Teeth to the right of me, teeth to the left of me, teeth in front of me –hello to the world of crocodiles and their many relatives in a new special issue of The Anatomical Record
Let us be honest here. If your sweet, little nine-year old came to you and said, “I want to spend my life exploring those big green things in rivers that have all those great teeth” what would you think? Most of us would immediately consider: Therapy! Fast! (This is obviously due to one's spouse's bad genes!) “Sweetheart,” we would ask, “Aren't you interested in those fascinating whales? Maybe our curious monkey-relatives? Wouldn't you like to study the regal great cats? Or, perhaps, the magnificent and ever-beautiful array of birds? How about the noble and determined turtle?” “Nope,” says your future heir, “really think those scaly things with the great chompers are where it's at!” Great, a thousand hours of sensitivity training, making sure they never played with toy guns, decorating their rooms with happy unicorns and smiling butterflies, taking them to see only the animals they could actually pet at the children's zoo, and giving everyone on their baseball team a trophy so they had a positive self-image even if all they could hit with a bat was themselves, and the repository of all your hard work, hopes, and dreams wants to spend their life with some of the scariest denizens that have ever inhabited our world!! Where did we err? What is wrong with the kid?
Well, apparently, nothing, as there seem to be lots and lots of now big kids similarly fascinated (and most of them are not in prisons!). A bask (bet you did not know that is what a group of crocodiles is historically called?; JL's relatives in Florida call a group of their alligator cousins a “tsuris” – literally, trouble, in Yiddish) of such folks have come together to share their findings, thoughts, and opinions on crocs of all ilks in this extraordinary Special Issue of The Anatomical Record entitled, “The Age of Crocodilians and Their Kin: Anatomy, Physiology, and Evolution”. The Special Issue is Guest Edited by Professors Casey Holliday of the University of Missouri School of Medicine and Emma R. Schachner of Louisiana State University Health Sciences Center (Holliday & Schachner, 2022, this volume.). The Special Issue explores both the anatomy and physiology of living and fossil crocodylomorphs (described below, but basically the group of pseudosuchian archosaurs that are generally included in present-day crocodilians and their extinct relatives; hang-in there, translations to come.)
First a nod to our intrepid Guest Editors, Casey and Emma (we have worked too closely and too long for formalities). Our Guest Editors are two energetic stars in the study of functional anatomy of living crocodilians and on the reconstruction of reptilian ancestors in the prehistoric world, often based upon their own findings on living forms. To any who have met them, they are also really interesting people who do interesting things (JL comment: sort of like HFS who studies all sorts of fascinating beasties; no comments on JL, please). First, a few words about the junior member of the team, Emma Schachner. Emma is a product of vertebrate paleontological royalty, having taken her PhD at the University of Pennsylvania with Peter Dodson, who is, with only a little hyperbole, a living god in the world of prehistoric beasts (Peter's influence has been ubiquitous; he was, for example, JL's anatomy table-mate, big-sib, and life-line at Yale during what seems like the Late Cretaceous; see Laitman, 2009). Indeed, Co-Guest Editor Holliday was a student of noted paleontologist Larry Witmer who was a student of Peter's student David Weishampel, thus making Casey an academic great-grandchild of Peter's as well (we feel as if we should bow before them!). Emma is an animal person – fascinated both by those that are alive and those she figuratively brings back to life from fossils. For example, she adores and trains dogs, especially her pit bulls Mila and Augustus – who have their own Instagram account, @thevelvetburritos (she is also an afficionado of Middle and Late Republican Roman history, hence the names!) When not with her pooches, she spends most Sundays shooting at United States Practical Shooting Association (USPSA) matches (Do you think someone who lives in Louisiana and studies alligators would join the crochet club on weekends?) Oh, and in her spare time Emma has authored many insightful studies on the anatomy of living and extinct reptilians, including in The Anatomical Record, for example: on insights into the evolution of the respiratory system in nonavian theropods (Schachner, Lyson, & Dodson, 2009); new interpretations of the dinosaurian respiratory apparatus from the postcranial skeleton (Schachner, Farmer, McDonald, & Dodson, 2011); comparison of the feet of archosaurs from study of pedal proportions in the Triassic bipedal archosaur Poposaurus gracilis (Farlow, Schachner, Sazzarin, Klein, & Currie, 2014); further reconstructions of the functional anatomy of Poposaurus gracilis (Schachner et al., 2020); and on the bronchial tree of living dwarf caimans (Schachner, Diaz Jr, Echois, Osborne, & Hedrick, 2022, this issue).
