Although 2020 was an all around shit show for the world, there were a few interesting bits of paleontology. Perhaps none more interesting than this potential overhaul to pterosaur reconstructions. Now, I haven’t really written anything about pterosaurs on my site yet (aside from some basic rundowns of news stories), so this marks an interesting way of christening the occasion. Pterosaurs are a fascinating group of critters that showcase yet another example of how animals can get airborne. They are also enigmatic in their origin and evolution.
One thing that we seemed to be confident about for a long time now is that pterosaurs had fuzz. It wasn’t fur in the mammal sense, and it sure as hell wasn’t feathers (more on that in a minute), but instead a third (or fifth, when counting arthropods and some plants) form of insulative covering. At least, that’s what I thought we knew up until about last year.
It may just turn out that this seemingly rock-solid interpretation of pterosaur outer coverings has been wrong all along.
The paper makes some pretty hefty claims regarding dinosaur metabolism, and as such, has received a fairshare of media coverage touting this as the latest evidence for “warm-blooded” (i.e., automatic endothermic) dinosaurs.
Every time there is a major headline like that, I feel obliged to go back to the source to see what the media has likely overblown. In this case, media claims don’t seem that far off what was written in the actual paper, which is not necessarily good. Some of these claims do extend beyond the reach of the available evidence (e.g., there actually is no comparison with other contemporaneous reptiles of the region, weakening any arguments for metabolic thermoregulation).
It’s been an age since I’ve done one of these paper breakdowns, but I think this one warrants a more thorough analysis, especially given the implications of the interpretations.
The latest edition of Peter Uetz’s Reptile Database has just been released, adding 80 new species to the group, pushing Reptilia over 11,000 species strong. Along with this comes the phenomenal realization that Reptilia may actually be the most speciose group of tetrapods alive today.
That is pretty huge. As I mentioned some five years ago, Reptilia has traditionally been viewed as being more speciose than mammals, but still way below birds. These new results suggests that reptile species are at least on par with those of birds, if not beyond them. Interestingly, this time around much of that increase in species was due to new discoveries, rather than the elevation of subspecies. There are still so many new species to discover in this group.
According to Uetz:
However, birds still have way more subspecies than reptiles, namely 17,991 subspecies of birds while reptiles have only 2,310 subspecies (or 3,304 if you include nominate subspecies). In general, ornithologists seem to like subspecies more than herpetologists, so there appear to be cultural preferences at play.
This is definitely a change of pace from previous decades where lumping and a reluctance to nominate new species, kept reptilian species counts way down. It appears that many of the lumpers from previous eras, have since been replaced in herpetology, or they moved over to ornithology. Which is not to say that there’s still not a problem with lumping in herpetology.
An exact breakdown of species by higher taxonomic level is currently unavailable, but a comparison to the data from July 2018, with data from my last entry on this is still plenty telling:
Amphisbaenia = 196 (+8)
Lacertilia = 6512 (+525)
Serpentes = 3709 (+213)
Chelonia = 351 (+10)
Crocodylia = 24 (-1)
Sphenodontia = 1 (+0)
Without a doubt, Squamata is the reason for this huge increase in year-by-year numbers. This is not that surprising given that Squamata has always been viewed as the most speciose group of reptiles. The small size of many squamates makes them easy to overlook, whereas the large size of most turtles and all crocodylians, makes them relatively easy to find (that said, expect Crocodylia to surge up by at least three species in the near future). Even within Squamata, lizard species outpace snakes nearly two-fold in both total described species and new species discovered. Again, the larger size of snakes relative to lizards is likely responsible for this. Smaller animals just tend to get more overlooked.
I suspect that as the years go on, we will continue to see Reptilia grow in species number at an accelerated pace compared to mammals and birds. This group has been overlooked for so long, that much of these results are happening because people have finally bothered to start looking. The big question now is when will this accelerated pace start slowing down?
July marks the 21st anniversary of my website, and that’s…pretty cool. As the old joke goes, my site is now old enough to drink. Well, old enough to drink in the U.S.A., where we have stupidly high drinking laws (thanks, M.A.D.D.).
This post is going to be different from my usual style. I’m not a huge fan of celebrating arbitrary milestones, but given the magnitude of this one I figured it’s worth mentioning. Besides, it’s been kind of revealing seeing how my site has evolved over two decades.
