Nomenclature | Morphology | General | Skull Characters | Colouration | Scutellation | Size

Nomenclature

First of all, where do the Paleosuchus species fit in the grand scheme of things ? Here’s the scoop:

Kingdom
Animal
Phylum
Chordata (animals with spinal chords)
Sub Phylum
Vertebrata (animals with cartiliginous skeleton, and a backbone consisting of vertebrae protecting the spinal chord)
Class
Reptilia
Order
Crocodylia
Sub-order
Eusuchia (from the Greek 'Eu' = typical;'soukhos'=crocodile)
Family
Alligatoridae (all alligators and caimans: from Spanish ‘El’ = the; ‘lagarto’ = a lizard.
Genus
Paleosuchus (from Greek: ‘Palaios’ = ancient; ‘soukhos’ = the name for crocodile in one part of Egypt)
Species
P. trigonatus (from Greek: ‘tres’ = three; ‘gonia’ = angle; ‘atus’ = Latin suffix meaning provided with. It is assumed that the name was given by its describer to refer to the prominent triangular dorsal scutes of the species, especially as depicted in a very early drawing.

Common names include: Schneider's smooth-fronted caiman, Schneider's dwarf caiman, smooth-fronted caiman, mountain caiman (Venezuala), "cachirre", "jacare coroa".

P. palpebrosus (from Latin: ‘palpebra’ = eyelid; ‘osus’ = suffix meaning full of, or prominent. Name refers to the bony eyelids, or palpebrals of this species. Note that both Paleosuchus species have these palpebrals.

Common names include: Cuvier's dwarf caiman, dwarf caiman, red caiman (Surinam), black caiman (a local name in some Sth American countries - which is a tad confusing), "cachirre", "jacare coroa".

Sub species
None recognised.

Paleosuchus trigonatus was first described to science in 1801 by Schneider. At the time, he called it Crocodilus trigonatus. It is not known where the type-specimen was collected from - which is the usual procedure for scientific naming. The species has undergone several name changes since that time:

No, Crocodylus niloticus isn’t a typo. The name given to the Nile crocodile was later proven to be based on a diagram that was in fact a Paleosuchus trigonatus! Under the zoological naming standards (International Commission on Zoological Nomenclature), the first scientific name given to an animal after 1758 stands - even if it turns out to be inaccurate. So, officially, the name Crocodylus niloticus belongs to the smooth-fronted caiman. However, the ICZN also has the power to overrule to avoid confusion or inconvenience. Obviously, C niloticus would cause such confusion, so Paleosuchus trigonatus stands. Once a name is accepted widely for over 50 years, it must not be displaced ! P trigonatus has rarely been challenged since Schmidt’s review in 1928.

Paleosuchus palpebrosus was described in 1807 by Cuvier, as Crocodylus palpebrosus. The type-locality is listed as ‘Cayenne’, and the specimen still exists in the Museum National d’Histoire Naturelle in Paris. Like trigonatus, palpebrosus has undergone several reviews of its name:

So, the first person to name both species as they are known today was Schmidt, in 1928. The names are now almost universally accepted.


Morphology

Morphology is the study of the phases, or forms, of an organism. In this section, we'll look at what makes a Paleosuchus a Paleosuchus, and what differentiates trigonatus from palpebrosus. Things like skull characteristics, scale arrangements, colouration, etc are discussed.

General

All caimans are part of the alligatoridae family. Alligatorids differ from crocodilids in at least 2 aspects:
  1. The 4th tooth on each side of the bottom jaw fits into a socket within the upper jaw, and so is usually not visible when the jaws are closed
  2. There are no ISO's on the body, only the head. These are sensing organs: check out crocodilian.com for details. Crocs have these on their body as well as their head.

Caimans differ from alligators by having more extensive osteoderms (ie. their skins contain more of the bony plates); and they lack the bony septum that divides the alligator's nasal opening (seen in the skulls). Alligators are from more temporate climates than the tropical caimans.

Paleosuchus do not have the inter-orbital ridge that other caimans do, and they have only 4 teeth in the premaxilla - most caimans (ie. members of the caiman and melanosuchus genus') have 5 teeth in this part of their jaw.

Many authors speculate that the lack of Inter-orbital ridge in Paleosuchus is due to their adaptation to swift-water habitats. Since they are not exclusive to swift-water habitats, and other crocodilians that do not have inter-orbital ridges don't go near swift-water habitats, I'm not exactly convinced of this one! Paleosuchus evolution is not well known at all, so anything said about adaptations etc are pure speculation at this stage. Much more study is required.

