Sunday, November 20, 2011

SVP 2011 Roundup - Crocodylomorph Edition Part 3

Crocodylomorph Morphology and Systematics
(in order of presentation)
"Comparative morphometrics and phylogenetic perspectives on the morphospace of the crocodyliform skull." Wilberg, E.
  • presents a quantitative approach for assessing skull shape in Crocodyliformes (helping to avoid subjective intermediate assignments)
  • compared multiple methodologies for comparing skull shape
    • 2D geometric morphometrics (homologous landmarks and sliding semi-landmarks) - results suggest 3 or 8 shape categories
    • Eliptical Fourier Analysis (EFA) of skull outlines - results suggest 3 shape categories
  • overall skull shape should not be used as a discrete character in phylogenetic analyses, but can help in evaluating ecological and functional trends within claes
"Evolution of the otic region of fossil Crocodyliformes." Montefeltro, F. and Larsson, H.
  • terrestrial taxa - large, more vertical otic apertures and recess, relatively large tympanic membranes
    • notosuchians show the most extreme expansion of the otic region and well developed scar for the attachment of the tympanic membrane = very good hearing
  • semi aquatic and aquatic taxa - reduced otic apertures and tympanic membranes
    • extreme reductions in Metriorhynchidae = hearing may have been insignificant
  • quadrate fenestra may have played a role in hearing

"Crocodyliform aquatic locomotion and axial flexibility: comparative vertebral anatomy of mesoeucrocodylians." Felice, R. and O'Connor, P.
  • quantified vertebral metrics to evaluate whether crocodylians possess specialized skeletal morphology associated with a semi-aquatic lifestyle
  • terrestrial taxa - dorsal centra are about as wide as they are tall
  • semi-aquatic taxa - dorsal centra are wider than tall
"Jaw mechanics of crocodiles reveal their fast mastication." Suzuki, D., Hayashi, S., Chiba, K., and Tanaka, K.
  • observed movement of the cartilago transiliens (CT) in the musculus pterygoideus anterior (MPA) in extant crocs using CAT scans
  • the CT retains a rough surface on the lateral wing of the pterygoid, making it useful for studying fossil taxa
  • MPA moves the CT anteriorly = rapid jaw closure
"Phylogenetic patterns, homoplasy, and the evolution of the antorbital fenestra in Crocodyliformes." Leardi, J., Pol, D., and Fernandez, M.
  • phylogenetic analysis to evaluate the pattern of character evolution of the antorbital fenestra
  • closure of the antorbital fenestra occurred independently up to 8 times within Crocodyliformes (mostly in Mesoeucrocodylia)
  • antorbital fenestra independently reappears in some notosuchians (possibly in basal thalattosuchians)
  • suggests that the antorbital fenestra in Crocodyliformes is extremely homoplastic
"Fleshing out the neosuchian tree: a reevaluation of the crocodyliform Shamosuchus from the Cretaceous of Asia." Turner, A. and Brochu, C.
  • Shamosuchus is important in understanding the character changes occurring at the origin of Eusuchia
  • reevaluation of Shamosuchus species reveals only three valid species: S. djadochtaensis, S. gradilifrons, and S. ancestralis
  • results suggest a diverse Shamosuchus clade in the Cretaceous of eastern Asia
"Cranial anatomy and osteology of Gavialis gangeticus using computerized axial tomography: implications for gavialoid phylogeny." Gold, M.
  • ontogenetic changes in gharials are likely obscuring data
  • description of the cranial anatomy of a hatchling G. gangeticus based on CT data
  • reveals numerous ontogenetic of the skull and braincase
  • morphological data seem to support the molecular data, that certain plesiomorphiuc states in   are secondarily reversed
"A geometric morphometric analysis of Crocodylus niloticus: osteological evidence for a cryptic species complex." Nestler, J.
  • geometric morphometric analysis of the variation in the skull of C. niloticus
  • variation in population in broadly based on river basins
  • at least 3 distinct populations within the species with at least 2 being more distinct from each other than from other members of the species (and at least one may be endangered) = cryptic species complex, supporting molecular data from previous studies
  • paleontology can inform on conservation and issues of diversity
"The evolution of exoskeletal ossifications in notosuchian crocodyliformes." Hill, R. and O'Connor, P.
  • most notosuchians show a general trend toward the reduction of dorsal osteoderms along with the expansion of the caudal osteoderm shield
  • general trend towards the reduction of surface ornamentation in favor of increased internalization
  • Pakasuchua - most extreme reduction of osteoderms; robust articulating shield of osteoderms surrounding the tail; reduced osteoderms around the dorsosacral transition; presence of ossified tendons (first reported in Crocodyliformes)
  • osteoderm reduction trend in notosuchians may be associated with decreased body size and terrestrial habitat

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