Reptilian Rants

_Ceratosaurus_ skeleton from the NMNH website

Yes, yet another entry involving dinosaurs. Given their popularity, you’d think that I’d have a better write up of them on my site. >:)

It will happen one day. Until then, there are plenty of great places on the web to learn about dinosaurs.

That said, let’s tackle the meat of the matter.

Snively, E. and Russell, A.P. 2007. Functional Variation of Neck Muscles and Their Relation to Feeding Style in Tyrannosauridae and Other Large Theropod Dinosaurs. The Anatomical Record. Vol. 290: 934-957.

This paper is just an awesome testament to just how much we can learn about animals by studying their skeletons alone.

The authours studied the cervical (neck) vertebrae and skulls of 15 theropod dinosaurs from 3 major clades.

The family: Tyrannosauridae

• Daspletosaurus
• Albertosaurus
• Gorgosaurus
• Tarbosaurus
• Tyrannosaurus (Nanotyrannus as well, but it was placed as a probable junior synonym of Tyrannosaurus).

Carnosauria

• Allosaurus
• Sinraptor
• Monolophosaurus

Neoceratosauria

• Ceratosaurus

Abelisauridae

• Carnotaurus
• Abelisaurus
• Majungatholus

It should be noted that, where possible, multiple species within a genus were used.

_Allosaurus_ skull from UCMP Berkeley's site

The authours studied the muscle scars left on the cervical vertebrae and rear skulls of every specimen. By carefully studying the location of each scar, and comparing it to the Extant Phylogenetic Bracket (EPB) – which would be birds and crocodylians – it was possible for them to determine which scar belong to which neck muscle.

Neater still; the size of a muscle scar, at its origin, is proportional to the cross sectional area of that very muscle (at least when comparing homologous muscles).

What does it all mean? Basically, the authours were able to deduce (with reasonable accuracy) the overall size of the muscles found in these theropod’s necks, just by measuring the size of the muscle scars left on the cervical vertebrae themselves.

Now how cool is that?

The end results featured 3 representative species:

1. Tyrannosaurus rex
2. Allosaurus fragilis
3. Ceratosaurus nasicornis

Each one was a “poster child” for a particular feeding method.

_T.rex_ skull from Biocrawler dinosaur encyclopedia

Tyrannosaurs (especially Tyrannosaurus) employed a puncture and pull method that required strong muscles for pulling the neck up and sideways (somewhat similar to the feeding method used by crocodiles when on land).

Neoceratosaurs showed strong ventral musculature suggesting strong downward force was being used. They also show strong dorsal and lateral musculature, which suggests that they employed a “hit and run” method of attack that would be similar to white pointer sharks, or Komodo dragons.

Last, but certainly not least, Allosaurus and its ilk were more similar to the speedy dromaeosaurs (Deinonychus, Velociraptor) in hunting style. Strong ventral musculature helps to corroborate previous studies (such as Emily Rayfield’s FEA study) that Allosaurus used its head like a hatchet, and slammed it down into prey animals. The long, strong forearms were probably used first to hold prey and brace it for the killing strike.

All in all, this was a fascinating paper. One with the potential to change all future reconstructions of these animals.

So keep your eyes tuned to Discovery Channel, as I’m sure they are bound to make a special that will incorporate this data (they always do).

~Jura

This is actually a re-write of a previous blog post that got lost in the void of cyberspace when I clicked the “save” button.

Needless to say, I’m not feeling as driven to write everything all over again. As such, I’m just going to touch on the highlights.

I’ve been in internet connection hell for the past 2 weeks, so I’m a bit behind on the reptile news. This latest one comes from about a week ago.

Study finds that dinosaurs had sex as youths.

A study by Gregory Erickson and colleagues has found that dinosaurs did not wait until they were fully grown up, before engaging in sex.

Though the finding is touted as a surprise, the reality is far from that. The scientists in question studied the bone microstructure of 7 theropods that were found near eggs (therefore, expected to be the parents of said eggs). These theropods were also of close relation to birds (clades: Oviraptorosauria and Deinonychosauria). What they found was that a members of each clade showed signs that they were still growing while watching their eggs.

In the grand scheme of things, this is not surprising. Sexual maturity hits reptiles, mammals, fish and amphibians before full body size is achieved. It is often represented as a time when maximal growth rate ends (as resources get diverted to egg/sperm production).

The only exceptions to this rule are Avians. Birds reach full adult size extremely fast (1 year, or less for most species). Sexual maturity trails way behind at 2-4 years in many of the larger animals. The reasoning behind this is due to the mechanical limitations of flight in birds. The musculature required to sustain flight, is not available in birds until they reach adult size. As flight is the main means of escape from predators, it behooves birds to reach flight status as quick as possible.

Well, needless to say, few dinosaurs flew (Microraptor gui being the only example I can think of), so the pressure to hit adult size was just not there for dinosaurs.

In the end this report can be filed under: Assumed and Now Validated.

This finding, along with many other findings over the past couple of years just helps to remind us that birds evolved from dinosaurs; not the other way around.

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Reference

Erickson, G.M., Curry Rogers, K., Varricchio, D.J., Norell, M.A., Xu, X. 2007. Growth Patterns in Brooding Dinosaurs Reveals the Timing of Sexual Maturity in Non-Avian Dinosaurs and Genesis of the Avian Condition. Biology Letters Published Online. doi: 10.1098/rsbl.2007.0254