was a basal ornithomimosaur from the Early Cretaceous Period of what is now Mongolia. Unlike later, more derived ornithomimosaurs, Harpymimus still possessed teeth, although they appear to have been restricted to the lower jaw (dentary). The holotype specimen (IGM 100/29, Mongolian Academy of Sciences, Ulan Bator, Mongolia)consists of an almost complete skeleton, lacking portions of the pectoral girdle, pelvic girles, and hindlimbs. It was recovered at Dundgovi Aimag (Eastern Gobi Province), from an exposure of the Shinekhudug Formation (Shinekhudukskaya Svita; Hauterivian to Barremian). The etymology of Harpymimus involves a reference to the fearsome Harpy of Greek mythology (Greek harpyiai = “Harpies” + Greek mimos = “mimic”). Only a single species is known for this genus, H. oklandnikovi. Other dinosaurs collected from the Shinekhudug Formation at Dundgov include the ceratopsian Psittacosaurus mongoliensis and the ornithopod Altirhinus kurzanovi.Diagnosis and Morphology
Kobayashi & Barsbold (2005, p. 100) diagnose Harpymimus as follows: “Eleven dentary teeth, which are anterior in position; transition between anterior and posterior caudal vertebrae at eighteenth caudal; traiangular-shaped depression of dorsal surface of supragelnoid buttress of scapula; low ridge dorsal to depression along posterior edge of scapular blade; small but deep collateral ligament fossa on lateral condyle of metacarpal III.” The holotype skull of Harpymimus is virtually complete, but badly crushed laterally, obscuring some anatomical detail. There is evidence of a rhampotheca (beak) covering the upper jaw which, in concert with the dentary teeth, was likely employed for grasping and holding onto prey. It’s general appearance was much like that of later ornithomimosaurs (long-necked, long arms with sharp grasping claws, and long legs). The dentition of Harpymimus differs from that of another basal ornithomimosaur, Pelecanimimus polyodon, in that teeth are restricted to the dentary and number between ten and eleven. Pelecanimimus possessed seventy-five dentary teeth, as well as an additional 145 teeth in the maxillae and premaxillae. The small teeth of Harpymimus were probably used only for grabbing and holding prey, unlike those of many other non-avian theropods, which were adapted to cutting or piercing (Kobayashi & Barsbold (2005, p. 119). Of all the known ornithomimosaurs, only Harymimus and Pelecanimimus retain teeth, a trait which is plesiomorphic (“primitive”) for the clade Orithomimosauria. The anteroposterior length of the skull is approximaley 262 mm, more than twice its approximate height and less than half the length of the neck (approximately 600 mm).Phylogeny
Kobayashi & Barsbold (2005, pp. 118-123) have conducted a detailed cladistic analysis of this taxon and have determined that Harpymimus is basal to the clade of Garudimimus brevipes plus Ornithomimidae, yet is more derived than Pelecanimimus polyodon. The conclusions of this analysis support the model that ornithomimosaurs originated in either eastern Asia or in Europe prior to the Barremian (130-125 million years ago), the migrated to North America during or at some time before the Late Cretaceous.Copyright © 2008 Answers Corporation


Plantenetende dino wisselden tanden ong. om de  twee maanden

 18 juli 2013   0


Wetenschappers hebben ontdekt dat plantenetende dinosaurussen hun tanden opvallend vaak wisselden. Gemiddeld ging een tand maar één tot twee maanden mee.

Gelukkig hadden de dino’s genoeg reserve-tanden ‘liggen’: onder elke tand zaten tot wel vijf reserve-exemplaren op hun kans te wachten.

Dat schrijven onderzoekers in het blad PLoS ONE. Ze baseren hun conclusies op een onderzoek naar twee gigantische plantenetende dino’s: Diplodocus en Camarasaurus.

Om te achterhalen hoelang de tanden van deze dinosaurussen meegingen, richtten de onderzoekers zich op dentine. Dit is een laagje in een tand, dat zich tussen de kroon en het glazuur bevindt. Dit laagje groeit gedurende het leven van een dier. Door te kijken hoe omvangrijk het laagje is, kan worden vastgesteld hoelang een tand meeging.


Uit het onderzoek blijkt dat Diplodocus elke tand gemiddeld elke 35 dagen wisselde. Onder elke tand zaten zo’n vijf reserve-exemplaren. Camarasaurus wisselde zijn tanden gemiddeld elke 62 dagen en had drie reserve-tanden op voorraad. “Een bijna 30 meter lange plantenetende dinosaurus had elke één tot twee maanden op elke plek een nieuwe tand,” concludeert onderzoeker Michael D’Emic.

Kwaliteit of kwantiteit
De tanden van de plantenetende dino’s gingen klaarblijkelijk dus maar even mee.

“Bij de plantenetende dinosaurussen was kwantiteit belangrijk dan kwaliteit als het om het maken van tanden ging.”

En dat staat haaks op de manier waarop grote zoogdieren die vandaag de dag nog in leven zijn, tanden produceren. Voor hen is kwaliteit juist belangrijker.

