyrannosauroids was a complex process. The metatarsal has morphological affinities to the corresponding metatarsal II of Appalachiosaurus montgomeriensis, and along with the results of phylogenetic analysis this suggests that Late Cretaceous Appalachian tyrannosauroids were relict forms isolated on the landmass.

In order to assess how similar Appalachiosaurus and Albertosaurus libratus are, their functional morphology was compared with emphasis on bite force, velocity, dentition, and skull construction with implication on possible feeding behaviors. It was found that despite their skeletal similarities and velocities, they likely filled two different ecological niches which may or may not have influenced a possible retention of basal features in Appalachiosaurus.

Rare remains of tyrannosauroid dinosaurs from the Aguja Formation in West Texas indicate the presence here of a relatively gracile species, comparable in form and adult size toAppalachiosaurusor subadult albertosaurines,GorgosaurusandAlbertosaurus. Histologic analysis of one of the specimens indicates that the Aguja tyrannosaur attained an adult size substantially smaller than adult albertosaurines (700 kg, 6·5 m body length). The frontal bone is narrow with a wide orbital slot and a bipartite joint for the postorbital, features thought to be diagnostic of Albertosaurinae; but there is a tall sagittal crest and reduced parietal wedge separating the frontals on the midline, features thought to be diagnostic of Tyrannosaurinae. The tall sagittal crest may be a synapomorphy of Tyrannosaurinae, and the Aguja tyrannosaur is herein referred to that clade. However, the unique combination of character states exhibited by the frontal prevents confident attribution to any known species. The Aguja tyrannosaur provides further evidence that North American Campanian tyrannosauroids were remarkably diverse for such large predators, and that each species was apparently endemic to a relatively small geographic province.

There exists a major gap in the fossil record of tyrannosauroid theropod dinosaurs spanning the early part of the Late Cretaceous. We report on skeletal remains referable to Tyrannosauroidea indet. from the Turonian Bissekty Formation at Dzharakuduk in the central Kyzylkum Desert of Uzbekistan. Phylogenetic analysis of the hypodigm places the Bissekty tyrannosauroid as a non-tyrannosaurid tyrannosauroid more basal than the Campanian tyrannosauroids Appalachiosaurus and Bistahieversor from North America.

The fossil record of tyrannosauroid theropods is marked by a substantial temporal and morphological gap between small-bodied, Barremian taxa, and extremely large-bodied taxa from the latest Cretaceous. Here we describe a new tyrannosauroid, Xiongguanlong baimoensis n. gen. et sp., from the Aptian–Albian Xinminpu Group of western China that represents a phylogenetic, morphological, and temporal link between these disjunct portions of tyrannosauroid evolutionary history. Xiongguanlong is recovered in our phylogenetic analysis as the sister taxon to Tyrannosauridae plus Appalachiosaurus , and marks the appearance of several tyrannosaurid hallmark features, including a sharp parietal sagittal crest, a boxy basicranium, a quadratojugal with a flaring dorsal process and a flexed caudal edge, premaxillary teeth bearing a median lingual ridge, and an expanded axial neural spine surmounted by distinct processes at its corners. Xiongguanlong is characterized by a narrow and elongate muzzle resembling that of Alioramus . The slender, unornamented nasals of Xiongguanlong are inconsistent with recent hypotheses of correlated progression in tyrannosauroid feeding mechanics, and suggest more complex patterns of character evolution in the integration of feeding adaptations in tyrannosaurids. Body mass estimates for the full-grown holotype specimen of Xiongguanlong fall between those of Late Cretaceous tyrannosaurids and Barremian tyrannosauroids, suggesting that the trend of increasing body size observed in North American Late Cretaceous Tyrannosauridae may extend through the Cretaceous history of Tyrannosauroidea though further phylogenetic work is required to corroborate this.