Our lead Guest Editor, Casey Holliday, can best be described as a “force of nature”; you know when Casey is in the room! He is energy personified, and divides his time between his robust studies on reptilian anatomy and paleontology, teaching and advancing his beloved students, and showing his own family the wonders of nature. Despite his Twitter handle @CrocHolliday, our research into Casey has not (yet) proven his link to the other famous Holliday (John Henry “Doc” Holliday, dentist – also from Penn – better known for his exploits with lawman Wyatt Earp) but it does appear that he may be a cousin of former president Grover Cleveland on his mother's side (they even look a little alike; btw, Cleveland was the only US President who was elected, then defeated, then re-elected again; hmm…let us not go there!) Casey is the poster child of the functional anatomist who explores (with gusto, and an array of cutting-edge technologies) the anatomy of living forms to gain insight into reconstructing past ancestors and chart the pathways of their evolution. He has become one of the leading comparative reptilian anatomists/paleo-anatomists in the world today and has published extensively. Casey's science has often graced our pages covering, for example: new cephalic vascular anatomy in flamingos (Holliday, Ridgely, Balanoff, & Witmer, 2006); new insights into dinosaur jaw anatomy (Holliday, 2009); study of trigeminal nerve morphology in alligators with implications for understanding crocodyliform facial sensation and evolution (George & Holliday, 2013); studies on the frontoparietal fossa and dorsotemporal fenestra of archosaurs for interpreting anatomy in dinosaurs (Holliday, Porter, Vliet, & Witmer, 2020); explorations of the nose of gharials to understand airflow and acoustics (Bourke, Fontenot, & Holliday, 2022, this volume); new approaches in imaging to understand anatomy and mechanics of crocodilian jaw muscles (Holliday et al., 2022, this volume); biomechanical assessment of the craniomandibular complex of the notosuchian, Araripesuchus gomesii (Nieto, Degrange, Sellers, Diogo, & Holliday, 2022, this volume); and the effects of skull flattening on suchian jaw muscle evolution (Sellers et al., 2022, this volume). Thanks to both Casey and Emma (Figure 1a, b) for sharing their best science so often in our journal!
Now to the main course. First off, as one will readily see, it is not so easy to tell “who-is-who” is the murky waters of living and extinct crocodilian nomenclature and systematics. In truth, one often needs a scorecard to distinguish amongst the groups. The authors of this editorial were weaned in the forests of primatology and anthropology in which taxonomic names (and groupings) are far simpler: basically, you get a troop or two of monkeys, a shrewdness of apes and us, and a conspiracy of lemurs and friends (bet you did not know the plural names for the last two?; btw, most of what you need to know about the lemurs and such can be gleaned from the “Madagascar” movies.) Throw in fuzzypithecus and some bumpypithecine ancestors from the Miocene, Pliocene, and Pleistocene, and that's the primate cosmos (please, no hate mail from the paleoanthropologists out there; we know how hard you worked and fought over placing a shard of bone in Australopithecus africanus, Homo erectus or H. sapiens, but there's only a handful of genera and a dozen or so species, so deal; btw, JL, got smacked hard when he inadvertently named a new subspecies – Homo erectus newyorkensis - in The Anatomical Record in 2001, Laitman & Tattersall, 2001; interesting tale, have a read!).
Now back to crocs and their relatives. In today's world, crocodiles, alligators, and their less well-known relatives, caimans and gharials, are the living members of a magnificent clade of archosaurian (literally, “ruling”) reptiles named Crocodylomorpha. This group is, in a word, extraordinary, and in the pre-modern world, stemming back to the Triassic Period of the Mesozoic Era roughly some 201–252 million years ago, consisted of species that encompassed niches far beyond those of the familiar crocodiles and alligators of today. Unlike today's river and swamp-dwelling carnivores, there were species that lived on land and those that swam in the depths of the oceans. There were groups that were omnivores, insectivores, and even herbivores (can you imagine giant croc relatives having the equivalent of a salad?). Their diversity was vast and as diverse, maybe more so, than their media-hogging cousins, the dinosaurs (btw, “dinosaur” connotes a diverse group of reptiles forming the clade Dinosauria of which the only living members are birds; yup, that chicken is a relative of velociraptor!). While countless children hug their cuddly triceratops (an ornithischian, or “bird-hipped” dinosaur), chubby brachiosaurus (a sauropod, or “lizard-footed” dinosaur) or fierce-looking tyrannosaur (a theropod, or “wild-beast footed” dinosaur) – and often know only of these prehistoric mega-stars - the ancestral world was full of many other magnificent reptilian relatives. And that's really the point of this novel Special Issue: to bring to the fore the diversity, often unknown anatomy, physiology, entwining relationships, and evolutionary paths of many species that, while loved and known to the reptilian cognoscenti, are often underappreciated and overshadowed by focus on their better-known cousins. So, get out of the spotlight T-Rex, it's not all about you today!
