Silvisaurus condrayi

You wait long enough, and history starts to pile up, like falling snow (only history doesn't melt away and has a way of churning back to the surface). In paleontology, we've just passed two centuries with Megalosaurus (1824) and Iguanodon (1825). I was thinking about the topic of this post and how it was a relatively recent name, even though it felt old, but then realized that 1960 is not quite as recent as it was when I first read about Silvisaurus in the mid-1980s. I'm not tracking stats to any great degree, but it's probably safe to say there aren't a lot of people reading this who were mid-career when the scientific description of Silvisaurus condrayi was published.

Anyway, for all that, Silvisaurus feels like a much more old-timey dinosaur, something that was described by Brown or Osborn in the 1910s in an issue of the Bulletin of the American Museum of Natural History. Maybe it's the simple name, or the restoration that came with the description, or some kind of personal incredulity that anyone was bothering to describe a dinosaur in 1960. It just feels temporally out-of-place in the history of dinosaur paleontology. (The other one that feels especially like this is Fabrosaurus, which by all rights should date to the 1920s at the latest rather than 1964.)

Another reason why Silvisaurus may seem older than it is is its obscurity. It's just never received a lot of attention. There are only two real descriptions of it, the original (Eaton 1960) and Carpenter and Kirkland (1998); everything else can be classified under thumbnails, passing mentions, or cladogram filler. The 2023 designation of S. condrayi as the state land fossil of Kansas offers tantalizing hints that more can be added to the holotype, but to date such has not escaped to the wider paleontological community. (It did earn a nice skeletal display at the University of Kansas Natural History Museum, photos below. Stegopelta and Nodosaurus can eat their hearts out!) Of course, it's not that strange for ankylosaurs to linger in obscurity, especially those that didn't have tail clubs. Even if they're well-represented, they get left by the wayside for the most part. Everybody talks about Edmontonia and Panoplosaurus but nobody does anything about them, for example.

Silvisaurus condrayi at the KU Natural History Museum. Photo from Wikimedia Commons by NGPezz. CC-BY-4.0. Skull *and* vertebrae? A titanosaur would kill to be this well-represented.

The type and only known specimen of S. condrayi was found in the mid-1950s by Warren Condray on his ranch in Ottawa County, north-central Kansas. Mr. Condray took the interesting step of writing his senator, Frank Carlson, about the find. (To be fair, in the 1950s there may have been more U.S. Senators than people with an academic interest in dinosaurs. Theodore Eaton, Jr., who described the genus and species, wasn't a dinosaur person, for example. In fact, his description of Silvisaurus appears to be his only direct contribution to dinosaur paleontology. Maybe that's another reason why Silvisaurus seems old-fashioned.) Senator Carlson then contacted the chancellor of the University of Kansas, and in July of 1955 Russell Camp, a preparator from the KU Natural History Museum, went to Condray's ranch to collect the specimen. Much like Stegopelta, the bones had been partially exposed by erosion and trampled by cattle. The work of preparation was perhaps not as daunting as for S. landerensis and its 300 pounds of fragments, but it doesn't sound like a joyful enterprise; Eaton (1960) mentioned that "preparation in the laboratory was a tedious and difficult task on account of the hard, 'ironstone' matrix and the fragility of many of the bones."

The specimen came from the middle of the Terra Cotta Clay Member of the Dakota Formation, in Eaton's interpretation about a third of the way up the Dakota. This is regarded as Albian in age (late Early Cretaceous) (Carpenter and Kirkland 1998). Unlike several other middle Cretaceous mid-continent ankylosaurs discussed in this blog, this one seems to have been buried in a terrestrial setting rather than being a bloat-and-float. The cross-bedded sandstones also included leaves attributed to oak, beech, sycamore, and sassafras (Eaton 1960) (or leaves that looked similar, given the historical tendency to use modern names for fossil leaves). Eaton regarded the site as part of a low-relief coastal plain, featuring a warm-temperate forest resembling that of the modern southeastern Piedmont (so, think like Atlanta, Georgia or Greenville, South Carolina). The meaning of the name is not stated right out, but given "silva" is Latin for "forest", the leaves probably suggested the genus name. With "condrayi" doubtless honoring Warren Condray, we get something like "Warren Condray's forest lizard".

Once all had been said and done, the type specimen, KUMNH 10296, included a skull, part of the left mandible, five cervical vertebrae in physical form plus impressions of at least three more, five dorsal vertebrae, a sacrum and presacral rod together apparently numbering eleven vertebrae, two "fairly complete" caudal vertebrae and three partial molds, four cervical ribs, an unspecified number of dorsal ribs, a chunk of ilium, a bone Eaton doubtfully described as a left pubis (actually a left sternal plate; Carpenter and Kirkland 1998), the distal end of the right femur, a terminal phalanx, and "numerous" osteoderms (Eaton 1960). A couple of dorsals were missing when Carpenter and Kirkland (1998) revisited KUMNH 10296, the sacral complex had been reduced to six verts, and the "numerous" osteoderms amounted to three cervical half-rings, a large spine, and a flat plate probably from the pelvic region. The missing dorsals may have reappeared by the time the mount was made, as it seems well-stocked in that department. It appears that the skeleton was associated but not fully articulated at burial (Eaton 1960).

