A reanalysis of the fossilized remains of a sauropod unearthed in China in the 1980s is providing new insights into what is the longest necked group of sauropods known.
The fossils were discovered in the red sandstone of the Shishugou Formation in northwest China in 1987 and consisted primarily of its mandible (lower jaw), skull fragments and a few vertebrae and dated to approximately 162mya (Late Jurassic). It was named Mamenchisaurus sinocanadorum with the genus name being an accidental misspelling with Mǎménxī being mistaken for Mǎmíngxī. The second or species name is in honor of the China–Canada Dinosaur Project team which discovered it.
This genus appears to possess the longest necks of the sauropods (consisting of 50% of their total body length), with Mamenchisaurus sinocanadorum having the longest atnearly 50' in length which is some six times the length of that seen in giraffes and about one and a half times the length of a bus. Basically, it likely possessed the longest neck of any creature that ever lived.
They discovered that one of the secrets for achieving this length was that the vertebrae, much like those seen in some long-necked bird species such as flamingos and swans, has numerous hollow air pockets, making them considerably lighter than those completely full of heavy marrow and tissue. The researchers estimate that these hollow portions accounted for up to 77% of the vertebrae's mass.
A fossilized rod of bony tissue was found during the excavation might have been what is called a "cervical rib" that would have been a stiff extension of the vertebra acting like a brace but at the cost of some flexibility.
In any case...
The full paper describing the find is Re-assessment of the Late Jurassic eusauropod Mamenchisaurus sinocanadorum Russell and Zheng, 1993, and the evolution of exceptionally long necks in mamenchisaurids with the Abstract made available below:
The fossils were discovered in the red sandstone of the Shishugou Formation in northwest China in 1987 and consisted primarily of its mandible (lower jaw), skull fragments and a few vertebrae and dated to approximately 162mya (Late Jurassic). It was named Mamenchisaurus sinocanadorum with the genus name being an accidental misspelling with Mǎménxī being mistaken for Mǎmíngxī. The second or species name is in honor of the China–Canada Dinosaur Project team which discovered it.
This genus appears to possess the longest necks of the sauropods (consisting of 50% of their total body length), with Mamenchisaurus sinocanadorum having the longest atnearly 50' in length which is some six times the length of that seen in giraffes and about one and a half times the length of a bus. Basically, it likely possessed the longest neck of any creature that ever lived.
They discovered that one of the secrets for achieving this length was that the vertebrae, much like those seen in some long-necked bird species such as flamingos and swans, has numerous hollow air pockets, making them considerably lighter than those completely full of heavy marrow and tissue. The researchers estimate that these hollow portions accounted for up to 77% of the vertebrae's mass.
A fossilized rod of bony tissue was found during the excavation might have been what is called a "cervical rib" that would have been a stiff extension of the vertebra acting like a brace but at the cost of some flexibility.
In any case...
The full paper describing the find is Re-assessment of the Late Jurassic eusauropod Mamenchisaurus sinocanadorum Russell and Zheng, 1993, and the evolution of exceptionally long necks in mamenchisaurids with the Abstract made available below:
Abstract
The sauropod genus Mamenchisaurus, from the Late Jurassic–Early Cretaceous of East Asia, has a convoluted taxonomic history. Although included in the first cladistic analysis of sauropods, only recently has the monophyly of Mamenchisaurus, and the anatomical diversity of the many penecontemporaneous East Asian eusauropods, been evaluated critically. Here, we re-describe the holotype and only specimen of M. sinocanadorum. Although the original diagnosis is no longer adequate, we identify several autapomorphies that support the validity of this species, including an elongate external mandibular fenestra and distinctive pneumatic structures on the cervical centra. We incorporate new data into a phylogenetic character matrix that also includes Bellusaurus and Daanosaurus, both of which are known only from juvenile material and are often hypothesized to be neosauropods (or close relatives thereof). We recover all species of Mamenchisaurus as part of a radiation of predominantly Middle–Late Jurassic East Asian eusauropods, but the genus is non-monophyletic, underscoring the need for further systematic revision of mamenchisaurid taxonomy. Analyses that score ontogenetically variable characters ambiguously recover Bellusaurus and Daanosaurus as juvenile mamenchisaurids, a hypothesis supported by several features that are unique to mamenchisaurids or exhibit little homoplasy, including anteriorly bifurcate cervical ribs. Finally, computed-tomography reveals extensive vertebral pneumaticity in M. sinocanadorum that is comparable to that of the largest sauropods, and updated scaling analyses imply a neck over 14 m long, rivalling estimates for other exceptionally long-necked sauropods. Previous work has suggested that the elongated cervical ribs of particularly long-necked sauropods such as M. sinocanadorum stabilized the neck by limiting its mobility. Given that extent of pneumaticity responds dynamically to a bone’s habitual loading, we propose that long cervical ribs – and other structural modifications that limited flexibility – promoted the evolution of increasingly long necks by producing a more predictable biomechanical milieu amenable to increased pneumatization.
The sauropod genus Mamenchisaurus, from the Late Jurassic–Early Cretaceous of East Asia, has a convoluted taxonomic history. Although included in the first cladistic analysis of sauropods, only recently has the monophyly of Mamenchisaurus, and the anatomical diversity of the many penecontemporaneous East Asian eusauropods, been evaluated critically. Here, we re-describe the holotype and only specimen of M. sinocanadorum. Although the original diagnosis is no longer adequate, we identify several autapomorphies that support the validity of this species, including an elongate external mandibular fenestra and distinctive pneumatic structures on the cervical centra. We incorporate new data into a phylogenetic character matrix that also includes Bellusaurus and Daanosaurus, both of which are known only from juvenile material and are often hypothesized to be neosauropods (or close relatives thereof). We recover all species of Mamenchisaurus as part of a radiation of predominantly Middle–Late Jurassic East Asian eusauropods, but the genus is non-monophyletic, underscoring the need for further systematic revision of mamenchisaurid taxonomy. Analyses that score ontogenetically variable characters ambiguously recover Bellusaurus and Daanosaurus as juvenile mamenchisaurids, a hypothesis supported by several features that are unique to mamenchisaurids or exhibit little homoplasy, including anteriorly bifurcate cervical ribs. Finally, computed-tomography reveals extensive vertebral pneumaticity in M. sinocanadorum that is comparable to that of the largest sauropods, and updated scaling analyses imply a neck over 14 m long, rivalling estimates for other exceptionally long-necked sauropods. Previous work has suggested that the elongated cervical ribs of particularly long-necked sauropods such as M. sinocanadorum stabilized the neck by limiting its mobility. Given that extent of pneumaticity responds dynamically to a bone’s habitual loading, we propose that long cervical ribs – and other structural modifications that limited flexibility – promoted the evolution of increasingly long necks by producing a more predictable biomechanical milieu amenable to increased pneumatization.
Comment