Halszkaraptor and what it means for Dromaeosaurids

Halszkaraptor escuilliei by Joschua Knuppe

Today saw the announcement of one of if not the biggest dinosaur discovery of 2017: the description of Halszkaraptor escuilliei, a small, semi-aquatic fishing dromaeosaurid from Mongolia. Yes, seriously, swimming raptors. Not only is this inferred to be a fish-eating animal (With ISOs to boot!) but the specimen preserves a flattened forelimb that forms a paddle-like hand, and its proportions cluster with wing-propelled diving birds and marine reptiles in morphometric analyses. This thing is a true aquatic swimmer, and basically what happens when a raptor dinosaur copies a penguin or auk.

But while I could go on and on about the anatomy and what that means for the biology of this interesting taxon, I'll refrain from that here because, in all honesty, it's gonna be talked about everywhere else by people better-equipped to talk about it than me. Instead what I'll be talking about here is the new subfamily, halszkaraptorines, and their placement among other dromaeosaurids. The newly-founded members of this subfamily include the aforementioned Halszkaraptor escuilliei, the similar but incomplete Mahakala omnogovae, and the fragmentary Hulsanpes perlei, known only from a foot and partial braincase. All of these taxa seem to be from inner Mongolia (though note that Halszkaraptor's exact location of origin is unknown), but there's fragmentary material of what might be more specimens from Canada. The incomplete nature of Mahakala and Hulsanpes make it difficult to figure out if they have all the same aquatic adaptations as Halszkaraptor, but what we do know of them is that they're similarly small-bodied and long-legged dinosaurs with short forelimbs. Mahakala might even preserve a similar paddle-like morphology of the forelimb, but it's difficult to tell without more material.

Traditional dromaeosauridae is made up of three groups: the thin-snouted and long-legged unenlagiinae of the southern continents; the mostly small-bodied, winged microraptorines; and the extremely popular macropredatory eudromeosaurines (which are split up further into velociraptorines and dromaeosaurines). Halszkaraptorines are right at the base of all other groups as the earliest-branching dromaeosaurids, and thus some parts of their anatomy might be a decent example of what the ancestral dromaeosaurid looked like. But here's the thing: as you move from them up the tree closer to eudromaeosaurs, an interesting pattern emerges.

Phylogeny from Cau et. al. 2017 with added taxa notes.

According to this phylogeny, dromaeosaurids start out as short-armed, long-legged taxa, something akin to terrestrial storks, and presumably feeding on small prey items like fish and small vertebrates before developing longer forelimbs, shorter legs, and boxier skulls. The two basalmost groups, halszkaraptorines and unenlagiines, both show adaptations for aquatic feeding, and even further up the tree Microraptor shows direct evidence of fish-eating. So three out of the four major divisions of dromaeosaurids show evidence of piscivory.

Would this suggest that all dromaeosaurids came from a piscivorous or stork-like, long-legged ancestor? I wasn't the only person to suggest this, as some of my friends came to a similar conclusion after reading through the paper. If this is the case then what does that mean for evolutionary models, particularly involving the origin of birds and flight, like the neoflightlessness hypothesis? Is a long-legged, short-armed body form ancestral to paravians? Troodontids also have this kind of bodyplan and they're even closer to birds in most recent phylogenies. If non-eudromaeosaurian dromaeosaurids are engaging in extensive fish-eating, then would the shift to eudromaeosaurs be a shift from fish-eating to macropredation, similar what's seen in some birds and marine mammals? Certainly there are a lot of interesting perspectives to think about going forward.

This was a short post but I hope it'll help everyone realize just how bizarre and fascinating this new little theropod is. I hope it and its relatives get a lot of love and attention from theropod workers, and hopefully new members of its subfamily will start popping up now that people know what to be on the lookout for.

Until next time, stay sharp!

SVP 2017 - Day 4

And now for the final day at SVP 2017.