It is interesting to see the very limited comparative material available. Eaton included almost no comparisons with other ankylosaurs in the anatomical description, leaving that for a section at the end, and even there the roster consisted of essentially two taxa: Ankylosaurus and Edmontonia rugosidens under two names, its own and the disguise of the American Museum of Natural History mount of "Palaeoscincus costatus", AMNH 5665, which is also actually Edmontonia rugosidens. As you might guess, with such limited companions, the diagnosis is along the lines of a thumbnail sketch of ankylosaur anatomy.

The skull is broadly like that of Edmontonia, but the skull armor is not well-defined (due to preparation; Carpenter and Kirkland 1998). It is longer than wide (33.2 cm [13.7 in] long versus 25.3 cm [10.0 in] wide), with a slightly domed cranium but without large postorbital horns. One of the features that has attracted much comment over the years (or at least much repetition of the original comment) is the presence of premaxillary teeth almost to the tip of the jaw, such that a beak would be confined to the very end of the mouth. The other feature that has attracted interest is the large inflated nasal sinuses. As discussed a few years ago, Eaton (1960) interpreted the sinuses as a resonating chamber, producing a sound "about E or F, four octaves above middle C." As I wrote in 2021, this is "surprisingly high-pitched, at keys 101 or 102 [92 or 93] on an extended piano, or 5274.041 or 5587.652 Hz. (In fact, it's so high-pitched something doesn't seem right. Either Eaton or I have misinterpreted something in the sound physics, those aren't resonating chambers, or Silvisaurus went through life projecting the majestic sound of tinnitus.)" The skull as found was broken in such a way that Eaton could examine the endocranial cavity, which is no longer physically accessible after prep (Carpenter and Kirkland 1998). If you're curious, he estimated a cavity volume of about 70 cubic centimeters, with a relatively large medulla.

Silvisaurus the tea kettle? Photo from Wikimedia Commons by NGPezz. CC-BY-4.0.

The postcranial anatomy is unremarkable for a nodosaur (even without having much in the way of comparisons). The most interesting bits are hints about the osteoderms that may explain features of the restoration. Eaton interpreted "unusually massive" caudal ribs as supporting muscles that swung the tail as well as dermal spikes, by analogy to "Palaeoscincus" which at the time was restored with a fringe of large spikes along the side of the tail. He stated that the type specimen "has some dermal plates almost in places on the ends of the [caudal] ribs, and a pair tilted upward on either side of the base of the neural spine, but none of these is clear enough for satisfactory illustration." Arrgh. Maybe just a photo, then? "In Figure 13 the ribs are even longer and heavier, but the centrum is narrower, suggesting that this vertebra was farther back but carried more prominent spines." Reportedly "numerous dermal plates are scattered among the other elements of the skeleton, but they show almost no meaningful association." He illustrated a few samples, including a large spike attributed to the shoulder, a hexagonal scute attributed to a band along the ribs, and "irregularly crested plates" attributed to the shoulder (recognizable today as partial cervical half-rings). These all fed into the charmingly dated restoration at the end of the paper, which shows the protagonist slinking along with crouched limbs, a very short tail, the facial expression of a satisfied turtle, and a distinctive interpretation of ankylosaur armor. It's a gridwork cobblestone arrangement at heart, with no evidence of the cervical rings (not even really over the shoulder per Eaton's suggestion, although there are some spines placed there), a Polacanthus-esque sacral shield, and a series of progressively larger spikes lining the side of the tail, providing a sort of spike-fan that would show up in restorations through the 1980s. (Years later Spicomellus would offer evidence that some ankylosaurs did give that last idea a try.)

The next time Silivisaurus was dusted off for extensive work was Carpenter and Kirkland (1998). Two general observations from their work are that the original preparation was a bit too enthusiastic, and some of the illustrations in Eaton (1960) are off. Many more ankylosaurs are brought in for comparison, but what emerges, for me at least, is a general impression of average-ness. The diagnosis and description are littered with "more than genus A but less than genus B", or if another genus has an unusual feature, Silvisaurus lacks it. It's either the "economy model" nodosaur or the Platonic ideal of one, depending on how flowery you're feeling. About the only things it had to itself as of 1998 are a proportionally narrow premaxillary beak and a bony node just behind the nares. The redescription came 28 years after the original description, and 2026 is 28 years after 1998; it would be interesting to see how it fares with another 28 years of ankylosaur work in the books. (Lots of ankylosaurs out there for redescription, students!)

References

Carpenter, K., and J. I. Kirkland. 1998. Review of Lower and middle Cretaceous ankylosaurs from North America. New Mexico Museum of Natural History and Science Bulletin 14:249–270.

Eaton, T. H., Jr. 1960. A new armored dinosaur from the Cretaceous of Kansas. The University of Kansas Paleontological Contributions: Vertebrata 8:1–24.