SVP Day 3

OK, day 3, still alive.

The first session this morning was on saurischians dinosaurs, the major group that includes sauropods and theropods.

My supervisor, Phil Mannion, was the first talk I was awake enough for (*cough*), and gave us a run-through of sauropods from the infamous Late Jurassic (~150 million years old) Tendaguru formation from Tanzania. With new revisions, the sauropod fauna from here are remarkably similar in terms of higher taxa to sites known from Iberia, China, and the US, although only somphospondylans, a quite advanced group, are known from Tendaguru.

Sticking with sauropods, a new species was discussed from China, along with implications of its vertebrae for neck evolution, one of the most striking features of these animals. By dissecting modern birds, you can actually model the muscles of different necks and compare this to the fossil record to reconstruct the fleshy parts of their necks. Preliminary research shows that sauropods probably had long tendons with light muscles, which fits quite nicely with the idea that these things were great at conserving weight, along with internal air sacs and skeletal pneumaticity (holes, in the vertebrae for example).

Afternoon session! Decided to go for the one on the influence of the geological record on biological patterns in deep time, and the relative completeness of both.

The first talk was looking at how to estimate stratigraphic completeness in a river-based deposition system. Patterns of sedimentation follow a regular cycle, and can be used to look at evolutionary rates on a very fine generational scale, which can be combined with biological analyses of species to see how fast they’re evolving. Preliminary work, but looks cool!

Marsupials next, something I know nothing about. So typically, we measure abundance per species just based on the number of specimens, which can be used to assess biogeography and abundance patterns over intervals such as the Cretaceous/Paleogene mass extinctions. The next level up is using species-level datasets to assess biodiversity patterns. But these counts are biased by the way in which we have sampled the fossil record. In Late Cretaceous mammals from the US, a survey of museum specimens revealed that there are tonnes more in collections than we are aware of from the published literature. This is known as taxonomic detection bias, and has been relatively under-studied with respect to the inherent biases in the fossil and geological records. This problem is exemplified in marsupials, as many specimens are just not named in collections (about half in the sample discussed), which means that we’re most likely severely under-estimating biodiversity and abundance when using these collections.

Sticking with mammals, we looked at how North American mammals interact with climate to drive their beta diversity, which is a measure of spatial turnover in species. Turns out that troughs in diversity throughout the last 50 million odd years correspond quite strongly to drops in temperature, and provides a nice model for predicting how mammals will respond to future changes in global climate. The next talk was pretty much the same, but focussed more on ungulate mammals (those with even-hoofed feet). Although the study was inherently flawed, as it used data from the Paleobiology Database, which I’m pretty sure is incomplete throughout the Paleocene and Eocene for mammals, and diversity curves produced were assumed to reflect genuine patterns, without consideration of sampling biases.

The next two talks were pretty much the same, so skipperood out for a quick break. Sticking with mammals though, we delved into the world of macroevolution, considering the tempo of their body size evolution over the Cretaceous/Paleogene boundary. The idea is that when large dinosaurs all went kaboom, mammals adapted into the unoccupied ‘niche’ space and radiated within this. It turns out, that if you use a model-based approach, there might be a change in tempo of evolution, but this reveals nothing about the mode, and when you look in detail there might not have actually been a change as previously asserted.

Keeping on the theme of macroevolution, we explored why latitudinal diversity gradients exist. This phenomenon is the idea that we have increased diversity along the equator, which decreases polwewards due to some combination of variables, and exists for many modern animals. This could be something to do with energy gradients, or land area, or the range of available environments. But when did this pattern actually come to exist in modern faunas? Well, using sub-sampling methods that account for biases in area size and abundance of specimens, it’s actually pretty difficult to tell, due to the error margins for some of the data points. Ah well. Day 3 done for now!

Don’t forget to check out the Palaeocast coverage of the event!