Siquisiquesuchus
Encyclopedia
Siquisiquesuchus is an extinct genus
of gavialoid
crocodilia
n. It is known from cranial remains and a few postcrania
l bones found in Miocene
-age rocks in northwestern Venezuela.
MBLUZ–P–5050, a nearly complete skull and lower jaws. It was found near Lara in rocks of the Early Miocene-age Castillo Formation
. Two other partial skulls, partial vertebrae, a thigh bone
, partial upper arm
, and partial shin bone
were recovered from another locality. These bones were described by Christopher Brochu and Ascanio Rincón in 2004. The type species
is S. venezuelensis.
Like other gavialoids, Siquisiquesuchus had a long, narrow rostrum
on its skull, accounting for approximately 60% of the skull's length. The number of teeth in the premaxilla
ry bones at the tip of the snout is not known, but the maxilla
e making up most of the rostrum had at least 20 teeth each, and the dentaries of the lower jaws had at least 23. Some details of the described skulls cannot be determined because the sutures
are not visible.
Siquisiquesuchus was found by Brochu and Rincón to be the oldest known gavialoid from South America, sharing various anatomical details with Gryposuchus colombianus
(to which it is particularly similar) and other South American gavialoids. Later studies have concurred with a gavialoid identity, finding the genus to be related to such genera as Gavialis, Gryposuchus, Ikanogavialis
, and Piscogavialis
. Vélez–Juarbe and colleagues (2007) found it to be a gryposuchinae gavialid
, while Jouve and colleagues (2008) did not assign families or subfamilies. Brochu and Rincón noted that Siquisiquesuchus was found in marginal marine deposits. This, along with similarities to Old World
gavialoids, was interpreted as evidence that gavialoids "dispersed across a marine barrier to the Neotropics during the Tertiary
."
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of gavialoid
Gavialoidea
Gavialoidea is one of three superfamilies of crocodylians, the other two being Alligatoroidea and Crocodyloidea. Although many extinct species are known, only the gharial Gavialis gangeticus and possibly the False gharial Tomistoma schlegelii are alive today.-Classification:Gavialoidea contains the...
crocodilia
Crocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
n. It is known from cranial remains and a few postcrania
Postcrania
Postcrania[p] in zoology and vertebrate paleontology refers to all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g...
l bones found in Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
-age rocks in northwestern Venezuela.
Description
Siquisiquesuchus is based onHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
MBLUZ–P–5050, a nearly complete skull and lower jaws. It was found near Lara in rocks of the Early Miocene-age Castillo Formation
Castillo Formation
The Castillo Formation is a Mesozoic geologic formation. Dinosaur remains diagnostic to the genus level are among the fossils that have been recovered from the formation.-See also:* List of dinosaur-bearing rock formations...
. Two other partial skulls, partial vertebrae, a thigh bone
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
, partial upper arm
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
, and partial shin bone
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
were recovered from another locality. These bones were described by Christopher Brochu and Ascanio Rincón in 2004. The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
is S. venezuelensis.
Like other gavialoids, Siquisiquesuchus had a long, narrow rostrum
Rostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
on its skull, accounting for approximately 60% of the skull's length. The number of teeth in the premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
ry bones at the tip of the snout is not known, but the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
e making up most of the rostrum had at least 20 teeth each, and the dentaries of the lower jaws had at least 23. Some details of the described skulls cannot be determined because the sutures
Suture (anatomical)
In anatomy, a suture is a fairly rigid joint between two or more hard elements of an animal, with or without significant overlap of the elements....
are not visible.
Siquisiquesuchus was found by Brochu and Rincón to be the oldest known gavialoid from South America, sharing various anatomical details with Gryposuchus colombianus
Gryposuchus
Gryposuchus is an extinct genus of gavialoid crocodilian. It is the type genus of the subfamily Gryposuchinae. Fossils have been found from Argentina, Colombia, Venezuela, Brazil and the Peruvian Amazon. The genus existed during the early and middle Miocene epoch. One recently described species, G...
(to which it is particularly similar) and other South American gavialoids. Later studies have concurred with a gavialoid identity, finding the genus to be related to such genera as Gavialis, Gryposuchus, Ikanogavialis
Ikanogavialis
Ikanogavialis is an extinct genus of gryposuchine gavialoid crocodilian. Fossils have been found from the Urumaco Formation of Venezuela. The strata from which remains are found are late Miocene in age, rather than Pliocene as was once thought....
, and Piscogavialis
Piscogavialis
Piscogavialis is an extinct genus of gryposuchine gavialid crocodylian. The only species yet known is P. jugaliperforatus. Fossils of Piscogavialis have been found from the Mio-Pliocene Pisco Formation of the Sacaco Basin in southern Peru...
. Vélez–Juarbe and colleagues (2007) found it to be a gryposuchinae gavialid
Gavialidae
Gavialidae is a family of reptiles within the order Crocodilia. Gavialidae consists of only one surviving species, the gharial , which is native to India. Many extinct species are also known...
, while Jouve and colleagues (2008) did not assign families or subfamilies. Brochu and Rincón noted that Siquisiquesuchus was found in marginal marine deposits. This, along with similarities to Old World
Old World
The Old World consists of those parts of the world known to classical antiquity and the European Middle Ages. It is used in the context of, and contrast with, the "New World" ....
gavialoids, was interpreted as evidence that gavialoids "dispersed across a marine barrier to the Neotropics during the Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
."