Rise of Animals

Question 1

What are the oldest animals discovered so far?

Answer 1

Fossil embryos and larvae 0.15-1.2mm in diameter from the Precambrian Doushantuo Formation in southwest china
Some of these embryos are lobed and resemble those of living animals including molluscs and some annelids (however relating these embryos to living forms is controversial as none of them display developmental characteristics exactly like those of invertebrate larvae alive today

Question 2

What are the oldest macroscopic fossil animals?

Answer 2

The Ediacaran animals which range in age from 565-543 MYA they consist of frond like animals, probable sea anemones, disc-like probable jellyfish and some that resemble trilobites and molluscs

Question 3

What are vendobionts?

Answer 3

This is the term used to describe ediacaran forms which appear unrelated to extant taxa

Question 4

Why are the Ediacaran animals affinities to Cambrian or living groups unclear?

Answer 4

These animals are frequently poorly preserved

Question 5

What are the two proposed hypopthesis for the relationships of the vendobionts?

Answer 5

That they represent a group of animals unrelated to extant forms that died out completely
That they represent stem groups of extant taxa such as cnidarians

Question 6

What are the oldest examples of ediacaran animals?

Answer 6

Fossils from eastern newfoundland 575-560MYA

Question 7

What discovery has led to the suggestion that Ediacaran animals represent a single clade that is probably unrelated to any living animals/

Answer 7

A paper in 2004 reported that a new deposit of the Newfoundland formation preserves fossils in finer sediment than those previously known, these fossils have the same quilted frondose and plumose structures seen elsewhere but also show evidence of a semi-rigid internal skeleton
This leads to the suggestion that ediacaran animals represent a dead end lineage that was replaced by the animal phyla that appeared just before or during the Cambrian explosion

Question 8

What provides evidence for metazoan life in the late Precambrian?

Answer 8

Trace fossils which represent burrows, crawling tracks and feeding scratches provide further evidence for metazoan life in the late Precambrian as burrows probably require triploblastic level of organisation though crawling traces can be made by animals that lack body cavities like flatworms

Question 9

What characterizes the early Cambrian?

Answer 9

This period 543-519 MYA is characterized by a layer of tiny <1mm-5mm fossil shells most of which were either cone like or cap shaped termed small shelly fossils, they are thought to represent the remains of early molluscs

Question 10

What two periods are the early Cambrian divided into?

Answer 10

The subtrilobitic perios before the appearance fo the trilobites and trilobitic where trilobites are present

Question 11

What are trilobites?

Answer 11

These are group of organisms that appeared about6519 MYA and were the dominant group of marine arthropods for nearly 300 million years

Question 12

What is the Burgess Shale?

Answer 12

This is the best known Cambrian fossil deposit discovered by the American palaeontologist Chrales Doolittle Walcott and is about 505 MYA
It contains exceptionally well preserved fossils showing traces of soft anatomy and in many cases detail in three dimensions
The fauna of this fossil deposit contains a huge variety of animal forms some seem related to extant groups such as sponges, cnidarians and bilaterians scuh as priapulids, polychaetes and arthropods however the majority of the fossils do not fall into extant groups

Question 13

Other than the burgess shale what other important Cambrian fossil sites are there?

Answer 13

Chengjiang in southern China and Sirius Passet in North Greenland these are both slightly older than the Burgess shale at 515 and 517 MYA respectively
These sites both contain fossils similar to those found in the Burgess Shale with their older age suggesting that the burgess shale contains the remains of a relict fauna

Question 14

What are the problematica?

Answer 14

This is a term used to refer to the enigmatic Cambrian forms reflecting their uncertain affinities
Early researches such as Wlacott shoehorned many of these organisms into extant phyla while more recently others such a Gould have advocated placing these organisms into a Phyla of their own

Question 15

Why the Cambrian Explosion is named the way it is?

Answer 15

All of the Cambrian fossil sites date from a narrow window of only 15 million years in the lower and middle Cambrian this is preceded by a large 26 MY gap until the Ecidiaran faunas is seen the fact that the appearance of Cambrian animals is so sudden has led to the term Cambrian explosion

Question 16

What is Darwin’s Dilemma with reference to the Cambrian explosion?

Answer 16

Darwin saw this explosion as a critical problem for his theory of evolution as it suggested rapid rather than gradual change. Darwin believed this was most likely due to inadequacy fo the Precambrian fossil record

Question 17

What is the disparity debate?

Answer 17

This is a debate over the nature of the Cambrian explosion Simon Conway Morris believes that the Cambrian animals mostly represent branches off the lineages that led into extant groups of animals causing him to suggest that the disparity of Cambrian animal taxa is little different from that which we see in extant groups believing that animal groups evolved over a long period of time by the same conventional evolutionary mechanisms we see right throughout the evolutionary history of animals
Gould on the other hand believes that many of the Cambrian animals do not fit within extant phyla and thus beling to lineages that no longer exist on earth, as such the disparity or range of body plans of animals alive today is less than it was in the Cambrian interpreting these disparate lineages as having been the result of evolutionary processes that have not occurred again in the history of life on earth. Gould sees the Cambrian explosion as a fundamental lesson for our understanding of life whereby an early flowering of disparate animal forms has been winnowed down by the grim reaper of contingent extinction