Susisuchus is a small crocodyliform genus from Early Cretaceous Brazil. Its best-known species, S. anatoceps, is represented by a partially articulated skeleton from the Crato Formation that preserves a distinctive four-row dorsal armour shield and impressions of skin around the forelimbs and hand. The backbone and palate have also made the genus important in debates about the origin of Eusuchia, the group that includes living crocodilians. It is one of the Brazilian lineages in the ancient crocodylomorph catalogue.
The fossil combines traits that do not all point in the same direction. In particular, researchers have interpreted the internal nostril’s bony margins differently, and that affects its position in phylogenetic analyses. The anatomy is informative precisely because the question remains testable.
Quick facts
| Species | S. anatoceps and S. jaguaribensis |
|---|---|
| Age | Early Cretaceous: Berriasian–Barremian and Aptian records |
| Region | Ceará, northeastern Brazil |
| Holotype | SMNK 3804 PAL, partially articulated skeleton |
| Notable preservation | Skin impressions around the forelimbs and right-hand digits |
| Armour | Four principal dorsal rows with accessory osteoderms |
| Vertebrae | Amphicoelous trunk vertebrae; some cervical centra show incipient procoely |
| Main debate | Palatal anatomy affects whether Susisuchidae falls within Eusuchia |
What can the fossils tell us?
Salisbury, Frey, Martill and Buchy described Susisuchus anatoceps in 2003 from the Nova Olinda Member of the Crato Formation in northeastern Brazil. The holotype SMNK 3804 PAL is incomplete but partially articulated, preserving skull and mandible, parts of the axial skeleton, forelimbs and osteoderms. Skin impressions remain around both forelimbs and the digits of the right hand. The carcass was interpreted as having dried before it entered the lagoon basin, a taphonomic inference from preservation rather than a directly observed event.
The dorsal armour has two paravertebral rows and two accessory rows on each side, producing a tetraserial shield. The arrangement was notable among Early Cretaceous crocodyliforms and was compared with the more derived eusuchian-type armour. It is evidence about the osteoderms’ positions; it does not by itself show that Susisuchus was a direct ancestor of modern crocodilians.
The holotype has amphicoelous thoracic, lumbar and caudal vertebrae, with both ends of each centrum concave. Other specimens show slightly procoelous cervical vertebrae, and one has a platycoelous form. This combination has been used in arguments about the evolution of vertebral articulation near Eusuchia. The observations depend on which individual and vertebral region is being described; they should not be flattened into one label for the entire spine.
S. jaguaribensis was named in 2009 from UFRGS-PV0001K, the posterior portion of a skull from the Lima Campos Basin. Its Berriasian–Barremian deposits are older than the Aptian Crato rocks that yield S. anatoceps. The species differs in skull-roof contacts and the shape of the squamosal process. Its skull was estimated at around 10 centimetres and the body at about 65 centimetres by comparison; the rest of the skeleton is not preserved, so those are estimates rather than measured total length.
The position of the internal nostril, or choana, relative to the pterygoid bones has been central to the debate. A 2018 study described a specimen whose choana appeared fully enclosed by pterygoids, a feature associated with Eusuchia, and recovered Susisuchidae within that group. A 2020 reassessment argued that at least some palatal sutures indicate palatine participation at the front of the opening, consistent with a non-eusuchian neosuchian. The specimens are preserved from different views and the sutures are difficult to read; the phylogenetic result depends on that anatomical interpretation.
Histological sections of a referred ulna and rib preserve growth marks. The ulna shows 17 lines of arrested growth, while the rib records fewer, plausibly because ribs remodel and erase earlier tissue. The authors interpreted the combined evidence as slow growth and an adult or late-subadult individual. This supports the possibility that S. anatoceps remained small-bodied, but one histological sample cannot establish a species-wide maximum size or every individual’s age.
The Crato Formation is famous for finely laminated lagoonal limestone and exceptional preservation of plants, insects, fish, amphibians, pterosaurs and soft tissues. Needle-like, similar-sized teeth are consistent with capturing small aquatic prey. No gut contents establish a diet. The skin impressions near the forelimbs document a local body covering but do not preserve the animal’s colour or full external anatomy.
The genus combines an advanced-looking dorsal shield with vertebral and palatal features interpreted as less derived in some analyses. That mosaic makes it relevant to the transition near Eusuchia. Phylogenetic placement changes when new specimens or revised palatal scores are added. It is more accurate to describe Susisuchus as a close comparative branch than to call it a proven ancestor of living crocodilians.
A partially articulated fossil from the Crato lagoon
Salisbury, Frey, Martill and Buchy named Susisuchus anatoceps in 2003 from the Nova Olinda Member of Brazil’s Crato Formation. The holotype SMNK 3804 PAL is a partial but partly articulated skeleton. It includes skull and lower jaw, parts of the vertebral column, forelimbs and osteoderms. Skin impressions around both forelimbs and the digits of the right hand provide a rare glimpse of soft tissue, though not a complete body outline.
