Lizards, serpents (snakes) and rhynchocephalia
Skin shed at one time
Tail autotomy (They can lose tails)
Tail composed of bones all the way to tip
Regenerating tail looks different in many species (not true in all though)
They produce a long cartilaginous rod – they do not reproduce the bones that were initially there
In the middle of each vertebra is a premade zone of weakness. They are designed to break – not
just the bones, but also the muscles, which are prepackaged into modules that tear apart
separately. Blood vessels made to break and easily break down, so very little trauma, little blood
loss. When you pull the tail off, something is released triggering tail to wiggle to distract predator.
The cartilage that is regenerated generally doesn’t break. So, when it regrows its tail, can no longer
break from that point onward. So, loses tail closer and closer to body.
This is an ancestral state for lepidosaur, but some species have lost this.
Ancient clade of reptiles dating back to Triassic period (over 200 million years)
Today, a single species: the Tuatara (Sphenodon). Only in New Zealand.
But there was quite a bit of diversity throughout mesazoa.
Very tempting to think of tuatara as model for ancestor of all lizards – but don’t because it’s wrong.
Several important synapomorphies for rhyncocephalia
Acrodont teeth in rhyncocephalians
Specifically refers to how teeth are attached to skull: There are three different arrangements,
Acrodont (on top of jaw), pleurodont (next to jaw on inside margin), or thecodont (from within the
jaw, deep into a socket, each tooth surrounded by bone, like human teeth)
Teeth on palatine
All mammals just have teeth on margins, but many primitive vertebrates have teeth all over inside
Rhyncocephalians have a second row of teeth on palatine bone on top of mouth.
Premaxillary teeth are replaced by a bony outgrowth during ontogeny, as they develop. Premaxillary bone is at front of skull
Rhyncocephalia means “beak head” because of premaxillary bones replacing front teeth
No penis! Like almost all birds. They get their two cloaca together to transfer sperm.
Diapsid skull lacking external tympanum
Lower temporal opening has jugal bone – all lizards have lost the lower bar, the jugal bone, but the
tuatara has it. But if we look at rhyncocephalian fossils, we see that most are also lacking the jugal
bone, so tuatara seems to have reevolved lower temporal bar. So this is NOT an ancestral trait!
Only find on New Zealand, but extinct on many islands because Maori, who colonized New
Zealand, brought rats, which eat baby tuataras. So only islands that are ratfree have tuataras
today. The Cook Strait has one island called Stephens Island, and half of the world population of
tuataras are on this island.
Baby tuataras are called pocket toots
Life in the slow lane – take 13 years to reach sexual maturity and can live at least 60 years, but
there was one captured as an adult and lived 70 more years, a wild one that lived 88 years, so live
a really long time. Eggs take between 11 and 16 months to hatch.
Like turtles and crocodiles, the babies have an “egg tooth” – hardened piece of epidermis,
technically a caruncle, used to poke hole in egg, then it falls off. Lizards and snakes actually have a
real tooth that does the same thing
They also have temperature sex determination
They live in a remarkably cold place, which is why they do everything slowly – the mean
temperature in winter is 9 degrees C (48 F) and in summer, 16 C.
Those are average daytime temps – but most of their activity is at night!
Diet: primarily carnivorous. Basically eat anything they can catch. Since they’re slow, it’s limited.
Generally insects (like the weta)
Tuatara and shearwater – they coexist, but a tuatara will eat the baby shearwaters. Sit and wait
hunting for the most part
Said to have a “third eye” on top of head – only seen when it’s a baby, covered by opaque scale as
it grows. If you look at it under a microscope, it has a lens, nerve connection, it IS an eye! (Parietal
Some lizards have it too, like iguana. The eyes can detect differences in light level, and it’s
suspected that it plays a role in temperature regulation. The pineal gland, that regulates circadian
rhythm, is connected to the eye.
Conservation efforts by New Zealand govt – to get rid of rats, take helicopters, fly over an island
and blanket island with rat poison. Wipe out all the rats on an island!
In Wellington, NZ, built a huge fence, eradicate rats, and reintroduce tuataras back onto mainland
in the Karori Wildlife Sanctuary.
Squamata: 9412 Squamata
Lizards and snakes. Serpents are in the middle of lizards, so lizards is a paraphyletic group.
Squamata comes from latin for “scaly” but all reptiles have scales… Professor Losos prefers just
calling them lizards, or Sauria
About 70 of them
Basically bones in the belly, ribs from the bottom side up. Tuatara and crocodiles and turtles have
them, but lizard do not. Sometimes called “abdominal ribs”
Two penises. Outpocketings of cloacal wall – tissue that grows out from that. Stored inside out in
cloaca, like a glove pulled inside out.
All kinds of ornamentation! Old idea was “lock and key” idea, that different species couldn’t mate
because parts couldn’t matc