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Ancient, species-poor lineages persistently occur across the Tree of life. These lineages are likely to contain unrecognized species diversity masked by the low rates of morphological evolution that characterize living fossils. Halecomorphi is a lineage of ray-finned fishes that diverged from its closest relatives before 200 Ma and is represented by only one living species in eastern North America, the bowfin, Amia calva Linnaeus. Here, we use double digest restriction-site-associated DNA sequencing and morphology to illuminate recent speciation in bowfins. Our results support the delimitation of a second living species of Amia , with the timing of diversification dating to the Plio-Pleistocene. This delimitation expands the species diversity of an ancient lineage that is integral to studies of vertebrate genomics and development, yet is facing growing conservation threats driven by the caviar fishery.

SummaryAncient, species-poor lineages persistently occur across the Tree of Life. These evolutionarily unique lineages are likely to contain unrecognized species diversity masked by the low rates of morphological evolution that characterize living fossils [1, 2]. Halecomorphi is a major clade of ray-finned fishes that diverged from its closest relatives over 200 million years ago [3, 4] yet is represented by only one recognized living species in eastern North America, the Bowfin Amia calva Linnaeus. Here, we use double digest restriction-site associated DNA (ddRAD) sequencing and high-resolution computed tomography to illuminate recent speciation in the bowfins. Our results support the resurrection of a second living species of Bowfin with the timing of diversification dating to the Pleistocene. In turn, we expand the species diversity of an ancient lineage that is integral to studies of vertebrate genomics and development [2, 3, 5], yet is facing growing conservation threats driven by the caviar fishery [6].

Although the fossil record of the Late Cretaceous eastern North American landmass Appalachia is poor compared to that from the American West, it includes material from surprisingly aberrant terrestrial vertebrates that may represent relictual forms persisting in relative isolation until the end of the Mesozoic. One intriguing question is to what extent eastern and western North American faunas interspersed following the closure of the Western Interior Seaway during the Maastrichtian Stage of the Late Cretaceous ca. 70 Ma. Isolated remains from the Atlantic Coastal Plain in New Jersey have been preliminarily identified as the bones of crested lambeosaurine hadrosaurids, a derived clade known from the Cretaceous of Asia, western North America, and Europe, but have not been formally described. We describe the partial forelimb of a large hadrosaurid from the late Maastrichtian New Egypt Formation of New Jersey. The ulna preserves multiple deep scores identifiable as shark feeding marks, and both bones show ovoid and circular marks attributable to invertebrates. This forelimb is very similar to another partial antebrachium from the same area that shows evidence of septic arthritis. Both these specimens and a complete humerus from the same unit are closely comparable to the lower forelimbs of lambeosaurines among hadrosaurid dinosaurs. Although the absence of lambeosaurine synapomorphies observable on the New Egypt Formation forelimbs precludes their definite referral to Lambeosaurinae, they show that a morphotype of large hadrosauromorph with distinctly elongate forelimbs existed in the latest Maastrichtian of eastern North America and allow for a revision of the latest Cretaceous biogeography of crested herbivorous dinosaurs.

The timing of non-avian dinosaur decline is one of the most debated subjects in dinosaur palaeontology. Dinosaur faunas from the last few million years of the Mesozoic appear far less diverse than those from earlier in the Cretaceous, a trend that could suggest non-avian dinosaur extinction occurred gradually. However, the limited nature of the latest Cretaceous dinosaur record outside western North America has obscured patterns in dinosaur diversity just before the extinction. Here, I describe two associated skeletons and several isolated fossils recovered from the New Egypt Formation of New Jersey, a latest Maastrichtian unit that underlies the K–Pg boundary. The larger skeleton appears to be a small-bodied adult from a lineage outside Hadrosauridae, the dominant group of these animals during the Maastrichtian, that persisted along the eastern coast of North America. Smaller specimens are identifiable as juvenile hadrosauromorphs. These results substantiate an important assemblage of herbivorous dinosaurs from the poorly-known Cretaceous of eastern North America. The marine depositional setting for these skeletons demonstrates that proposed ecosystem preferences among hadrosauromorphs may be biased by post-mortem transportation, and the adult skeleton has implications for assessing the proposed relictual nature of Late Cretaceous eastern North American vertebrates.