The specimen was interpreted as a carcass that had dried before entering the lagoon basin. That explanation follows the arrangement and preservation of the remains; it is a taphonomic hypothesis, not a witnessed event. The fine-grained limestone is famous for preserving delicate fossils and soft-tissue traces.
A four-row dorsal shield
The main back armour consists of two paravertebral rows with two accessory rows on each side. This tetraserial arrangement was compared with the dorsal shield of more derived eusuchians. The osteoderms are direct evidence of how the armour was organised in the preserved body. Similarity to a later group does not establish direct ancestry: the trait may have arisen in a side branch or been retained from a broader ancestor.
Other skeletons referred to S. anatoceps add separate observations. MPSC-R1136 preserves more vertebrae, shoulder elements and osteoderms. MPSC-R1137 is a partially articulated hind limb. These fossils expand the anatomical record, but only the holotype preserves the original type association; referred specimens should not be silently fused into one individual.
Vertebrae preserve a changing pattern
The holotype’s thoracic, lumbar and caudal centra are amphicoelous, concave at both ends. Other material includes slightly procoelous cervical vertebrae, where one end is concave and the other convex, and a platycoelous cervical centrum with flatter ends. This mixture is relevant to how vertebral articulations changed along the crocodyliform backbone and through evolutionary time.
The details depend on vertebral position and specimen. A shorthand claim that the genus had either “primitive” or “modern” vertebrae would conceal that variation. Nor does a vertebral joint shape alone establish swimming performance or land posture; those questions require the full skeleton and biomechanical comparisons.
Two species from distinct Early Cretaceous settings
Susisuchus jaguaribensis was described in 2009 from UFRGS-PV0001K, the rear portion of a skull from the Lima Campos Basin. Its Berriasian–Barremian deposits predate the Aptian Crato Formation. The species is distinguished by skull-roof sutures and the shape of the posterolateral squamosal process. Its skull was estimated at about 10 centimetres and the body at roughly 65 centimetres through comparison, because the rest of the skeleton is missing.
S. anatoceps comes from the younger Crato rocks. The two species therefore document Susisuchidae at separate times and basins in northeastern Brazil. A genus-level relationship does not mean they lived together or had identical body proportions. The fragmentary type of S. jaguaribensis also limits how much of its soft anatomy and locomotion can be reconstructed.
Why the palate has changed the family tree
The choana is the internal opening linking the nasal passage to the throat. In advanced eusuchians it is enclosed by the pterygoid bones. A 2018 description of specimen FPH-243-V interpreted its choana as fully enclosed by pterygoids and used that observation to recover Susisuchidae within Eusuchia.
A later specimen, GP/2E 9267, was described in 2020 with palatine bones apparently contributing to the anterior margin of the opening. The authors also re-examined published images of FPH-243-V and argued that the same pattern may be present there. Under that reading, Susisuchidae lies outside Eusuchia among neosuchians. Sutures are difficult to assess in flattened or differently exposed fossils, and the specimens do not present every surface in the same view. For that reason, the distinction should be explained rather than hidden behind one supposedly permanent family-tree position.
Growth evidence and body size
Histological work examined sections from an ulna and a rib of a referred individual. The ulna preserves 17 lines of arrested growth. The rib has fewer visible lines, likely because rib tissue remodels and can erase earlier growth records. The researchers interpreted the combined sample as indicating slow growth and an adult or late-subadult animal.
The results raise the possibility that small size was not simply a juvenile condition in S. anatoceps. However, one sampled individual cannot establish a maximum adult length for the species. Histology offers evidence about that individual’s growth; population-level variation requires more specimens.
What the Crato ecosystem can and cannot tell us
The Crato limestone preserves a diverse lagoon ecosystem of plants, insects, fish, amphibians, pterosaurs and other vertebrates. The similar needle-like teeth of Susisuchus are compatible with taking small aquatic prey. There is no reported stomach content that confirms a fish meal. Its association with lagoon deposits suggests a connection to water but does not prove that it was fully aquatic or never travelled on land.
The animal’s distinctive armour, mixed vertebral condition, small body and disputed palate make it a valuable comparison in early neosuchian evolution. They do not establish it as a direct ancestor of living crocodilians. A careful reconstruction can show the partial skeleton’s proportions and shield while leaving colour, exact gait and daily behaviour as inference.
Frequently asked questions
How many Susisuchus species are known?
Two named species are recognised: S. anatoceps from the Aptian Crato Formation and S. jaguaribensis from older Berriasian–Barremian deposits.
What soft tissues were preserved?
Skin impressions occur around both forelimbs and the digits of the right hand in the S. anatoceps holotype.
Why is the palate controversial?
Studies differ over whether the palatine bones contribute to the front margin of the choana. That changes whether the group is placed inside or outside Eusuchia in some analyses.
Was Susisuchus a direct ancestor of living crocodilians?
No direct ancestry is demonstrated. It is a close comparative branch that preserves a useful combination of traits near the origin of Eusuchia.