CENOCERATOPSIA
Across the warmer parts of the globe, herds of giant herbivorous ornithopods dominate the landscape. However, when trudging through the forests and swamps of tropical Asia, and to a lesser extent tropical Africa and South America, observers will often come face to face with dinosaurs of a very different kind – the parrot-beaked ceratopsians.
HISTORY
The ceratopsians first appeared in Early Cretaceous Asia and soon branched into two successful Laurasian groups (among several smaller ones). The Asian Protoceratopsidae were comparatively primitive forms that were usually hornless or, at most, in possession of a small nasal horn. While staying small, they became exceedingly abundant in places like the arid plains of Mongolia. Far more spectacular were members of the North American family Ceratopsidae which attained huge sizes (sometimes surpassing today's Indian megahorn, see below) and sported a dizzying array of facial horns, spikes and bosses. During the Campanian perhaps a dozen species of these frilled giants marched along the western shores of the interior seaway. However, as the Maastrichtian progressed, ceratopsid diversity waned.
The family made a comeback of sorts during the Palaeocene and Early Eocene, evolving into spectacular behemoths such as †Brontoceratops, the most massive ceratopsian ever known. Alas, these magnificent beasts vanished around the Eocene-Oligocene boundary.
At the same time, however, their smaller protoceratopsid cousins were having a more productive time. They grew larger and stranger, moving into niches vacated by their recently departed cousins. In terms of higher-level diversity, the Late Oligocene was the heyday of the protoceratopsids when a variety of weird lineages could be found throughout the Northern Hemisphere.
As the Neogene dawned, a number of factors conspired against this parrot-beaked menagerie. The Haughton impact at the close of the Oligocene led to localized extinctions in Asia and practically wiped them out in North America. Finally they quite certainly had difficulty coping with the spreading grasslands. The narrow beaks and slicing dentition of most species was great for tearing into tough bark and cycads, but considerably less efficient at processing grass than the square bills and grinding teeth of hadrosaurs. While the other groups dwindled, one line of protoceratopsids abandoned the characteristic scissor-teeth of their ancestors, allowing them to exploit a wider range foods (although they never produced a specialised grazer). These were the Caenoceratopia, which by the Late Miocene had regained much evolutionary lost ground. They soon became the dominant large browsers of southern Eurasia and made headway into Africa.
During the Pliocene or perhaps end-Miocene, they entered North America and marched across the Panama isthmus to become established in South America for the first time (as far as we know) in ceratopsian history. Then came the climatic seesaw that was the Quaternary. The lush woodlands which the ceratopsians favored appeared and vanished with the ebb and flow of the glaciers to the north. Today the caenoceratopians are no longer present in North America and northern Eurasia; but they continue to thrive in the warmer parts of Asia, Africa and throughout South and Central America.
FEATURES
One glance at its homely face is enough identify the creature in front of you as a ceratopsian. A unique bone called the rostral sits at the tip of the snout and, when combined with the predentary at the tip of the lower jaw, creates a narrow beak. Jutting out the back of its skull is a frill of bone formed by the parietals and squamosals. This frill can be used for display as well as providing an extended surface area for huge jaw muscles, giving the animal a formidable bite. Members of the extant clade Caenoceratopia share a number of additional features which separate them from their protoceratopsid ancestors. The ischium is now fairly straight, losing the pronounced downward curve. On the face, many of the ornamental features of the long extinct Ceratopsidae have convergently re-evolved, including horns on the nose and brows. Unlike the smooth-edged frill of protoceratopsians, those of caenoceratopsians may be decorated with prominent knobs and spikes.
The most characteristic feature is, however, in the teeth. The tooth batteries of early ceratopsians were arranged to form a set of vertical blades. In effect, they chewed their food with a set of garden shears – a trait which probably allowed them to subsist on tougher vegetation than their contemporaries. (This feature is still used by the undaurs, which in general eat tougher stuff than the gihugrongos with which they coexist.) However, it is difficult to imagine this mechanism as being anywhere as effective as the grinding batteries of hadrosaurs.
When the caenoceratopians appeared in the Late Oligocene, their dentition progressively shifted towards a duckbill-like configuration where the crowns of the teeth rasp against each other to crush and grind plant food. This made chewing far more efficient than in earlier designs and was probably the key to their success. However, the teeth of caenoceratopians can easily be distinguished from those of hadrosaurs in being fewer in number, more robust in form and two to four times larger relative to body size. The teeth often bear prominent cusps and ridges which helps them to process plant matter that most ornithopods consider unpalatable.