The whole thing started way back in 1998 as a response to the general lack of reptile information on the web, and over the years it has grown into what it is today. I’m skipping ahead of myself, though. First, we need to go back a little further.
This is a short status update for the site. When I switched up the theme for the site back in 2014, I did so with the intent of making it more interaction friendly. That included threaded comments and the ability to subscribe to those comments. A couple of days ago I noticed that both the post subscription and comment subscription options had stopped working (the latter had completely disappeared). I dove into the backend to see what was causing the trouble and I think I’ve been able to fix it. Now when you go to a comment or reply there should be a box at the bottom that lets you choose to subscribe to the comment thread and be notified via e-mail if you would like to get updates.
The other thing I noticed is that I was getting a lot of e-mail bounces for confirmation e-mails on subscriptions. I changed the e-mail for the site to a more Reptipage-specific e-mail, so that should no longer happen anymore.
NOTE: If you do hit subscribe but still don’t see any confirmation e-mail come through (it should be near instantaneous), check your spam folder. I’ve found that there are quite a few e-mail providers that are autoblocking these confirmation e-mails. If that’s the case, just whitelist the e-mail sent from the site and that should fix the problem.
[NOTE: Post has been updated to include a section on scale size]
This has certainly been an interesting year. Two papers dropped in the past three months that have put the brakes on a recent trend in paleo-art. That trend? Why the feather-coated T. rex of course.
First, in March, we saw the release of a paper detailing a new species of Daspletosaurus and its relationship to D. torosus.
Carr, T.D., Varricchio, D.J., Sedlmayr, J.C., Roberts, E.M., Moore, J.R. 2017. New Tyrannosaur with Evidence for Anagenesis and Crocodile-Like Facial Sensory System. Scientific Reports. 7(44942):1–11.
In this paper, Carr et al. argue for the designation of a new Daspletosaurus species, D. horneri. The authors argue, based on skull shape and chronostratigraphic position, that D. horneri was the direct ancestor to D. torosus. I thought that the authors put forth a compelling argument for this anagenic event and backed up their position well. Interestingly, this part of the paper should have been the most controversial. As anyone who has read anything from Horner and Scanella over the past eight years can attest, arguing for a direct ancestor-descendant relationship for dinosaurs is difficult to do and even harder to win over others in the field. So it is somewhat surprising to see a case for anagenesis in Daspletosaurus taken so well by the palontological community. All the more so given that it involves a tyrannosaur, the poster children for “cool guy” dinosaurs.
Instead, the most controversial part of the paper wound up being their soft-tissue reconstruction of the face for D. horneri. The author responsible for the soft-tissue reconstruction was Jayc Sedlmayr of Louisiana State University. Sedlmayr did his doctorate on osteological correlates for vasculature in extant archosaurs (birds & crocs). He is the seminal alumnus of the WitmerLab and thus is well within his wheelhouse for this type of soft-tissue reconstruction. Sedlmayr borrowed heavily from the work of another WitmerLab alumnus, Tobin Hieronymus, whose PhD work involved osteological correlates for integument on the skulls of animals. Although the skin is often well away from the underlying bones on most of the body, there are exceptions when it comes to the skull. There, areas that are not heavily muscled, tend to show intimate connections between the skin and the underlying bone. Hieronymus used these connections to determine how different integumentary appendages (scales, hair, feathers) affect the underlying bone (Hieronymus & Witmer 2007; Hieronymus et al. 2009). The authors found that the surface texture along the skull of D. horneri was “hummocky”. That is, it was covered in lots of closely packed ridges. According to Hieronymus & Witmer (2007), this texture correlates to scales as the overlying integumentary appendage. Thus, according to the authors, D. horneri had a scaly face (this is grossly oversimplified as the authors were able to piece together a variety of different integument variants along the skull, but you get the idea).
Scaly tyrannosaur cannonball one had been shot.
Then two weeks ago, we saw the release of another paper on tyrannosaur integument. However, unlike the previous paper, this one was specifically dedicated to integumentary types in tyrannosaurids.
