In order to estimate bite force with any reasonable confidence, we'd need to have a rough idea of how much jaw muscles Spinosaurus had. Unfortunately there are no good cranial materials to reconstruct jaw muscles in Spinosaurus - the bits at the back of the skull where the muscles would have attached are not known for Spinosaurus. Therefore we won't know for sure.

However, we can fairly confidently assume that Spinosaurus would have similar skull proportions to those of close relatives like Baryonyx or Irritator. These theropods had long narrow skulls with not much space for jaw muscles. From what we know of Spinosaurus skull materials, we can be sure that it also had smallish jaw muscles (for an animal of that size).

Extrapolating from size estimates (I presume body size, e.g. body mass, body length, whatever) would not give you a good estimate for Spinosaurus, for the very reasons I outlined above, i.e., spinosaurs had smaller jaw muscles compared to other theropods of similar sizes. Using body size will grossly overestimate bite force.

(posted in Fossils)

1. Megalosaurs (including Torvosaurus) are only known from partial skulls so it would be extremely difficult to estimate mechanical advantage accurately, even more so for bite force. Having said that, mechanical advantages calculated for Eustreptospondylus and Dubreuillosaurus (both preserve more skull elements) are comparable if not higher than that of T. rex (Sakamoto, 2010). But like Mike's already mentioned, T. rex has other features that indicate that it had larger, stronger jaw muscles compared to megalosaurs, maybe giant carcharodontosaurs like Carcharodontosaurus and Giganotosaurus, and DEFINITELY Spinosaurus.

2. It's difficult to say with 100% certainty if these mounted skull reconstructions are correct, because the skull and mandible of Torvosaurus is only known from incomplete specimens. I will say that the third photo (I presume from the Lourinha Museum) looks strangely like it borrows heavily from T. rex. Here is a link to a pdf that figures the maxillary bone of the Lourinha Torvosaurus (Fig. 6):

http://www.museulourinha.org/pt/Omateus … roofs).pdf


References:
Sakamoto, M. 2010. Proc. R. Soc. B 277, 3327-3333. doi: 10.1098/rspb.2010.0794

(posted in Mammals)

no one's mentioned the short tail yet; and longish legs.

(posted in Mammals)

Just for clarification, a genet cat (Genetta tigrina), or Cape genet or large-spotted genet, is not a felid but a viverrid, more closely related to other genets and civets than to any felid.

Ill ask for clarification as a non-specialist: does this mean that contamination (which, by the way, I'm a bit confused on what exactly the contaminant is) is generally restricted to crops of the same species or close varieties, e.g. GM corn to non-GM corn, and not GM corn to dandelion? Because we're always led to believe that there is going to be an imminent emergence of a 'super-weed'... If it really is a GM crop to non-GM variety contamination, then what are the risks or undesirable effects of such a contamination?

...but of course, it's not every day we actually witness a squirell getting run over (and not quite completely either) or animals in pain, and it can be an upsetting experience.

(posted in Mammals)

The method these authors used (the same one I use) is notorious for underestimating absolute bite force so it is not a good reference for that sort of biting performance. Having said that, these studies are meaningful in a comparative context; how do relative biting performances compare between a grey wolf and a large cat of similar size, or what is the underlying evolutionary pattern in biting performance within a given group, like Carnivora?

Like Peter said, psi is pressure (pound-force per square inch [lbf/in^2]), while bite force is measured/calculated in the scientific literature in Newtons (N). Psi can be converted into Pascals (Pa; N/m^2), where 1 psi is approximately 6894.757 Pa. That's roughly 10N/mm^2. Assuming that this 1500 psi bite was recorded at a single tooth with a sharp tip (~ 1 mm^2 in surface area just for simplicity's sake), then that would be 10N bite force. So unless I've done something wrong, it seems entirely possible to me that a grey wolf can bite with a pressure of 1500psi. But I guess it really depends on how large a surface that 1500psi was measured on...