Dinosaurs are notable for their extensive skeletal pneumaticity, a feature that may have helped facilitate the development of various ‘extreme’ body plans in this group. Despite its relevance to understanding the evolution of the avian body plan, this feature has only been described in detail for a few non-avian dinosaurs, and cranial pneumaticity outside the braincase remains poorly documented. I describe facial pneumatic features in members of the Dromaeosauridae, a clade of hypercarnivorous dinosaurs closely allied to birds. Variation in the pneumaticity of the nasals and jugals, the position and shape of the pneumatic fenestrae of the maxilla and the border of the antorbital fossa shows that facial pneumaticity differed substantially among closely related dromaeosaurids and other bird-like dinosaurs. Ancestral state reconstructions of facial pneumaticity in coelurosaurs suggest a complex evolutionary history for these features. Surprisingly, the general trend along the path towards birds was the loss or reduction of superficial pneumatic features on the snout and cheek. Some facial pneumatic features seem to have evolved secondarily in some derived bird-like forms. The results show superficial facial pneumaticity did not increase in coelurosaurs and emphasize the complexity of the evolution of pneumatization in the lineage leading to birds.

During the Cretaceous period, North America was divided into two landmasses, the eastern Appalachia and western Laramidia. Recent research on several sites scattered across the eastern margin of North America has allowed for the analysis of vertebrate faunas from the once obscure terrestrial fossil record of Appalachia, revealing the landmass harbored a distinctive fauna composed of mostly relict forms. One geological unit that has produced a comparatively extensive record of terrestrial vertebrates, including non-avian dinosaurs, is the middle Campanian Tar Heel Formation of North Carolina. Here, the first definitive occurrence of a dromaeosaurid from the Tar Heel Formation is reported on the basis of a tooth from a fairly large member of that group. This tooth clusters with those of dromaeosaurine dromaeosaurids from the western United States and Canada in morphometric analysis, differing in morphology and size from other dromaeosaurid teeth from southeastern North America that have been assigned to saurornitholestines or considered indeterminate. The tooth described herein is intermediate in size between those of smaller dromaeosaurids like Saurornitholestes and gigantic forms like Dakotaraptor, filling the gap between larger- and smaller-bodied dromaeosaurids from the Late Cretaceous.

The evolution of birds from dinosaurs is a subject that has received great attention among vertebrate paleontologists. Nevertheless, the early evolution of the paravians, the group that contains birds and their closest non-avian dinosaur relatives, remains very poorly known. Even the most basal members of one paravian lineage, the Dromaeosauridae, already show a body plan that differs substantially from their closest non-paravian relatives. Recently, the dromaeosaurid Halszkaraptor escuilliei was described from the Cretaceous of Mongolia. Halszkaraptor possesses numerous unserrated premaxillary teeth, a platyrostral rostrum with a developed neurovascular system, an elongate neck, bizarrely-proportioned forearms, and a foreword-shifted center of mass, differing markedly from other paravians. A reevaluation of the anatomy, taphonomy, environmental setting, and phylogenetic position of H. escuilliei based on additional comparisons with other maniraptorans suggests that, rather than indicating it was a semiaquatic piscivore, the body plan of this dinosaur bears features widely distributed among maniraptorans and in some cases intermediate between the conditions in dromaeosaurids and related clades. I find no evidence for a semiaquatic lifestyle in Halszkaraptor. A phylogenetic reevaluation of Halszkaraptorinae places it as the sister clade to Unenlagiinae, indicating the bizarre features of unenlagiines previously interpreted as evidence of piscivory may also represent a mosaic of plesiomorphic, derived, and intermediate features. The anatomy of Halszkaraptor reveals that dromaeosaurids still possessed many features found in more basal maniraptoran and coelurosaur clades, including some that may have been tied to herbivory. Rather than being a semiaquatic piscavore, Halszkaraptor was a basal dromaeosaurid showing transitional features.

The Cretaceous landmass of Appalachia has preserved an understudied but nevertheless important record of dinosaurs that has recently come under some attention. In the past few years, the vertebrate faunas of several Appalachian sites have been described. One such locality, the Ellisdale site of the Cretaceous Marshalltown Formation of New Jersey, has produced hundreds of remains assignable to dinosaurs, including those of hadrosauroids of several size classes, indeterminate ornithopods, indeterminate theropods, the teeth, cranial, and appendicular elements of dromaeosaurids, ornithomimosaurians, and tyrannosauroids, and an extensive microvertebrate assemblage. The theropod dinosaur record of the Ellisdale site is currently the most extensive and diverse known from the Campanian of Appalachia. Study of the Ellisdale theropod specimens suggests that at least four or more non-avian theropod taxa are represented at the site, including tyrannosauroids, ornithomimosaurs, several different morphotypes of dromaeosaurids that are the first of that clade described from New Jersey, and indeterminate theropods. The specimens are important for increasing current knowledge about the theropod diversity of the Atlantic Coastal Plain (ACP) during the Campanian by representing the most speciose assemblage of the group during the time in the ACP as well as for shedding light on Appalachian dinosaur ecology and biogeography generally.