Morning Session

• Baron: Baron's not convinced by his own current classification of Ornithoscelida: actually thinks ornithischians are within Neotheropods or possibly Averostrans. (The world’s gone mad!)
• Baron: New data on Pisanosaurus has it as a silesaurid in their analyses: actually supports his idea that they're averostrans as that would mean we shouldn't find Triassic ornithischians at all as they would have to originate in the early Jurassic. (The same time we start finding the earliest averostrans.)
• Baron: Ceratosaurs show close similarities to ornithischians, such as the form of the illium, the shape of the femoral head, and their vertebrae. Some ceratosaurs even have ossified tendons in their back vertebrae, a feature typically associated with ornithischians.
• Baron: Chilesaurus comes up as a ornithischian in their phylogeny. They got criticism as they didn't include any derived tetanurans in their analysis, but the original Chilesaurus paper lacked any ornithischians for it to group with either. They're going to add more derived taxa in future phylogenies to better test this, as well as fix and increase their character list to see how things change.
• Baron: If Baron's right, this would mean that any "theropod" that isn't an Averostran (Coelophysis, Dilophosaurus, Tawa, etc) aren't theropods, as the definition of theropod is anything closer to Passer/Allosaurus than Triceratops and Diplodocus, and they'd be from before the Allosaurus-Triceratops split. Instead they'd be proto-Ornithoscelidans.
• Regalado Fernández: "Prosauropods" are still paraphyletic, but different nodes form independent monophyletic families that are pending descriptions/naming. Suggests numerous monophyletic groups of sauropodomorphs rather than a single lineage leading to sauropods.
• Regalado Fernández: Phylogeny suggests that quadrupedality arose twice within sauropodomorphs: within the riojasauridae (which is getting expanded) and Anchisauria.
• Holwerda: New updated phylogeny on basal sauropods has Patagosaurus is sister to Cetiosaurus, an interesting discovery as the mid-Jurassic Gondwanan desert was often thought to be a barrier to north-south dinosaur taxa.
• Moore: New phylogeny shows mamenchisaurids are a natural group, but Omeisaurus comes up as the basal-most diplodocoid. Weird.
• Waskow: Mother’s Day Quarry diplodocid specimens come from extremely small adult diplodocids. Seems to represent a population of Morrison diplodocids trapped on an island in the middle of the Sundance Sea, though this is debatable given that no large islands are known from the Sundance. Shows that diplodocids also underwent dwarfism like some macronarians.
• Waskow: Long bone histology suggests that they reached skeletal and sexual maturity at the same time as other much larger diplodocids, but that they grew at a much slower rate.
• Bansal: Sauropod ossified tendons in the neck were flexible enough to allow for movement, but stiff enough to support the weight of the neck. Future analyses of how these ossified tendons work structurally in the neck could give new insight to their biomechanics.
• Button: Morphospace analyses of the lower jaws of herbivorous dinosaurs reveals repeated trends in dinosaur skull shape evolution, suggesting specializations in different gut-processing herbivorous taxa. However, while (traditional) saurischians had a large disparity in skull shape, ornithischians all tended to cluster in the same area of the diagram. This suggests that while non-chewing saurischian taxa needed to modify the shape of the jaw to feed on specific types of plants, ornithischians could feed on their wide range of food types via chewing without the need to modify their jaws.