(posted in Evolution)

Birds...which do exist

Well, here's a link to the simple English Wikipedia:
http://simple.wikipedia.org/wiki/Bruise

And here's the NHS's page about bruises:
http://www.nhs.uk/chq/Pages/1057.aspx?C … goryID=726

Here is a link to an article on this very photo:
http://www.huffingtonpost.com/2012/01/2 … 39178.html

It seems the animal is about 15-16 feet long

(posted in Mammals)

By mammals, I presume you mean carnivorous mammals? The reason that there is no definitive answer is because the only real 'field' recording of bite force in large carnivorous mammals (if not in all mammals) is of the spotted hyena (Binder & van Valkenburgh, 2000), but also due to inherent individual variation. Other workers have attempted to estimate bite force from skeletal measurements, but there is a large degree of uncertainty in how muscle parameters are estimated. Indeed, Binder & van Valkenburgh (2000) observed that bite force continued to increase with the age of the individual despite reaching adult size in terms of somatic growth. This implies that some muscle anatomy (architecture, mass) keeps growing, and this change in muscle properties were not captured from external measurements.

Further, bite force is highly correlated with body size, so the larger the animal, the higher the bite force. Thus, animals like the polar bear and tiger tend to have the highest estimated absolute bite forces (Christiansen & Wroe, 2007). On the other hand, size adjusted bite force metrics can tell you something about their biomechanical performances in terms of biting, particularly their feeding ecology. According to Christiansen & Wroe's (2007) estimated relative bite force metrics, the highest biter amongst their carnivore sample was the brown hyena followed by the olingo, the least weasel, Sulawesi palm civet, and striped hyena, just to name the top 5.


References

<p class="p1">Binder W.J., Van Valkenburgh B. 2000 Development of bite strength and feeding behaviour in juvenile spotted hyenas (Crocuta crocuta). Journal Of Zoology 252, 273-283.

<p class="p1">Christiansen P., Wroe S. 2007 Bite forces and evolutionary adaptations to feeding ecology in carnivores. Ecology 88(2), 347-358.

(posted in Mammals)

Google told me 4 feet = 122 cm. In which case, sounds about right, don't you think?

(posted in Mammals)

I haven't had an opportunity to look at the body skeleton of Panthera atrox but I have seen a cast of the skull, which is huge (450 mm in length). The skull of P. atrox is roughly 113% the length, and about 114% the size (geometric mean), of a large P. leo skull (400 mm). This proportion jumps to about 145% if we compare to an average P. leo skull length (310 mm).

On the other hand, the body mass of P. atrox is about 350 kg while that of P. leo on average is about 170 kg, so the former being about 2 times heavier than the latter. Converting this to a length ratio, you can take the cubic root, and you get P. atrox being roughly 127% in length of P. leo, which is roughly similar to the 5ft/4ft ratio of 1.25 (125%).

So I'd say this diagram is in the correct range, within margin of error.

Hi Michael,

You should stick to your dreams and become a palaeontologist one day!

Anyway, Deinonychus is actually a lot smaller than depicted as 'Velociraptor' in Jurassic Park and anything influenced by JP. So the 1.5 m height is closer to its actual size. The skull of Deinonychus is about 35-40 cm in length.

(posted in Mammals)

Right, of course; thanks Corwin.

In a way, it's kind of like the scaling equation: M2 = aM^b where a is the intercept (scaling constant) and b is the slope (scaling factor); I guess in this case, a=L1/L2 and b is the scaling exponent=3.

(posted in Mammals)

Christiansen and Harris (2005) using a suite of osteological predictor variables estimate a range of 220-360 kg. Their estimates for Smilodon fatalis range between 160-280 kg.

(posted in Mammals)

Hello,

Sorkin estimated body mass for Smilodon populator by scaling the maximum body mass of the modern Siberian tiger according to skull lengths. His exact calculation is:

M_Smilodon = M_tiger * (L_Smilodon/L_tiger)^3

where M is the mass and L is the skull length.

However, I don't see why he raised the ratio of the linear variables (L_Smilodon/L_tiger) to the power of three: the idea behind this is obviously the 1/3 scaling relationship between length and mass, but since the skull lengths are represented as ratios, there is no longer any dimensionality to this ratio variable, so this cubic transformation seems excess to me... Perhaps that is why the resulting body mass is rather high...