The evolution of birds from dinosaurs is a subject that has received great attention among vertebrate paleontologists. Nevertheless, the early evolution of the paravians, the group that contains birds and their closest non-avian dinosaur relatives, remains very poorly known. Even the most basal members of one paravian lineage, the Dromaeosauridae, already show a body plan that differs substantially from their closest non-paravian relatives. Recently, the dromaeosaurid Halszkaraptor escuilliei was described from the Cretaceous of Mongolia. Halszkaraptor possesses numerous unserrated premaxillary teeth, a platyrostral rostrum with a developed neurovascular system, an elongate neck, bizarrely-proportioned forearms, and a foreword-shifted center of mass, differing markedly from other paravians. A reevaluation of the anatomy, taphonomy, environmental setting, and phylogenetic position of H. escuilliei based on additional comparisons with other maniraptorans suggests that, rather than indicating it was a semiaquatic piscivore, the body plan of this dinosaur bears features widely distributed among maniraptorans and in some cases intermediate between the conditions in dromaeosaurids and related clades. I find no evidence for a semiaquatic lifestyle in Halszkaraptor. A phylogenetic reevaluation of Halszkaraptorinae places it as the sister clade to Unenlagiinae, indicating the bizarre features of unenlagiines previously interpreted as evidence of piscivory may also represent a mosaic of plesiomorphic, derived, and intermediate features. The anatomy of Halszkaraptor reveals that dromaeosaurids still possessed many features found in more basal maniraptoran and coelurosaur clades, including some that may have been tied to herbivory. Rather than being a semiaquatic piscavore, Halszkaraptor was a basal dromaeosaurid showing transitional features.

The faunal changes that occurred in the few million years before the Cretaceous–Palaeogene extinction are of much interest to vertebrate palaeontologists. Western North America preserves arguably the best fossil record from this time, whereas terrestrial vertebrate fossils from the eastern portion of the continent are usually limited to isolated, eroded postcranial remains. Examination of fragmentary specimens from the American east, which was isolated for the majority of the Cretaceous as the landmass Appalachia, is nonetheless important for better understanding dinosaur diversity at the end of the Mesozoic. Here, I report on two theropod teeth from the Mount Laurel Formation, a lower-middle Maastrichtian unit from northeastern North America. One of these preserves in detail the structure of the outer enamel and resembles the dentition of the tyrannosauroid Dryptosaurus aquilunguis among latest Cretaceous forms in being heavily mediolaterally compressed and showing many moderately developed enamel crenulations. Along with previously reported tyrannosauroid material from the Mt Laurel and overlying Cretaceous units, this fossil supports the presence of non-tyrannosaurid tyrannosauroids in the Campanian–Maastrichtian of eastern North America and provides evidence for the hypothesis that the area was still home to relictual vertebrates through the end of the Mesozoic. The other tooth is assignable to a dromaeosaurid and represents both the youngest occurrence of a non-avian maniraptoran in eastern North America and the first from the Maastrichtian reported east of the Mississippi. This tooth, which belonged to a 3–4 m dromaeosaurid based on size comparisons with the teeth of taxa for which skeletons are known, increases the diversity of the Maastrichtian dinosaur fauna of Appalachia. Along with previously reported dromaeosaurid teeth, the Mt Laurel specimen supports the presence of mid-sized to large dromaeosaurids in eastern North America throughout the Cretaceous.

The Arundel Clay of Maryland is among the only Early Cretaceous terrestrial units known from eastern North America. Research on some theropod dinosaur bones from this layer has indicated the presence of two ornithomimosaur taxa in the assemblage. However, a recent paper discussed issues with the definite assignment of any of these unguals to Ornithomimosauria and suggested that morphological differences originally interpreted to be indicative of the presence of two ornithomimosaurs could be explained by positional variation. Here, I show that substantial evidence persists for the presence of two ornithomimosaurs in the Arundel Clay assemblage, even considering the recent description of positional variation in ornithomimosaur pedal unguals. Furthermore, the argument against the confident assignment of these unguals to ornithomimosaurs is shown to be based on oversimplified comparisons that do not take into account the combination of features in the Arundel specimens that allow for their assignment to that clade. Although several small points made in the initial paper describing the Arundel specimens are incorrect or unsubstantiated, the differences between the Maryland unguals are outside the spectrum of positional variation and are indicative of the presence of two ornithomimosaurs in the Arundel Clay assemblage.

