16-20: Amniota: Reptilia, Aves, Mammalia Flashcards
Describe the differences and relationships between Synapsids, Anapsids and Diapsids
Synapsids = One Skull Opening/Fenestration behind eye (includes Therapsids, Extinct Mammalian Ancestors, and all modern mammals)
Anapsids = No Skull Opening behind eye - might include turtles (based on skull anatomy) but this is debated
Diapsids = TWO Skull Openings behind eye - includes Lepidosaura (Lizards, Snakes and Tuataras) and Archosauromorpha (Crocodilians, Dinosaurs, Birds and possibly turtles)
Summarise the appearance and evolution of Reptilia
Possibly emerged around 350 mya - first unquestionable reptile is Hylonomus, around 312 mya
Major radiation in Permian gave rise to Synapsida, Anapsida and Diapsida
Numerous and diverse in Mesozoic era (e.g., Turtles appeared)
Second great radiation in late Triassic (200 mya) gave rise to dinosaurs and pterosaurs
Birds evolve around 150 mya
All non-avian Dinosaurs extinct by 65 mya -> mammals diversify and increase in size
Describe what was mentioned about the Icthyosaurs
They were extinct aquatic reptiles that thrived during much of the Mesozoic (until around 90 mya)
They evolved from unknown land reptiles, and were viviparous (egg was laid and hatched inside body)
What does “Sauropsida” refer to?
“Sauropsida” largely overlaps with Reptilia, but is broader as it includes all extinct stem-group relatives of reptiles and birds
Summarise the debate surrounding the position of Turtles within the Reptilian Phylogenetic Tree
They were traditionally placed as sister taxon to other reptiles, because their skull anatomy appeared to place them within the subclass Anapsida
However, molecular data has increasingly supported their position within the Diapsida (Hedges and Poling, 1999) - possibly even within the Archosauria along side Crocodilians (2012)
Describe the structure of the amniote egg, and explain the advantages it brings as an innovation
- The amniote egg has a leathery outer shell, which provides external protection and interaction with environment
- Chorion - allows nutrients to pass through and provides protection
- Allantois - forms a sac that facilitates respiration and stores waste (fills up as yolk sac dwindles); eventually fuses with chorion
- Amnion - covers embryo and fills with amniotic fluid for protection
- Air space - for pipping (embryo pierces the inner membrane and starts lung ventilation in air space)
It allows expansion into new niches, as amniotes are no longer bound by the need to reproduce aquatically - the embryo is protected and nourished on land
Also, it lessens the size restriction of single-membrane fish eggs AND better protects the embryo
Describe some key differences reproduction in amphibians and reptiles
- Reptiles show no metamorphosis
- Reptiles show internal fertilisation
- Reptiles lay eggs on land (and they have a shell)
- Extra-embryonic membranes in reptiles
Brieflydescribe Palaeoythris (an early amniote from around the C-P boundary) and the key distinguishing features compared to amphibians
Palaeoythris had a much less sprawling gait and more robust bones - no need to swim anymore
(It was an agile insectivore that appeared similar to modern lizards)
Describe the further anatomical developments seen in Procolophon (reptile from Late Permian to Late Triassic) compared to earlier reptiles like Palaeoythris
- Larger fore- and hind-limbs
- More massive hip- and shoulder girdles
- Stronger vertebral column
-> Much better adapted for fast locomotion
State some key characteristics of the class Reptilia
- Tough, dry skin with keratinous scales
- Ossified skeleton
- Amniotic eggs - no larval stage
- More complex nervous system than ancestors
- More efficient and flexible circulatory system (septated heart)
- Larger lungs with thinner membranes -> more SA and more efficient movement of air
Describe the Anapsid groups mentioned in the lecture
Procolophodon - lived from late Permian to end of Triassic (250-200 mya), broad skull, peg-toothed plant eaters -> fairly similar(ish) to other reptiles
Scutosaurus - lived from Lower to Upper Permian (260 mya) in Africa and Eurasia -> massively built, armoured reptile with complex teeth
Lecture mentions turtles (order Testudines) - but it seems to be controversial if they actually are Anapsids
Describe the key features of Turtles (Testudines)
First appeared in the late Triassic (around 200 mya)
Enclosed within a shell (carapace) with fused vertebrae and lost intercostals
Oviparous and carnivorous
Since the ribs are immobile, with the lungs attached dorsally, breathing must be aided by the Post-Pulmonary Septum, and contraction of a range of different muscles for expiration and inspiration to drive the necessary pressure changes
Describe the process of turtle evolution proposed by Lyson (2013)
Note: Morphological divergence aligns with phylogenetic divergence, and remains plausible whether turtles are considered as crown-Diapsida or not!