Dat de tanden van de plantenetende dinosaurus zo relatief kort meegingen, is goed te verklaren.

Diplodocus en Camarasaurus waren echte giganten die dagelijks enorme hoeveelheden planten naar binnen werkten. Waarschijnlijk sleten hun tanden daardoor snel af, waardoor het nodig was om deze regelmatig te vervangen.

Plant-eating dinosaurs replaced teeth often, carried spares” – PLoS ONE
De foto bovenaan dit artikel is gemaakt door xx (cc via Flickr.com).



 27 oktober 2011 2

Nieuw onderzoek wijst erop dat plantenetende dinosaurussen elk jaar enorme afstanden aflegden om aan eten te komen.

De onderzoekers bestudeerden de isotopen in 32 gefossiliseerde tanden van Camarasaurussen. De verhouding waarmee deze isotopen in tanden voorkomen, wordt bepaald door het water dat de dinosaurussen drinken. Zo is dus aan de tanden te zien waar de dino’s precies uithingen.

Onderzoeker Henry Fricke ontdekte dat de verhouding van de zuurstofisotopen in vijf maanden tijd geleidelijk aan veranderde. Dat wijst erop dat de dinosaurussen regelmatig (dat was waarschijnlijk seizoensgebonden) op reis gingen naar andere gebieden.


De plantenetende dinsoaurussen konden wel vijftien meter lang worden en hadden enorm veel voedsel nodig (zo’n 450 kilo per dag) om dat lijf te onderhouden. Wanneer hun gebied een periode van droogte doormaakte, reisden ze waarschijnlijk naar gebieden waar nog wel groen te vinden was. Soms legden ze daarvoor wel 300 kilometer af, zo is in het blad Nature te lezen.

Onderzoekers vermoeden al langer dat dinosaurussen migreerden, maar dit is het eerste overtuigende bewijs daarvan. Waarschijnlijk reisden de dino’s in grote groepen, zodat ze wat minder kwetsbaar waren. Vleesetende dino’s volgden de Camarasaurussen waarschijnlijk op hun tocht en stilden hun honger mogelijk door de plantenetende reisgenoten te verorberen.


Dinosaur teeth hold first clues to migration” – Newscientist.com
De foto bovenaan dit artikel is gemaakt door Márcio Luiz (via Wikimedia Commons).




Homalocephale   calathocercos -Maryanska et Osmolska 1974-
Archosauria: Ornithischia: Pachycephalosauria: Homalocephaliidae
Locality: Omnogov, Gobi Desert, southern Mongolia
Late Cretaceous (Late Campanian-Early Maastrichtian), 74 million years ago
Meaning of the name; “even-head”Homalocephale calathocercos is a pachycephalosaurid, literally ‘thickheads’.
The top of their skulls were 3 to 4 inches thick- solid bone usefully protecting a walnut-sized brain.
This thickening of the skull would allow these animals to act like the modern sheep and goats where the males compete for females by
Other indications that these dinosaurs head-butted can be seen in the stiff spinal column.
This made it robust enough for the forces applied when contact occurred.
The angle of articulation of the skull and the neck vertebrae (which puts the head in just the right position) makes butting
safe and not a back-breaking exercise.
These dinosaurs had tiny teeth ideal for shredding plant material.
Pachycephalosaurids may have had a lifestyle very like that of modern deer and goats and even may have congregated in small herds.

June 20, 2011  Filed under: Thyreophora

Hylaeosaurus is the most obscure of the three animals used by Sir Richard Owen to first the new group Dinosauria, in 1842. The first Hylaeosaurus remains to be found were dug up by Gideon Mantell in 1832.Gideon Mantell originally estimated that Hylaeosaurus was about 7.6 m long, or about half the size of the other two original dinosaurs,Iguanodon and Megalosaurus. Modern estimates range up to 6 metres in length.Factbox //Name: Hylaeosaurus, meaning ‘woodland reptile’ Size: 4m long  Food: plants Lived: about 130 million years ago in the Early Cretaceous Period in southern EnglandThe fossils are entombed in a slab of limestone that can still be seen in London’s British Museum. Perhaps out of respect for the first generation of palaeontologists, no one has taken the trouble to actually prepare the fossil specimen, which seems to have been left by a dinosaur closely related to Polacanthus.Only the front part of the dinosaur was found. Palaeontologists had to guess how the legs and body armour looked, but they are pretty certain that it looked like a long lizard with a cloak of sharply spiked armour running from its neck right down to the tip of its tail.Hylaeosaurus was a slow-moving herbivore that nibbled ferns and other green plants for its food. If it was attacked, Hylaeosauruswas protected by its heavy armour and intimidating spikes.It was a fairly typical nodosaur, with three long spines on its shoulder, two at the hips, and three rows of armour running down its back. It may also have had a row of plates down its tail. It had a long head, more like the head of a Nodosaurus than an Ankylosaurus and a beak, which it probably used to crop low-lying vegetation.