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.

During the Cretaceous period, North America was divided into two landmasses, the eastern Appalachia and western Laramidia. Recent research on several sites scattered across the eastern margin of North America has allowed for the analysis of vertebrate faunas from the once obscured terrestrial fossil record of Appalachia, revealing the landmass harbored a distinctive fauna composed of mostly relict forms. One geological unit that has produced a comparatively extensive record of terrestrial vertebrates, including non-avian dinosaurs, is the Tar Heel Formation of North Carolina. Here, I report the first definitive occurrence of a dromaeosaurid from the Tar Heel Formation in the form of a tooth from a fairly large member of that group. This tooth, like others previously discovered from the southeastern portion of North America, compares favorably with those of saurornitholestine dromaeosaurids from the western United States and Canada. The North Carolina tooth differs in morphology and size from previously reported southeastern North American dromaeosaurid teeth, but is still assignable to a saurornitholestine dromaeosaurid, evincing that the diversity of carnivorous bird-like dinosaurs in the southeastern part of North America during the Late Cretaceous may have been rather low. The tooth, which is intermediate in size between those of smaller dromaeosaurids like Saurornitholestes and gigantic forms like Dakotaraptor, helps fill the gap between larger- and smaller-bodied dromaeosaurids from the Late Cretaceous.

Direct documentation of the ecology of past life is often rare when the fossil record is comparatively poor, as in the case of the terrestrial fauna of the Maastrichtian of eastern North America. Here, I describe a femur and partial tibia shaft assignable to theropods from the Maastrichtian Big Brook locality of New Jersey. The former, identifiable to a previously undetected morphotype of large ornithomimosaur, bears several scrapes identifiable as the feeding traces of sharks, adding to the collection of terrestrial vertebrate remains bearing such marks from the state. The latter is littered with tooth marks and punctures from possibly multiple crocodyliform individuals, the first documented occurrence of such traces on dinosaur bone from the Maastrichtian of the Atlantic Coastal Plain. Additionally, its surface is dotted with likely traces of invertebrates, revealing a microcosm of biological interaction from the Maastrichtian New Jersey shoreline. Previously, the massive Campanian crocodylian taxon Deinosuchus rugosus and the slightly smaller Cenomanian-age Texas crocodyliform Deltasuchus motherali have been shown as important drivers of terrestrial vertebrate taphonomy in eastern North America. The report of crocodyliform bite marks on the ornithomimosaur metatarsal shaft in this manuscript reveals that crocodylians continued to play role in the taphonomy of large dinosaurs in eastern North America through the end of the Mesozoic. The preserved invertebrate traces add to the sparse record of their traces on dinosaur bone, and the presence of shark scrapes on the femur supports the “bloat-and-float” model of terrestrial vertebrate fossil deposition in eastern North America.

Among the most recognizable theropods are the tyrannosauroids, a group of small to large carnivorous coelurosaurian dinosaurs that inhabited the majority of the northern hemisphere during the Cretaceous and came to dominate large predator niches in North American and Asian ecosystems by the end of the Mesozoic era. The clade is among the best-represented of dinosaur groups in the notoriously sparse fossil record of Appalachia, the Late Cretaceous landmass that occupied the eastern portion of North America after its formation from the transgression of the Western Interior Seaway. Here, the prootic of a juvenile tyrannosauroid collected from the middle-late Campanian Marshalltown Formation of the Atlantic Coastal Plain is described, remarkable for being the first concrete evidence of juvenile theropods in that plain during the time of the existence of Appalachia and the only portion of theropod braincase known from the landmass. Phylogenetic analysis recovers the specimen as an “intermediate” tyrannosauroid of similar grade to Dryptosaurus and Appalachiosaurus. Comparisons with the corresponding portions of other tyrannosauroid braincases suggest that the Ellisdale prootic is more similar to Turonian forms in morphology than to the derived tyrannosaurids of the Late Cretaceous, thus supporting the hypothesis that Appalachian tyrannosauroids and other vertebrates were relict forms surviving in isolation from their derived counterparts in Eurasia.

