Palpebrosus nest, from Medem 1981.
Combined air temperature, metabolic heat from embyos, decay of vegetable material in the nest, and the proximity to termite mounds maintains nest temperature.
Nests that reach the high temperatures (31- 32°C) are usually built on top of older nests - not near active termite mounds. It appears that the extra insulation from the cool soil is enough to maintain temps above 31°C.
The incubation time for trigonatus is longer than for most crocodilians, being over 100 days - often as long as 115 - 117 days.
The nests that are built beside termite mounds have an interesting thermal gradient. The temp of the active termite mound is about 34°C, and the outer edge of the nest is about 28°C. These are both too hot and too cool for successful incubation. The eggs are laid at the edge of the termite mound, where the temp is between 30 - 32°C.
I'm constantly amazed at these reptiles. Prior to detailed studies being done, it was a bit of a mystery how these guys managed to pull off the correct incubation temperatures within the closed-canopy of the rainforest. It's interesting to note that they seem to instinctively know where to build the nest. If not beside a termite mound, some are reported to nest by rotting trees - again utilising the decay process combined with the nesting material to incubate successfully.
Again, the crocodilian adaptations amaze!
Females guard the nest. In the wild, it seems that the level of defense is not as great as that exhibited by, for example, the American alligator. It appears that this can be quite dangerous for the smaller caimans. Attacks on humans at this time have been reported by Medem and Gorzula - who had his inflatable boat sunk by an adult trigonatus in response to imitations of hatchling spectacled caiman calls.
After incubation period, which as mentioned is over 100 days, the female opens the nest. In certain circumstances, the male will open the nest. This was observed by Medem, who noted that a female had been captured in the area a few months earlier - probably the mother. The parents' assistance is necessary for trigonatus, since the eggs are normally encased in hard termite workings (ie. excrement).
After hatching, the young start to disperse after only about 7 days or so. Unlike many croc species, parental protection and group cohesion ceases at this time.
Females nest at intervals of about 3 years, producing clutches of about 15 eggs. This equates to about 5 eggs per year for each adult female. Egg mortality seems to be low. Due to the quick dispersal of the hatchings and the therefore the short period that the adult remains with the group, hatchling mortality appears to be quite high.
Indications from rate of egg production, slow growth rates, high initial hatchling mortality, and the abundance of juveniles in the population, are that juvenile and adult mortality is low.
The dispersal rates continue for at least the first 10-20 years of life. Juveniles regularly move overland to land-locked pools and ditches. There appear few barriers to their dispersal within Amazonia.
Growth rates are slow compred to other species. Magnusson estimates that a male will take about 20 years to reach sexual maturity (about 75cm SVL), and a females about 11 years (about 63cm SVL).
The young of trigonatus have a golden cranial table, giving them the local name of "crowned caiman" in Brazil.
The size of the eggs is about 6.5 x 4.2cm, and 66 - 73g, with the hatchlings being around 23cm long and weighing about 43 - 47 grams. P trigonatus and P palpebrosus both have high 'relative clutch masses'. This is the total mass of the clutch compared to the average mass of laying females. The relative egg mass of Paleosuchus species is about 1% of the mass of the female. Compare this to, say, the saltwater crocodile with a value of about 0.14%. In other words, whilst the Paleosuchus species are among the smallest members of the crocodilia, the eggs they lay, and the young produced, are about the same size as the largest of the crocodiles.
The nests are of the mound type - though in Surinam, intermediate nests have been found on floating mats of vegetation. The sites chosen are exposed to sunlight for a minimum of 1 hour per day. The nests are usually found in gallery forest, although they have also been found on small islets in Surinam. In these cases, there was no mound - the eggs were buried at the highest point of the islet, exhibiting the same characteristics as Caiman crocodilus using intermediate nests.
Nest material is soil mixed with rotten and green leaves, grasses and twigs, with grass and green leaves also used for the lining. The nests are about 50 cm high, and about 1.5 m wide. They contain an egg chamber at the centre - consisting mainly of earth or clay mixed with debri. In older nests, the earth becomes hardened and forms a cover that protects the eggs and keeps the temperature fairly constant.
In one nest, the egg chamber was about 56cm from the border of the nest, and was around 10cm deep and 15cm wide. The top layer of eggs were about 36cm from the top of the nest, the lowest about 46cm from the top. The top layer were deposited in a circle, the lower layers were irregular. All eggs were covered in a sticky mucous substance. The eggs of palpebrosus have very rough shells, at least in captivity, and it's been suggested that the sticky substance may serve to protect the female from internal damage when laying the eggs. This substance may also protect the eggs from fungus attack.
