It is almost always due to some very special circumstances that traces of land animals survive, as by falling into inaccessible caves, or into an ice crevasse, like the Siberian mammoths, when the whole animal is sometimes preserved, as in a refrigerator.

as ^{(省略句) 作为方式状语从句}

It is almost always due to some very special circumstances that traces of land animals survive, as (traces of land animals survive) by falling into inaccessible caves, or into an ice crevasse, like the Siberian mammoths, when the whole animal is sometimes preserved, as (the whole animal is preserved) in a refrigerator. ^内容补全

• The fossils are sometimes preserved, as in ice caves. ^{正如在冰洞中一样}
• They behave as expected. ^{他们如预期般行事}
• The child reacted as his mother would. ^{这孩子像他母亲一样反应}

crevasse ^{n.deep open crack in the ice of a glacier （冰川的）裂缝}

• The climber fell into a crevasse. ^{登山者掉进了冰川裂缝}
• They crossed a dangerous crevasse. ^{他们穿越了一条危险的冰缝}
• Snow hid the deep crevasse. ^{雪覆盖了深深的裂缝}

mammoth ^{n.an animal similar to an elephant with long hair that lived a very long time ago 猛犸象}

• The mammoth lived thousands of years ago. ^{猛犸象生活在几千年前}
• A frozen mammoth was discovered. ^{一只冻住的猛犸象被发现}
• Mammoth bones were unearthed. ^{猛犸象骨骼被挖掘出土}

This is what happened to the famous Beresovka mammoth which was found preserved and in good condition.

表语从句 ^{解释主语内容}

• This is what I meant. ^{这就是我想说的}
• That was what he experienced. ^{那就是他所经历的}
• Here is what they discovered. ^{这是他们发现的内容}

In his mouth were the remains of fir trees -- the last meal that he had before he fell into the crevasse and broke his back. ^{表系主(主语太长，全部倒装)}

The remains of fir trees ― the last meal that he had before he fell into the crevasse and broke his back ― were in his mouth. ^{没有必要用圆周句、掉尾句}

全部倒装 ^{谓语提前使句式更强调(在主语较长时，常使用 表语 + 系动词 + 主语 的倒装结构。)}

• Gone are the days of innocence. ^{天真无邪的日子一去不返}
• Gone are the days when my heart was young and gay.
• On the floor were toys and clothes. ^{地板上散落着玩具和衣服}
• On the floor were piles of books, magazines and newspapers. 
• Happy is the man who learns from failure. ^{能从失败中学习的人是幸福的}
• Happy is he who has a sound mind in a sound body.

The mammoth has now been restored in the Palaeontological Museum in St. Petersburg.

restore ^修复

• The painting was restored to its original state. ^{这幅画被恢复成原来的样子}
• The old car has been restored. ^{这辆旧车已被修复}
• The museum restored the ancient artifacts. ^{博物馆修复了古代文物}

Other animals were trapped in tar pits, like the elephants, sabre-toothed cats, and numerous other creatures that are found at Rancho la Brea, which is now just a suburb of Los Angeles.

trap ^{v.to prevent sb. from leaving a place, especially a dangerous place 使困在某处;困住}

• Miners were trapped underground. ^{矿工被困在地下}
• He was trapped in a burning car. ^{他被困在燃烧的车中}
• The tourists were trapped by the flood. ^{游客被洪水困住了}
• Dozens of people were trapped in the rubble when the building collapsed. 
• There's no way out! We're trapped!
• After chipping through a wall which was eighteen inches thick, they found that a man had been trapped in the chimney.

tar pit ^{an accumulation of natura tar at the earth’s  surface, especial one that acts as a trap for animals and preserves their bones 沥青坑：地表中天然沥青的集聚场所，尤指使动物不慎陷入其中并保存了它们的骨骼的天然沥青聚集点}

• The fossil was found in a tar pit. ^{化石在沥青坑中被发现}
• Tar pits can preserve bones. ^{沥青坑可以保存骨骼}
• Many ancient animals were trapped in tar pits. ^{许多古动物被困在沥青坑中}

saber-toothed cat / sabre-toothed cat ^{(42 million years ago ~ 11,000 years ago)}

A saber-toothed cat, also called saber-toothed tiger, is any member of various extinct groups of predatory mammals that were characterized by long, curved saber-shaped canine teeth. The large maxillary canine teeth extended from the mouth even when it was closed.

Apparently what happened was that water collected on these tar pits, and the bigger animals like the elephants ventured out on to the apparently firm surface to drink, and were promptly bogged in the tar.

collect ^{v.if a substance collects somewhere, it gradually goes there（ 物体）聚集}

• Rain collected in the bucket. ^{雨水聚集在桶中}
• Water collected at the bottom of the pit. ^{水聚集在坑底}
• Snow collected on the branches. ^{雪积在树枝上}

bog ^{v.to make sth. sink into mud or wet ground（使某物）陷入泥沼}

• The jeep was bogged down in mud. ^{吉普陷入了泥中}
• The tank got bogged down in mud.
• They got bogged during the hike. ^{他们在徒步中陷入泥地}
• The tank bogged in the wet field. ^{坦克陷入湿地}

And then, when they were dead, the carnivores, like the sabretoothed cats and the giant wolves, came out to feed and suffered exactly the same fate.

suffer a ... fate ^{遭遇...命运}

• They suffered the same fate as their ancestors. ^{他们遭遇了和祖先一样的命运}
• The animals suffered a cruel fate. ^{这些动物遭遇了残酷命运}
• The whole village suffered a tragic fate. ^{整个村庄遭遇了悲惨的命运}
• The refugees have suffered an appalling fate.
• The Casino, where she had often danced, had suffered a similar fate.
• The disciples were terrified that they would suffer the same fate as Jesus. 

giant wolf / dire wolf ^{n. a large wolf-like mammal that inhabited North America during the Pleistocene epoch (2,000,000 years ago ~10,000 years ago) 恐狼}

• The Dire Wolf is a pack fighter that benefits when it has other wolfallies around. ^{惧狼是成群结队的攻击者，当有其他同盟的狼在附近时可以得到一些好处。}
• They include the endangered Mexican Wolf and giant Saguaro cactus. ^{包括了濒危的墨西哥狼和巨大的萨挂诺仙人掌。}

There are also endless numbers of birds in the tar as well.

also ... as well  ^{语义重复（Redundancy） 也有…而且也是；又…且也}

• She not only bought a new car, but she also bought a luxury house as well. ^{她不仅买了一辆新车，甚至还买了一套豪宅。【强调范围之广（强调包含关系）】}
• The teachers were tired after the school trip, and the students were also exhausted as well. ^{学校旅行结束后老师们很累，而学生们其实也一样疲惫不堪。【强调参与者之多】}
• He is a talented musician, and he also happens to be a professional athlete as well. ^{他是个有才华的音乐家，而且同时竟然也是一名职业运动员。【强调额外的信息（多重叠加）】}