Paleosuchus species have skins that contain more extensive osteoderms than any other species. This makes their skins almost worthless to the skin-trade - a fact which, along with their smaller size, saw these species escape the widespread hunting of crocodilians over the early and middle parts of this century. This greater ossification extends to the bony eyelids that are very prominent in this genus.

The lack of interorbital ridge gives rise to the common name 'smooth-fronted' caimans - just as the distinctive form of this ridge gives rise to the name 'spectacled' caiman for Caiman crocodilus sp.

Paleosuchus have a brown iris. The only other crocodilian with this colour is Osteolaemus tetraspis, or the Dwarf crocodile, from West Africa. Strangely enough, O tetraspis also has a degree of ossification of the eyelid, well developed dorsal armour, and inhabits rainforests. It seems to be the closest species, ecologically, to Paleosuchus.


Skull Characters

OK, it's time to get more detailed. First of all, we'll look at the skulls of Paleosuchus. Then, we'll look at their scale characteristics and colour. After this, you will be able to distinguish a Paleosuchus from any other crocodilian, and also trigonatus from palpebrosus!! Here goes...

The skulls of Paleosuchus palpebrosus is compressed into what is often referred to as a 'dog-like' shape. It is short, blunt, with an upturned tip, and a relatively high skull. It has a prominent 'canthus rostralis' - which is a ridge separating the side of the snout from the top of the head along a line from the corner of the eye to the 4th maxillary tooth. This gives P palpebrosus a steep lateral slope to its snout. Check out the skull diagrams page for the pretty picture.

In comparison, P trigonatus has a more elongated snout, longer and slimmer, and lower relative to palpebrosus. Trigonatus, though having a steep lacrimal area (ie. just in front of the eyes), lacks the canthus rostralis, and so has a more rounded snout.

The external mandibular foramen is the hole in the side of the bottom jaw bone, towards the rear. It serves as a place for attachment of muscles, and is formed by several bones. The shape of this foramen is distinctive for each species of Paleosuchus. P palpebrosus has a relatively small foramen, with a jagged edge. The width of this hole is less than the distance from its edge to the bottom of the jaw (the angular bone). In trigonatus, the width of the hole is greater than the distance to the inferior edge of the angular bone, and the edges are smooth.

The nasal bones in palpebrosus usually fuse together in adults. In trigonatus, they retain the median suture - giving adults a characteristic longitudinal groove. The nasal bones of trigonatus also project further into the nasal opening in the skull than they do in palpebrosus.

The supratemporal fossae are not present in palpebrosus. They are, however, distinct in juvenile trigonatus, fusing in adults. This lack of supratemporals in adults is a distinction of Paleosuchus species.

The palatal fenestrae in palpebrosus are almost kidney-shaped, and very wide at the posterior end. Those in trigonatus are narrower, especially posteriorly.

So, most of the differences in the skulls of the two owe much to the more extensive ossification of palpebrosus. This is indicated by the smaller foramen, the fusion of bones, the 'smoother' skull, and rough edges to some of the foramen.

Well, now that you know all this stuff about their skulls, let's move on.....

Colouration

It's all fine and dandy to know the skull characters, but if you're after a dwarf caiman, it's a tad difficult to check out the skull of the little fellow in the pet store to see what he is! So, let's start by looking at the colour of these dudes.

Palpebrosus has a reddish brown head. This will vary between individuals, but it generally holds true, though some may have a darker colour to the cranial table (ie. the top of their head). The bottom jaw has alternating lighter and darker bars or blotches on it. The dorsal area is very dark - almost black. Ventrally, it has both cream and dark pigmentation in roughly equal amounts. The cream colour can be almost a horn colour. The tail has alternating light and dark bands or blotches. The eyes, as mentioned, are brown. Juveniles have light yellow or brown cranial tables, and brown heads.

Trigonatus has a darker head - usually dark brown. The bottom jaw is the same colour as the head, but with yellow bars. The dorsal area is dark brown. Ventrally, the cream pigmentation dominates, with smaller areas of dark pigment. The tail has dark and light bands on it. All pigmentation becomes duller with age. Juveniles have light yellow or brown cranial tables, and light dorsal bands. The eyes are brown.


Scutellation

Scutellation refers, basically, to the scale characteristics.

Just quickly, the main differences between palpebrosus and trigonatus are in the number of scales in various regions: ventral scales (ie. those on their tummy); the number in the single tail crests; the number between their hindlegs; and the formation of those in the double crest of the tail.

