Leptocleididae is a family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 of small-sized plesiosaur

Plesiosaur

Plesiosauroidea is an extinct clade of carnivorous plesiosaur marine reptiles. Plesiosauroids, are known from the Jurassic and Cretaceous Periods...

s that lived during the Early Cretaceous

Early Cretaceous

The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...

 period (early Berriasian

Berriasian

In the geological timescale, the Berriasian is an age or stage of the Early or Lower Creteceous. It is the oldest or lowest subdivision in the entire Cretaceous. It spanned between 145.5 ± 4.0 Ma and 140.2 ± 3.0 Ma...

 to early Albian

Albian

The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...

 stage). Leptocleidus

Leptocleidus

Leptocleidus is an extinct genus of pliosaurid plesiosaur, belonging to the family Leptocleididae. It is the only known pliosaur to be found in sediments on the Isle of Wight.-Etymology:In short, the term Leptocleidus means "slender clavicle"...

and Umoonasaurus

Umoonasaurus

Umoonasaurus is an extinct genus of plesiosaur belonging to the family Leptocleididae. This genus lived approximately 115 million years ago in shallow seas covering parts of what is now Australia. It was a relatively small animal around 2.5 m long...

had round bodies and triangle shaped heads. Hilary F. Ketchum and Roger B. J. Benson (2010), transferred Brancasaurus

Brancasaurus

Brancasaurus is an extinct genus of plesiosaur from the Early Cretaceous of what is now Germany. The type species is Brancasaurus brancai, first named by Wegner in 1914 in honor of German paleontologist Wilhelm von Branca...

, Kaiwhekea

Kaiwhekea

Kaiwhekea is an extinct genus of plesiosaur from the Late Cretaceous of what is now New Zealand. The type species, Kaiwhekea katiki, was first described by Arthur Cruickshank and Ewan Fordyce in 2002. Kaiwhekea was approximately 7 meters long and lived around 69-70 million years ago...

, Nichollssaura and Thililua

Thililua

Thililua is a genus of polycotylid plesiosaur, containing one species, T. longicollis. The name Thililua is derived from that of an ancient aquatic god from local Berber mythology; longicollis refers to the animal's long neck. Thililua has been found in Late Cretaceous rocks in the High Atlas...

to this family. However, Ketchum and Benson (2011) reassigned Kaiwhekea and Thililua to their original positions, as an elasmosaurid and a polycotylid, respectively.

Phylogeny

Cladogram

Cladogram

A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...

 based on Ketchum and Benson (2010):
Cladogram based on Ketchum and Benson (2011):