In De Bello Gallico, Gaius Julius Caesar describes the various campaigns waged by the Romans under his leadership against the ‘Gauls’ and the geography, wildlife, and the various tribes of the lands he observed during his time in ‘Gallia’. Caesar remarks in one passage in chapters 26–28 of book 6 on the large mammals of an area of wilderness known to him as ‘Hercynia Silva,’ the Hercynian Forest. This passage, analyzed previously by several authors who identified the animals Caesar described and compared his descriptions with those of several mythological creatures, allows for a unique glimpse into the large mammal fauna of Germany of ~ 2000 years ago, as the mammals Caesar mentions include several species either locally extirpated from Germany or extinct altogether. Here, I review these descriptions and prior analyses of their meaning to compile a faunal list of the Hercynian forest megafauna from the Classical period. Additionally, I briefly statistically compare this faunal to several from Pleistocene Germany. These comparisons serve to both demonstrate changes in the megafauna of Europe during the late Quaternary and the use of classical sources in paleobiogeography and paleoecology.

The fossil record of dinosaurs from the Early Cretaceous of Eastern North America is scant, especially since a few stratigraphic units from the east are fossiliferous. Among these stratigraphic units, the Arundel Clay of the eastern seaboard has produced the best-characterized dinosaur faunas known from the Early Cretaceous of Eastern North America. The diverse dinosaur fauna of the Arundel Clay has been thoroughly discussed previously, but a few of the dinosaur species originally described from the Arundel Clay are still regarded as valid genera. Much of the Arundel material is in need of review and redescription. Among the fossils of dinosaurs from this stratigraphic unit are those referred to ornithomimosaurs. Here, the researcher describes ornithomimosaur remains from the Arundel Clay of Prince George’s County, Maryland which may be from two distinct ornithomimosaur taxa. These remains provide key information on the theropods of the Early Cretaceous of Eastern North America. Recent discoveries of small theropod material from the Arundel Clay possibly belonging to ornithomimosaurs are also reviewed and described for the first time. The description of the Arundel material herein along with recent discoveries of basal ornithomimosaurs in the past 15 years has allowed for comparisons with the coelurosaurNedcolbertia justinhofmanni, suggesting the latter animal was a basal ornithomimosaur rather than a “generalized” coelurosaur as it was originally described. Comparisons between the Arundel ornithomimosaur material and similar Asian and European specimens suggest that both extremely basal ornithomimosaurs and more intermediate or derived forms may have coexisted throughout the northern hemisphere during the Early Cretaceous.

Deinosuchus is a genus of large crocodylian that inhabited North America during the Late Cretaceous. This massive predator has become one of the most well-known prehistoric organisms, with a considerable amount of literature on its biogeography, ecology, and evolution published. However, ontogenetic changes of Deinosuchus and other species of extinct large, predatory crocodyliforms have remained poorly understood because of a lack of remains known from juvenile individuals and issues surrounding the ability of histological analysis of adult material to provide information on yearly growth. Here, I describe a tooth from a juvenile Deinosuchus estimated at less than 1m in total body length. As the first reported specimen of a juvenile Deinosuchus, to the author's knowledge, in the literature, the new fossil evinces the extremely small size of young individuals of this taxon compared to adults more than 8 m and 3,500 kg. Furthermore, the tooth shows that some morphological discrepancies existed between the dentition of juvenile and adult Deinosuchus individuals, including the size of the nutritive region. In addition to being the first specimen of Deinosuchus from northeastern North America described in detail, the tooth emphasizes the biological extremes of attaining large body size in Deinosuchus and may add support to the hypothesis that the ontogeny of gigantic crocodyliforms was characterized by extended periods of juvenile growth.

The snapping turtle species Chelydra serpentina, which has a wide range across North America, is extremely tolerant to cold and even freezing conditions. Here, I describe a single caudal vertebrae referred to Chelydra serpentina from the Late Pleistocene of New Jersey which represents the northernmost known occurrence of the species in eastern North America and the closest known occurrence of the species to a glacier or ice sheet in the continent during the Pleistocene. The specimen, which was collected at Ramanessin Brook in Holmdel, New Jersey, affirms that the Pleistocene deposits which line the banks of the popular Cretaceous site are not taphonomically biased to preserving larger fossils and in the future may yield an assemblage of small vertebrates. Introduction. The chelydrids, more commonly known as snapping turtles, are a family of large freshwater turtles that are represented presently by the two genera Chelydra and Macrochelys. The first appearance of this turtle family comes from the Late Cretaceous of Montana (Whetstone, 1978), and extinct species are known from Asia, Europe, and North America (e.g. Pidoplichko & Tarashchuk, 1960; Klein & Mors, 2003; Danilov & Parham, 2008).