Direct ancestors of extant animals

[Reptilia]

My knowledge of a proper terminology is very poor, so forgive me if I say something which doesn't sound right from a scientific standpoint. I simply wonder if there are extinct animals that we can safely assume would have looked exactly like their extant counterparts, maybe just in a different size.

I give a few examples of what I have in mind, but I'm not 100% sure if they actually fit this category, so correct me if I'm wrong: Megalania prisca and Varanus komodoensis, Canis dirus and Canis lupus, Ursus spelaeus and Ursus arctos, Carcharodon megalodon and Carcharodon carcharias, etc.

Links to scientific papers, images and various sources would be welcome.

[BlueKrono]

That's a pretty solid list there. I've seen Gigantopithecus depicted with orangutan hair pattern and even color, but of course there's no way to truly know in the absence of preserved hairs or depictions by prehistoric humans on cave walls, which, of the species you mentioned, I'm not sure any exist.

[stargatedalek]

Absolutely none of those are an ancestor to the modern equivalent.

Actually, Megalania (or as some call it and I prefer it; Varanus komodoensis prisca) is probably descended from the modern Komodo dragon.

I can't speak for bears or wolves, but Megalodon probably looked very little like a great white shark, its closest living relatives are mako sharks (of which it was not ancestral).

I'm fairly certain there are no extinct species of which we have a living direct descendant (unless you count things like "whatever the first chicken was assuming it wasn't as some are now" or "the initial goldfish hybrids of several as yet not 100% determined species").

Actually, there are a few extinct animals, IE Raphus, that still have almost direct ancestral genera alive today.

[Reptilia]

Actually, Megalania (or as some call it and I prefer it; Varanus komodoensis prisca) is probably descended from the modern Komodo dragon.

That means that Komodo dragons already existed before Megalania?

I can't speak for bears or wolves, but Megalodon probably looked very little like a great white shark, its closest living relatives are mako sharks (of which it was not ancestral).

So restorations of Megalodon as a generic giant shark are likely wrong?

[Pachyrhinosaurus]

The only case where a direct fossil ancestor is known for a modern species is with Bison where Bison priscus evolved into B. latifrons, which evolved into B. antiquus to B. occidentalis to finally the modern B. bison.

[stargatedalek]

Actually, Megalania (or as some call it and I prefer it; Varanus komodoensis prisca) is probably descended from the modern Komodo dragon.

That means that Komodo dragons already existed before Megalania?

I can't speak for bears or wolves, but Megalodon probably looked very little like a great white shark, its closest living relatives are mako sharks (of which it was not ancestral).

So restorations of Megalodon as a generic giant shark are likely wrong?

Megalania is a great example of gigantism. When the Komodo, an already large predator, found a full sized continent with prey to match it adapted to take best advantage.





I would say if anything Megalodon should be far more generic! The white shark is a lot more distinct than often given credit, everything from the visible border of dark and light on its flanks to its bulky proportions is unique to it alone.

[Papi-Anon]

Recent depictions of Megalodon have it as a 50-something foot long, stockier version of modern great whites instead of the classic scaled-up great white interpretation. Whether the coloration was similar or not is anyone's guess.

No one here mentioned ancient humans! Correct me if I'm wrong, but wasn't Heidelbergensis the direct ancestor to Neanderthals, Denisovans, and (anatomically) modern humans? Since modern-day humans of caucasianoid and mongoloid ancestry are descendants of some cross-breeding between those three species wouldn't that put Heidelbergensis as the last single ancestral species?

On the subject of ancestors, I keep reading Pikaia as being referred to as the ancestor of vertebrates, has that been confirmed or is that an exaggeration?

[Gwangi]

I would say if anything Megalodon should be far more generic! The white shark is a lot more distinct than often given credit, everything from the visible border of dark and light on its flanks to its bulky proportions is unique to it alone.

The salmon and porbeagle shark disagree with you on visible borders and bulky proportions.

[Crackington]

I was also  wondering about the early humans. I know there is scant evidence, but are we able to say that Australopithecus is ancestral to modern humans?

