Черепаха Протостега

Classification

The classification of Protostega was complicated at best. The specimen that E. Cope discovered in Kansas was hard to evaluate with the preservation condition. The fossil shared many characteristics with two other recored genus named Dermochelys and Chelonidae. Cope wrote about the characteristics that distinctly separated this particular species from the two controversial groups. The differences he described were that the fossil had a reduced or lacking amount of dermal ossification on the back, the articulation of the pterygoid and quadrates manner, presplenial bone in the jaw was present, no articular process on the back side of the nuchal, simple formation of the radial process on the humerus and a peculiar bent formation of the xiphiplastra. He concluded that genus Protostega and species Protostega gigas was an intermediate form of the two groups Dermochelys and Chelonidae.

Protostega: Late Cretaceous Extinct Turtles

Protostega skeletal reconstruction in the Rocky Mountain Dinosaur Resource Center, Woodland Park, Colorado

Protostega (‘first roof’) is an extinct genus of sea turtle containing a single species, Protostega gigas. Its fossil remains have been found in the Smoky Hill Chalk formation of western Kansas (Hesperornis zone, dated to 83.5 million years ago) and time-equivalent beds of the Mooreville Chalk Formation of Alabama. Fossil specimens of this species were first collected in 1871, and named by Edward Drinker Cope in 1872. With a length of 3 metres (9.8 ft), it is the second-largest sea turtle that ever lived, second only to the giant Archelon, and the third-largest turtle of all time behind Archelon and Stupendemys.

Древние животные

5. Огромные птицы (Моа)

Dinornis robustus

Гигантские моа – были самыми большими птицами, когда-либо существовавшими. Представители Dinornis robustus обитали на Южном острове в Новой Зеландии и достигали до 3,6 метров в высоту и 250 кг веса.

Стоит лишь с облегчением вздохнуть, что этих птиц с длинными раздирающими когтями, острым клювом и длинными ногами, уже не существует.

6. Самая большая ящерица (Мегалания)

Megalania prisca

Этого монстра нередко называли “драконом-дьяволом”. При 7 метрах в длину и 400-700 кг веса, они были самыми большими наземными ящерицами, которые когда-либо жили.

Хотя считалось, что мегалании вымерли, кости, обнаруженные в Австралии, указывают на то, что им всего 300 лет, и некоторые ученые предполагают, что они все еще живут в Австралии.

7. Огромная многоножка (Артроплевра)

Arthropleura

Артроплевры были самыми большими наземными беспозвоночными на Земле, вырастая до 2,6 метров в длину. Они являются родственниками современных многоножек, но жили 340-280 миллионов лет назад.

Кроме того, они могли вставать, опираясь на нижнюю половину тела. Настало время взглянуть страху в глаза.

8. Гигантский ленивец (Мегатерии)

Megatherium americanum

Хотя эти гигантские версии милых пушистых ленивцев считаются травоядными, специалисты считают, что их длинные предплечья и острые когти были предназначены для питания мясом.

Мегатерии вымерли около 2000 лет назад. Они достигали 6 метров в высоту, весили почти 4 тонны и ходили на задних лапах. Интересно, что они являются родственниками современных броненосцев.

9. Гигантская рыба (Дунклеостей)

Dunkleosteus terrelli

Эта гигантская рыба в длину достигала 9 метров и была известна, как одно из самых свирепых и страшных существ из когда-либо живших. Дунклеостей жил в поздний девонский период 360 миллионов лет назад.

Этой рыбе не нужны были зубы, так как ее острые как бритва челюсти могли раскусить любую доисторическую акулу надвое. А когда дунклеостей не питался, он потирал свои челюсти друг о друга словно самозатачивающиеся ножницы.

Geological Paleoenvironment

The Late Cretaceous was marked with the highest temperatures and elevated CO2 concentrations in history. Due to the warmer weather, large epicontinental seaways were created. During the Mid-to Late Cretaceous period the Western Interior Seaway covered the majority of North America and would connect to the Boreal and Tethyan oceans at times. The seaway that covered the states was a shallow but expansive body of water. Within these regions are where the fossil of Protostega gigas have been found.

