Euhelopus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Euhelopodidae

Genus:Euhelopus

Species:Euhelopus zdanskyi

Introduction

Euhelopus zdanskyi roamed the earth at the height of the Jurassic period, when dinosaurs dominated the land and sauropods such as Euhelopus were among the most populous orders of dinosaur. The sauropods included many of the largest land animals yet discovered, though Euhelopus ranked along the middle of the sauropod scale in size.

First unearthed in the early twentieth century in China, Euhelopus originally went by the name Helopus, meaning simply “marsh foot.” However, the name was later changed to Euhelopus ("true marsh foot") in 1956. The dinosaur was originally considered part of the Camarasauridae family, but scientists soon realized that its unusually long neck and other unique characteristics shared with close relatives, such as Mamenchisaurus, called for further classification or taxonomic adjustment. Conflicting sources classify Euhelopus (and its closest relations) as a member of the Euhelopodidae family and as a member of the Eusauropoda taxon.

Classification

Traditionally, paleontologists relied largely on the hierarchical Linnaean system, developed by Carolus Linnaeus in 1735, to classify dinosaurs. This system comprises different tiers of classification (such as class, order, genus, and species) based on shared characteristics within each grouping. Species, the lowest tier, is based on the most specific shared traits. Additional tiers have also been added to the order and family groupings.

Within the Linnaean system, dinosaurs have long been split into two basic orders—Ornithischia and Saurischia—based on their skeletal structure (although in the twenty-first century some researchers began to challenge this longstanding division). Euhelopus falls into the saurischian order, which comprises dinosaurs known for more lizard-like skeletons, as opposed to the more bird-like ornithischians. Specifically, saurischian dinosaurs have pelvic, or hip, bones that are angled down and forward, like modern lizards, rather than down and back, like modern birds.

The saurischian order then breaks down into numerous suborders, infraorders and families. Paleontologists have classified Euhelopus as a member of the Sauropodomorpha suborder, whose members are recognized as large four-legged, herbivorous dinosaurs with long necks. Euhelopus is further identified as a member of the sauropods, one of two Sauropodomorpha infraorders. These terrestrial giants came later than members of the other infraorder (prosauropods). They thrived during the Middle and Late Jurassic periods and continued into the Cretaceous. They were also quadrupedal—whereas prosauropods walked on two legs—with small heads relative to their long necks and large body size.

The sauropods break down into numerous family groups, including Cetiosauridae, Neosauropoda, and Camarasauridae. Although originally classified as a member of the camarasaurid family, Euhelopus and several closely related species later earned an entirely new family designation. Based on their extraordinarily long necks and their placement in the Late Jurassic, Euhelopus and several sibling species became members of the Euhelopodidae family. However, debate has arisen over these family classifications.

Scientists may also use another classification system, called phylogenetic or cladistic classification. This system classifies animals in family trees, called cladograms, grouped by common ancestry. Each split in the tree creates a new group based on shared physical traits. Within this system, Euhelopus belongs to the Sauropoda clade, which is further divided into numerous smaller clades, or branches, of the family, including Eusauropoda, Neosauropoda, and Macronaria. Under this system, Euhelopus is often placed in the neosauropoda clade, and remains closely related to Mamenchisaurus. There is still contention regarding more specific phylogenetic classification of Euhelopus; other clades the dinosaur has been classified under include Titanosauriformes and Euhelopodidae.

Anatomy

Paleontologists used two skeletons, one nearly complete, and one skull as the basis of studies of Euhelopus. This evidence indicates that Euhelopus possessed the large, quadrupedal body, with long neck and tail, of the sauropods. Though Euhelopus was smaller than many sauropods, it possessed the distinctively long neck that resulted in the creation of a new dinosaur family, Euhelopodidae. This long neck possessed 19 vertebrae and extended to 5 meters, half its body length. Though the skull fossil was discovered without teeth, the shape of the skull had a distinctive stout and box-like shape, and the structure indicated rows of teeth growing in the side and back of the jaw as well as the front. Euhelopus also had large nostrils atop its skull. The dinosaur's forelimbs were as long as its hind, giving it a more elephant-like posture. This skeletal structure supports conclusions that Euhelopus and other sauropods walked on land, debunking earlier theories that they were aquatic animals who needed the buoyancy of water to support their heavy bodies.

Dinosaurs have generally been regarded as cold-blooded animals, like modern lizards, though the term “cold-blooded” is deceptive. Modern lizards are ectothermic, meaning that they rely on the sun and other environmental factors to warm their bodies. Though science has traditionally held dinosaurs, specifically non-avian dinosaurs, to be ectothermic, evidence suggests that some might have been endothermic, meaning that they could heat their bodies from within by consuming food. Scientists continue to debate whether sauropods such as Euhelopus might have been ectotherms, endotherms or something in between.

Intelligence

Scientists have used encephalization quotient (EQ), a measure based on brain and body size, to estimate animal intelligence. Slower-moving herbivores tend to fall lower on the EQ scale than their faster, carnivorous, predatory counterparts. The sauropods, with their vast bodies and small heads, are believed to have fallen on the lowest end of that scale. Sauropods, including Euhelopus, likely ranked around 0.2 on the EQ scale.