(posted in Evolution)

I'll point out that even though the clouded leopard has longer canines than any other modern cat, it still has a 'conical' tooth rather than a 'sabre' tooth canine morphology. This means that the cross-section of the canine is more rounded like all other modern cats as opposed to the flattened canine cross-sections of sabretooth cats. Further, sabretooths have extremely reduced lower canines (they're nearly indistinguishable from incisors) while clouded leopard has relatively tall lower canines (quite tall, even compared to other modern cats). So strictly speaking, clouded leopard doesn't show a convergence with sabretooth cats in canine morphology, and it is quite likely that the functions or selective pressures were different between clouded leopard and sabretooth cats.

Also, just to reiterate what Paolo said, all modern cats including the large cats (Panthera species and clouded leopard) are more closely related to each other than to any sabretooth cats; some studies using ancient DNA do tend to support this. Sabretooth cats in turn probably are more closely related to each other than to any living species of cats. However, both groups, Machairodontinae and Felinae, are considered to be true cats (Felidae) so are more closely related to each other than to, say hyena or civets. These groups and others are feliform (cat-like) carnivores and are more closely related to each other than to caniform (dog-like) carnivores, which include dogs and bears among other things.

(posted in Mammals)

This recent study by Ki Andersson and colleagues (http://www.plosone.org/article/info:doi … ne.0024971) shows that sabretoothed carnivores (e.g., machairodontines, nimravids) probably killed prey in the same size range as those of modern carnivores. This is because biting depth decreases with increasing prey size, making it difficult for even those sabre-toothed carnivores with extremely long canines to deliver a lethal bite. Thus, the authors conclude that sabre-toothed carnivores evolved as a result in a shift in killing/biting function rather than a shift in prey. In other words, sabretoothed cats (and nimravids) may not be megaherbivore specialists as previously (and maybe widely) perceived...

As Dave's mentioned, it's quite likely that Tyrannosaurus rex would have had the highest bite force out of these four species. In terms of biting efficiency (the mechanical advantage), Carcharodontosaurus (and by phylogenetic inference, Giganotosaurus as well) have pretty impressive biting capabilities, but if you include muscle force and calculate bite force, then Tyrannosaurus beats these two by almost an order of magnitude. Although the region of the skull that housed the jaw closing muscles in Spinosaurus is almost completely unknown, deduction from other spinosaurs that do preserve some of these elements (Baryonyx, Irritator) indicates that it most likely had the weakest bite force out of these three by a huge difference.

While slime molds aren't commonly eaten, there are some historical references that elude to them being eaten. For instance, there are records from ancient China dating back to the times of the First Emperor that depict 'meat-like' clumps being dug out of the ground. These are thought to be one of the life-cycle stages of a slime mold. More recently, a 25.5 kg 'meat-like' mass was discovered in 1992 from Shaanxi, China, and apparently was tasted. The taster is quoted as remarking, "When raw, has the fragrance resembling that of a rose, and when cooked, has the texture of meat".

As a Japanese I've eaten quite a few things from the ocean but not sea hares. It's not commonly eaten in Japan (not widely anyway), mostly because they're not particularly delicious and can be poisonous due to the fact that sea hares eat algae that could be poisonous depending on region or season. But they are eaten in certain regions of Japan but it still requires caution because they could be poisonous depending on season or algal blooms. Supposedly they are tasteless, very crunchy, and are eaten by stewing with sweet and spicy flavouring.

I think what Ron wants to know is why cats have evolved much larger body sizes than dogs. For instance, in the extant felids alone, all Panthera species (snow leopard, leopard, jaguar, tiger and lion) all exceed 50 kg on average (mean body mass). Even the cheetah weighs close to 50 kg and the puma weighing more than 50 kg. That's three (or maybe two) instances of independent size increase in the extant cats.

If you add the fossil ones, then you get the North American jaguar (P. onca augusta) at around 35~100kg, the American cave lion (P. atrox) at around 350 kg, among others for the crown clade. But there's also the very large sabretoothed cats with Smilodon at around 200~300 kg (depending on the mass estimation) and Xenosmilus also around that weight.

