Friday, August 25, 2017

SVP 2017 - Day 3

And now for the third day at the Society of Vertebrate paleontology. Apologies as this post is a bit shorter than the others due to a large number of the talks I attended being either embargoed. Take that as meaning that there's a lot of really amazing secret papers getting published soon. ;)

Morning Sessions

  • Herrera-Flores: The rates of different morphological tooth and jaw forms in squamates change over time, but the highest diversity of tooth forms didn't appear until the late Cretaceous.
  • Herrera-Flores: Mosasauroids possess the largest disparity of tooth and jaw forms of all squamate groups tested. Suggests they utilized a wider range of feeding methods than seen in modern lizards.
  • Campbell Mekaraki: Throughout history there have been lots of phylogenies of the induvidual families/groups of pythonomorphs (mosasaurs, snakes, aigialosaurs, and dolichosaur), but few if any studies looking at all pythonomorphs together, which causes some confusion about how they’re all related to each other and whether the groups are actually natural. This is one of the first phylogenies putting all the groups together, but sadly since the character list largely stemmed from specific pythonomorph group characters, the phylogenies were not able to accurately determine with high certainty the relationships of all the different taxa. Further studies need to find more robust characters to better determine relationships.
  • Campbell Mekaraki: Nonetheless, despite high uncertainty, a number of common trends appeared in the phylogeny. Mosasauroids showed up as polyphyletic, with russelosaurines and mosasaurines being giant aigialosaurs which independently evolved open-ocean aquatic adaptations and gigantic size (something also seen in other studies). Dolichosaurs might also be polyphyletic, though many taxa also group together within aglialosaurs, although one unnamed dolichosaur taxa fell consistently within derived tylosaurines. (This specimen is apparently notorious for doing this in phylogenies.)
  • Campbell Mekaraki: This phylogeny found two positions for snakes. Option one has them as the sister group to mosasaurines and mosasaurine-line agilosaurs, meaning that they're aigialosaurs and mosasauroids. The second option shows them splitting off from the new mosasauroid + aigialosaurs + dolichosaur group. The former seems less likely.
  • Augusta: Dolichosaurus falls within the genus in Coniasaurus in recent phylogenies, suggesting it should be synonymized. This is a problem because the two genus were named in the same year and same publication by the same author on the same page, so you could choose either as the owner of the new name as ICZN rules don't apply. Authors propose sinking Dolichosaurus and keeping Coniasaurus as the latter has a larger number of papers dedicated to it, as well as more species in its genus.
  • Papparella: Plesiopelvic (back-swept ilium) vs hydropelvic (forward-swept ilium) conditions in mosasauroids. The authors make a (rather controversial) claim that the forwards-oriented bone of the pelvic in hydropelvic mosasaurs often though to be the main illium shaft is actually derived from a separate projection of the illium. Using a traditional phylogeny, this hydropelvic condition evolved at least 3 times independently in the group. 
  • Ramezani: New specimen of Buriolestes from Santa Maria with a complete 3D skull and complete braincase. This allowed for a good reconstruction of the endocast, which shows close similarities to other sauropodomorph dinosaurs.
  • Ramezani: A new type of early dinosaur from the same region. Unsure about what exactly it is.
  • Ramezani: New very well-preserved articulated herrerasaurid specimen still being prepared. Might be a new species.
  • Ramezani: Janner Site of the Santa Maria formation has produced a specimen of a much larger sauropodomorph. Pending analysis. Might be new species.
  • Ramezani: Large block including 4 sauropodomorphs preserved together. Again, might be a new taxon.
  • Breeden: Unnamed silesaurid taxa from the Hayden Quarry. Lots and lots of material has been found since the first specimen in 2007. Seems to be the same thing as Eucoelophysis, and groups together with it in phylogenies.
  • Habib: Azhdarchids = “Giant awesome murder heads.”
  • Habib: Albertan azhdarchid currently housed at the Royal Tyrrell museum was suggested to be Quetzalcoatlus, but actually seems to be a new taxa. Represents a robust, short-necked pterosaur morphology otherwise only known from Romania, showing that this morphology is more widespread than thought. Will be named and described soon.
  • Habib: Big heads of azhdarchids might seem to be bad at flight (tips forwards the center of mass, makes them front-heavy), however, they do create a major advantage for azhdarchids. Big heads allow better ability for pterosaurs to utilize "forward sweep," which is caused when the tilting of the forwards of the body causes the wings to flap in a more forwards-backwards pattern, moving air both over the wings and directing the air on the tip of the wings towards the body. This produces dynamic and powerful lift at the cost of some slight stability control, which azhdarchids could easily accommodate.
  • Mannion: Average completeness and number of species of crocodylomorphs is noticeably affected by extinction events, like the K-Pg extinction.
  • Drymala: New quadrupedal pseudosuchian taxa (NCSM 21722). Head sadly eroded away, but it eroded along the midline allowing for analysis of the internal structure of the skull. Has simple osteoderms along the back, tiny heart-shaped osteoderms along the underside of the tail, and elongate, slender osteoderms under the neck.
  • Drymala: Possesses a semi-oposable reverse hallux on the underside of the forelimb. Unsure what this strange configuration is for: not known from close relatives. Pops up as the sister taxon to Dromicosuchus, which is from the same basin but a different layer.
  • Foffa: New specimen of a metriorhynchid (NHMUK PV OR 46797 - “the Melksham Monster”) possessing a deep and robust jaw and a poorly ornamented skull, both of which are unusual traits for middle Jurassic metrioryhnchids. Teeth also very closely resembles Geosaurus, and falls as a sister taxon to that genus, making it the earliest known member of Geosaurini and the earliest macropredatory metrioryhnchid.
  • Voegele: Partially articulated juvenile Thoracosaurus found in a marine environment. Preserved cell and microstructure tissue.
  • Hastings: High reptile diversity from a miocene marine faunal deposit in Virginia. Five adult Palaeophis virginianus vertebrae; 41 crocodilian teeth, vertebrae, and large osteoderms (seems to come from Thecachampsa, one tooth suggests a large animal in excess of 5 meters); and representatives of the main modern sea turtle branches are present.
  • Lichtig: Turtle trackways are very distinctive due to their awkward gait. The earliest known turtle trackways predate the earliest known turtle fossils by many millions of years and could be used to determine the evolutionary history of turtle gait.
  • Wu: Two new skulls of ‘Tomistoma’ petrolica allowed for a better understanding of its skull morphology, as well as comparison with the modern Tomistoma schlegelii to find out its phylogenetic position. Phylogeny does not support a sister relationship between this taxa and the modern type species, presenting the need to erect a new genus.

