Eutheria

Question 1

Placental mammals

Answer 1

extended intrauterine gestation
up to 3 molars (except Otocyon fox, Trichechus manatee, and Heliophobius rodent)
reduced number incisors (3 or fewer)
lack epipubic bones

most replace premolars, canines and incisors

Question 2

Juramaia

Answer 2

Cretaceous eutherian
5 premolars
epipubic bones

Question 3

Placental super-ordinal groups

Answer 3

Xenarthra
Afrotheria
Laurasiatheria
Euarchontoglires

Question 4

Exceptions to mammal 7 cervical vertebrae

Answer 4

3 manatee species in Trichechus genus- 6

3 sloth species in Bradypus and Choleopus genera, 8-10 and 5-6 respectively

In sloths, variation between individuals, not for manatees

Question 5

Why 7 cervical vertebrae

Answer 5

Buchholtz (2012, 2014)
developmental connection between diaphragm and cervical spinal nerves constrains capacity of vertebral regionalisation to vary
diaphragm innervated by phrenic nerves derived from cervical spinal nerves, which traverse pleural cavity from neck to top of abdomen
To change number of vertebrae, would need to change somitogenesis, but is needed for diaphragm formation

Question 6

Primaxial-abaxial shift

Answer 6

Primaxial mesoderm= somite –> skeletal elements
abaxial mesoderm= lateral plate –> limb girdles

Buchholz and Stepien, 2009, proposed that ribcage and girdles shifted downwards in Bradypus, making the neck longer and tail shorter, but total number of vertebrae conserved

Proof:
mammal embryos, 7th vertebral centrum ossifies last
In Bradypus, last to ossify is well anterior to ribcage- not last cervical vertebrae, primaxial vertebral identities unchanged

Question 7

Mammal pseudogenes

Answer 7

whales and manatees- more olfactory pseudogenes
blind mammals- optical pseudogenes
vegetarian pandas- pseudogene for taste receptor for amino acids in muscle tissues