In contrast, the largest modern canid is the grey wolf at around 35 kg, and even in the fossil record you rarely see dogs exceeding 50 kg (the Dire wolf is 50~80 kg or so). While it has been reported that Epicyon (a borophagine taxon) can be up to 170 kg (Sorkin, 2008 LETHAIA 41: 333-347), all estimates from that study are rather large (Smilodon at 470 kg), so sticking with the Paleobiology Database, Epicyon would be around 85 kg. So nothing in the order of the largest fossil large cat as far as I am aware.

So perhaps it is genetic like David W suggests?

(posted in Mammals)

Hi Yustine,

I understand that it may be difficult to find relevant studies on the internet or indeed in libraries, but comparative anatomy is a basis for taxonomy so there are in fact hundreds of research using comparative anatomy; it may be that a lot of this was done in the 18th-19th (and maybe early 20th) century by people like Linnaeus, Cuvier and many prominent palaeontologists and tracing them may be difficult.

But here is a simple explanation about Feliformia on Wikipedia (http://en.wikipedia.org/wiki/Feliformia). Like Carlos mentioned, one of the unifying features of Feliformia is in the auditory bulla or ear bones. Also, hyenas and cats have very similar numbers and arrangements of foramina (or openings) for nerves and blood vessels, at the base of the skull. Dogs are very different from these two.

Manabu

Hi Tom,

Sorry for the delayed response, I'm not sure why we didn't get around to answering you before.

I think that overall your lineart is great but I think the way the neck is being held looks a bit unnatural. Perhaps not so abruptly bent at the base of the neck? Also your forelimb looks a bit too fat. Maybe reduce it down by at least 20% of what you have here? Now I'm not an expert on forelimb mobility, but I think they should be tucked back against the flanks a bit more like a bird would hold its wings close to its body (but not folded up so much as in birds).

Anyway, as a reference, here is Greg Paul's restoration of Coelophysis bauri (http://press.princeton.edu/blog/2010/09 … sis-bauri/) with the robust form in the middle. I think Paul always does a good job of getting the proportions right so I like to consult his reconstructions from time to time. However, in the off chance that you seek to sell your art, I must regrettably inform you that if you do use his reconstruction as a guide you may have to get permission from him (http://gspauldino.com/products.html)

(posted in Mammals)

According to genetic similarities, the cheetah is closely related to the puma and jaguarundi. There are a bunch of fossil cheetah-like and puma-like cats that likely fill the gap between the two modern puma species and modern cheetah, but their interrelationship is yet unclear.

That depends on how one would estimate size.

(posted in Evolution)

Perhaps, jgh means coevolution? Even then, sea scorpions would have played zero part in human evolution; sea scorpions (I presume eurypterids and close relatives) were long extinct when the first humans, or indeed any ape appeared in the fossil record...

I think it's safe to say that not some but most researchers in palaeontology would say that 'dinosaurs are still with us today in the form of birds'. This is precisely for the reason that Heinrich says: birds are dinosaurs. Just the same as humans are mammals. If all other mammals aside from humans died out, you wouldn't say that mammals went extinct; mammals would be alive in the form of humans. So the same can be said for dinosaurs; all other forms of dinosaurs died out except for birds.

We know this is true because a lot of non-bird dinosaurs that were very closely related to birds look almost identical to fossil ancestral birds. It is very difficult to distinguish a fossil bird from a non-bird fossil dinosaur. A lot of the time, the distinction is purely based on your definition of the group 'birds'.

I don't know about height but it would have been about 1000 kg based on its femur length.