Eggs are oblong shaped, white, and vary from about 71.5mm x 40mm to around 62mm x 39mm, and weigh between 61 and 70 gms. The number of eggs is between 13 and 15 per nest. Nest temperatures reported by Medem are: 27°C environmental temp; 28°C at 5cm depth; and 31°C at 22cm depth. Incubation period, which is dependent on temperature, is about 90-92 days.
The young palpebrosus call from within the shell, as is noted for most crocs. The adult, usually the female, will open the nest - the earth chamber being too strong for the young to break through. The young have a light brown cranial table, which darkens after about 6 months.
When hatching in captivity, movement of the eggs seems to promote hatching. The young burst from the eggs, after breaking the egg shell with the caruncle (egg tooth). Upon hatching, they are covered by the transparent layer of sticky mucous. They remain hidden among the nest material for several days, not moving to the water. Medem reported that one individual that was placed into water died 2 days later. It is not known whether this directly killed the hatchling or exactly what the purpose of the mucus coating is.
Parental care appears to be somewhat limited, but is still largely within the normal bounds described for most crocodilians. The discrepancies may be more due to the lack of information rather than the lack of defense behaviour.
Captive individuals are noted to become quite aggressive after nesting. They are reported to hiss and threaten people who are collecting the eggs for artificial incubation. This behaviour is described for both males and females.
Various authors report little defensive behaviour, and then go on to note that the adults respond to imitations of juvenile distress calls, also reporting tail slapping behaviour, biting the water, and other threatening behaviour. In captivity, the adults of the group (ie. not just the parents), will defend the young.
The hatchlings are about 23cm long. This is total length, and about 50% is tail. Medem reports snout-vent lengths (SVL) of 11 - 11.9cm, and tail lengths of about 11.6cm to 12.3cm. The changes in this proportion are included in the Morphology section. The weight of the hatchlings is between 40 - 50 gm.
It would seem that dispersal and therefore parental protection is similar to trigonatus - though there is almost no specific data on this for palpebrosus. Like trigonatus, palpebrosus hatchlings are usually found singly or in pairs, and without adult protection.
P palpebrosus has been bred a number of times in captivity. Two German reports both mention the roaring of the male dwarf caimans. One report is of an 'improbably loud thundering, which was terminated with a loud bang of the male'. My translation is probably a tad ordinary! Another describes the roaring as a guttural grunt, as opposed to actual roaring, as in the alligator. This indicates that courtship in palpebrosus is as complex as in other crocodilians.
The roaring seems not to directly precede mating. Mating takes place at night, and in the water. The male clasps itself laterally to the floating female, and brings his cloaca next to hers for copulation. In deep water, they float thus, although it can occur in shallow water (less than 50cm depth). Mating lasts for between 5 and 10 minutes, after which both submerge for a period.
In both German reports I've read, nesting took place in May, and both places had lower temperatures in the Northern Winter. Mating appears to have taken place during December/January time. Luthi notes that in January, the female increased in scope, and stopped feeding, yet didn't begin nesting until mid-May.
Construction of the nest is carried out by both parents. The entire group of animals within the enclosure becomes excited at this time. A collective 'group behaviour' seems common. The female or male will attack in defense of the nest, and the female is said to regularly be in the water facing the nest.
In one report, the egg laying took place over a period of 6 - 7 hours. In this case, 9 eggs were laid. The female then arranged them in the nest using her jaws, also widening the egg chamber with the jaws. This arranging took about 1 hour. Afterwards, the nest was closed, and the female pressed the material down firmly.
When eggs were taken from the nest, strong attacks by the female occurred. The female was very hostile, and charged from the water at any disturbance within the enclosure. It remained on the nest for long periods after people had left the space.
After 3 days, the eggs had a white band, and were 6 - 7 cm long.
After 3 months, the female lost interest in the nest. Notably, after one of the eggs was returned to the nest, the female became defensive once again. It is assumed that the female smelled the egg. She opened the nest, and carried the young caiman to the water. This is notably different to those reports where the young didn't enter the water for the first few days.
The young lose weight over the first 4 weeks or so, as they live off the remainder of the egg yolk.
A young Paleosuchus palpebrosus.