Papagaios, Life & Times on a Speculative Archipelago - Papagotitans

Extract from ‘Bigger, Weirder, Scalier! – An Encyclopedia of Prehistoric Reptiles’ published in 2020 by DK Limited, a subsidiary of Penguin Random House.

The reptiles in the previous chapters lived in ancient swamps, forests, deserts and plains. It’s time to cast off and sail to island habitats. Today islands are home to many strange reptiles – think of the giant Galapagos tortoises, or the Komodo dragon – and it was just as true in the past.

[…several pages later…]

The lizards of the Papagaios, known as Papagolacertidae are all descended from a small number of individuals that rafted to the islands on floating debris. These arrivals would have been small, no more than 10cm long, and quickly evolved into many shapes and sizes to take advantage of the many vacant niches on islands that were home only to insects and seabirds.

Even today, many Papagaian lizards are small, but the islands’ most famous reptiles are on the larger side. They are the papagotitans – the giant lizards of the Papagaios – and include some of the largest, and most unique, reptiles since the time of the dinosaurs.

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The papagotitans diverged from their smaller relatives around 32mya, and while varying greatly in appearance and lifestyle, they are far more closely related to each other than any of their smaller cousins.

Most scientists today split the papagotitans into three main branches, though some say they should be in as many as seven groups. However, the traditionally accepted groups are the macrocaudates, the platydonts and the petrodermids.

Macrocaudates

The most common of three lineages of papagotitans are the macrocaudates. Named for their long tails, which in many cases are as long as the rest of their body, the macrocaudates are exclusively carnivores.

Those at the smaller end, such as Carcinovenator, are hunters of terrestrial crustaceans and giant insects, and measure around 50cm from nose to tail. The largest macrocaudates are considerably bigger, with some even in more recent times clocking in at 3m or more.

The group first evolved on the island of São Thomás de Aquino 28mya, and later migrated to most other islands in the archipelago.

Fun Fact Box:

In a strange quirk of taxonomy, the group is named for the late Oligocene Corneops macrocaudatus, formerly called Macrocaudatus macrocaudatus, but reclassified into the Corneops genus after a closer look at its fossils.

At over 2m long, Corneops macrocaudatus was top predator of its day and lived on the three central islands of Milagres, Santuário and São Thomás de Aquino hunting any large organisms it came across. Its evolution paralleled that of the large ground birds, implying a predator-prey race into gigantism. Like modern macrocaudates, it likely killed its prey by administering a strong bite and waiting for the animal to bleed out, though grappling prey is another potential option.

The Corneops genus all bore a bony crest over each eye, likely used in sexual selection, but many fossilised eye crests are scarred, suggesting some use in fighting others of the same species. As no modern macrocaudates possess such notable crest, it is hard to say for sure.

Platydonts

Of the three groups of papagotitans, the least numerous in terms of both genera and species are the platydonts. As a whole, they are heavier built than macrocaudates of similar body length, and due to their pillar like legs and raised walking posture are also taller. Their tails, however, are shorter and less flexible, though heavily muscled, and balancing out the proportionately large head. It is within this head, that the group’s most notable feature is found.

Macrocaudates and basal petroderms have simple dentition with seven to nine conical teeth, followed by a more than a dozen arrowhead-like slicing teeth. Platydonts as their name, meaning flat-tooth, suggests have similar conical front teeth, but only two pairs of slicing teeth on each side. The rest of their jaw houses broader, flatter teeth, akin to mammalian molars. This variety of teeth permits platydonts to eat almost anything they come across, and grind up or crush tougher seeds and shells. As a result, all species are omnivorous to varying degrees.

The best evidence to the origins of their diet comes from a 24 million year old fossil of Platydon santuarii, preserved with stomach contents including seeds of a small bird bones, clinker shrub seeds and fragments of crustacean shell. It seems that if a platydont could eat something, it would, and if it couldn’t, it would try anyway. A noble effort on islands that were still very young and regularly reshaping their ecosystems.

Petrodermids

While many papagotitans survive by being big, strong, and not picky in their diet, the petrodermids have opted for a stranger lifestyle. The first known member of the group was Petrodermus oviphagus of 25mya. Despite being more basal in the group, P. oviphagus had all the traits that would make the group successful.

As the name suggests, it survived primarily on the plentiful eggs of marquinhets, laid in crevices on stony beaches and the bases of cliffs. To reach them, P. oviphagus became a nimble climber with long, thin limbs and large grasping feet, allowing it to weave in and out of every nook and cranny for delicious eggs. But eggs are rarely left unattended and angry parents are dangerous foes.

The genus name, Petrodermus, or stone-skinned, is in reference to the scales on the lizard’s face and back that grew to be thick enough to reduce damage from parental beaks. P. oviphagus was less protected than its modern kin, but fossils show considerable armour especially around the eyes and neck. The limbs remained unarmoured, but where likely held close to the body to protect them during feeding. A reduced tail also minimised a chance of being grabbed while fleeing. It isn’t known if they were camouflaged, but can be inferred so from the prevalence of the trait in modern relatives.

Eggs are a treasure trove of nutrients and then, as now, marquinhet breeding grounds drew in hungry bellies from all around. P. oviphagus would have used its big eyes not only to look out for unguarded nests and vengeful parent birds, but rival hunters in the form of opportunistic macrocaudates and platydonts, but also more elusive, tentacled foes on their first venture out of the rockpools.