(meaning “very high lizard”, referring to the tall neural spines on its vertebrae) was a genus of duckbill dinosaur similar in appearance to Corythosaurus. Like Corythosaurus, it had a tall, hollow rounded crest, although not as large and straight. It is known from the remains of two species from the Late Cretaceous of Alberta, Canada, and Montana, USA, and is the latest hollow-crested duckbill known from good remains in North America. It was an obscure genus until the description of nests, eggs, and hatchlings belonging to H. stebingeri in the 1990s.Description
Hypacrosaurus is most easily distinguished from other hollow-crested duckbills (lambeosaurines) by its tall neural spines and the form of its crest. The neural spines, which project from the top of the vertebrae, are 5 to 7 times the height of the body of their respective vertebrae in the back, which would have given it a tall back in profile. The skull’s hollow crest is like that of Corythosaurus, but is more pointed along its top, not as tall, wider side to side, and has a small bony point at the rear. Unlike other lambeosaurines, the passages for the airways do not form an S-curve in the crest (at least not in H. altispinus). The animal is estimated to have been around 9.1 meters long (30 feet). As with most duckbills, its skeleton is otherwise not particularly remarkable, although some pelvic details are distinctive. Like other duckbills, it was a bipedal/quadrupedal herbivore. The two known species, H. altispinus and H. stebingeri, are not differentiated in the typical method, of unique characteristics, as H. stebingeri was described as transitional between the earlier Lambeosaurus and later Hypacrosaurus. Photographs of an adult H. stebingeri skull show an animal that looks very similar to H. altispinus.Classification
Hypacrosaurus was a lambeosaurinae hadrosaurid,and has been recognized as such since the description of its skull. Within the Lambeosaurinae, it is closest to Lambeosaurus and Corythosaurus, with Jack Horner and Phil Currie (1994) suggesting that H. stebingeri is transitional between Lambeosaurus and H. altispinus, and Michael K. Brett-Surman (1989) suggesting that Hypacrosaurus and Corythosaurus are the same genus. These genera, particularly Corythosaurus and Hypacrosaurus, are regarded as the “helmeted” or “hooded” branch of the lambeosaurines, and the clade they form is sometimes informally designated Lambeosaurini.Discovery and history
The type remains of Hypacrosaurus remains were collected in 1910 by Barnum Brown for the American Museum of Natural History.The remains, a partial postcranial skeleton consisting of several vertebrae and a partial pelvis (AMNH 5204), came from along the Red Deer River near Tolman Ferry, Alberta, Canada, from rocks of what is now known as the Horseshoe Canyon Formation (early Maastrichtian, Upper Cretaceous). Brown described these remains, in combination with other postcranial bones, in 1913 as a new genus that he considered to be like Saurolophus. No skull was known at this time, but two skulls were soon discovered and described.During this period, the remains of small hollow-crested duckbills were described as their own genera and species. The first of these that figure into the history of Hypacrosaurus was Cheneosaurus tolmanensis, based on a skull and assorted limb bones, vertebrae, and pelvic bones from the Horseshoe Canyon Formation. Shortly thereafter, William Diller Matthew identified an American Museum of Natural History skeleton (AMNH 5340) as Procheneosaurus, from the Two Medicine Formation of Montana. These and other taxa were accepted as valid genera until the 1970s, when Peter Dodson showed that it was more likely that the “cheneosaurs” were the juveniles of established lambeosaurines. Although he was mostly concerned with the earlier, Dinosaur Park Formation genera Corythosaurus and Lambeosaurus, he suggested that Cheneosaurus would turn out to be composed of juvenile individuals of the contemporaneous Hypacrosaurus altispinus. This idea has become accepted, although not formally tested. Matthew’s ProchFalse Doctrineaurus, meanwhile, was not quite like the other Procheneosaurus specimens studied by Dodson, and for good reason: it was much more like a species that would not be named until 1994, H. stebingeri.“H. stebingeri”
The new species Hypacrosaurus stebingeri was named for a variety of remains, including hatchlings with associated eggs and nests, found near the top of the late Campanian (Upper Cretaceous) Two Medicine Formation in Glacier Creek, Montana, and across the border in Alberta. These represent “the largest collection of baby skeletal material of any single species of hadrosaur known”.Species
H. altispinus, the type species, is known from 5 to 10 articulated skulls with some associated skeletal remains, from juvenile to adult individuals. H. stebingeri is known from an unknown but substantial number of individuals, with an age range of embryos to adults. The hypothesis that H. altispinus and H. stebingeri form a natural group excluding other known hadrosaur species may be incorrect, as noted in Suzuki et al.’s 2004 redescription of Nipponosaurus; their phylogenetic analysis found that Nipposaurus was more closely related to H. altispinus than H. stebingeri was to H. altispinus.Paleobiology
As a hadrosaurid, Hypacrosaurus would have been a bipedal/quadrupedal herbivore, eating a variety of plants. Its skull permitted a grinding motion analogous to chewing, and its teeth were continually replacing and packed into dental batteries that contained hundreds of teeth, only a relative handful of which were in use at any time. Plant material would have been cropped by its broad beak, and held in the jaws by a cheek-like organ. Its feeding range would have extended from the ground to ~4 m (13 ft) above.
Copyright © 2007 Answers Corporation.


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