Exam 27: The Rise of Animal Diversity

The last common ancestor of all bilaterians is thought to have had four Hox genes (genes that regulate development of posterior-anterior axes and body segments). Most extant cnidarians have two Hox genes, except Nematostella, which has three Hox genes. On the basis of these observations, some have proposed that the ancestral cnidarians were originally bilateral and, in stages, lost Hox genes from their genomes. If true, this would mean that

During chordate evolution, what is the sequence (from earliest to most recent) in which the following structures arose? 1) amniotic egg 2) paired fins 3) jaws 4) four-chambered heart

Please use the following information to answer the question(s) below. Figure 27.2 Fishes that have swim bladders can regulate their density and thus their buoyancy. There are two types of swim bladder: physostomous and physoclistous. The ancestral version is the physostomous version, in which the swim bladder is connected to the esophagus via a short tube (Figure 27.2). The fish fills this version by swimming to the surface, taking gulps of air, and directing them into the swim bladder. Air is removed from this version by "belching." The physoclistous version is more derived and has lost its connection to the esophagus. Instead, gas enters and leaves the swim bladder via special circulatory mechanisms within the wall of the swim bladder. -The presence of a swim bladder allows the typical ray-finned fish to stop swimming and still

Which of these, if true, would support the claim that the ancestral cnidarians had bilateral symmetry? 1) Cnidarian larvae possess anterior-posterior, left-right, and dorsal-ventral aspects. 2) Cnidarians have fewer Hox genes than bilaterians. 3) All extant cnidarians are diploblastic. 4) All cnidarians are acoelomate.

Which of the following animal groups is entirely aquatic?

Which of these might have been observed in the common ancestor of chondrichthyans and osteichthyans?

Fossil evidence indicates that the following events occurred in what sequence, from earliest to most recent? 1) Protostomes invade terrestrial environments. 2) Cambrian explosion occurs. 3) Deuterostomes invade terrestrial environments. 4) Vertebrates become top predators in the seas.

Evidence of which structure or characteristic would be most surprising to find among fossils of the Ediacaran fauna?

The feeding mode of the extinct conodonts was

Which of these characteristics added most to vertebrate success in relatively dry environments?

Which of the following are the most abundant and diverse of the extant vertebrates?

Chordate pharyngeal slits appear to have functioned first as

If wild dogs take part in cooperative hunting, they will likely have a better outcome than if they hunt alone, especially if they share the prey. The dogs that cooperate are increasing the survival probability of one another. This is an example of

What should be true of fossils of the earliest tetrapods?

One important evolutionary change that occurred with the rise of animals is

Why is the amniotic egg considered an important evolutionary breakthrough?

Some researchers claim that sponge genomes have homeotic genes (genes that regulate development of anatomical structures), but no Hox genes (genes that regulate development of posterior-anterior axes and body segments). If true, this finding would

-What is true in the molecular phylogeny (B) that is not true in the traditional phylogeny (A)?

Which of the following belong to the lobe-fin clade?

Sponges are most accurately described as