In this paper, the authors set out to survey all known instances of “skin” impressions for tyrannosaurids. Their list of taxa included Albertosaurus, Tarbosaurus, Daspletosaurus, and Gorgosaurus. Their results pretty definitively indicated that scales were the predominant integumentary appendage on tyrannosaurids. The authors then went on to speculate why that would be if earlier tyrannosauroids had filamentous integument. They performed an ancestral character state reconstruction based on Parsimony and Bayesian-based trees from Brussatte and Carr 2016. Their results found that filaments came out strongly as the ancestral character for tyrannosauroids, but by no later than Tyrannosauridae proper, a reversion to scales had taken effect. The authors attributed this to body size evolution. Namely, larger tyrannosauroids reverted to scales over protofeathers.
Most folks who visit my site by now have seen the big dinosaur news that has hit the interwebs. A new study from Matthew Baron, David Norman and Paul Barrett from University of Cambridge and the Natural History Museum of London, has seriously challenged the classic interpretation of dinosaur phylogeny.
Although originally thought of as two unrelated branches of Reptilia that grew to immense size during the Mesozoic (e.g., Charig et al. 1965), for the last 43 years the group, Dinosauria, has been considered monophyletic (i.e., sharing a single origin) with the subgroups, Saurischia & Ornithischia, forming the first major branches within the group (Bakker et al. 1974). Saurischians, or “reptile hips” were aligned together by their similar hip shapes, skull characters (e.g., open antorbital fenestrae), and inferred soft tissues (e.g., air sacs). Ornithischians, or “bird hips” shared a hip structure that was superficially similar to that of birds, with a pubis that pointed caudally rather than rostrally, along with a variety of unique skull characters such as a neomorphic bone known as the predentary.
Study after study showed that this relationship was sound, and so it stayed that way. The problem with getting the same answer over and over again is that one eventually stops questioning it. Consistent results become common knowledge, and may even graduate to dogma. That’s not so bad if that common knowledge is true, but all too often many of these “obvious” cases wind up being just so stories upon closer inspection.
In this day and age there are no shortage of books, websites, and videos dedicated to debunking classic paleo myths. The majority of this mythbusting focuses on myths about dinosaurs. As the poster children for paleontology, this isn’t that surprising. With so many takes on this subject it comes as no surprise that all of the classic dinosaur myths have long since been debunked, such as dinosaurs as low-energy tail draggers, walking around like Godzilla, being evolutionary failures, inferiority to mammals, being pee brained monsters, etc.
However, as quickly as these classic dinosaur myths have been eradicated, new ones have come and taken their place. These myths/misconceptions are routinely cited today without any question despite being just as erroneous as the myths that preceded them.
This is the start of a new series I want to cover on the site: dispelling modern myths in vertebrate paleontology. Given the bent of my website, these myths/misconceptions will largely stay focused on reptile-related animals, though I am open to taking the occasional foray into other animal groups if the myths are egregious enough (which is to say that suggestions are welcomed).
The seminal installment for this series is one that I see mentioned time and again:
Today, the largest turtle alive is easily the leatherback turtle (Dermochelys coriacea), at a whopping 916 kg (2,015 lbs, Eckert & Luginbuhl 1988). On land, the largest turtle goes to Chelonoidis nigra (Galápagos tortoise) which has been reliably recorded as reaching up to 417 kg (919 lbs) in weight (Guinness World Records). However, both extant turtles are dwarfed in size by an immense land tortoise that lived as little as 1.7 million years ago, in the Pleistocene.
In another example of slow-cooked science, this paper was the culmination of over three years worth of work collecting data on tegus. For the study, the authors looked at adult black and white tegus (Salvatore merianae). Tegus are an interesting group of lizards. They are the largest members of the family Teiidae and are often referred to as the monitor lizards of the new world, due to their convergent lifestyles (highly predaceous, active foragers). Besides their varanid-like demeanor, tegus are also known for their enormous jowls, especially in the males. The jowls hold the pterygoideus muscles, the big jaw snappers, which have been shown to increase in size for males during the breeding season (Naretto et al. 2014). As reptiles, tegus have been assumed to follow the standard ectothermic lifestyle of requiring external sources of heat to warm their bodies and maintain stable body temperatures. Looking at the natural history of the animals, tegus appear to fit the mold pretty well. They have distinctive winter and summer activity levels. In the summer, the animals regularly maintained body temperatures of 32–35°C, and in the winter they let their body temperatures drop to the temperature of their burrows (15–20°C). This is all fine and good for a bradymetabolic, ectothermic lizard, but when the researchers tracked body temperatures over time they discovered something completely unexpected.