Evolution of Jurassic Marine Reptiles

The long-term ecology and evolution of marine reptiles in a Jurassic seaway

 

Marine reptiles flourished in the Mesozoic oceans, filling ecological roles today dominated by crocodylians, large fish, sharks and cetaceans. Many groups of these reptiles coexisted for over 50 million years (Myr), through major environmental changes. However, little is known about how the structure of their ecosystems or their ecologies changed over millions of years. We use the most common marine reptile fossils—teeth—to establish a quantitative system that assigns species to dietary guilds and then track the evolution of these guilds over the roughly 18-million-year history of a single seaway, the Jurassic Sub-Boreal Seaway of the United Kingdom. Groups did not significantly overlap in guild space, indicating that dietary niche partitioning enabled many species to live together. Although a highly diverse fauna was present throughout the history of the seaway, fish and squid eaters with piercing teeth declined over time while hard-object and large-prey specialists diversified, in concert with rising sea levels. High niche partitioning and spatial variation in dietary ecology related to sea depth also characterize modern marine tetrapod faunas, indicating a conserved ecological structure of the world’s oceans that has persisted for over 150 Myr.

Image credit: Nikolay Zverkov.

Ref & abstract credit :https://www.nature.com/articles/s41559-018-0656-6

 

Dinosaurs of Lost Landmass

 Lost Landmass Of Appalachia

It was 90 million years ago there was two landmasses: Appalachia and Laramidia divided by a sea , later on they will become Utah and Alberta.
A lack of fossils from Appalachia (eastern North America) Made it the ‘lost landmass.’
 
In the Mesozoic Era (252 to 66 million years ago) Appalachia, named for the Appalachian Mountains, was an island land mass separated from Laramidia to the west by the Western Interior Seaway. The seaway eventually shrank, divided across the Dakotas, and retreated towards the Gulf of Mexico and the Hudson Bay. This left the island masses joined in the continent of North America as the Rocky Mountains rose.

The Cenomanian to Maastrichtian of the Late Cretaceous saw the flooding of the interior of North America by the Western Interior Seaway, which created the eastern landmass of Appalachia and the western landmass of Laramidia. Though Appalachian dinosaur faunas are poorly known, they are nevertheless important for understanding Cretaceous dinosaur paleobiogeography and ecology.

 Image : A typical Appalachian Dinosaur Acrocanthosaurus

The landmass of Appalachia harbored a diverse dinosaur fauna from the Aptian to the Maastrichtian stages of the Cretaceous. Data suggest that North American faunas of the Aptian were differentiated at the genus level to an extent, but a distinct east-west division was not present.  At the family level, the biogeographic data compiled from Aptian North American dinosaur faunas suggest that even though genera were different across regions, the same clades were present across the continent. This Aptian North American fauna would therefore have included basal ornithomimosaurs, the carcharodontosaurid Acrocanthosaurus akotensis, dromaeosaurids (especially the taxon Deinonychus), nodosaurids, iguanodontians, basal neoceratopsian dinosaurs, possibly the orodromine dinosaur Zephyrosaurus, and titanosauriform sauropods. Albian-Cenomanian North American faunas include nodosaurids, dromaeosaurids, macronarian sauropods, carcharodontosaurids, and basal hadrosauroids. The absence of therizinosaurs and oviraptorosaurs from eastern North America during this time is considered ambiguous, as a large portion of the Arundel facies theropod material remains to be formally studied. During the Albian, orodromine dinosaurs are no longer found in Appalachian dinosaur faunas , though orodromines and other small ornithopod dinosaurs are known from all three western North American dinosaur faunas from the same time . Nevertheless, western and eastern faunas still share nodosaurids, iguanodontians, and titanosauriformes . The lack of faunal data from the Dakota Formation and Paluxy Formation may have caused the calculation of inflated values for their Simpson similarity index and Jaccard coefficient. Among the better-known western faunas, these values are all fairly high , suggesting relative faunal homogeneity in the western portion of North America.