• Nabahvizadeh: Jaw muscles in palatal-feeding ornithischians connected from underneath the jugal to the lateral dentary ridge. This brings the jaw musculature attachment further forwards on the dentar, and is a trait seen in some modern palatal-feeding lizards and extinct dicynodonts. Also implies that many palatal-feeding ornithischians might have had stronger bite forces than expected.
• Godefroit: Kulindadromeus is a thing. Analysis of filaments show numerous similarities with those of Sinosauropteryx. Support a homology with feathers.
• Godefroit: Kulindadromeus is the oldest dinosaur with feathers: the quarry is Aalenian-Bathonian rather than Oxfordian. Earliest known feathers occur on an ornithischian.
• Bell: Numerous small ornithischians from Lighting Ridge. One tooth represents a large Muttaburrasaurus-like taxon: tooth ridges are very similar to that taxa. Another large iguanodontian skeleton from Lightning Ridge represents one of the most complete iguanodontians from the continent. Might be same taxa as the tooth, but the front-half and jawline of the skull from the new specimen is missing, so impossible to tell..
• Bell: Two more small-bodied taxa represented by limb bones and jaw fragments.
• Bell: New dating analyses find Lightning Ridge to be late Cretaceous (Cenomanian, 96 mya).
• Wilson: “Rubeosaurus” is a junior synonym of Styracosaurus ovatus. Holotype bones are misidentified.
• Fowler: “Dannyceratops” (not official name, name of quarry) represents the earliest known of chasmosaurine taxon. Shows a lot of synapomorphies not seen in later taxa.
• Fowler: “Judiceratops tigris” has a lot of issues in terms of supposed phylogenetic relationships and form of the frill. Should be re-analyzed as the frill fragments don't fit well together like other ceratopsians, so they might be misidentified.
• Zheng: New basal ankylosaurine dinosaur with an elongate nodosaur-like snout and a large tail club from Eastern China. Shows a strange mix of both basal and derived features.
• Arbour: Zuul! Zuul’s tail club osteoderms are asymmetrical. Ankylosaur tail club knobs are actually quite taxonomically distinct and have good characters for phylogenies. Might suggest sexual selection was heavily at play in ankylosaurs tail club evolution.
• Arbour: Zuul has lots of skin and keratinous sheath preservation over the osteoderms. Skin is similar to other ankylosaurs: keratin sheaths are so well preserved you can see growth rings like you might see on a cow's horns.
• Arbour: Zuul #2! Second Zuul specimen from a smaller individual found in collections. Despite being only slightly smaller, it has an unfused postorbital horn, something typically seen in very young ankylosaurs. Rest of the specimen might be at the Zuul quarry.
• Brown: Borealopelta has really thick keratinous sheets over its bony armor. Keratin reaches out way past the bony cores. Suggests we might be severely underestimating the size of nodosaur spikes (and keep reading).
• Brown: Longest disparity of bony osteoderms size vs keratin length and width takes place on the cervicals. The keratin-to-osteoderm ratio is strictly allometric, the longer the induvidual bony spines of the osteoderms, the longer in proportion the keratinous sheet that covers it. Rough length of the keratinous sheets in Borealopelta can be determined via an equation. (Maybe could also be used for other ankylosaurs?)
• Brown: There's one exception to the above rule: the parascapular spine is much, much larger than determined by the equation. The keratinous sheet is many degrees larger than those on any of the other osteoderms, and a cross-section through the spine shows the largest bony osteoderm on Borealopelta as a tiny little circle within the thick keratinous covering.
• Brown: The allometric levels in the osteoderm-keratin length is consistent with a sociosexual display features (like horns and antlers) rather than defensive features like anti-predator spines. Supports the idea that nodosaur spines were involved in (and perhaps the evolution of which was primarily driven by) sexual selection.

