Speeds and gaits of dinosaurs

The known relationships of speed, gait and body size (derived mainly from mammals) are used to determine the gaits and theoretical maximum speeds of dinosaurs. Speed estimates are made for 62 dinosaurs (representing 51 genera) and are supplemented with information from comparative anatomy and from dinosaur trackways. It is concluded that smaller bipedal dinosaurs were capable of running at speeds up to 35 or 40 km/h. The so-called "ostrich dinosaurs" are credited with maximum speeds less than 60 km/h, and possibly as low as 35 or 40 km/h. Larger bipedal dinosaurs were probably restricted to walking or slow trotting gaits, with maximum speeds in the range 15-20 km/h. Most quadrupedal dinosaurs seem to have been restricted to a walking gait. Stegosaurs and ankylosaurs may have had maximum speeds as low as 6-8 km/h. Sauropods may have attained 12-17 km/h, and some ceratopsians may have been capable of trotting at speeds up to 25 km/h. On a weight-for-weight basis the speeds of dinosaurs are generally lower than those of mammals

Preferred gaits of bipedal dinosaurs

Measurements of trackways have been used to determine the gaits and speeds of 267 bipedal dinosaurs. Most of these dinosaurs used a walking gait, with mean relative stride length about 1.3 (i.e. with stride length about 1.3 times estimated height at the hip). For running dinosaurs mean relative stride length is about 3.7. Very few of the track-makers selected a trotting gait (defined by relative stride length between 2.0 and 2.9). It is suggested that the preferred walking and running gaits represent energetic optima, and that the trot was a transitional gait of high energetic cost

Aestivation among ornithopod dinosaurs of the African Trias

Thulborn, Richard A. 1978 07 15: Aestivation among ornithopod dinosaurs of the African Trias. Lethaia. Vol. 11, pp. 185–198. Oslo. ISSN 0024–1164. Dental and circumstantial evidence supports the theory that ornithopod dinosaurs of the African Red Beds responded to seasonal changes in their environment by resorting to aestivation (dry season dormancy). One group of ornithopods. the heterodontosaurids. apparently suppressed tooth replacement to permit efficient grinding of their plant food and probably replaced their entire cheek dentitions while aestivating. The sympatric fabrosaurid ornithopods had a simple open‐and‐shut jaw action and replaced their teeth continuously in standard reptilian fashion. Seasonal dormancy must have imposed major constraints on the lives of fabrosaurids and heterodontosaurids. and these constraints are summarized in the model of a circannual life cycle. Copyrigh

The avian relationships of Archaeopteryx, and the origin of birds

The avian relationships of Archaeopteryx are assessed in terms of the 'stem-group' concept. The avian stem-group is defined, and its constituents are identified and described. Phylogenetic analysis of stem-group birds reveals that Archaeopteryx is no more closely related to modern birds than are several types of theropod dinosaurs, including tyrannosaurids and ornithomimids. Archaeopteryx is not an ancestral bird, nor is it an 'ideal intermediate' between reptiles and birds. There are no derived characters uniquely shared by Archaeopteryx and modern birds alone; consequently there is little justification for continuing to classify Archaeopteryx as a bird. Feathers are considered to be homologues or derivatives of epidermal scales (not of hairs); they probably originated as an insulating blanket in juvenile theropods, enabling them to match the activities of bigger animals, regardless of environmental temperature fluctuations. The furcula may have been present in various theropods, including allosaurids, caenagnathids (oviraptorids) and tyrannosaurids. Several possible definitions of the class Aves are examined. It is concluded that the boundary between reptiles and birds is best placed at a pronounced 'morphological gap'. This measure ensures that most animals conventionally regarded as 'birds' will be retained in the class Aves-though Archaeopteryx would be transferred to the dinosaur suborder Theropoda. This definition also ensures that birds will be distinguished from reptiles by an extensive set of osteological characters. The origin of the class Aves (as defined here) would probably coincide with the origin of avian flight; it is unlikely that Archaeopteryx can provide any direct evidence about the origin of modern avian flight, regardless of its locomotor abilities. The 'morphological gap' between reptiles and birds is not necessarily a deficiency of the fossil record; the 'gap' may be real evidence that birds originated by evolutionary saltation-and not by gradual stages. The origin of birds is not a problem to be equated with the origin of Archaeopteryx; it is a problem to be found in the 'morphological gap' that precedes the first appearance of volant birds. The concept of the 'proavis' has outlived any usefulness it might once have had, and should be abandoned