Pencil restoration

The Mooreville Chalk formation was a geological formation in North America, which was a part of the subcontinent of Appalachia. This strata was formed from pelagic sediment and with in this sediment, primitive Protostega specimens have been discovered.

Discovery and History

Protostegids family locations

The first known Protostega specimen (YPM 1408) was collected on July 4 by the 1871 Yale College Scientific Expedition, close to Fort Wallace and about 5 months before Cope arrived in Kansas. However the fossil that they found was never described or named. It wasn’t until E. D. Cope found and collected the first specimen of Protostega gigas (meaning giant) in the Kansas chalk in 1871. A variety of bones were found in yellow cretaceous chalk from a bluff near Butte Creek.

Protostega wasn’t recorded or found anywhere else in the world until 1953, when the first recorded remains of the Late Cretaceouse turtle was found in New Zealand by J. Wiffen. The specimen represented the first southern hemisphere record within the Protostegidae family. J. Wiffen described the specimen as being very similarly to the genus Protostega gigas and thought that it was another mysterious specimen found. In the end the fossil was recorded as small species of Protostegidae family specimen, due to the missing skull bones that hold distinguishing features to properly classify the specimen completely. This discovery still has relevant value because the finding of species within the same family, that share very common characteristics, give the fossil record more geological and paleoenvironment information of this families locations around the world. There have now been multiple findings of specimens in the Protostegidae family found at multiple locations around the world but only one Protostega gigas found in the Wester Interior Seaway in North America.

Description

Body Structure: A few of Protostegas defining characteristics are their massive bodies and limb skeleton. From the fossil record, they are known to have reached up to 3 meters in length. Cope’ s Protostega gigas discovery reveled that their shell had a reduction of ossification that helped these huge animals with streamlining in the water and weight reduction. The carapace was greatly reduced and the disk only extending less than half way towards the distal ends of the ribs. Cope described other greatly modified bones in his specimen including an extremely long coracoid process that reached all the way to the pelvis and a humerus that resembled a Dermochelys.

Limb Structure: Their limb structure gave them the ability to move swiftly through the water due to their elongated finger like structures, that created a paddle formation, great for beating through the sea. Their limb structures were designed for permeate resistance from the heavy and dense water of the seas. They developed a special articulation that allowed their hypoplastra to turn directly inward at a right angle, so it would meet in the midline of an overlapping joint. Creating better movement of their limbs.

Body structure of fossilized Protostega

Skull Structure: Edward Cope described the uniqued Protostega gigas to have a large jugal that reached to the quadrate along with a thickened pterygoid that reached to the mandibular articulating surface of the quadrate. The fossil featured a reduction in the posterior portion of the vomer where the palatines meet medially. Another fossilized specimen showed a bony extension, that would have been viewed as a beak, was lacking in the Protostega genus. The premaxillary beak was very shorted then Archelon. In front of the orbital region was elongated with broadly roofed temporal region. The jaws of the fossil showed a large crushing -surfaces. The quadrato-jugal was triangular with a posterior edge that was concave and the entire bone was convex from distal view. The squamosal appeared to have a concave formation on the surface at the upper end of the quadrate. In Cope’s fossil the mandible was preserved almost perfectly and from this he recorded that the jaw was very similar to the Chelonidae and the dentary had a broad for above downward with a concave surface, marked by deep pits in the dentary.

Habitat and Feeding: Due to their streamlining body features, these turtles thrived in open seas. Specifically the Western Interior Sea of North America, where the majority of the Protostegidae family fossils have been discovered.

While living in the open seas, Cope concluded that these animals were most likely omnivores and consumed a diet of hard shelled crustacean creatures, due to the long symphysis of its lower jaw. Along with probably consisted of seaweed and jellyfish or scavenged on floating carcasses as well, like modern turtles.

Predators: Sharks have been discovered to have been a possible predator of Protostega. Two specimens have been discovered by paleontologist that found one specimen with a teeth marks, and one with an embedded tooth fragment from an extinct shark called Cretoxyrhina mantelli.

Поделитесь в социальных сетях:vKontakteFacebookTwitter
Напишите комментарий