Shape shifting dinosaurs: the cause of premature extinction - Jack Horner 2011

Shape shifting dinosaurs: the cause of premature extinction - Jack Horner 2011

1. Fascination with dinosaurs?

   • big
   • different
     • Morphologicaly
       • Used to define different species
         • Limitations
           • Museums
             • Bones precious
               • Barrier to cutting open bones
             • Ego
               • Find the biggest and best dinosaur possible
                 • New species by size and morphology
               • Want to name a new dinosaur
                 • Origonal name sticks, second name gets thrown out
                   • Torosaurus now triceratops
                   • Anatatitan becomes Edmontosaurus
   • Extinct

2. 1970

   • Where are all the juveniles?
     • Assumed that juveniles would be easily identified
       • Anything that looked a little different got named as a new dinosaur

3. 1975

   • Dr. Peter Dodson - University of Pennsylvania
     • Growth in dinosaurs is more like chicken and less like reptiles
       • Allometric (relative) Cranial (skull) Ontogeny (growth)
         • Example: Cassowary
           • Birds with crests grow to around 80% before the crest starts to grow
             • Retention of juvenile characteristic well into ontogeny
               • Looks like two different species
             • REFERENCE :
         • Relative skull growth
         • Example: Hypacrosaurus
           • If it grew in a linear fashion it would have a crest around half the size of the adlut

4. Hell creek formation

   • Produces last dinosaurs

5. Dinosaur species - Skulls that change shape during ontogeny

   • Pachycephalosaurs, Stygimoloch and Dracorex
     • Cant determine relationship fully by looking at morphology
       • Spike on Dracorex are growing, spike on Stygimoloch are reabsorbing and dome is growing and Pachycehalsaur dome is solid and spikes are still reabsorbing
         • Easy to hypothesize that this is a growth series but need evidence
   • Triceratops
     • Horner and Goowdin 2006 - Major cranial changes during triceratops ontogeny : http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1635501/
       • Juveniles grow horns grow backwards and then start to grow forwards and the triangular spikes along the frill as juviniles flatten out when they are older
       • Cut open the skulls and found degree of sponginess relative to age. Smallest skull is spongy, intermediate was spongy however largest one is spongy also.
         • Torosaurus - 3m long skull looks like triceratops but has mature bone
           • Has holes in its frill.
             • John Scannella 2010
               • 5 questions for John Scannella http://www.britannica.com/blogs/2010/09/torosaurus-is-triceratops-5-questions-for-paleontologist-john-scannella/
               • Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): Synonymy Through Ontogeny http://www.bioone.org/doi/abs/10.1080/02724634.2010.483632
               • Hole starting to form in triceratops and shows as open in Torosaurus. Also found transitional skulls
                 • ‘Nedoceratops’: An Example of a Transitional Morphology 2010 - http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0028705
           • No juvenile Torosaurus found to date
   • Anatatitan is a juvenile Edmontasaurus
     • Cranial Growth and Variation in Edmontosaurs (Dinosauria: Hadrosauridae): Implications for Latest Cretaceous Megaherbivore Diversity in North Americahttp://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0025186
   • T-rex and nanotyranus
     • Nano had 17 teeth has juvenlie bone, tyrannosaurus had 12 and more mature bone
       • Less teeth as they get older
         • Dinosaur Census Reveals Abundant Tyrannosaurus and Rare Ontogenetic Stages in the Upper Cretaceous Hell Creek Formation (Maastrichtian), Montana, USAhttp://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0016574

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