The Latest in the World of Dinosaurs (Chessiecon 2018)

As I discussed in my previous post, I attended a lecture on new updates dinosaur paleontology by Tim Holtz, a professor at the University of Maryland, during Chessiecon last weekend. I took detailed notes, partly for the benefit of a friend and a friend's kid who are both obsessed with dinosaurs, and partly because I'm embarrassed by how much about dinosaurs I've forgotten: they were a childhood special interest that I haven't thought about much in a while.

Anyway, here's the summary, with links for as many things as I could find them for.

New Dinosaur Species

Forty-eight new dinosaur species from the Mesozoic were described in 2017, and forty-one have been described so far this year. New genera described in in the past year include:

• Macrocollum, possibly the earliest prosauropod yet discovered.


• Ledumahadi, possibly the earliest sauropod yet discovered. It wasn't fully quadrupedal and had flexed rather than pillar-like forearms. (Bipedalism is the ancestral condition for dinosaurs.)


• Halszkaraptor, a dromaeosaur, but very goose- or penguin- like, and apparently aquatic.


• A full-body fossil of a baby bird preserved in amber from about 99 million years ago was found.


• Borealopelta, one of the best-preserved dinosaur finds ever. It's a nodosaur with the keratin sheathes and skin on its horns and armor preserved. This means we can get a clear idea of what they would have looked like in life. It appears to have been countershaded (dark on top, light on the bottom), which is usually camouflage against predators that can look down on prey. We only see this in mammals when they're a lot smaller than Borealopelta, but the Cretaceous had much larger predators.

The Early Triassic Keeps Shrinking

Contrary to popular belief, the geologic time scale of eras (like the Mesozoic), periods (like the Jurassic), and epochs (like the Pleistocene), isn't actually defined in terms of specific amounts of time in the past. Instead, it's defined in terms of particular rock strata and features that can be found around the world, allowing one to identify certain rocks as of the same age without necessarily knowing what age they are. This means, for example, that the end of the Cretaceous is defined as the appearance of the iridium layer that signals the impact event that wiped out the dinosaurs, and by the disappearance of dinosaur and other fossils, not as being exactly 65 million years ago.

Today, the exact points at which geologic time periods begin are defined via the Global Boundary Stratotype Section and Point markers hammered into the rock at particularly clear rock faces in national parks around the world. For example, the start of the Cambrian is officially marked by a marker in a particular rock face in a nature preserve in Newfoundland. (I mentioned this to the author friend I was at the convention with, and I think I might have talked her into including a visit to one of these in the novel she's working on.)

Anyway, one consequence of this is that, as geological dating techniques are refined, it is possible that the starts, ends, and lengths of geologic periods may shift. In particular, the dates for the start and end of the Early Triassic were revised this year, and it appears to have been only four-and-a-half million years long, while the Middle Triassic was about ten million years long and the Late Triassic was about thirty-six million years long.

Did the Dinosaurs Get Their Start Because of Rain?

A new hypothesis published this year suggested that the dinosaurs took over on land in the Late Triassic due to a period of intense rainfall called the Carnian Pluvial Event near the start of the otherwise arid epoch. This period, about two million years long, led to a major diversification in tree species, which seems to have benefited dinosaurs at the expense of the pseudosuchians--the subgroup of archosaurs that includes modern crocodiles--that had previously been dominant on land.

Dinosaurs seem to have had a delayed take-over in North America, where they don't become dominant until the end of the Late Triassic. This may be due to the Central Atlantic Magmatic Province, the second largest episode of vulcanism since the end of the Precambrian. Rock from this period includes the Hudson River Palisades and some of the hills at Gettysburg.

Gaits and Dinosaur Tracks

This year, some very tiny tracks of either a baby raptor or a very small species of raptor (such as Microraptor) were discovered.

More importantly, though, a study of dinosaur tracks in Culpepper, VA that was published this year suggests that dinosaurs didn't have distinct fast and slow gaits (i.e. walking, trotting, and running) as mammals do. Instead, like birds, bipedal dinosaurs seem to have had a single gait that they could use at fast and slow speeds.

Brooding Eggs

A recent survey paper looked at which dinosaur species' nests were open on top, indicating that the parents brooded the eggs, keeping them warm by sitting/laying on them to provide body heat. It appears that this trait originated in the basal pennaraptora, meaning that it was unique to oviraptorosaurs, dromaeosauridae ("raptors"), trooodontidae, and avialae (flying dinosaurs, including Archaeopteryx).
In other words, only raptors, raptor-like dinosaurs, and birds seem to have sat on their nests: others, including Maiasaura, the famous "good mother lizard," didn't.

Why Did Neornithes Survive the KT Extinction?

It's well-known at this point that neornithes--the ancestors of modern birds--survived the extinction at the end of the Cretaceous Period, while other dinosaurs, including some flying ones, did not.  One possible explanation for this that was introduced this year is that it is due to the global forest collapse that resulted from the impact event at the end of the Cretaceous.  Trees seem to have been absent worldwide for over a thousand years after the impact event, with ferns the dominant land plants.  Why would this matter?  The early neornithes appear to have all been ground-nesters, while other late Cretaceous birds all nested in trees, which would have put them in serious difficulty when trees vanished, or marine.  (It's less clear why marine birds would have been at serious disadvantage, but they may have also laid eggs in trees?)