CENOCERATOPSIAในส่วนของโลกที่อุ่น ฝูงยักษ์ herbivorous ornithopods ครองภูมิทัศน์ อย่างไรก็ตาม เมื่อ trudging ผ่านป่าไม้และหนองน้ำของเอเชียเขตร้อน และขอบเขตอาฟริกาและอเมริกาใต้น้อยกว่า ผู้สังเกตการณ์จะมัก face to face with ไดโนเสาร์ชนิดแตกต่างกันมาก – ceratopsians beaked นกแก้วประวัติCeratopsians การปรากฏตัวครั้งแรก ในเอเชียก่อน Cretaceous และเร็ว ๆ นี้ branched เป็น Laurasian ประสบความสำเร็จ 2 กลุ่ม (หมู่หลายคนเล็ก) Protoceratopsidae เอเชียฟอร์มดั้งเดิมดีอย่างหนึ่งที่มักจะ hornless หรือ ที่สุด ในความครอบครองของแตรเล็กโพรงจมูก ได้ พักเล็ก พวกเขากลายเป็นไปมากมายในสถานที่เช่นราบแห้งแล้งของมองโกเลีย สมาชิกของครอบครัวอเมริกันเหนือ Ceratopsidae ที่ได้ขนาดใหญ่ (บางครั้ง surpassing megahorn อินเดียวันนี้ ดูด้านล่าง) และ sported เรย์ระหว่างหน้าแตร spikes และผู้บังคับบัญชา ได้งดงามมาก ในระหว่างการ Campanian ทีโหลพันธุ์ยักษ์เหล่านี้ครุยเดินตามชายฝั่งตะวันตกของ seaway ภายใน อย่างไรก็ตาม ขณะที่ Maastrichtian หน้าไปเพียงใด ความหลากหลาย ceratopsid wanedครอบครัวได้กลับมาประเภท Palaeocene และ Eocene ต้น พัฒนาเป็น behemoths งดงามเช่น †Brontoceratops, ceratopsian ขนาดใหญ่ที่สุดที่เคยรู้จัก อนิจจา สัตว์สวยงามเหล่านี้ศาสดารอบขอบ Eocene Oligoceneในเวลาเดียวกัน อย่างไรก็ตาม ลูกพี่ลูกน้องของพวกเขา protoceratopsid ขนาดเล็กได้มีเวลามากขึ้น พวกเขาเติบโตใหญ่ และคนแปลก หน้า ย้ายไปตรงไหน vacated โดยลูกพี่ลูกน้องของพวกเขาเพิ่งพรากจากกันมา ในแง่ของความหลากหลายสูงกว่า Oligocene สายมั่งคั่งของ protoceratopsids เมื่อพบความหลากหลายของเชื้อชาติแปลกตลอดซีกโลกเหนือเป็นยุคนีโอจีนจะเริ่มขึ้น ปัจจัยสมคบกันกับ menagerie นี้นกแก้ว beaked Haughton ผลกระทบที่ปิด Oligocene ที่นำไป extinctions เป็นภาษาท้องถิ่นในเอเชีย และจริงเช็ดพวกเขาออกในอเมริกาเหนือ ในที่สุด พวกเขาค่อนข้างแน่นอนมีปัญหาเผชิญกับ grasslands ประมาณ Beaks แคบและแบ่ง dentition พันธุ์มากที่สุดถูกฉีกขาดเป็นเปลือกเหนียวและ cycads มาก แต่มากน้อยประสิทธิภาพประมวลผลหญ้ากว่าใบสี่เหลี่ยม และบดฟันของ hadrosaurs ในขณะที่กลุ่มอื่น ๆ dwindled, protoceratopsids บรรทัดหนึ่งถูกทอดทิ้งสุนัขฟันลักษณะของบรรพบุรุษ อนุญาตให้ใช้ประโยชน์อาหารช่วงกว้าง (แม้ว่าพวกเขาไม่เคยผลิต grazer พิเศษ) เหล่านี้ถูก Caenoceratopia ซึ่ง โดย Miocene สายได้จากพื้นดินหายไปมากวิวัฒนาการ พวกเขาเร็ว ๆ นี้กลายเป็น เบราว์เซอร์ใหญ่หลักของทวีปยูเรเชียทางตอนใต้ และเจริญก้าวหน้าในแอฟริกาDuring the Pliocene or perhaps end-Miocene, they entered North America and marched across the Panama isthmus to become established in South America for the first time (as far as we know) in ceratopsian history. Then came the climatic seesaw that was the Quaternary. The lush woodlands which the ceratopsians favored appeared and vanished with the ebb and flow of the glaciers to the north. Today the caenoceratopians are no longer present in North America and northern Eurasia; but they continue to thrive in the warmer parts of Asia, Africa and throughout South and Central America.FEATURESOne glance at its homely face is enough identify the creature in front of you as a ceratopsian. A unique bone called the rostral sits at the tip of the snout and, when combined with the predentary at the tip of the lower jaw, creates a narrow beak. Jutting out the back of its skull is a frill of bone formed by the parietals and squamosals. This frill can be used for display as well as providing an extended surface area for huge jaw muscles, giving the animal a formidable bite. Members of the extant clade Caenoceratopia share a number of additional features which separate them from their protoceratopsid ancestors. The ischium is now fairly straight, losing the pronounced downward curve. On the face, many of the ornamental features of the long extinct Ceratopsidae have convergently re-evolved, including horns on the nose and brows. Unlike the smooth-edged frill of protoceratopsians, those of caenoceratopsians may be decorated with prominent knobs and spikes.The most characteristic feature is, however, in the teeth. The tooth batteries of early ceratopsians were arranged to form a set of vertical blades. In effect, they chewed their food with a set of garden shears – a trait which probably allowed them to subsist on tougher vegetation than their contemporaries. (This feature is still used by the undaurs, which in general eat tougher stuff than the gihugrongos with which they coexist.) However, it is difficult to imagine this mechanism as being anywhere as effective as the grinding batteries of hadrosaurs.When the caenoceratopians appeared in the Late Oligocene, their dentition progressively shifted towards a duckbill-like configuration where the crowns of the teeth rasp against each other to crush and grind plant food. This made chewing far more efficient than in earlier designs and was probably the key to their success. However, the teeth of caenoceratopians can easily be distinguished from those of hadrosaurs in being fewer in number, more robust in form and two to four times larger relative to body size. The teeth often bear prominent cusps and ridges which helps them to process plant matter that most ornithopods consider unpalatable.
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