Futabasaurus suzukii
- Rodrigo
- 4 hours ago
- 4 min read
Age
Late Cretaceous (Santonian)
86.3–85 Ma
Taxonomic Classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: †Plesiosauria
Family: †Elasmosauridae
Genus: †Futabasaurus
Species: Futabasaurus suzukii
Morphological Description
Futabasaurus suzukii is an elasmosaurid plesiosaur represented by the holotype specimen NSM PV15025, which comprises a partial skull and mandible, a series of vertebrae extending from the cervical to sacral regions, ribs, the clavicular arch, the pelvic girdle, and appendicular elements. The preserved portion of the skeleton measures approximately 3 m in length (from the posterior cervical region to the sacrum), and the total body length is estimated to have ranged from 6.4 to 9.2 m in life.
The skull is teardrop-shaped and is estimated to be approximately 40 cm in length. A notable feature is the relatively wide spacing between the orbit and the external naris, with the latter positioned dorsal to the fifth maxillary alveolus. The dentition consists of recurved, conical teeth bearing fine, irregular longitudinal ridges.
In the axial skeleton, the posterior cervical vertebrae exhibit a distinct ventral notch. The clavicular arch is characterized by a posteriorly elongated interclavicle and a prominent median embayment along its anterior margin.
The appendicular skeleton displays features that distinguish Futabasaurus from other elasmosaurids. Notably, the humerus is significantly longer than the femur, with a length ratio of approximately 1.16, representing a key diagnostic trait. In addition, the femur exhibits well-developed muscle attachment sites, particularly for the m. caudofemoralis, which forms a pronounced posterior projection.
Etymology
The genus name Futabasaurus is derived from the Futaba Group, the geological formation in Fukushima Prefecture, Japan, where the holotype specimen was discovered.
The species name suzukii honors Tadashi Suzuki, the discoverer of the holotype specimen, who found the fossil in 1968.
In Japan, the species is commonly referred to as “Futabasuzukiryu” (フタバスズキリュウ, 双葉鈴木竜) rather than its scientific name.
Biological Interpretation
Futabasaurus suzukii inhabited the Japanese archipelago during the Late Cretaceous (Santonian), likely occupying nearshore to inner shelf marine environments.
Histological evidence from the humerus and femur indicates bone collapse consistent with decompression syndrome, suggesting that this taxon engaged in frequent deep-diving behavior. Furthermore, numerous shark teeth have been recovered in close association with the specimen, including one embedded near the tubercle of the right humerus and two within neural spines. These findings indicate either predation by sharks or post-mortem scavenging.
As a member of Elasmosauridae, Futabasaurus conforms to the general plesiosaurian bauplan, possessing an elongated neck and paddle-like limbs. Compared to more basal representatives of the clade, it exhibits an increased number of cervical vertebrae and a proportionally longer neck.
Gastroliths are also present, with approximately 40 stones recovered in association with the specimen. These range from 10 mm to 120 mm in diameter and consist primarily of mudstone and sandstone. Their presence suggests a functional role in either mechanical digestion or buoyancy regulation.
Among marine vertebrate fossils discovered in Japan, Futabasaurus suzukii is arguably the most famous. As one of the earliest discovered plesiosaurs in Japan, its discovery story is particularly remarkable.
In the 1960s, Tadashi Suzuki, a second-year middle school student, became interested in fossil excavation after reading Ichiro Yanagisawa's book “Oitate on the Eastern Side of the Abukuma Mountains.” Near his aunt's residence along the Okugawa River in Iwaki City, where the Futaba Group is exposed, Suzuki frequently collected marine fossils, including shells and shark teeth.
In October 1968, he discovered shark teeth and a vertebra on the riverbank. These remains were later identified as belonging to a plesiosaur by Dr. Ikuo Obata and Dr. Yoshikazu Hasegawa of the National Museum of Nature and Science. They subsequently joined the excavation effort.
The reconstruction of the skeleton took approximately four years and resulted in one nearly complete adult specimen and partial remains of six juveniles. The holotype is currently housed in the National Museum of Nature and Science in Ueno, Tokyo, where it is considered one of the museum's most important exhibits.
Editer: Rodrigo
References
Sato, Tamaki; Hasegawa, Yoshikazu; Manabe, Makoto (2006). "A new elasmosaurid plesiosaur from the Upper Cretaceous of Fukushima, Japan". Palaeontology. 49 (3): 467–484.
「あの首長竜を50年前に高校生が発見した必然-フタバスズキリュウ｢発見50年｣-」（佐藤たまきと。『東洋経済オンライン』2018年8月13日付）
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