Dinosaur Myths and Misinformation

Abstract

This page explores some of the popular misconceptions about dinosaurs; about how much we actually know about them, and about how well the evidence supports some of our most cherished beliefs concerning dinosaurs.

Keywords: dinosaur, warm blooded, meteor, Jurassic, Cretaceous, bird origins

Introduction

The current popular interest in dinosaurs – which has been evident since Michael Crichton’s novel, Jurassic Park, was made into a big budget movie and spawed its slew of successors – is not new. The writer well remembers poring over dinosaur books in his boyhood, and indeed watching movie and television dramas depicting impossible interactions between dinosaurs and people. However, in the intervening 30 or 40 odd years, the representations of the dinosaurs themselves have changed markedly.

A modern ‘Renaissance Period’ in the study of dinosaurs began "in the late 1960s and early 1970s, when Polish palaeontologists mounted ... expeditions into Mongolia. At about the same time, John Ostrom from Yale University began collecting in the Lower Cretaceous Cloverly Formation of Montana and Wyoming. Among his important discoveries was the small theropod dinosaur Deinonychus. This discovery led Ostrom to examine the possibility that dinosaurs were not the slow, sluggish ectotherms that they had been portrayed as at times, but were very active, possibly even endothermic. Ostrom also noted similarities between Deinonychus and the early bird Archaeopteryx, thus reviving the debate that birds had a dinosaur origin" (Carpenter 2002).

Either way, it is Bad Science.

• How long did dinosaurs “rule?”
• How large were dinosaurs?
• Were dinosaurs “warm blooded?”
• Are birds really the descendants of dinosaurs?
• Were the dinosaurs wiped out by a meteor impact?

But first, let us answer the question, what are Dinosaurs?

Bad Language – Dinosaur Success

Let’s begin by analysing the common, throw-away pronouncement that dinosaurs were one of – or simply "the" – most successful group of animals, ever. They ruled the earth for ~165 Ma (million years). Often, this will be followed up with the comparison that humans have only been around for ~0.2 Ma. These assertions are typical of the dinosaur phenomenon: they contain sufficient elements of truth to sound authoritative, but the language is so sloppy that the statements have no precise meaning, and the conclusion is a non sequitur.

First of all, what is a dinosaur in this context? Most well-versed kids and a few adults will know that the dinosaurs comprise two orders: the Ornithischia and Saurischia (read more). Accepting for the moment that both orders arose from a common ancestor, i.e. that the Dinosauria is a natural group (a clade), then it has the rank of superorder. So this is the first bit of imprecision to clear up: Any statements about dinosaurs being around for 165 Ma, then, apply to the orders or to the entire superorder.

(For comparison, stem group representatives of the order to which we humans belong, Primates, date from the earliest Tertiary, approximately 65 Ma. The oldest known true primates occur about 55 Ma, near the Paleocene/Eocene boundary. On the other hand, the order Euselachii, which includes the sharks, has been around since the Late Devonian: at least 360 Ma.)

Moreover, there are many other groups of animals and plants which have endured far longer. A small brachiopod, the genus Lingula, springs to mind. This animal has endured virtually unchanged since the Cambrian: 500 Ma or so. The fern genus, Osmunda, has been around since the Triassic, when there lived a species virtually identical to the extant O. claytoniana (Phipps et al. 1998). But Lingula and Osmunda have never ruled the world whereas dinosaurs did. Or, more precisely, ruled the land, because dinosaurs never made it into the oceans. The large Jurassic and Cretaceous marine beasts, the mosasaurs and so on, were not dinosaurs.

Dinosaurs as Large Animals

Introduction and Definitions

Possibly the most celebrated feature of dinosaurs, at least as far as the lay public is concerned, is their large size. If one judged from the hype alone, you might think all dinosaurs were very large, that dinosaurs accounted for all large animals during Mesozoic, that they were the only really large creatures ever to live upon the planet, and that nothing comparable lives today.

• Length, which can be measured easily and objectively from any complete skeleton. For example: "The largest head of any dinosaur belongs to the ceratopsian Torosaurus with a massive 2 m long skull" (Carpenter 2002).
• Height, which may require some interpretation of the animals’ life posture, though such reconstructions are likely to be relatively accurate.
• Weight, the estimation of which is more difficult and quite subjective, though some anatomical clues (the size of muscle attachment scars, the size and strength of bones) provide a general indication. At the present state of the art, weight estimates determined by various techniques can easily vary by a factor of three or more. For example, published weight estimates for Diplodocus carnegei range from 5.8 to 18.5 tonnes (Norell et al. 1995, p. 24).