Appalachian dinosaurs

Acrocanthosaurus	Cretaceous	carnivore	- Large carnivorous carcharodontosaurid found in Maryland.
Ammosaurus	Jurassic	herbivore	- Small herbivorous sauropodomorph found in Connecticut.
Anchisaurus	Jurassic	herbivore	- Small herbivorous sauropodomorph found in Connecticut.
Appalachiosaurus	Cretaceous	carnivore	- Large tyrannosauroid from Alabama.
Arkansaurus	Cretaceous	carnivore	-An indeterminate theropod from Arkansas. Many paleontologists believe it could be related to Ornithomimus.
Astrodon	Cretaceous	herbivore	- Large herbivorous sauropod found in Maryland.
Claosaurus	Cretaceous	herbivore	- A primitive hadrosaur. The only known fossil specimen found got washed into the Western Interior Seaway. It is believed to be from Appalachia because it was found closer to the Appalachia side of the sea and is unknown from Laramidia.
Coelosaurus	Cretaceous	carnivore/omnivore	- May be synonymous with Ornithomimus.
Deinonychus	Cretaceous	carnivore	- A medium-sized raptor found in Maryland.
Diplotomodon	Cretaceous	carnivore	- A dubious name for a species of tyrannosauroid from New Jersey, possibly for Dryptosaurus or a potentially new genus.
Dryptosaurus	Cretaceous	carnivore	- Medium-sized tyrannosauriod from New Jeresy.
Eotrachodon	Cretaceous	herbivore	- A hadrosaur from Alabama known from a nearly complete skeleton.
Hadrosaurus	Cretaceous	herbivore	- First known dinosaur skeleton from the United States. Discovered in 1858 in Haddonfield, New Jersey.
Hypsibema	Cretaceous	herbivore	- Little known hadrosaur first discovered in North Carolina in 1869. Better material of a second species was found in Missouri.
Lophorhothon	Cretaceous	herbivore	- A hadrosaur from Alabama with skull fragments discovered.
Niobrarasaurus	Cretaceous	herbivore	- Another example of a nodosaurid dinosaur from Kansas.
Parrosaurus	Cretaceous	herbivore	- A junior synonym of Hypsibema missouriensis. It is the state dinosaur of Missouri.
Priconodon	Cretaceous	herbivore	- A nodosaur from Maryland found only from fossilized teeth.
Propanoplosaurus	Cretaceous	herbivore	- A nodosaurid dinosaur from Maryland.
Podokesaurus	Jurassic	carnivore	- Small therapod from Connecticut River Valley, may be synonymous with Coelophysis.
Silvisaurus	Cretaceous	herbivore	- A herbivorous nodosaur from the state of Kansas. Similarly to Claosaurus, This specimen found was probably washed into the Western Interior Seaway. It is believed to be from Appalachia because it was found closer to the Appalachia side of the sea.
Tenontosaurus	Cretaceous	herbivore	- A herbivorous iguanodontid whose fossil remains have been discovered in Maryland.
Zephyrosaurus	Cretaceous	herbivore	- A herbivorous hypsilophodontid whose fossil remains have been discovered in Maryland and Virginia.

Reference :
*http://palaeo-electronica.org/content/2018/2123-appalachia-biogeography
*Wikipedia articles #https://en.wikipedia.org/wiki/Appalachia_(Mesozoic)
*https://en.wikipedia.org/wiki/List_of_Appalachian_dinosaurs
 Image credits :Wikimedia commons : Dmitry Bogdanov

Mansourasaurus shahinae - New Species of Titanosaur from Egypt

A New Titanosaur Species discovered in Egypt: Mansourasaurus shahinae.

Mansourasaurus shahinae, was a type of titanosaur-sauropod (long-necked plant-eating) dinosaurs which roamed Earth around 80 million years ago during Cretaceous period. 

Prominent hypotheses advanced over the past two decades have sought to characterize the Late Cretaceous continental vertebrate palaeobiogeography of Gondwanan landmasses, but have proved difficult to test because terrestrial vertebrates from the final ~30 million years of the Mesozoic are extremely rare and fragmentary on continental Africa (including the then-conjoined Arabian Peninsula but excluding the island of Madagascar). Here we describe a new titanosaurian sauropod dinosaur, Mansourasaurus shahinae gen. et sp. nov., from the Upper Cretaceous (Campanian) Quseir Formation of the Dakhla Oasis of the Egyptian Western Desert. Represented by an associated partial skeleton that includes cranial elements, Mansourasaurus is the most completely preserved land-living vertebrate from the post-Cenomanian Cretaceous (~94–66 million years ago) of the African continent. Phylogenetic analyses demonstrate that Mansourasaurus is nested within a clade of penecontemporaneous titanosaurians from southern Europe and eastern Asia, thereby providing the first unambiguous evidence for a post-Cenomanian Cretaceous continental vertebrate clade that inhabited both Africa and Europe. The close relationship of Mansourasaurus to coeval Eurasian titanosaurians indicates that terrestrial vertebrate dispersal occurred between Eurasia and northern Africa after the tectonic separation of the latter from South America ~100 million years ago. These findings counter hypotheses that dinosaur faunas of the African mainland were completely isolated during the post-Cenomanian Cretaceous.

Image credit: Andrew McAfee, Carnegie Museum of Natural History

Ref & abstract credit : https://www.nature.com/articles/s41559-017-0455-5

Caihong juji - newly discovered Jurassic theropod

The newly discovered Jurassic theropod Caihong juji, had a beautiful iridescent coloration .
This new theropod shows an array of bony features, as well as plumage characteristics and putative melanosome morphologies not previously seen in other Paraves, and thus further informs the pattern of character acquisition close to the origin of avian flight.

The Jurassic Yanliao theropods have offered rare glimpses of the early paravian evolution and particularly of bird origins, but, with the exception of the bizarre scansoriopterygids, they have shown similar skeletal and integumentary morphologies. Here we report a distinctive new Yanliao theropod species bearing prominent lacrimal crests, bony ornaments previously known from more basal theropods. It shows longer arm and leg feathers than Anchiornis and tail feathers with asymmetrical vanes forming a tail surface area even larger than that in Archaeopteryx. Nanostructures, interpreted as melanosomes, are morphologically similar to organized, platelet-shaped organelles that produce bright iridescent colours in extant birds. The new species indicates the presence of bony ornaments, feather colour and flight-related features consistent with proposed rapid character evolution and significant diversity in signalling and locomotor strategies near bird origins.

Image credit: Velizar Simeonovski, Field Museum.
Ref  & abstract credit :https://www.nature.com/articles/s41467-017-02515-y