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Thread: Were any of our ancestors bigger than us?

  1. #1
    Join Date
    Apr 2010

    Were any of our ancestors bigger than us?

    Are homo sapiens the largest/ fiercest creature in our evolutionary history?
    It seems we evolved from small fish, to small warm blooded reptilians to small furry primates etc.
    It seems odd to me that in such a long evolutionary history, we are the largest in our family tree?
    "It's only a model....?" :-)

  2. #2
    Join Date
    Feb 2005
    Two large primates

    That's as big as any of our relatives ever got, so far as I know.

  3. #3
    Join Date
    Oct 2006
    The primates bigger than us are not ancestral to us. All of our primate ancestors are smaller than us. Even before primates were primates, their immediate ancestors were already tree-dwellers, maybe on average bigger than modern squirrels or weasels but still smaller than the biggest monkeys. Life in trees just isn't usually conducive to massive size. And any primarily ground-dwelling ancestors would be from so long ago that they were rather soon after, or even within, the age of dinosaurs, during which mammals stayed pretty small no matter where they lived (which established a starting point that would take time to get away from for any that ever would do so at all).

    But back before the age of dinosaurs, we could have had some bigger ancestors. Before the dinosaur-mammal competition settled into dividing the niches up so mammals dominated at small sizes and dinosaurs dominated at large sizes, large sizes were pretty common in both lineages, and we have no way to tell which species from back then were and weren't ancestral to us. The largest Permian synapsids were comparable to today's rhinos & hippos. More typical average sizes, with plenty of examples both above and below, might have been more like 1Ĺ meters (5') in length, which is less than an average human height but loosely the same overall body size range as us, given the differences in proportions making us leaner for our heights and them stockier & heavier for their lengths. (At that size they'd have smaller limbs but bigger torsos & skulls.)

    I believe the earliest identifiable amniotes (a stage of development before synapsids & diapsids were synapsids & diapsids; the ancestors of both) were all in the size range of most modern non-Komodo lizards. But before that, there's another round of large sizes among our possible ancestors, back when they were still essentially amphibians. Some of those could get as big as crocodiles... again, with no way to tell which ones were and weren't our ancestors. Before that, into the age of land-walking fish, we're looking at a group that wasn't really small for fish but was usually smaller than us, more like an average or slightly above-average dog in most cases, but the group did include Eusthenopteron at almost 2 meters and Tiktaalik above that and up to 3. Before that, we're talking about aquatic sarcopterygians, which are a pretty big group of fish overall. The biggest known one was 7 meters long. Both modern groups that are still "fish" can get up to 2 meters long.

    So, between our fishy, amphibianish, and reptilish ancestors from before the dinosaurs and all the way back into the water, our ancestors' sizes could have fluctuated above and below our current size more than once.

  4. #4
    Join Date
    Apr 2010
    i wonder if the bigger a species is, the more ‘locked’ into a particular niche.. the less able to adapt to changing environmental conditions.
    This is just speculation, but in this scenario- large creatures grow larger or go extinct (unless isolated on an island)
    that could explain why we are bigger than our ancestors?
    is there any generally observed process where species evolve to be larger and larger in a 1-way ratchet effect.... or do you get a zigzag graph if you plot the history of a species?
    e.g. the ancestors of horses started off very small...
    I believe there is evidence that on isolated islands, animals seems to evolve smaller sizes... possibly explaining ‘hobbits’ (homo florensis).
    And obviously, life started small... so presumably most liviing things have stayed small?
    "It's only a model....?" :-)

  5. #5
    Join Date
    Jun 2005
    Regarding the size issue, Iím under the impression that larger animals tend to have a longer lifespan and thus longer reproduction cycle, which does tend to make them less adaptable.

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