- Milleretta showed broad, L-shaped ribs and paired gastralia
- Eunotosaurus showed further broadening of ribs (T-shaped), and shortening of the drunk to 9 dorsal vertebrae
- Odontochelys showed broadening of dorsal neural spines, just 5 pairs of gastralia
- Proganochelys showed complete encapsulation of the scapula within the shell (appears very turtle-like) and ossification of carapace, also just 4 pairs of gastralia
Describe the relationships between the main sub-groups within Diapsida
Lepidosauria:
- Tuataras
- Snakes (+ Amphisbaenians)
- Lizards
[The latter two/three comprise Squamata, the largest reptilian order]
Archosauria:
- Crocodilians
- Dinosaurs incl. Birds (via Theropods)
When did the first Diapsids appear, when did they radiate and what were the distinctive features of the earliest Diapsids?
First appeared in Upper Carboniferous (300 mya)
-> These were athletic, with small, sharp teeth and large neck orbits
Radiated in Late Permian
What is notable about the evolution of the Tuatara?
Share many features with their Mesozoic ancestors (one of the slowest rates of morphological evolution among the vertebrates)
Describe the key features of lizards
Lizards are a diverse group of terrestrial burrowers and climbers
Most live in hot and arid climates - all are ectothermic
Moveable eyelids, keen vision, limited hearing
Semi-solid urine and diverse feeding mechanisms
They are technically paraphyletic, as some lizards are more closely related to snakes than they are to other lizards
Describe the key features of the Amphisbaenia
“Worm-like Squamates”
- Most lack limbs, although a few have front limbs
- Robust skull for burrowing
- Absence of visible eyes and ears - hidden under skin
- Can walk backwards as well as forwards
Interesting biogeography - several major dispersals in Cenozoic, after breakup of Pangaea, implying continental drift may play less of a role in dispersal than previously thought
Describe the key features of the Suborder Serpentes
Limbless Squamates, lacking pectoral AND pelvic girdles (though vestiges thereof in boas and pythons)
Ribs along length of body increase rigidity
Highly kinetic skull (4 bar system -> gape can be very large) allows diverse feeding options
Jacobson Organ - a richly innervated chemosensory epithelium (forked tongue places food particles onto organ, can detect heat from prey)
Describe the features of the Crocodilians
Largest living reptiles (5-7m) with 64-68 teeth
Found in fresh AND saline water (salt glands can remove excess salt)
Closest living relatives to birds (and dinosaurs)
Describe the locomotion of the Dinosauria common ancestor, and the kind of adaptations this may have required
BIPEDAL with fully erect posture (like all dinosaurs except Cerotopsians)
Needed hind limbs much longer and more robust than forelimbs (and specific adaptations in bones such as the cervical vertebrae, fibia, tibula, etc. to support this)
Name some of the bones whose features (e.g., size, connection to other bones or muscles) are synapomorphies of Dinosauria
Ischium, Ilium + Pubis (Upper leg/Hip)
Tibia + Fibula (Lower leg)
Radius and Humerus (Upper limb)
Several bones in skull
What are the two main groups of dinosaurs, what are some key sub-groups within these, and what key feature distinguishes them?
Saurischia (“Lizard-Hipped”) and Ornithischia (“Bird-Hipped”)
Saurischia includes Sauropodomorpha and Theropoda, while Ornithischia includes Thyreophora, Margniocephalia and Ornithopoda
The structure of the hip joints is distinctly different between these two groups
Note: birds actually evolved from Saurischia, not from “Bird-Hipped” Ornithischia
When were the earliest known dinosaurs (and what were two examples)?
Earliest part of the Late Triassic (231 mya)
Eoraptor and Herrasaurus were two examples
Explain why some dinosaurs were quadrupedal, despite their common ancestor being bipedal?
This is a very rare transition in evolutionary history, but happened in three Ornithischian lineages
The most popular explanation is the expansion of head size and armouring of the skull - which may partially explain it, but the selection pressures in each of the three cases were different
-> Maybe more BR? ;)
Name the (mentioned) characteristics which can be reconstructed from fossil evidence using biological understanding?
