The Genome of the Last Surviving Member of an Order from which Dinosaurs, Birds, Mammals... [View all]

[NNadir]

...and modern reptiles evolved has been sequenced.

The paper to which I'll refer is this one: The tuatara genome reveals ancient features of amniote evolution (Gemmel et al., Nature, https://doi.org/10.1038/s41586-020-2561-9).

An amniote is an animal whose embryonic development takes place in an amiotic fluid surrounded by a membrane called a chorion. This class of animals includes all reptiles, birds, and mammals.

The paper is open sourced, anyone can read it. It describes the last member of a class of animals which once dominated the Earth before branching out to evolve as dinosaurs, birds, modern reptiles, and mammals including that somewhat destructive animal the human being.

An excerpt from the abstract:

The tuatara (Sphenodon punctatus)—the only living member of the reptilian order Rhynchocephalia (Sphenodontia), once widespread across Gondwana1,2—is an iconic species that is endemic to New Zealand2,3. A key link to the now-extinct stem reptiles (from which dinosaurs, modern reptiles, birds and mammals evolved), the tuatara provides key insights into the ancestral amniotes2,4. Here we analyse the genome of the tuatara, which—at approximately 5 Gb—is among the largest of the vertebrate genomes yet assembled. Our analyses of this genome, along with comparisons with other vertebrate genomes, reinforce the uniqueness of the tuatara. Phylogenetic analyses indicate that the tuatara lineage diverged from that of snakes and lizards around 250 million years ago.

From the introduction:

The tuatara (Sphenodon punctatus)—the only living member of the reptilian order Rhynchocephalia (Sphenodontia), once widespread across Gondwana1,2—is an iconic species that is endemic to New Zealand2,3. A key link to the now-extinct stem reptiles (from which dinosaurs, modern reptiles, birds and mammals evolved), the tuatara provides key insights into the ancestral amniotes2,4. Here we analyse the genome of the tuatara, which—at approximately 5 Gb—is among the largest of the vertebrate genomes yet assembled. Our analyses of this genome, along with comparisons with other vertebrate genomes, reinforce the uniqueness of the tuatara. Phylogenetic analyses indicate that the tuatara lineage diverged from that of snakes and lizards around 250 million years ago.

It is also a species of importance in other contexts. First, the tuatara is a taonga (special treasure) for Māori, who hold that tuatara are the guardians of special places2. Second, the tuatara is internationally recognized as a critically important species that is vulnerable to extinction owing to habitat loss, predation, disease, global warming and other factors2. Third, the tuatara displays a variety of morphological and physiological innovations that have puzzled scientists since its first description2. These include a unique combination of features that are shared variously with lizards, turtles and birds, which left its taxonomic position in doubt for many decades2. This taxonomic conundrum has largely been addressed using molecular approaches4, but the timing of the split of the tuatara from the lineage that forms the modern squamates (lizards and snakes), the rate of evolution of tuatara and the number of species of tuatara remain contentious2. Finally, there are aspects of tuatara biology that are unique within, or atypical of, reptiles. These include a unique form of temperature-dependent sex determination (which sees females produced below, and males above, 22?°C), extremely low basal metabolic rates and considerable longevity2.

A graphic from the paper:



The caption:

a, The tuatara, (S. punctatus) is the sole survivor of the order Rhynchocephalia. b, c, The rhynchocephalians appear to have originated in the early Mesozoic period (about 250–240 million years ago (Ma)) and were common, speciose and globally distributed for much of that era. The geographical range of the rhynchocephalians progressively contracted after the Early Jurassic epoch (about 200–175 Ma); the most recent fossil record outside of New Zealand is from Argentina in the Late Cretaceous epoch (about 70 Ma). c, The last bastions of the rhynchocephalians are 32 islands off the coast of New Zealand, which have recently been augmented by the establishment of about 10 new island or mainland sanctuary populations using translocations. The current global population is estimated to be around 100,000 individuals. Rhynchocephalian and tuatara fossil localities are redrawn and adapted from ref. 1 with permission, and incorporate data from ref. 2. In the global distribution map (c, top); triangle = Triassic; square = Jurassic; circle = Cretaceous; and diamond = Palaeocene. In the map of the New Zealand distribution (c, bottom); asterisk = Miocene; cross = Pleistocene; circle = Holocene; blue triangle = extant population; and orange triangle = population investigated in this study. Scale bar, 200 km. Photograph credit, F. Lanting.

It's well worth a look, and again, open sourced. It's well worth a look.

If interested, enjoy...

I wish you a safe, healthy and pleasant weekend.