ScienceDaily: Fossil of History’s Most Successful Mammal: Prehistoric ‘Rodent’ May Have Set the Stage for Life in Trees, Herbivorous Diets

Like modern rodents, “primitive” multituberculates were already fully equipped to go anywhere and eat anything.

A diverse group of extinct rodent-like mammals called multituberculates is generally considered one of the most successful stories in mammalian evolution. Analysis of a newly discovered Chinese Jurassic specimen, Rugosodon eurasiaticus, reveals that the “evolving” features ensuring multituberculate success were actually present from its earliest appearance in the rock record.

Multituberculates are distinguished from rodents largely by their very bumpy back teeth—the source of their name (multi=many; tubercle=bumps). In fact, the new fossil’s name, Rugosodon, means “wrinkled teeth.”1

Multituberculates coexisted with dinosaurs, as seen in the Jurassic and Cretaceous formations of the fossil record. But their story didn’t end with the dinosaurs. They continued to be represented higher in the fossil record, well into the Tertiary formations. Evolutionists think this means they survived the extinction of the dinosaurs by millions of years. By evolutionary reckoning, the multituberculates occupy a record-setting slot on the evolutionary timeline. Their story supposedly lasted over 100 million years, longer than any other in mammalian history. Since they apparently occupied the same ecological niches as rodents—in other words, pretty much everywhere both terrestrial and arboreal—they presumably lost in competition with rodents and finally died out in the Oligocene epoch.

RugosodonRugosodon eurasiaticus, a 17 cm (6.7 inch) rodent-like fossil from Jurassic rock believed to be 160 million years old in eastern China, is a “multituberculate.” This diverse group of extinct animals are distinguished from rodents by the very wrinkly surfaces of their molars and premolars. They also have ankle joint anatomy that would have given them great agility on, under, and off the ground. IMAGES: Top to bottom: the fossil, a sketch of it,2 and an artist’s conception by April Isch/University of Chicago/Science Shot.3

primitive-teethThe “wrinkly” occlusive surfaces of Rugosodon’s molars (“m” and “M”) and premolars (“p” and “P”) are not just random bumps. Their arrangement creates a blade-like texture, and the interface between upper and lower teeth produces tongue-in-groove contact that would greatly enhance dietary possibilities. From its “first” appearance in the fossil record, the multituberculate mammal thus displays teeth designed to eat plants. IMAGE: C.-X. Yuan et al., “Earliest Evolution of Multituberculate Mammals Revealed by a New Jurassic Fossil,” Science 341 (16 August 2013): 779–783, doi: 10.1126/science.1237970.

The Secret to Success

What was the secret of multituberculate success? Their rodent-like front incisors combined with multifunctional molars and premolars would have made munching on small animals, crushing seeds and nuts, and slicing through all sorts of plant material readily available options for multituberculates. And their highly mobile ankle joints—which normally enable tree-dwelling animals to negotiate uneven surfaces—likely equipped their limbs with the ability to fill whatever niche they chose.

Multituberculates in the fossil record appear to have been able to burrow, leap, and climb. Zhe-Xi Luo, co-author of the study published in Science, says, “The later multituberculates of the Cretaceous [era] and the Paleocene [epoch] are extremely functionally diverse: Some could jump, some could burrow, others could climb trees and many more lived on the ground. The tree-climbing multituberculates and the jumping multituberculates had the most interesting ankle bones, capable of ‘hyper-back-rotation’ of the hind feet.” It is the “early” appearance of these adaptations that has attracted attention. Luo says, “What is surprising about this discovery is that these ankle features were already present in Rugosodon—a land-dwelling mammal.”

Discovery of this fossil in China also broadens the multituberculate presence in the Jurassic fossil record from Europe to Asia. Luo explains, “This new fossil from eastern China is very similar to the Late Jurassic fossil teeth of multituberculates from Portugal in western Europe. This suggests that Rugosodon and its closely related multituberculates had a broad paleogreographic distribution and dispersals back-and-forth across the entire Eurasian continent.”

