Dinosaur nose mystery resolved?

Popular animations of dinosaurs in Jurassic Park and Walking with Dinosaurs are palaeontologically speaking “state of the art”.  That is, except for the beasts’ noses.  A close observer will have seen Tyrannosaurus and Triceratops with nostrils high on their snouts, and appealing brachiosaurs apparently breathing through the tops of their heads.  Such reconstructions rely on the position of the nasal passages where they enter the skull, and in dinosaurs such bony nostrils are large and complicated.  Traditionally, dinosaur reconstructors have gone for the rear of the cavity for the positions of the fleshy nostrils.

Despite their extinction at the end of the Cretaceous Period, dinosaurs have many living close relatives, such as birds, crocodiles and some primitive lizards.  All of them have fleshy nostrils situated at the front of the bony openings.  For that matter, so do mammals.  For several years Lawrence Witmer of the College of Osteopathic Medicine at Ohio University (Athens) has been pondering on this, even setting up the DinoNose project.  Not only did Witmer apply the principle of parsimony to this intriguing issue, but noted the marks left on skulls by the blood vessels that supply the muscles that enable land vertebrates to snuff the air in many interesting and useful ways.  Such marks appear on dinosaur skulls, towards the forward end of the nasal openings.  The outcome is a fundamental revision of  dinosaur physiognomy (Witmer, L.M. 2001.  Nostril position in dinosaurs and other vertebrates and its significance for nasal function.  Science, v. 293, p. 850-853).  The next logical step is to seek signs that carnivorous dinosaurs did indeed snarl.

Cambrian Explosion:  Shropshire hits the news

As if by magic, nearly all animal phyla suddenly appear in the fossil record around 545 Ma, at the base of the Cambrian period.  The most famous of these are trilobites, a group within the phylum Arthropoda, for enthusiasts of which the Cambrian of Shropshire has long been a happy hunting ground.  Temporary excavations into the Protolenus Limestone of Comley have revealed a somewhat diminutive, though nonetheless startling relative that helps resolve the long-running debate over the origins of animals (Siveter, D.J., Williams, M. and Wlaoszek, D.  2001.  A phosphatocopid crustacean with appendages from the Lower Cambrian.  Science, v. 293, p. 479-481).  Superbly preserved in calcium phosphate, the tiny beast reveals great detail of its body parts, peeping from between a two-valve, spherical carapace.  It is possibly an early ostracod, and certainly a crustacean.  That such an advanced arthropod occurs close to the base of the Cambrian lends support to the view that animal diversification into extant phylla, and some vanished ones too, may have gone on far back into the Neoproterozoic.  The other view is that this radiation was explosive, beginning only 10 Ma or so before the base of the Cambrian.

The “long-fuse” hypothesis for the emergence and diversification of the animals is also supported by differences in the molecular biology of distantly related modern animals.  Assuming that accumulation of genetic change is steady, and can be calibrated by the coexistence of such groups as far back as the Cambrian, the “molecular clock” for animals probably started between 700 to 1500 Ma ago.  The problem, of course, is that only animals with hard parts or which miraculously had soft tissue rendered preservable by mineralization can assist palaeobiologists resolve the issue.  That is unfortunate, as such fossils occur only after about 5 Ma before the start of the Cambrian, and the large ones are exclusively Cambrian or younger.  The “explosion” was the sudden appearance of skeletal material, using calcium compounds such as carbonates or complex phosphorus-bearing material.  Such is the fascination with the detail of phyllogeny, that the trigger for the explosive emergence of hard parts is often overlooked.

See also:  Fortey, R.  2001.  The Cambrian Explosion exploded?  Science, v. 293, p. 438-439.

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