Weight, Speed, Strength, Some Behaviour, Blood Temperature and Colour
Explain how weight of an extinct organism (e.g., a Dinosaur) can be reconstructed, how reliable the methods are, and the significance of working this out
Significance: Body Mass is actually the MOST important biological measure, as it impacts MANY key biological processes
The traditional method was to create a sculpture, based on the fossil evidence, then weigh the sculpture and scale up to full size - this was obviously unreliable and controversial
Another approach has been to find a skeletal measurement that seems to correlate well with body size among living species, and extrapolate [HOWEVER, large error bars when extrapolating outside calibration range - e.g., dinosaurs - resulting in a wide range of estimates]
You can also scan and digitalise physical skeletons, then estimate total body volume using software and calculate mass using known vertebrate tissue density [This is more reliable BUT does require a complete skeleton]
-> MORE POSSIBLE BR ;)
Explain how Sellers and Manning estimated the top speed of dinosaur species, and the advantage of this method over the more traditional methods of doing so
They created a musculoskeletal computer model of various species based on fossil evidence, then ran a simulation of their speeds
This allowed them to directly address assumptions about the animal’s morphology, whereas traditional methods, such as anatomical comparisons, bone scaling and ground reaction force analyses hide these assumptions
Describe the significance of bones in reconstructing dinosaur biology and physiology
Bones are the main things that actually fossilise, meaning they are often the most significant preserved part of an organism and offer the most evidence
Their shape and size is important for estimating strength, AND modelling them helps to estimate top speed
Explain the debates surrounding the long necks of certain dinosaurs
It was previously argued that the largest dinosaurs were TOO large to be terrestrial, and thus must have been aquatic
However, there are trackways of these dinosaurs on land, and their lungs would not have been able to expand sufficiently if they were 8m deep in water, due to the pressure
There are, admittedly, other challenges to having a long neck, e.g., the heart has to work harder to pump blood up to the head, but giraffes prove this is possible to overcome
What was the debate surrounding a potential dinosaur heart first described in 2000?
Fischer et al claimed the fossil had a four-chambered heart and implied a high metabolic rate in the dinosaur
However, researchers in Chicago criticised this paper in 2003 for interpreting too much from an incomplete fossil, and also stated that the presence of a four-chambered heart in dinosaurs is to be expected due to its presence in birds and crocodiles, making this a less diagnostic feature than initially claimed
Describe what is meant by “neck springs?”
Neck Springs are a proposed explanation for how a dinosaur with a long neck (for example Diplodocus) may have solved the problem of raising its heavy neck again after lowering it to feed
Drawing comparison with the modern turkey, it was suggested that dorsal ligament tension would have extended the neck back up
Give some examples of how some behaviours/ecology can be inferred/reconstructed from dinosaur fossils
- The thick skulls of Stegaceras have been interpreted as evidence that they engaged in ramming behaviour when competing for mates, like sheep
- The modified (fused) caudal vertebrae of Ankylosaurus formed a club -> could have been used as a weapon for fighting
- Footprints can provide evidence for prey/predator ecology - though have to be careful to not assume too much because could just be two unconnected individuals walking through a similar area
What are the main theories for the function of the frills of Triceratops?
Most popular theory in recent years has been sexual selection (i.e. ornamental function)
However, some have argued that the damage commonly seen on these structures aligns well with a deer-style intraspecific pushing combat - Farke (2004) showed that this was possible, but there is currently insufficient evidence to infer that it DID happen
Some have also argued that the frills were for defence against predators, e.g., T rex, which was around at the same time
Note: horn mass:reach ratio suggests Triceratops would be an unusual example if their horns were for fighting
Are dinosaurs thought to be warm or cold blooded - and what is the evidence for this?
WARM-BLOODED (Homoiothermic)
They had nests similar in structure to modern bird nests, which only makes functional sense if warm-blooded parents were warm blooded
The low SA:Vol ratio of dinosaurs also makes cold-bloodedness unlikely
How can the colour of extinct species be interpreted?
The DNA that would have encoded pigment proteins cannot be preserved long enough to offer any evidence
However, other things that contribute to pigmentation (such as metals!) can survive, and thus offer SOME clues about the colour of dinosaurs
Also bear in mind that dinosaur vision was different to our own, so colour would have been selected differently as well
State some key similarities and differences between birds and reptiles
- Egg-laying
- Scales on legs
- Pneumatised bones
- Several skeletal similarities (e.g., Columella - single middle ear bone; lower jaw consists of several bones; intertarsal ankle joint)
-> Birds are ENDOTHERMIC, have 4-CHAMBERED HEARTS, and have FEATHERS
