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27-689: The New Egypt Formation is a Late Cretaceous ( Maastrichtian ) geologic formation of the Monmouth Group in New Jersey, United States. The basal New Egypt is a massive clayey, glauconitic marl that closely resembles the Navesink Formation into which it grades below. Ammonites and other invertebrates found at the Spheno Run site correlate well with the middle Severn Formation of Maryland. Spheno Run has so far produced

54-480: A maximum adult length of 2.2 metres (7.2 ft). Hesperornitheans were the only Mesozoic avialans to colonize the oceans. They were wiped out in the Cretaceous–Paleogene extinction event , along with enantiornitheans and all other non-avian dinosaurs. Most of what is known about this group rests on analyses of single species, as few provide sufficiently complete fossils for analysis. Although some of

81-653: A northward course towards Asia. In the Southern Hemisphere, Australia and Antarctica seem to have remained connected and began to drift away from Africa and South America. Europe was an island chain. Populating some of these islands were endemic dwarf dinosaur species. In the Late Cretaceous, the hadrosaurs , ankylosaurs , and ceratopsians experienced success in Asiamerica (Western North America and eastern Asia). Tyrannosaurs dominated

108-614: A remarkable number of vertebrate specimens, especially from marine reptiles, including: carapace elements from at least two species of turtles, Peritresius ornatus and Taphrosphys sulcatus ; various bone elements from at least two species of mosasaurs including a sizable fragment of dentary bone from Prognathodon rapax and numerous shed teeth from Mosasaurus maximus . Vertebrate remains also include material from sharks, particularly teeth and unusually large vertebral centra from an individual lamniform shark Squalicorax pristodontus , bony fish, and, rarely, dinosaurs. In addition to

135-547: A resting position the feet projected sideways from the body, which would have prevented them from walking upright. The anatomy of their toes suggests that hesperornitheans had lobes of skin for propulsion underwater similar to grebes , rather than being webbed. The dense bones of these animals decreased their buoyancy, making diving easier. However, morphometric comparison with modern diving birds suggests that hesperornitheans share more similarities with diving ducks and cormorants rather than with loons or grebes . The snout

162-536: A very different dinosaurian fauna, with most predators being abelisaurids and carcharodontosaurids ; and titanosaurs being among the dominant herbivores. Spinosaurids were also present during this time. Birds became increasingly common, diversifying in a variety of enantiornithe and ornithurine forms. Early Neornithes such as Vegavis co-existed with forms as bizarre as Yungavolucris and Avisaurus . Though mostly small, marine Hesperornithes became relatively large and flightless, adapted to life in

189-575: Is an extinct and highly specialized group of aquatic avialans closely related to the ancestors of modern birds . They inhabited both marine and freshwater habitats in the Northern Hemisphere, and include genera such as Hesperornis , Parahesperornis , Baptornis , Enaliornis , and Potamornis , all strong-swimming, predatory divers. Many of the species most specialized for swimming were completely flightless. The largest known hesperornithean, Canadaga arctica , may have reached

216-479: Is it particularly evident that a true systematic decline was ever in place, especially with the discovery of smaller pterosaur species. Several old mammal groups began to disappear, with the last eutriconodonts occurring in the Campanian of North America . In the northern hemisphere, cimolodont , multituberculates , metatherians and eutherians were the dominant mammals, with the former two groups being

243-559: The Deccan Traps , both of which have been firmly dated to the time of the extinction event. In theory, these events reduced sunlight and hindered photosynthesis , leading to a massive disruption in Earth's ecology . A much smaller number of researchers believe the extinction was more gradual, resulting from slower changes in sea level or climate . Hesperornithes Hesperornithiformes Sharpe , 1899 Hesperornithes

270-600: The Late Cretaceous of North America. Small hesperornithean bones are known from the freshwater deposits of the Late Cretaceous of the Judith River Group as well as the Hell Creek and Lance Formations , and in several Eurasian sites. These species were about the size of a cormorant or a loon. The clade Hesperornithes was originally named as a subclass of Aves by Furbringer in 1888. However, it

297-859: The Cretaceous Period derived from the German name Kreidezeit , and T is the abbreviation for the Tertiary Period (a historical term for the period of time now covered by the Paleogene and Neogene periods). The event marks the end of the Mesozoic Era and the beginning of the Cenozoic Era. "Tertiary" being no longer recognized as a formal time or rock unit by the International Commission on Stratigraphy ,

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324-850: The K-T event is now called the Cretaceous—Paleogene (or K-Pg) extinction event by many researchers. Non- avian dinosaur fossils are found only below the Cretaceous–Paleogene boundary and became extinct immediately before or during the event. A very small number of dinosaur fossils have been found above the Cretaceous–Paleogene boundary, but they have been explained as reworked fossils , that is, fossils that have been eroded from their original locations then preserved in later sedimentary layers. Mosasaurs , plesiosaurs , pterosaurs and many species of plants and invertebrates also became extinct. Mammalian and bird clades passed through

351-477: The body, as in loons , grebes or penguins . Hesperornithids must have been powerful swimmers and divers but extremely ungainly on the land, and probably spent little time ashore except to nest. They were rather long-bodied, and measured about 6 feet (180 cm) long. Some researchers think that on land they had to slide on their bellies and push with their legs; the hip and knee joints were shaped such that these species could not move them dorsoventrally, and in

