Amygdalodon

*Amygdalodon patagonicus*

**Amygdalodon** is a Primitive Sauropod from middle Jurassic period, approximately 180 to 171 million years ago, from the Toarcian to the Aalenian, in what today is Argentina. Amygdalodon was a large basal sauropod, measuring 15 meters long and 4 meters high and weighing more than tons. It had a robust body that was supported by four solid legs, a long tail and a neck topped by a small head. It had almond-shaped teeth, from which its name comes, they are compressed laterally and slightly curved inwards. It is considered a Cetiosauridae due to particularities in the vertebrae that only have simple lateral depressions. It weighed about 1.48 tonnes and was about 39.4 feet (12 meters) long. Three different individuals, although none are complete, are known. Overall verly little of the animal has ever been found.

Its name means "almond tooth". It was named by Cabrera in 1947. Its teeth were oval - shaped. It used to live about 170 mya in South America.

## Discovery

The holotype (MLP 46-VIII-21-1) consists of some vertebrae, ribs, four complete and three partial teeth, and a partial pelvis and shoulder-blade, of which was discovered in 1936. The type species, Amygdalodon patagonicus, was described by Cabrera in Argentina in 1947. Until 1936 sauropod fossils from Argentina were completely unknown then, prompted by Piatnitzky's brief mention of "bones of a saurian of no less than 5-7m long", Dr. Tomás Suero took a trip to Chubut to check out deposits overlying the Liassic of the Pampa de Agnia and discovered the remains of a Jurassic sauropod dinosaur around twice the size of Piatnitzky's estimation (in 1936).

## Description

His remains were found in the Province of Chubut, east of the town of Sierra de Pampa de Agnía, in Patagonia, Argentina. It belongs to the sediments of the Cerro Carnerero Formation. At least 2 specimens were found and possibly another one, from which teeth, cervical, dorsal and caudal vertebrae, ribs, distal part of the tibia and almost complete pubis were recovered. It was described by Cabrera in 1947, the fossils are cataloged No. 46-VIII-21-1 of the Department of Paleozoology, Vertebrates, of the La Plata Museum and were donated by the General Directorate of Fiscal Oil Fields.

The morphology of the teeth, which are characterized by their spatulate shape and absence of denticles in their crowns. An autapomorphic ornamentation pattern is observed in the enamel, formed by small circular pits aligned from the tip to the base, which are frequently seen joined by continuous grooves. Worn teeth show long facets of wear that extend to only one edge of the crown. This unique combination of characters allows Amygdalodon to be identified as a separate genus. Based on the phylogenetic analysis carried out, it is interpreted as a non-eusauropod sauropod. Thus the presence of derived dental characters present in the teeth of this taxon, such as the presence of crown-crown occlusion or the presence of buccal and lingual grooves, shows that some characters previously interpreted as seen only in Eusauropoda would have appeared earlier in the evolution of sauropods. However, due to the fragmentary nature of the material available, alternative positions place Amygdalodon within Eusauropoda. All material that originally referred to this species represents very basal eusauropod non-neosauropods. Amygdalodon is the only evidence in South America for a probable early basal eusauropod sauropod to the early Middle Jurassic showing global dispersal.

## Size

Amygdalodon is estimated to have been 12 metres (39 ft) long and 4 metres (13 ft) tall. This quadrupedal dinosaur had an estimated weight of over 5 tonnes (4.9 long tons; 5.5 short tons).

## Classification

Rauhut (2003) placed Amygdalodon as Eusauropoda incertae sedis based on examination of the type material. Later, a cladistic analysis conducted by Carballido et al. (2010) recovered the genus as a non-eusauropod sauropod. Holwerda and Pol (2018) concurred, recovering Amygdalodon as sister to Isanosaurus. A basal sauropod classification for Amygdalodon was supported by Pol and colleagues in 2022, with it showing the first signs of dental modification for bulk feeding that is retained later sauropods, but it does not have the vertebral features found in more derived sauropods. They found it in a polytomy with the Asian taxon Gongxianosaurus, and possibly related to South American Volkheimeria, though the latter had a very labile position.

## JPInstitute.com Description

Amygdalodon was a plant-eating giant from South America.

It was one of the earlier South American long-necked dinosaurs, and it lived many millions of years before the huge titanosaurs evolved. Since most of the fossils of the very first dinosaurs came from South America, it is possible that Amygdalodon's ancestors were the early prosauropods from that area.

Amygdalodon is classified as belonging to the same family as Cetiosaurus based on its teeth and some other skeletal similarities. Known from only a few bones and teeth, there is much still to be discovered about this genus.

## Links

http://web.archive.org/web/20031006070625/http://www.jpinstitute.com/dinopedia/dinocards/dc\_amygd.html#