Thegosis in herbivorous dinosaurs

THE name thegosis was coined by Every and Kühne1 for the short and powerful process of tooth sharpening which is accomplished in mammals by the grinding of one tooth against another. Thegosis produces sharp-edged, planar (or curved planar) wear surfaces on the teeth. The thegosis wear facets cut straight across boundaries between dentine and enamel and are typically marked with deep parallel striations (not necessarily coincident with the maximum slope of the wear facet). In some mammals thegosis keeps certain teeth sharply honed for use as weapons (as with the canines of suids and hippopotamids); in others thegosis sharpens the teeth which deal with food (as with the carnassial apparatus in felids)

Nest of the dinosaur Protoceratops

Thulborn, R A. 1992 04 15: Nest of the dinosaur Protoceratops. Lethaia, Vol. 25, pp. 145–149. Oslo. ISSN 0024–1164. Two different types of nests and eggs have been attributed to Protoceratops, a primitive‐looking ceratopsian dinosaur from the Upper Cretaceous of Mongolia. Comparisons with the reproductive traces of other Cretaceous dinosaurs reveal that conventional restorations of the Protoceratops nest are probably based upon the nest of an ornithopod dinosaur. Authentic nests of Protoceratops do exist, but these are smaller and less complex in structure than the nests of ornithopod dinosaurs. This misunderstanding, which has endured in popular and scientific literature for more than 50 years, underlies the widespread belief that Protoceratops laid its eggs in a crater‐like excavation. More probably the nest of Protoceratops comprised a shallow radial array of eggs concealed beneath a low mound of soil. *Ornithischia, eggs, nests, behaviour, Cretaceous. Copyrigh

Ornithopod dinosaur tracks from the lower jurassic of Queensland

Natural casts of seven small footprints have been identified on a single weathered block derived from the Precipice Sandstone (Lower Jurassic) of the Carnarvon Gorge, southeastern Queensland. The footprints are attributed to omithopod dinosaurs and are referred to the ichnogenus Anomoepus. They appear to be most similar to the ichnospecies Anomoepus gracillimus, originally defined on footprints from the Lower Jurassic of the northeastern United States. This identification is consistent with the presumed age of the Precipice Sandstone, since Anomoepus or closely related ichnotaxa are common in Leaver Jurassic sediments of the United States, Europe and southern Africa but have never been identified with certainty in Triasac sediments. The tracks described here were made by at least four dinosaurs, all estimated to have been about 30 cm high at the hip and less than 1 -3 m in total length. In their general appearance these animals probably resembled the small plant-eating dinosaur Fabrosaurus (Lesothosaurus), from the Lower Jurassic of southern Africa. Tracks of two animals provide estimates of walking speeds between 0.68 and 0.80 m/s (2.4 and 2.9 km/h). These footprints are the earliest evidence for the existence of omithischian dinosaurs in Australia

The Australian Triassic reptile Tasmaniosaurus Triassicus (Thecodontia: Proterosuchia)

This paper presents a reinterpretation of Tasmaniosaurus triassicus, a thecodontian reptile from the Knocklofty Formation (Early Triassic) of Tasmania. Tasmaniosaurus resembles the well-known thecodontian Chasmatosaurus and is included in the family Proterosuchidae (suborder Proterosuchia). Its skull is constructed on fairly standard proterosuchian lines, and there is no evidence to support the earlier suggestion that Tasmaniosaurus was an unusually long-snouted reptile showing resemblances to phytosaurs. A second Australian thecodontian, Kalisuchus rewanensis from the Arcadia Formation (Early Triassic) of Queensland, is also included in the family Proterosuchidae, but differs from Tasmaniosaurus in the structure of the snout and should be retained as a separate genus. The relationships of the Australian thecodontians are discussed, and new reconstructions of the skull are presented for Tasmaniosaurus and Kalisuchus