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''Acostasaurus'' (meaning "Acosta's lizard") is an extinct genus of possibly Thalassophonean
The type specimen is noted for possessing several features that pertain to a sub adult individual: for example, the sagittal crest is not fully ossified, as well as possessing undeveloped palatine wings. It is possible however that ''Acostasaurus'', like other
pliosaurid
Pliosauridae is a family of plesiosaurian marine reptiles from the Latest Triassic to the early Late Cretaceous (Rhaetian to Turonian stages) of Australia, Europe, North America and South America. The family is more inclusive than the archetyp ...
known from the Barremian
The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma ( million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is pre ...
of the Paja Formation
Paja may refer to:
* Paja, Iran, a village in Sari County
* Paja (given name), a Serbian masculine name
* Paja (surname)
* Paja Formation, geologic formation in Colombia
* Paja Brava
:''Paja Brava is also used in Spanish speaking countries to ref ...
, Colombia. The type specimen, UNDG R-1000, is known from a near complete skull, and postcranial elements including a complete hindlimb and various vertebrae.Marcela Gómez Pérez; Leslie F. Noè (2017). "Cranial anatomy of a new pliosaurid ''Acostasaurus pavachoquensis'' from the Lower Cretaceous of Colombia, South America". Palaeontographica Abteilung A. 310 (1–2): 5–42. . The specimen has an estimated size of over in length and in body mass.
Description
The type specimen is noted for possessing several features that pertain to a sub adult individual: for example, the sagittal crest is not fully ossified, as well as possessing undeveloped palatine wings. It is possible however that ''Acostasaurus'', like other plesiosaurs
The Plesiosauria (; Greek: πλησίος, ''plesios'', meaning "near to" and ''sauros'', meaning "lizard") or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia.
Plesiosaurs first appeared ...
, was paedomorphic
Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the physiological, or somatic, development of an organism, typically an animal. Neoteny is found in modern humans compare ...
.
From what is preserved, the orbits are large, rounded and deeply notched dorsally. The sclerotic ring of the specimen is also very large, suggesting that ''Acostasaurus'' was adapted to see in deep or murky waters.
An unusual feature of ''Acostasaurus'' is that it possesses a short mandibular symphysis, containing only 6 pairs of functional alveoli (5 and ½, considering that the symphysis terminates level with the middle of the sixth pair). The short, wide symphysis is one of the features which differentiates ''Acostasaurus'' from other contemporary pliosaurids such as the various brachauchenine
Pliosauridae is a family of plesiosaurian marine reptiles from the Latest Triassic to the early Late Cretaceous (Rhaetian to Turonian stages) of Australia, Europe, North America and South America. The family is more inclusive than the archetypa ...
pliosaurs from the formation. Other pliosaurids which possess this condition include the Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
taxon '' Simolestes'', which like ''Acostasaururs'' has large orbits, as well as a short symphysis.Noè, L. F. (2001). A taxonomic and functional study of the Callovian (Middle Jurassic) Pliosauroidea (Reptilia, Sauropterygia). Chicago Gómez-Pérez et al. note that the base of the functional alveoli in ''Acostasaurus'' are confluent with Meckel's canal as in ''Simolestes'', and that it also possessed a heavily swollen and ornamented sagittal crest
A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are exceptiona ...
to form a parietal knob, also found in ''Simolestes''.
Classification
As brachauchenine pliosaurs are the only pliosaurids known from the Barremian stage, especially from Colombia, Gómez Pérez et al. compared ''Acostasaurus'' to a variety of brachauchenine taxa in the paper. The authors however concluded that referral of the genus to the subfamily is problematic: ''Acostasaurus'' possessescaniniform
In mammalian oral anatomy, the canine teeth, also called cuspids, dog teeth, or (in the context of the upper jaw) fangs, eye teeth, vampire teeth, or vampire fangs, are the relatively long, pointed teeth. They can appear more flattened however ...
dentition, whereas brachauchenines possess longirostrine homodont dentition. As discussed before, ''Simolestes'' and other less derived pliosaurids possess similar dentition, especially in the arrangement that are present in ''Acostasaurus''.
References
{{Taxonbar, from=Q55603154 Pliosaurids Early Cretaceous reptiles of South America Barremian life Cretaceous Colombia Fossils of Colombia Paja Formation Fossil taxa described in 2017 Sauropterygian genera