Poster Session

• Brougham: Two new theropods from Lightning Ridge. One is vertebral and pelvic material from a large carcharodontosaurian taxa, the other is vertebrae from a small-bodied ceolurosaurian taxa. Neither groups show synapomorphies shared with megaraptorans, suggesting a larger diversity of theropod groups were present in the late Cretaceous of Australia.
• Lockley: Trackways from the Kayenta Sandtone near Moab, Utah show strict differentiation between ichnotaxa. One site area is associated with an exclusively Eubrontes-Kayentapus fauna representing exclusively large theropods. Site nearby but in the same layer shows Anomoepus-Otozoum ichnofauna representative of exclusively herbivorous dinosaur taxa. Suggests differences in habitat preferences between herbivorous and carnivorous dinosaur groups at these locations.
• Simon: New species of small-bodied Fumicollis-like hesperornithine from the Hell Creek formation. It's from the Bone Butte region (same location as the Dakotaraptor holotype).

Afternoon Session

• Berrett: Reanalysis of the Vulcanodon Quarry suggests the site is actually Hettagian or Sinemurian in age, making it much older than originally thought.
• Berrett: First phytosaur from Gondwana found in some older Triassic sites nearby. These new sites are filled with wood and has giant lungfish teeth the size of a human hand. Seems like a densely wooded environment similar to the petrified forest in the Chinle.
• Berrett: Interestingly, the new site preserves no evidence of sauropodomorph dinosaurs, despite being known from drier layers below and above it. This as well as the near-absence of early sauropodomorphs from Triassic sites representing well-watered forests might signify that they specifically avoided these kinds of habitats.
• Smith: New material from the holotype specimen of Cryolophosaurus, as well as a second specimen that’s quite a bit larger. Sadly the larger specimen is very fragmentary.
• Smith: Braincase allows for a good reconstruction of the neural anatomy. Dorsal vertebrae have little “bow tie” formations on the neural spines: very cute.
• Smith: New phylogeny suggests Cryolophosaurus is the sister taxa to Dilophosaurus in (interestingly) a monophyletic coelophysoidea.
• Fabbri: All the bones in the Ibrahim "neotype" specimen of Spinosaurus are incredibly dense. Also, all are of the same ontogenetic age: subadult 17 years old. Is against the idea of this specimen being a chimera.
• Fabbri: Ibrahim's Spinosaurus has incredibly dense bones, and the density levels of Spinosaurus bones clusters strongly with semi-aquatic birds and alligators, not with terrestrial birds and other theropods.
• Fabbri: Suchomimus shows up on the graph as having very dense bone, intermediate between “normal” theropods and subadult crocodilians. Still had an open medullary cavity, but the bone is densening. Suggests spinosaurids other than Spinosaurus might have already been experimenting with aquatic behaviors.
• Fabbri: Juvenile animals have less dense bones than adult ones. A juvenile specimen of Suchomimus clusters with birds, theropods, and baby crocodilians while the adult/subadult Suchomimus clusters in its intermediate spot. Similarly, while the subadult specimen of Ibrahim’s Spinosaurus groups with subadult alligators, larger isolated neural spines from elsewhere in Africa are even denser and cluster further into the center of aquatic taxa.
• Fabbri: Peramorphosis is involved in the evolution of spinosaurid skulls: shows numerous similarities in the changes to the skull bones to the evolution of bird beaks.
• Samathi: Two new species of megaraptorans. Taxon A is shorter than a man and only known from a tibia. Taxon B is known from limb elements and vertebrae from both an adult and juvenile individual. Adult is about human-height, juvenile the height of coyote. When plugged into a number of existing phylogenies these new taxa come up as close relatives of Australovenator no matter which is used. The phylogenies also find Datanglong to be a megaraptoran and Siamotyrannus to nest within early coelurosaurs.
• Bykowski: Homogenous global data set suggests that carnivorous dinosaurs were not responding to changes in prey body size. Instead, taxonomic turnover is driving morphological changes in different groups.
• Fiorillo: Alaskan dinosaur trackways from along a forested shoreline. Lots of hadrosaur tracks, a few ankylosaur tracks, some theropod tracks, and a crane-sized avian track all from the same locality. No ceratopsids, despite being very common from fossil sites on the north slope.
• Tanaka: We know that polar dinosaurs (like hadrosaurs) would often would breed in the high arctic given the presence of eggshells. In order to incubate their eggs, they probably utilized rotting vegitation in nest mounds.
• Tanaka: Hadrosaurs and sauropods of the  megaloolithidae egg family preferred mound nests. Sauropods of the faveloolithidae egg family preferred buried or geothermal nests.

And now, SVP 2017 has come to an end. Really sad that I had to leave and return to the hectic life that is undergrad. Nonetheless, I'm happy I was able to meet back up with my friends from last year's meeting, as well as make a bunch of new ones, and I can't wait for the opportunity to go again next year. (Assuming money won't be a problem.)

Until next time, thanks for another great event everyone! Keep Vertebrate Paleontology cool! Go SVP!

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!