[揽瓜阁精读] 247. 脊椎动物

冲啊~

Main point:
脊椎动物的进化推测和证明

Structure：
1. 说一个争议
● 强调争议的重要性：因为淡水和海水的生存进化过程截然不同
2. 说有争议的原因和可能得结果
● 脊椎动物的亲戚都住在海水里
● 大部分的鱼的化石都在淡水里
结论-> 脊椎动物可能是从海里转移到了淡水里

3. 争论的依据的证据是什么
● 一个是考古学家的数据：早期化石的脊椎动物的明显生活习惯
● 一个是水和盐在活着的鱼身体里的生理平衡

4. 说为啥判断从海里到河里-海里的证据
● 骨头的小碎片是最早的脊椎动物化石
● 早期踪迹比较分散，但是中期大量出现在固定范围类->著名的harding sandstone
● 直到最近，他们觉得可能是浅海或者河口盐度变化的地方

5. 说为啥判断从海里到河里-河里的证据
● 河里呢，不如海里物产丰富，没陆地植物也没动物，比较贫瘠
-> 不大可能捕食的时候从河口到淡水
● 但是河里有个有点：安全啊！适合繁衍，没天敌，没竞争者，环境稳定

-->最后拓展结论：先在河口附近捕食，然后变强大了可以和海里的动物竞争，再回到淡水里喂养后代
-->这个也不是科学家瞎猜测哦，有些鱼就是这个习性呢，比如salmon...

sevensevenseven

P1 争论：脊椎动物起源于海洋还是淡水。
              -海洋：有捕食、竞争和丰富的食物供应。
              -淡水：多细胞动物少，竞争和捕食者少，食物单一局限于藻类和单细胞生物。
P2 发现：与脊椎动物有关的p动物都生活在海里、
      结论1：脊椎动物最终都由海洋动物来的。
    【转折】因为鱼的存在和化石证据都包括淡水分支，所有脊椎动物的祖先可能是由海洋搬到淡水的。
P3 争论依据：1.古生物数据-早期化石脊椎动物的生存环境
                    2.在活鱼身上的水盐平衡（尤其是无颌鱼）
P4 发现：最老的脊椎动物的皮骨碎片证明脊椎动物在MO时期在HS这样局限性地区数量丰富。
     结论2：HS的脊椎动物生活在浅海区或者盐含量波动的入河口。
P5 淡水环境缺点：食物缺少
     结论3：因此从入河口进入淡水捕食可能性不大。
P6 淡水环境优点：生产繁殖和早期发育的天堂（无捕食者和竞争者、环境<盐、沉淀物、氧气>较入河口更稳定）
P7 推测：原始脊椎生物在淡水繁殖，发育到一定阶段到入河口和浅海部分生活。（以现代某几种鱼类举例）

xixio

247
生词：fauna动物群  sterile无菌的  estuaries河口

Most debated and most important question of origin of vertebrates: occurred in the sea or the fresh water
500 million years ago: fresh water—lack multicellular animals // sea—rich and diverse fauna
==>if in the sea---evolved in the contexts of acute predation, competition, and abundant food supplies
==>if in the fresh water---no predation, no competition and no varied food

The living protochordate relatives of vertebrate all live in the sea + vertebrate derived from marine ancestors
// most living and fossil fishes include freshwater branches--->ancestors of vertebrates might move from sea to fresh water

Debate sources:
1. Paleontological data—habitat of earliest fossilized vertebrates
2.physiology balance in living fishes

Small fragments of dermal bone--->oldest fossils
Figure 2: earliest traces are poorly characterized // in Middle Ordovician they are well known and abundant in …
Harding sandstone vertebrates---jawless fishes with bony shields--- inhabited shallow marine environments or estuaries with salinity

Freshwater----less productive---during early Paleozoic there were no freshwater or plants or animals---the river was more sterile---->not favor movement from estuaries into fresh water
// held an advantage: safe for reproduction and early development

Reasonable lifestyle: breeding in fresh water and feeding and growing in estuaries and the sea

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247脊椎动物
P1: debate question: whether origin of vertebrate occurred in the sea or in fresh water. If in the sea:body evolved acute predation , competition, and abundant food supplies. If in fresh water: no predators or competitors, food limited to algae and unicellular organisms.
P2:vertebrate derived from marine ancestors which may moved from the sea to fresh water
P3: two sources
P4: small fragments of dermal bone is considered the oldest V fossils. Earliest traces of V are sporadic（偶发的，零星的）and poorly characterized except Hs( jawless fish),which been believed to have inhabited shallow（浅的）marine environments or estuaries（入海口）
P5:freshwater rivers has lower production. Early P, rivers maybe more sterile（不育的，贫瘠的）than today
P6: freshwater rivers are food for reproduction and early development.
P7: freshwater protovertebrate would have grown slowly and had limited reproductive rate, so they move to nearby estuaries and coastal marine habitats.（解释从河到marine的原因）early P: born in fresh water and juveniles feeding and growing rapidly in the sea, same as l, s, s, and s today.