Small Dinosaurs

The smallest reliably known dinosaur is Compsognathus longus, known from the Lower Jurassic (including the famous Solnhofen Limestone) of western Europe, which attained an adult length of only 70 cm, including the tail.

Not much larger is another very small dinosaur, Heterodontosaurus, also Lower Jurassic, known from South African fossils.

Large Non-Dinosaurs

Excerpt from BBC site:

Crocodiles are quite close relatives of the dinosaurs, having evolved from the archosaur ancestors in the Triassic period. Crocodiles have changed very little since then, nearly all being armour-plated, semi-aquatic predators.

Other pliosaurs - Kronosaurus queenslandicus - 9 to 10 metres according to Wikipedia http://en.wikipedia.org/wiki/Kronosaurus

and the as yet unnamed taxon from Svalbard - 15 metres; see

http://www.nhm.uio.no/pliosaurus/english/index.html and http://www.sciencedaily.com/releases/2008/02/080229101002.htm

Sereno’s crocodile - Sarcosuchus or something similar?

An even larger crocodylian ...

By the Cretaceous period crocodiles had become very abundant and widespread. One of the most remarkable of the Cretaceous crocodiles comes from the Rio Grande in Texas. Named Deinosuchus ("terrible crocodile"), this is the largest crocodile so far found. Its skull is 2m in length and if this creature had the proportions of a typical crocodile then it may have attained a length of 15m and weighed around 2 tonnes. Deinosuchus was sufficiently large and heavy to have preyed on sizeable dinosaurs, catching them by stealth as they waded into lakes and rivers to drink.

Toward the end of the Age of Dinosaurs, during a time known as the Late Cretaceous, a new type of giant predator appeared along the southern coasts of North America. It was a huge species of crocodylian and is called Deinosuchus.

Neither a crocodile nor an alligator, it was an ancestor of both modern groups, but it reached weights of many tons and it had some features unique to the species. Average-sized individuals were bigger than the carnivorous dinosaurs with which they cohabited; the largest specimens were the size of a T-rex. This is the biography of these giant beasts, including the long history of their discovery, research about their makeup, and the first published evidence about their prey. Generations of people have stared at the 6-foot reconstructed skull at the American Museum of Natural History in New York, not realising that the only real bones in the specimen were bits of snout and lower jaw. New fossils and research show that the actual animal was quite different from the reconstruction, and now we can reliably assemble the skull and the remainder of the animal. The book also deals with the ancient life and geology of the coastal areas where Deinosuchus thrived, including its competitors and its prey, which likely included carnivorous dinosaurs among its numbers. Since Deinosuchus is found on eastern and western sides of the Great Inland Sea that split North America, it must have crossed this vast seaway during the Late Cretaceous. How and why the crocodylian crossed the seaway is the focus of a key chapter in the book. There is also detailed discussion of the methods used to determine the size of these giant animals, how we can date the fossils and describe their living environments, and why we can be sure who at whom 80 million years ago.

Link to Amazon ASIN= 025334087X</p>< /p>< /p>< /p>

modern blue whales (Balaenoptera musculus)

The Guinness Book of Records lists the largest blue whale ever measured as a 110 foot female taken off South Georgia (Southern Ocean). Although there is a degree of uncertainty about this measurement, there is, however, an undisputed 103 foot female on record.

convert to metres – around 30

Dinosaur Growth

Refer Gramling 2005 and Sander & Klein 2005

Conclusion

Nevertheless, dinosaurs definitely do include some of the largest representatives of any group known. For example, at 14 m, Tyrannosaurus and Gigantosaurus are the largest ever terrestrial carnivores (Carpenter 2002).

Seismosaurus is probably the longest dinosaur known to date, though only incomplete remains have been found. the animal was probably at least 40 metres, and possibly as long as 50 metres. The animal was certainly extremely heavy, also; possibly even heavier than the current record-holder, Brachiosaurus. Weight estimates for Brachiosaurus range from 31 to 87 tons.

Warm Blooded ... or Maybe Not?

Introduction and Definitions

Various sources would have one believe this question is effectively decided one way or the other whereas, in fact, the evidence either way is far from compelling.

But first, what does it mean to be “warm blooded?”

