Monotremata

Question 1

Ornithorhinchidae

Answer 1

Platypus
Ornithorhuncus anatinus only extant species/genus 9(duck-billed)
East coast of Australia
hindfoot spur, injects poison in males, intraspecific competition
“duck” bill- covered w skin and electrosensitive, primary means of prey detection- triangulation (eyes and ears covered w skin underwater)
aquatic- webbed feet
don’t carry round eggs, post-hatching young develop in burrow for around 4 months
keratin teeth, no enamel

Question 2

Tachyglossidae

Answer 2

Echidnas
Tachyglossus aculeatus- short-nosed
Zaglossus bruijni- western long-nosed
Zaglossus attenboroughi- Attenborough's
Zaglossus bartoni- Eastern long-nosed

Zaglossus highly endangered, only a few localities in New Guinea highlands
Diet of earthworms
Tachyglossus= mymercophageous, no teeth, degenerate lower jaw, sticky, protrusible tongue

“mastication” at back of mouth between keratinous base of tongue and roof of mouth
females seasonally develop pouch to protect and incubate egg

Question 3

Monotreme synapomorphies

Answer 3

cynodont-like pectoral girdle
excretory and reproductive tracts open into cloaca
adult females lay eggs, ovum meroblastic (asymmetric division)
adults lack teeth
cochlea not coiled

Question 4

Australia Mesozoic/tertiary fossil localities

Answer 4

Riversleigh (late Oligocene-Miocene, 20 ma)
Murgon (early Eocene, 55 ma)
Lightning Ridge, Dinosaur Cove, Flat Rocks (early Cretaceous)

Question 5

Obdurodon dicksoni

Answer 5

Oligocene (20 ma)
Riversleigh platypus
enamel-covered teeth
wrapping cingulum (australosphenidan clade character)

Question 6

Monotrematum

Answer 6

teeth found in Paleocene of Argentina, reflects geology (connection Australia -> South America)
at KT boundary, 66 ma

Question 7

Teinolophos

Answer 7

Flat Rocks, over 100 ma
teeth resemble those of Obdurodon- w tightly compressed anterior part and wrapping cingulum
believed to be closer to platypus- presence of electrosensitivity, based on cranial nerves:
-driven by trigeminal nerve V, therefore nerve large
-in platypus, evidence for high V3 (part of nerve innervating lower jaw)- mandibular canal enlarged
-fossil jaw also has larger mandibular canal

HOWEVER- small fossil therefore would expect big

if true, suggests ornithorhynchids have ancient history independent from echidnas, and lineages will have diverged over 100 mya (predates Oligocene). Would mean ghost lineage for echidnas.

Argues by Rowe et al. 2008- Teinolophos crown monotreme
Although previously considered stem based on molecules, morphology and ecology, which would indicate a much more recent ancestry for echidnas

Question 8

Dual origin hypothesis of tribosphenic occlusion

Answer 8

Luo et al. 2001 argue that Jurassic tribosphenic taxa like Ambondro and Asfaltomylos were closer to monotremes than therians, and consequently tribosphenic occlusion evolved convergently