378-524: The boundary with few extinctions, and evolutionary radiation from those Maastrichtian clades occurred well past the boundary. Rates of extinction and radiation varied across different clades of organisms. Many scientists hypothesize that the Cretaceous–Paleogene extinctions were caused by catastrophic events such as the massive asteroid impact that caused the Chicxulub crater , in combination with increased volcanic activity , such as that recorded in

405-596: The climate was warmer than present, although throughout the period a cooling trend is evident. The tropics became restricted to equatorial regions and northern latitudes experienced markedly more seasonal climatic conditions. Due to plate tectonics , the Americas were gradually moving westward, causing the Atlantic Ocean to expand. The Western Interior Seaway divided North America into eastern and western halves; Appalachia and Laramidia . India maintained

432-530: The front, thus allowing the lower teeth to disengage. Currently, the hesperornitheans are recognized as a very specialized lineage that is not ancestral to modern birds. Still, their relationship is close enough that they probably diverged from the ancestors of modern birds as late as the earliest Cretaceous . The earliest known hesperornithean is the Early Cretaceous Enaliornis . The majority of hesperornithean species are known from

459-664: The large predator niche in North America. They were also present in Asia, although were usually smaller and more primitive than the North American varieties. Pachycephalosaurs were also present in both North America and Asia. Dromaeosaurids shared the same geographical distribution, and are well documented in both Mongolia and Western North America. Additionally therizinosaurs (known previously as segnosaurs) appear to have been in North America and Asia. Gondwana held

486-417: The latter name. Clarke also defined the more inclusive group Hesperornithidae as all hesperornitheans closer to Hesperornis than to Baptornis . Hesperornitheans were originally combined with Ichthyornis in the paraphyletic group " Odontornithes " by Othniel Charles Marsh , in 1873. In 1875, they were separated as Odontolcae . The group was often considered to be related to loons and grebes, or to

513-636: The most common mammals in North America. In the southern hemisphere there was instead a more complex fauna of dryolestoids , gondwanatheres and other multituberculates and basal eutherians ; monotremes were presumably present, as was the last of the haramiyidans , Avashishta . Mammals, though generally small, ranged into a variety of ecological niches, from carnivores ( Deltatheroida ), to mollusc-eater ( Stagodontidae ), to herbivores (multituberculates, Schowalteria , Zhelestidae and Mesungulatidae ) to highly atypical cursorial forms ( Zalambdalestidae , Brandoniidae ). True placentals evolved only at

540-540: The numerous teleost fishes, which in turn evolved into new advanced and modern forms ( Neoteleostei ). Ichthyosaurs and pliosaurs , on the other hand, became extinct during the Cenomanian-Turonian anoxic event . Near the end of the Cretaceous Period, flowering plants diversified. In temperate regions, familiar plants like magnolias , sassafras , roses , redwoods , and willows could be found in abundance. The Cretaceous–Paleogene extinction event

567-407: The open sea. Though primarily represented by azhdarchids , other forms like pteranodontids , tapejarids ( Caiuajara and Bakonydraco ), nyctosaurids and uncertain forms ( Piksi , Navajodactylus ) are also present. Historically, it has been assumed that pterosaurs were in decline due to competition with birds, but it appears that neither group overlapped significantly ecologically, nor

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594-399: The smaller and more basal species, like those belonging to the subgroups Enaliornithidae and Brodavidae , might have been able to fly, the larger hesperornithids like Hesperornis and Baptornis had only vestigial wings. As in the case of modern foot-propelled diving birds, the femur and metatarsus of these animals were short, whereas the tibia was long. The legs were also set far back on

621-416: The vertebrate collection, Spheno Run also yields an abundance of invertebrate species including: twenty-two bivalves, seven gastropods, six cephalopods, and one each of echinoidea, porifera, and scaphopoda. It is rare to find such an extensive array of both vertebrate and invertebrate species within one horizon in New Jersey. The following taxa are known: Late Cretaceous During the Late Cretaceous,

648-433: The very end of the epoch; the same can be said for true marsupials . Instead, nearly all known eutherian and metatherian fossils belong to other groups. In the seas, mosasaurs suddenly appeared and underwent a spectacular evolutionary radiation. Modern sharks also appeared and penguin-like polycotylid plesiosaurs (3 meters long) and huge long-necked elasmosaurs (13 meters long) also diversified. These predators fed on

675-475: Was a large-scale mass extinction of animal and plant species in a geologically short period of time, approximately 66  million years ago (Ma). It is widely known as the K–T extinction event and is associated with a geological signature, usually a thin band dated to that time and found in various parts of the world, known as the Cretaceous–Paleogene boundary (K–T boundary). K is the traditional abbreviation for

702-406: Was generally ignored in the scientific literature in favor of the order-level name Hesperornithiformes , coined one year later. In 2004, Clarke became the first to define the hesperornithean group in terms of phylogenetics . Clarke defined Hesperornithes as all species closer to Hesperornis regalis than to modern birds, and regarded Hesperornithiformes as a junior synonym, though she did not define

729-420: Was long, and tipped with a slightly hooked beak. Behind the beak, the jaws were filled with a series of simple, sharp teeth which were set into a longitudinal groove. These probably helped to seize fish , like the serrated beak of mergansers . Unlike modern birds, they retained a joint between the lower jaw bones. It is believed that this allowed them to rotate the back portion of the mandible independently of

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