The Plot Thickens

The previous story of multituberculate success, put forth last year by researchers who surveyed multituberculate fossils from all over the world, asserted that these animals began with simpler anatomy and gradually evolved their versatile adaptive features. Presumably, their evolving ability to eat plant material coincided with the evolution of flowering plants in the mid-Cretaceous, enabling them to survive despite competition with dinosaurs. Comparing the fossils last year, researcher Alistair Evans reported, “Multituberculates seem to be developing more cusps on their back teeth, and the bladelike tooth at the front [a typical rodent feature] is becoming less important as they develop these bumps to break down plant material. At the height of multituberculate evolution, these animals had teeth as complex as many modern plant-eating mammals—an attribute that certainly contributed to their evolutionary success.”4

This smooth evolutionary story hit a bump in the road with the discovery of Rugosodon eurasiaticus in China’s early Jurassic Tiaojishan Formation. Like “later” multituberculates, Rugosodon displays a blade-like arrangement of cusps on its fourth premolar. This “blade” fits (“occludes”) nicely with the corresponding upper teeth cusps because they are offset a bit to achieve a perfect occlusive bite.

No orthodontic evolution was needed to help this creature eat its veggies! One might even suspect—if one were a creationist—that the multituberculate’s teeth were designed with vegetarian functionality from its inception. Furthermore, the authors of the study write, “Rugosodon shows that the Jurassic paulchoffatiids [a family of multituberculates] are strikingly similar to later multituberculates in four major tarsal [ankle] joints.”

A Likely Story?

So what is the evolutionary interpretation of this very non-primitive fossil? The authors attribute multituberculate success in subsequent evolutionary periods to the early evolution of complex teeth and highly mobile ankles that allowed them to exploit a wide variety of ecological niches and were therefore “crucial for later evolutionary success of multituberculates in the Cretaceous and Paleogene.”2

“Despite a great taxonomic diversity and a wide range of feeding adaptations over the long history of multituberculates, the morphology of their ankles is remarkably conserved” throughout their evolutionary history, the authors conclude. “The highly mobile tarsal joints are well suited for foot functions on uneven substrates (including arboreality) and are apparently versatile enough to be retained in fossorial [burrowing] and saltatorial [leaping] forms. Major diversifications of multituberculates in the Cretaceous and Paleogene have a structural underpinning in ankle bones of their common ancestor of the Jurassic, for which Rugosodon provides fresh fossil evidence.”2

Fine Design

The fine design of the multituberculates “early” in the fossil record is not supportive evidence for evolution but is rather a good example of our Creator’s design. According to the Bible, God created all kinds of land animals as well as man on the 6th day of Creation week, about 6,000 years ago. Each kind was fully functional and able to reproduce, varying within its created kind. The original animals were also vegetarians according to Genesis 1:29–30 and therefore did not have to wait to evolve the right kind of teeth to eat plants.

The mobility of multituberculates as well as their exquisitely designed dental equipment demonstrates not blind, purposeless, directionless, chance evolution but rather wonderfully intelligent design. The diversity of these animals illustrates not evolution over millions of years but variation within created kinds. And their occurrence in many parts of the fossil record is not evidence of their evolutionary appearance on earth but instead is consistent with their presence in many of the habitats catastrophically buried during the global Flood, less than two thousand years after God created them.

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Footnotes

  1. Rugosus is Latin for “wrinkles” and odon is Latin for “teeth.” Back
  2. C.-X. Yuan et al., “Earliest Evolution of Multituberculate Mammals Revealed by a New Jurassic Fossil,” Science 341 (16 August 2013): 779–783, doi: 10.1126/science.1237970. Back (1) Back (2) Back (3)
  3. news.sciencemag.org/paleontology/2013/08/scienceshot-meet-'wrinkly-tooth'-earliest-rodentlike-creature Back
  4. Quoted in News to Note, March 24, 2012. Back