And just to be pedantic, you should only capitalise the genus name and not the species name: so, Ekrixinatosaurus novasi

For a recent functional analysis on the forelimb stance of ceratopsians, you should look up Shin-ichi Fujiwara (University of Tokyo). He showed that the manus of Triceratops is in a semi-supinatet orientation (laterally facing manus; or the back of the hands facing outwards). The main weight-bearing digits would have been digits I, II and III, with digit II facing anteriorly and parallel to the direction of the forelimb stroke. Robust digits I-III and reduced digits IV and V are supposedly a shared ancestral feature in the bipedal common ancestor of Cerapoda (ceratopsians, pachycephalosaurs, ornithopods and close relatives).

hmm...I did not expect to stir up such a debate on importance of subjects but all I meant was to say that at high-school- (secondary-) level education, one should focus on core subjects like maths and fundamental science subjects like physics and chemistry before specialised subjects like geology or biology. You can choose whatever specialist subject to major in University or an equivalent higher-level education, but I think it is important to have basic fundamental training of core science subjects while younger. OK - so maybe someone might disagree again and say, geology and biology are also fundamental to science but what I mean is that geological or biological phenomena could be explained by physics and chemistry but the opposite is not entirely true.

(posted in Mammals)

Convergence is a difficult thing to assign to a single cause but it is likely that both hyenids and canids are adapted for similar ecologies or that they have similar evolutionary histories with regards to ecomorphology. Many modern hyenids and canids do have similar ecologies in that they are both highly cursorial, they tend to be long-distance pursuit hunters (when they hunt) and they use their jaws and teeth as their primary killing 'weapons' instead of forelimbs.

Hyenids seem to have started off from small arboreal ancestors that gave rise to dog-like species. Conversely, there are hyena-like bone crushing canids known from the fossil record. So a similar ecomorphological evolutionary history may play a part in their similarities as well, i.e. their ancestors may have been pretty similar.

Perhaps others on AAB can shed some more light on this?

(posted in Mammals)

I presume you mean carnivorous mammals and not us!

In which case, the lower canines of carnivores are indeed more anterior (or in front of) the upper canines when the jaws are closed, but when the jaws are open, the tips of the upper and lower canines tend to be aligned along the arc of jaw motion at certain gapes, and remain aligned till quite a wide gape. I suspect this range in gape at which the tips align must be some functionally important zone of biting, such as the typical range of prey sizes for that carnivore.

At least that's what it looks like from my ocelot skull cast I happen to have on my desk right now...

I sit in front of a computer most of the time, but I do go to museum collections to take measurements from and make observations of specimens. I tend to concentrate my museum visits to a week at a time and I go back to my computer and analyse the data I'd collected. I've never done field work.

Aside from field work and description of new fossils, which seems to be the mainstream image of palaeontologists, there are a lot of lab- or computer-based methods/studies that palaeontologists can make careers out of. For instance, there are a lot of incredible palaeontologists past and present that have exclusively worked on mathematical models of evolution using palaeontological data. Or wet-lab based studies on developmental embryology or molecular biology has founded the basis for a whole field called evolutionary developmental biology (or evo-devo) which more and more respectable palaeontologists are specialising in. Another field in palaeontology is biomechanics and functional morphology, where fossils are anlysed using simple 2D or sophisticated 3D biomechanical models to investigate the relationship between form and function and their (co-)evolution.

So you can be a palaeontologist in a number of different ways. Mathematical modelling of evolution obviously demands a good understanding of maths, statistics, computing among other things, while evo-devo requires a good set of skills in the wet-lab as well as computing and a good understanding of statistics. Biomechanics also requires an understanding of maths, mechanics (maybe engineering principals), computing (and imaging/graphics), but also statistics. And all of these disciplines can be placed within a phylogenetic framework which would definitely require some computing and maths/statistics.

So it is quite obvious that maths is really important in many disciplines of palaeontology, and I'd urge you to take maths seriously in high-school. It's much easier to understand statistics, biomechanics, phylogenetics, evolutionary models, etc, if you have a basic understanding of high-school level maths. Biology, chemistry, and physics would also be pretty useful, but maths>physics>chemisty>biology would be my ranking of importance. This is because biology runs on chemical principals, while chemistry is dictated by the laws of physics, and physics can be explained by maths. But that's just my opinion.

Hi Christopher,

Sorry for the delayed response.