Reproduction and Population

Little is known about reproduction among sauropods such as Euhelopus. Scientists have largely held that most dinosaurs were oviparous, like modern lizards and birds, meaning that they reproduced by laying eggs. However, fossilized egg evidence is limited for sauropods. Only beginning in the 1980s did researchers uncover embryonic sauropods and what are believed to be their associated eggshells. This evidence seems to confirm that at least some sauropods were oviparous. Specific fossilized egg evidence does not exist for Euhelopus, so conclusions regarding its habits are derived from related fossils.

Discoveries made in Argentina indicate that some sauropods hid their eggs beneath mounds of vegetation, likely to keep them warm and protect them from predators. Insufficient evidence exists regarding the post-natal treatment of hatchlings. Many other plant-eating herd dinosaurs, such as hadrosaurs and ceratopsians, are believed to have stayed with and cared for their hatchlings for some time, but current fossil evidence is indeterminate for sauropods.

The large numbers of collective fossils finds for sauropods and their wide geographic distribution across six continents suggests that the dinosaurs ranged in great numbers. Scientists believe sauropods to have been one of the dominant species during the Jurassic period, though their numbers appear to have declined in the Cretaceous. However, limited fossil evidence exists for Euhelopus, which may mean that this particular species did not reach the numbers of its relatives.

Diet

Euhelopus, like other sauropods, relied on plant life to sustain their diets. Their vast body size indicates that they likely had to spend a great deal of time eating, and they could not afford to be selective about the vegetation that they consumed. Scientists continue to debate the preferred posture of sauropods when feeding, but their long necks suggest that they were able to consume vegetation both high and low in a wide circumference. Much debate has erupted over whether sauropods could employ their long necks to stretch for higher-up vegetation, given the strain this effort might have placed on their heart. However, studies of Euhelopus and its close relative Mamenchisaurus indicate that the neck skeletons were lighter than thought and could potentially support intermittent efforts to reach for food. However, Euhelopus likely spent as much or more time reaching for food at a level parallel to and even lower than the height of its torso.

The Late Jurassic period was dominated largely by ferns and gymnosperms, such as cycads and conifers; flowering angiosperms did not appear until the Cretaceous, when the numbers of sauropods began to decline, being replaced by smaller herbivores such as hadrosaurs and ceratopsians.

Behavior

Very few fossils have been found of Euhelopus, making it difficult to evaluate the social habits and behavior of this specific species. However, communal fossil beds for related sauropods—particularly its closest relative, Mamenchisaurus—and the discovery of many collectively assembled sauropod footprints suggest that some sauropods moved in herds and were extremely gregarious, or social, in behavior. Some evidence suggests that sauropods might have moved in interspecies herds. Herd behavior is common among plant-eating dinosaurs as it provides individual members of a group with additional defense against predators. The wide geographic distribution of sauropods also suggests that they might have been migratory animals who moved from place to place in search of food.

Habitat and Other Life Forms

Euhelopus lived during the Late Jurassic period in what is now China. At the time, the global landscape was undergoing great changes. For millions of years, the modern continents had formed one giant landmass, known as a supercontinent, called Pangaea. During the Late Triassic period, this giant landmass began the slow process of breaking apart into what would become two new supercontinents, Gondwana and Laurasia. With these tectonic shifts, the landscape and climate of the dinosaurs changed as well, and by the Late Jurassic, much of the global landscape was rich with plant and animal life.

The climate in China, where Euhelopus and many other Jurassic fossils have been unearthed, was likely warm and humid much of the time. Lush, green forests of ferns, cycads, conifers, and other plant life covered much of the land, providing ample food for the large herbivores that thrived during this time. It was during the Jurassic period that dinosaurs came to dominate the faunal landscape. Fossil evidence indicates that Euhelopus, in particular, lived in wetland areas such as marshes, likely near rivers.

Jurassic China was diverse and well populated by dinosaurs. Fossil sites throughout the area have yielded an abundance of information regarding animal and plant life. In addition to sauropods, the region was also home to theropods, stegosaurs, carnosaurs, pterosaurs, and ornithopods, as well as fish and amphibians. Euhelopus and other sauropods likely shared their habitat with many other herbivores and were likely hunted or scavenged by carnivorous theropods and carnosaurs. Predator species found near the remains of Mamenchisaurus, a close relative of Euhelopus, include the carnosaurs Szechuanosaurus and Yangchuanosaurus.

Research

Euhelopus zdanskyi remains were first scientifically described in 1929. Swedish paleontologist Carl Wiman studied the fossils—two partial skeletons and a skull—from a site in the Meng-Yin Formation near Shandong, China, which was excavated by Austrian paleontologist Otto Zdansky. Wiman first named his find Helopus, but later, American paleontologist Alfred Romer re-named the new species Euhelopus.

Several fossil sites within China have yielded abundant finds, both for sauropods and contemporary families of dinosaur. Euhelopus was the first sauropod fossil to be unearthed in China, though not the first in the world. The very first sauropod discovery known to modern science was of an older relative, Cetiosaurus conybeari, in 1841.

Since the mid–nineteenth century, hundreds of fossil finds have been made for sauropods on every continent except Antarctica. Additional finds from China include Euhelopus's closest and much larger relative, Mamenschisaurus, of which seven different species of have been uncovered thus far in China between 1954 and 1996. Other close relatives unearthed in China's Lower Shaximiao Formation include two species of Omeisaurus as well as Shunosaurus lii.

Bibliography

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