Poster Sessions

  • Ryan: New centrosaurine ceratopsid from the Upper Oldman Formation. Phylogeny has the taxon come up as the sister to Coronosaurus.
  • Mallon: Ankylosaurs in North American ecosystems are frequently found in upside-down positions (70% of cases). The high rate of flipped-over specimens seems to be due to water transportation of dead individuals and bloating on the surface of the water during decomposition. While bloating, their heavy osteoderms (and in ankylosaurids, heavy tail clubs) leads to specimens flipping over while ballooning across the surface of the water. This is also consistent with depositional environments: ankylosaurs in Asia are often found preserved in dry regions, and thus are preserved upright without the high rates of flipped specimens. This is also similar to the high flipped rates seen in preserved glyptodont shells, which presumably also were transported by water and bloated before flipping.
  • Heckert: Smallest known aetosaur specimen. Might be a hatchling. Shows that juveniles have much more elongate and gracile limbs than adults, and that the osteoderms are present but not fully ossified.
  • Vinther: Borealopelta shows counter-shading levels consistent with open habitat preference. This makes sense given both the coastal environments of Laramidia at the time and the fact that the shoulder spikes and wide builds of many nodosaurs would have made it difficult to traverse dense forests.
  • Laing: New shuvusaurid taxa from the Hayden Quarry in the Chinle formation. Doubles the diversity of shuvusaurids at the time and shows early crocodilians filled bipedal herbivorous niches before many dinosaurs (like ornithischians).

Afternoon Sessions

  • Kundrat: First known case of alvarezsaurid eggshells and associated skeletal remains from the northern hemisphere. The chinese fossils shows an eggshell microstructure different from other known alvarezsaurid eggs and suggests northern hemisphere alvarezsaurids had different types of eggs than the larger southern hemisphere members with eggs preserved.
  • Funston: New oviraptorids. Specimens poached. Has a large crest composed of the nasal and prefrontal bones. 3rd digit is highly reduced while the first digit is very enlarged, a trend seen in other oviraptorids.
  • Funston: Another separate specimen is extremely small, has an unfused braincase and an unfused pygostyle. Despite this, it still has a rather large crest present. In the same pose as the three from the same block.
  • Funston: Fifth specimen is an adult. Has a fused pygostyle.
  • Funston: Smallest specimen is 33kg and the adult is 74kg. All the juvenile specimens are sitting in a sleeping position like Mei.
  • Funston: Sleeping individuals buried in a flood, not a sandstorm or “red beds” environment. Did not seem to be killed by a flood though: probably killed by exposure and buried by water later. Suggests communal roosting might be a basal trait for pennaraptorans.
  • Funston: Bad news for lumpers: even young oviraptorid individuals for this species have large, well-developed crests. Suggests species of oviraptorids known from only juveniles that lack crests actually do come from taxa that are crestless when mature.
  • Torices: Differently-shaped denticles in theropods suggest different dietary and tearing methods in different taxa. This analysis was used to determine how denticles affect tooth strength/shape.
  • Torices: Microwear shows that pretty much all predatory non-avian theropods are good at a “grip and rip” feeding styles, but different groups are better than others when it comes to stresses. Troodontid teeth and denticles are really bad at taking on stresses, Saurornitholestes is moderately good, and Dromaeosaurus is extremely good at absorbing stresses. This suggests that although all are of similar in body builds, troodontids were limited to feeding on small and/or soft pretty that couldn't fight back, Saurornitholestes were focused on medium-sized but still rather soft prey, and Dromaeosaurus was focusing on tougher, larger prey that puts up a fight.
  • Xing: Ossification rates in the sternum of small dromaeosaurids can be used to determine ontogenetic stages. Species with arboreal and gliding/volant habits might have developed ossifications earlier.

And there you have it. Tomorrow's the last day of SVP, and while I'll try to get another blog post out tomorrow night, I need to go to the dinner reception and prepare for an early flight the next morning, so final entry might get pushed back. Until next time, root for this poor little chelonian to escape the jaws of the Protosphyraena. Cheers!

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