There are some ideas around niche partitioning between the various stages of ontogeny in tyrannosaurs. If I remember correctly, there is a general lack of middle-sized theropods in tyrannosaur-bearing localities, with an abundance/diversity in small theropods (like dromaoesaurs, troodontids, ornithomimosaurs, etc.) and an abundance (but maybe not diversity) of large theropods (tyrannosaurs). The hypothesis is that the mid-sized theropod niche is occupied by the juvenile/sub-adult tyrannosaurs.

However, I doubt this is the cause of a seemingly late burst of growth in tyrannosaurs. Growth in most modern mammals and birds also can be modeled with a sigmoidal curve with a lag, exponential, and plateau stages so this pattern is not unique to tyrannosaurs. Of course, compared to crocodiles and other reptiles, and even other animals like elephants, reaching adult size of 5000 kg or more in about 20 years is actually really really fast; I think it takes up to 30 or more years for elephants to reach maximum size.

I think the intriguing thing about that particular study on tyrannosaur growth (Erickson et al., 2004; Nature 430: 772-775) is that they reveal that while T. rex and the other three tyrannosaurs studied (Daspletosaurus, Gorgosaurus, and Albertosaurus) all have a similar duration of an exponential growth stage, T. rex differed quite drastically in the slope of the curve.

I'm not a geneticist and it's been close to ten years since I've studied genetics so perhaps I may be overlooking something (maybe someone else on AAB can help me out if I've got something wrong), but according to the Wikipedia page on the chimpanzee genome (http://en.wikipedia.org/wiki/Chimpanzee_genome_project) and human genome evolution (http://en.wikipedia.org/wiki/Human_evol … great_apes
 the total similarity in the two genomes could be as low as 70%. I should probably ask our resident geneticists if this figure is indeed correct and if so, how did we come to the 95% (or I used to remember 98% from my undergrad days) value?

Anyway, assuming that the similarities are 95%, then the difference of 5% in the human genome would be 5% of 3 billion base pairs = 150 million base pairs. I think that's still quite a lot of genetic difference...

(posted in Mammals)

An alternative way of defining Mammalia is by the use of phylogenetics. For instance, we can say that any species descended from the common ancestor of monotremes and placentals would be a mammal. Even by this definition, there would be a few early mammal-like animals (e.g. Morganucodon) that would not be included in Mammalia.

Like Paolo has mentioned already, definitions can be more about semantics than biology, and in some sense doesn't have much impact on the understanding of the evolutionary relationship of early mammals. It's just about where to draw the line between "true" mammals and their close relatives.

I don't think there is such a thing as the true number of transitional species, in the same way that we don't know the true number of fossil species, or maybe even the true number of known living species.

First, it is impossible to know the true number of fossil species for the simple reason that we would never know for sure how much of the fossil record is actually missing.

Second, even if we did, the concept of a transitional fossil is quite vague that it could include quite a variety of fossil forms. In some ways, all non-avian theropod dinosaurs are transitional species because they have a combination of features that are shared with more primitive archosaurs (like crocodilians, though they aren't necessarily primitive) and birds. The transition from the primitive archosaur condition to the avian condition is spread across Theropoda, despite popular belief that bird features are only present in maniraptorans (the group including all the feathered relatives of Velociraptor, Troodon, Oviraptor, etc.). Therefore it is extremely difficult to say what is and what isn't a transitional fossil.

Third, it is debatable how many species there are in total. Others have discussed this in much more detail and clarity here at AAB already so I shan't go into it here, but the basic premise is that there are several ways of distinguishing species so it is difficult to know a true number of species.

Sorry for the late response. I don't know about the whole frill being covered in a keratinous sheath, but the idea that at least parts of the frill were covered in "a thick pad of cornified skin" was tested by Tobin Hieronymus and colleages in a paper from 2009.



Hieronymus, T.L., Witmer, L.M., Tanke, D.H., and Currie, P.J. 2009. The Facial Integument of centrosaurine ceratopsids: morphological and histological correlates of novel skin structures. Anatomical Record-Advances in Integrative Anatomy and Evolutionary Biology 292: 1370-96.

(posted in Mammals)

About the red eyes, I suspect that has something to do with albinism? Or perhaps you have a ruby eyed mottled Campbell's Rusian dwarf hamster?