On the pikaia point, Prof Simon Conway Morris of Cambridge University has recently identified an ancestor that may be the base for all the vertebrates:

https://www.cam.ac.uk/research/news/bag-like-sea-creature-was-humans-oldest-known-ancestor

[BlueKrono]

In absence of DNA evidence I don't think we can say for sure that something was directly from something else. With more recent species like hominids it's a pretty safe bet since there would likely be fossil evidence if there were any other option. But we always get surprises, like the enigma of the Denisovans. We know that we would have evolved from a deuterostome at around this time and a proto-vertebrate around Pikaia's time, but there may have been other species around at the time that were our actual forbears that just weren't preserved in the fossil record, just like someone millions of years in the future might assume that humans were descended from chimpanzees when in fact we are just two branches of the tree that split about 4 million years ago.

[stargatedalek]

I would say if anything Megalodon should be far more generic! The white shark is a lot more distinct than often given credit, everything from the visible border of dark and light on its flanks to its bulky proportions is unique to it alone.

The salmon and porbeagle shark disagree with you on visible borders and bulky proportions.

Touche! I forgot about our own local porbeagles, poor things don't get any love

It's still far from the norm among large or open ocean sharks despite near all popular depictions furthering that myth. Like how almost every dolphin in media ever is a Bottle-nose (even when labelled otherwise). It certainly isn't impossible to depict Megalodon with similar patterns, but given all of these species are so closely related and Megalodon is slightly removed I will still argue the colouration is less likely and its frequent use is entirely because of tropes.

Recent depictions of Megalodon have it as a 50-something foot long, stockier version of modern great whites instead of the classic scaled-up great white interpretation. Whether the coloration was similar or not is anyone's guess.

The proportions are also guesswork. It's only known from vertebrae and jaws.

[Halichoeres]

A couple of things make it hard to tell whether something is a direct ancestor. One is that phylogenetic reconstruction methods are clustering algorithms, so they can find sisters, but not mothers and daughters. That's just a byproduct of the underlying mathematics. So it's virtually certain that some things currently regarded as sister taxa are instead ancestor and descendant, although in each individual case it's exceedingly unlikely. For most kinds of organisms, the probability of fossilization is so low that it would really be asking too much to expect the record to preserve complete lineages.

It is possible to look at a tree that shows things as sisters and based on other information formulate a hypothesis that one is the other's ancestor. Strict Popperians might not even regard that as science, since the hypothesis is virtually impossible to refute. (Thankfully there are fewer strict Popperians than there used to be.)

Anyway, there are a few situations where you can reliably infer direct ancestors. You can get short-term (usually less than a million years) direct records of ancestors in varves, which are seasonal sediment layers in lakes that are deep enough to have anoxic layers with little turbidity. On a longer scale, you can get something very close to complete lineages from benthic foraminiferans and maybe graptolites. But for big vertebrates, it's too much to ask. The most we can say for Saccorhytus, Pikaia, Romundina, Tiktaalik, Thrinaxodon, Eomaia, Plesiadapis, or Australopithecus is that they were probably not-too-distantly related to our ancestors.

[Crackington]

I guess we could be stood in a museum looking at a fossil which really was one of our ancestors, but we could never know for sure in the absence of DNA evidence. We'd need time travel to be certain, now where's that pesky doctor!

[Gwangi]

Touche! I forgot about our own local porbeagles, poor things don't get any love

It's still far from the norm among large or open ocean sharks despite near all popular depictions furthering that myth. Like how almost every dolphin in media ever is a Bottle-nose (even when labelled otherwise). It certainly isn't impossible to depict Megalodon with similar patterns, but given all of these species are so closely related and Megalodon is slightly removed I will still argue the colouration is less likely and its frequent use is entirely because of tropes.

I have a lot of love for the Lamna genus. They're like pudgy little white sharks.  But overall I do agree with you, I find it frustrating that Megalodons are always scaled up white sharks.

[CAWCarcharo]

I think the Genus of Panthera is hard to exactly track in the direct ancestry part as Panthera leo ancestry to my knowledge has not been exactly determined, Panthera tigris has an distant ancestor recognised in Panthera zdanskyi but it lived around 2.55 to 2.16 million years ago while Panthera evolved around  1.6 to 1.8 million years ago and no transitional species of form has be determined or published upon, Panthera pardus has been confirmed to most likely have a described direct ancestor, Panthera onca may have directly evolved from Panthera gombaszoegensis which in turn could have evolved from either Panthera schreuderi or Panthera toscana (though it is thought that Panthera Toscana is an earlier form of Panthera gombaszoegensis and is therefore a synonym to Panthera gombaszoegensis) and Panthera uncia has a confirmed ancestor in Panthera blytheae though it is not direct.