More properly, we should be discussing endothermy (= homeothermy, homoiothermy), the ability of an animal to maintain a constant internal body temperature despite changes in the temperature of its external environment. Mammals and birds are homeotherms. They maintain their bodies at a constant, usually elevated, temperature by conserving heat generated as a result of metabolic activity, particularly in organs such as muscles and the liver. (Adapted from The New Penguin Dictionary of Science, 1998.)

Size Matters?

The co-existence of equally large marine reptiles – Liopleurodon was a euryapsid reptile (Class Reptilia, Order Plesiosauroidea) about 25 metres long; the size of a large dinosaur such as Apatosaurus. That Liopleurodon was certainly cold-blooded, makes it quite clear that it was not necessary for large, Late Mesozoic animals to be warm-blooded, but it doesn’t necessarily mean they weren’t either.

Dinosaurs as Active Animals

One of the articles of faith held by the warm-blooded lobby is that dinosaurs – particularly the very large species – were extremely active, fast and agile creatures. If true, it would probably strengthen the case for endothermy. However, recent research does not always support the fast/agile hypothesis:

The Fossil Heart Debate

Comparative anatomists since the time of Richard Owen have observed that birds and crocodilians have a four-chambered heart and have speculated that such a heart was present in extinct archosaurs as well. Until recently, no direct evidence of the cardiovascular system had been reported in any archosaur fossil. Fisher et al., however, using computerized tomography (CT) scanning, reported the discovery of a four-chambered heart with a single systemic aorta within the chest region of a dinosaur fossil dating from the Cretaceous. Even more surprising, the specimen reportedly was collected from channel sandstones of the Hell Creek Formation, a fluvial setting that rarely preserves soft tissues. Examination by one of us (Rowe) of the specimen in the North Carolina State Museum of Natural Science and examination of the CT imagery, however, lead us to conclude that the object is not a fossilized heart but an ironstone concretion. Such concretions are commonly found in Upper Cretaceous fluvial sediments of the North American western interior, often in association with dinosaur bones.

Response: Rowe et al. speculate that the object that we interpreted as a heart is an ordinary ironstone concretion. A casual inspection of its structure, however, indicates that it is a sandstone concretion, and its occurrence and our more extensive examinations support our original interpretation. ...

CT imaging has allowed identification of structures embedded within the chest concretion that are consistent with the shape, volume, position, and orientation of the more muscular portions of a heart (ventricles and aortic arch). It is logical to suspect that the structures formed the nucleus for the peculiar concretion that surrounds them. Permineralization of the structures is not implied, because organic residues may have initiated the mineralization of cements within the concretion. Time scales of months to tens of years--not millions of years, as Rowe et al. maintain--are common for many types of concretions.

The concretions submitted to museum curators are usually simple shapes (they are often suspected of being fossil eggs) and are seldom subjected to CT scanning to the same extent as the concretion studied by Fisher et al. No tubular structure associated with two contiguous ovoid structures has ever been reported within a concretion in such intimate association with a dinosaur skeleton before. Identification of the object as a fossil dinosaur heart need not assume structural identity with a crocodile heart or the preservation of relatively thin-walled structures. We continue to pursue our investigations of this unusual fossil.

Endothermy as an Apomorphy

established in the Triassic? surely not?

closest relatives - crocodilians - definitely not homeothermic

Conclusion

...

Origins of Birds

Introduction and Definitions

Birds evolved from dinosaurs – another hypothesis which the popular press has adopted as an article of faith when, in fact, the evidence is contradictory and difficult to interpret.

Conclusion

Here again, the evidence is complex and appears, in light of the present state of our knowledge, contradictory. The point to draw is not that the "popular" hypothesis is wrong, but that the jury is still out. Claims that birds arose from the Maniraptora are just Bad Science: we simply do not know. (Read more.)

Extinction

Dinosaurs were certainly very much on the decline towards the end of the Cretaceous; they may in fact have essentially gone extinct as a group before the other victims of the more general Cretaceous-Tertiary mass extinction.

> >"Six locations have now producted Paleocene dinosaur remains, primarily >teeth and more rarely bones, form screen-washed matrix obtained from the >upper part of the Hell Creek Formation, McCone County, Montana. These >fossils are thought to represent primary Paleocene deposition and are not >derived from Cretaceous bank sources..........."

> >I am curious about the disposition of Rigby’s findings. Have his >conclusions received additional attention? Have they been discredited? >Ignored? His extensive field work and lengthy supporting arguments seem, to >this lay person, to be quite convincing.