(posted in Mammals)

Here is a Wikipedia article on Campbell's dwarf hamster' diet (http://en.wikipedia.org/wiki/Campbell's_dwarf_hamster#Diet); apparently in the wild, they eat grains, seeds and vegetables.

I found through a Japanese fisherman's website (http://marinnagisa.cool.ne.jp/2009%208%201.html) - there's a picture of the fish halfway down the page. Another picture from the Tsukiji fish market in Tokyo (http://wwwalcott.com/asia/) - picture is at the bottomleft of the page.

And I finally found what I think you may have seen: the gurnard or sea robin (http://en.wikipedia.org/wiki/Sea_robin)

(posted in Mammals)

I think that would be a reasonable guess. I don't think any recordings of the saltwater crocodile has been published yet but as the American alligator currently has the highest recorded bite force, it would be expected of the saltwater croc or nile croc to have higher absolute bite forces.

Of course, this is within terrestrial tetrapods and maybe large marine vertebrates like the killer whale would have an even higher bite force; maximum bite force estimated for the great white shark seems to be about the same if not slightly higher than the maximum bite force recorded in alligator (Wroe et al., 2008; http://onlinelibrary.wiley.com/doi/10.1 … 4.x/full).

To add to what Dave's already listed, we should also remember that not all "shared" characteristics are present anymore in modern birds. For instance, early birds like Archaeopteryx still had teeth, clawed fingers on its hands, and a long tail, features (among many others) that made them almost indistinguishable from non-avian theropod dinosaurs (especially now that we know many other theropods possessed feathers). These features were subsequently lost in bird evolution so we don't see them anymore in living ones. But the fact that early birds were very dinosaurian in appearance and features firmly supports the idea that birds are indeed theropod dinosaurs.

If we're talking living reptiles, then my vote is also on the salt water croc (C. porosus). By my criterion of "How big and heavy is the head?" C. porosus wins the category of modern big scary reptiles.

If we extend this back in time to include extinct reptiles, then I'll have to put forward those huge pliosaurs.

(posted in Evolution)

To answer in a slightly different way,

1) life is not appearing out of nowhere: the arsenic utilising bacteria of Mono Lake (California) are not an entirely new and alien form of life with a separate origin from all other known life forms on earth (despite the media hype), but actually shares ancestors with other bacteria. Mono Lake's extremophile bacteria is a strain called GFAJ-1 of the family of bacteria known as Halomonadaceae. So it is a unique adaptation observed in an already known family of bacteria.

2) pretty much all living things have the ability to mutate: disease-causing agents such as bacteria or viruses just have extremely short generation times that beneficial mutations quickly get selected so that we see the effect even on an annual basis (like seasonal flu).

3) see John's answer

I think it is still premature to accept this idea. A recent study using ancient DNA seems to support a close relationship between the American Cave Lion (Panthera atrox), the Eurasian Cave Lion (Panthera spelaea) and the Lion (Panthera leo). Molecular evidences do not seem to support a close relationship between Panthera atrox and Panthera onca.

(posted in Mammals)

Agreed - looks like a pig

The wikipedia article cites Richard Dawkins's The Ancestor's Tale for the statement 'in Australia, marsupials displaced any placental mammals entirely, and have since dominated the Australian ecosystem', which I think is a strange source for this. Dawkins actually writes that other mammals in Australia died out early (with specific reference to a couple of teeth attributed to an extinct group of placentals found in Australia, but nothing younger than 55 million years). There is a difference between 'placentals died out' and 'placentals were displaced'. And there is no source cited by the Wikipedia article for the metabolic reasons.

Australia has been isolated for a long time, in which marsupials and monotremes had practically no competition from placentals. Bats and some rodents did get into Australia more recently but the great majority of placental mammals came with the first human settlers; after which placental mammals have been wreaking havoc. South America was also a haven for marsupials until it joined up with North America and placental mammals swooped in from the north, the so called Great American Interchange. During this exchange, northern placentals moving south was more prominent than southern marsupials moving north (the few exceptions being the N. American opossum). And in the south, placentals pretty much took over the ecosystem.