P. palpebrosus

Note the neat rows of the dorsals of palpebrosus. All rows are evenly keeled.
Post Occipitals
These are the enlarged scales behind the head. Palpebrosus almost invariably has 2 rows. The first row is composed of quite large scales, with sharp keels extending their length.
Nuchals
Next up are the nuchals. These scales are the rows that run down the neck region of crocodilians. In palpebrosus, there are usually 4 - 5 rows. The number of scales within these rows are often in the form of 2-3-4-3-2 (ie. the rows form an oval shape over the neck). There can just as often be 2 scales in all rows, though - but again, they would form an oval shape.
Dorsals
The dorsals of palpebrosus are all moderately keeled. There are about 18 rows length-wise (or longitudinally), and an average of 8 transverse rows (varies between about 6 - 10). All rows are quite neat, forming relatively straight lines down the length of the back. As the dorsals pass between the hind legs, they are almost always in four rows.
Ventrals
The ventrals in palpebrosus average about 21 or 22 longitudinal rows, and 16 transverse rows.
Tail - single crest
Contains between 16 and 21 scales - usually about 19 or 20.
Tail - double crest
Contains about 9 - 10 rows. Three or more of the posterior crests meet at the midline of the tail, and the enlarged scutes of these double crests project vertically.
Tail - lateral (side)
Small scales disrupt only 2 or 3 of the lateral rows.

P. trigonatus

Note the large keels on the outer rows of dorsals of this preserved P trigonatus. This also illustrates how 'disorderly' the dorsal rows are in trigonatus.
Post Occipitals
trigonatus usually has a single row of enlarged scutes, with sharp keels extending their length. This isn't definitive, though, as Medem reported many trigonatus with 2 rows.
Nuchals
In trigonatus, there are 4 - 5 rows - usually 4. The number of scales within these rows are often in the form of 2-3-2-2. There can just as often be 2 scales in all rows, though.
Dorsals
The outer rows of dorsals in trigonatus are highly keeled. The middle rows are very weakly keeled.There are about 18 rows length-wise (or longitudinally), and an average of 6 - 7 transverse rows. The dorsal rows of trigonatus are not nice and neat! Instead, they are often incomplete rows, and tend to run in wide lateral arcs along the back. As the dorsals pass between the hind legs, they are usually in two rows. This is often noted as a distinction between palpebrosus and trigonatus - though some specimens of trigonatus do in fact have 4 rows (so beware!).
Ventrals
The ventrals in trigonatus average about 19 or 21 longitudinal rows, and 10 - 12 transverse rows.
Tail - single crest
Contains between 17 and 19 scales - average is about 18.
Tail - double crest
Contains about 9 - 10 rows. Two or fewer of the posterior crests meet at the midline of the tail, and the enlarged scutes of these double crests project laterally.
Tail - lateral (side)
Small scales disrupt between 5 and 8 of the lateral rows.


Size

Paleosuchus palpebrosus is the smallest of the living crocodilians. Males will generally reach about 1.3 - 1.5 m, females about 1.2m. The maximum size recorded is 1.72m for a male, and 1.23m for females. Adults will weigh around 6 - 7 kg (at least in the wild).

P trigonatus is larger. Males can reach 2.2m, females usually about 1.3m. trigonatus of about 1.3m are considered mature adults. The weight of an adult can be up to 36 kg, but usually is around 9 kg at about 1.2m, and 20 kg at about 1.6m.

When born, both Paleosuchus hatchlings are about 23cm long, weighing about 50gms. At this stage, they are about 50% tail. This changes as they grow, such that large trigonatus will have tails that make up around 45% of their total length, whilst palpebrosus tails make up about 47 - 48% of total length. This is variable according to both individual and location. For example, in Colombia, Medem noted that both species have similar proportions, whereas Ouboter found a statistical difference in Surinam (where trigonatus had the smaller tail). There appears to be no difference between sexes in regard to this proportion.

Growth rates
There is a chart of growth rates in the CAPTIVE CARE GUIDE. Roughly, though, palpebrosus grow from 23cm at between 6 - 8 cm per year. Females will be sexually mature at about 1m (100cm); males at about 1.1m (110cm) - as a general guide. This will take about 10 years or so. Note that in captivity, with constant warm temperatures and regular easy feeding, they may achieve quicker growth.

trigonatus will grow from their 23cm at between 10 - 13cm per year. Magnusson considers males to reach sexual maturity in up to 20 years, and females at about 10 or 11 years.


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