> >Comments?

Well, I won’t go into too much of the details (since some of the authors on the following research are lurking on the net, and can post more fully if they wish), but here is the general post-1987 take on the "Paleocene" nonavian dinosaurs:

All of the alledged post-Cretaceous dinosaur material are isolated fragments (teeth, bone fragments, etc.) found in channel beds. These could have easily have been washed out of the sediment banks (of Cretaceous age) and redeposited in Paleocene rivers.

None (to my knowledge) of the dinosaur fossils from the Paleocene have been found in lake deposits, nor in aeolian (wind-produced) deposits, nor in nearshore marine environments. No articulated bones (which would imply little-to-no disturbance post-deposition) nor footprints (which would require a living animal to produce) have been found above (or at the same level) as indisputable Paleocene markers (pollen, mammals, etc.).

This all strongly suggests that the material currently described from the Paleocene was all reworked Cretaceous fossils.

However, I don’t think even the most extreme catastrophist thinks that every last individual of nonavian dinosaur was dead by the time all of the iridium dust fell out of the impact blast. If the K-T boundary is defined on the iridium spike, then it is (in my opinion) not unlikely that a few individuals of some of the late Maastrichtian species survived the blast. However, there is no evidence yet of breeding populations of nonavian dinosaurs in the Cenozoic, so the last of their lines may have only made it a few decades into the Paleocene.

Thomas R. Holtz, Jr. tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile Phone: 703-648-5280
U.S. Geological Survey FAX: 703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA 22092
U.S.A.

References

Carpenter, Kenneth 2002 (in press): Dinosauria (Dinosaurs). In Encyclopedia of Life Sciences. Nature Publishing Group, Macmillan.

Chatterjee, S. 1997: The Rise of Birds: 225 Million Years of Evolution. Johns Hopkins University Press, 312 pp.

Chen, P.; Dong, Z.; Zhen, S. 1998: Nature, 391: 147

Feduccia, A. 1999: The Origin and Evolution of Birds. Yale University Press, 405 pp.

Fisher et al. (2000): Science 288: 503.

Gramling, C. 2005: How fast does your dinosaur grow? Science 310: 1751.

Hutchinson, John R.; Garcia, Mariano (2002): Tyrannosaurus Was Not a Fast Runner. Nature 415, 1018 - 1021.

Ji, Q.; Currie, P.J.; Norell, M.A. 1998: Nature 393: 753; Zhou, Z.

Jones, T.D.; Farlow, J.O.; Ruben, J.A.; Henderson, D.H.; Hillenius, W.J. 2000: Nature 406: 716

Jones, Terry D.; Ruben, John A.;Martin, Larry D.; Kurochkin, Evgeny N.; Feduccia, Alan; Maderson, Paul F. A.; Hillenius, Willem J.; Geist, Nicholas R.; Alifanov, Vladimir 2000: Nonavian Feathers in a Late Triassic Archosaur. Science 288: 2202-2205.

Melchor, Ricardo N.; de Valais, Silvina; Genise, Jorge F. 2002: Bird-Like Fossil Footprints from the Late Triassic. Nature 417: 936-937.

Norell, Mark A.; Gaffney, Eugene S.; Dingus, Lowell 1995: Discovering Dinosaurs. Little, Brown and Company, 204 pp.

Ostrom, J. H. 1996: The Questionable validity of Protoavis. Archaeopteryx 14: 39-42.

Phipps, C.J.; Taylor, T.N.; Taylor, E.L.; Cuneo, N.R.; Boucher, L.D.; Yao, X. 1998: Osmunda (Osmundaceae) from the Triassic of Antarctica: an example of evolutionary stasis. American Journal of Botany 85: 888-895.

Sander, P. Martin; Klein, Nicole 2005: Developmental plasticity in the life history of a prosauropod dinosaur. Science 310: 1800-1802.

Xu, X.; Tang, Z.; Wang, X. 1999: Nature 399: 350

Xu, X.; Wang, X.; Wu, X. 1999: Nature 401: 262

Yu, Mingke; Wu, Ping; Widelitz, Randall B.; Chuong, Cheng-Ming 2002: The Morphogenesis of Feathers. Nature 420, 308 - 312

Zhang, Fucheng; Zhou, Zhonghe 2000: A Primitive Enantiornithine Bird and the Origin of Feathers. Science 290: 1955-1959.

Zhou, Z.; Wang, X. 2000: Vertebr. Palasiat. 38: 111