One of the pleasures of writing about our Special Issues is that it gives us an opportunity to look into the rich vault of The Anatomical Record and note with parental pride some of the science that has come before. In regards to the current topic, that includes living and prehistoric reptiles of many ilks, a thorough recounting would require a volume unto itself. Accordingly, we will, with upfront apologies to those not mentioned, offer but a sliver of our robust history. To begin, we note a most frequent contributor to The Anatomical Record in its early years, Professor Albert M. Reese, Sr. (1872–1965) of West Virginia University in Morgantown. Reese was for decades a zoologist, biologist, and Chair of the Department of Biology at West Virginia, and a prized scholarship for students in the biological sciences was established in his name. He was, by all accounts, one of the leading alligator anatomists/biologists of the early 20th century, and published scores of articles, both scientific and lay, on their anatomy, comparative anatomy, embryology, biology, and ethology. In 1915 he published a book which is still in print called The Alligator and their Allies (Reese, 2015). Reese was a prolific author and, indeed, published eight papers in The Anatomical Record itself between 1913 and 1947, all, save one (on a two-headed lamb, Reese, 1917b) on the anatomy or histology of alligators and their relatives. These included: the histology of the enteron (old name for the digestive tract) of the Florida alligator (Reese, 1913); on its blood (Reese, 1917a); comparison of cephalic glands of snakes and alligators (Reese, 1924); the origin of the alligator notochord (Reese, 1936); the laryngeal region of alligators (Reese, 1945); and, lastly, reactions of an alligator in an artificial environment (Reese, 1947). He always published alone, with titles that were a paragon of clarity and simplicity (a bit different from today's multi-line line mouthfuls!)
Taking a big jump in time we come to the early part of this century. Here we find a brilliant paper by Mason Meers (2003), of the University of Tampa, that highlighted the importance of studying crocodylian forelimb musculature, both for its own value and as a vehicle to gain insight into evolutionary relationships. This often-cited article was accompanied by an equally insightful commentary by none other than Peter Dodson (Dodson, 2003). Dodson took the podium, so to speak, to echo and support Meer's approach to bringing the neglected forearm region to the fore in discussions of crocodylian/reptilian/dinosaurian biology and systematics. The reason for great interest, of course, is that dinosaurs and their kin have long been classified largely by the structure and appearance of their bony hip and muscle morphology, arguably since the path-setting work by the great paleontologist Alfred Sherwood Romer (Romer, 1922). Meer's paper, and Dodson's commentary, helped usher in new investigations on the importance of forearm anatomy in crocodylian/dinosaurian evolution (see Laitman, 2003 for discussion). Meer's paper is also notable for the extraordinary cover that he created that similarly received great attention (Figure 2a). BTW, while we are still smiling over Meer's artistic genius, there is another, brilliant digital cover that he created (Figure 2b) to accompany his work with Australian colleagues on novel assessments by Finite Element Analyses (FEA) of biomechanical differences in the rostra of different species of crocodilians (McHenry, Clausen, Daniel, Meers, & Pendharhar, 2006).
While so many additional, excellent studies can be mentioned, there are two very special, Special Issues that we must comment on, both overseen by Peter Dodson: “Unearthing the Anatomy of Dinosaurs” (Dodson, 2009; Laitman, 2009; Laitman & Albertine, 2009) and its sequel, “The Hidden World of Dinosaurs” (Hedrick & Dodson, 2020; Laitman & Albertine, 2020). While “Dinosaur,” of course, gets its name in light, these issues cover many ancient, reptilian/archosaurian forms and the articles are often outstanding pieces of comparative anatomy. These Special Issues were replete with outstanding (highly cited) science by leading scholars. Indeed, the first Special Issue was, when published, amongst the most highly sought after in Wiley's (our publisher) history, and additional runs of the issue had to be printed (back in the day when journals were all hard copy!) The covers of these were also majestic (Figure 3 a, b). They are also of interest, due to Peter's own love of ceratopsian dinosaurs (those with the horns); he used his position as guest editor to highlight them, including having one triceratops triumphantly saunter away from a T-Rex that he had just sent to its eternal rest in the 2009 Special Issue (Larry Witmer, noted Tyrannosaurus scholar, complained bitterly requesting equal time!). BTW, this duo of Special Issues will soon be turned into a trilogy as a new volume in honor of Peter is currently in the works. It too will have dinosaur in the title (catches the audience, we guess) but discuss and describe the robust, prehistoric archosaurian world.
Reading the papers in this Special Issue we hear in our mind's ear the catchy tune of the early 20th-century song, “Hail, hail, the gang's all here.” Indeed, they are. In this issue you will find all the pseudosuchian archosaurs, crocodylomorphs, living crocodilians, eusuchians, mesosuchians, sebosuchians, thalattosuchians, and protosuchians that you have ever dreamed of; you will have your fill of up-close insights into living crocodiles, caimans, gharials, and those annoying alligators that keep trying to eat JL's Florida relatives; and you'll have more Triassic and Jurassic species to shake a pick-ax at that you could imagine from Dakosaurus, Araripesuchus, Zulmasuchus, Eopneumatosuchus to Poposaurus. Yes, dinosaurs will pop up, but in the background, in only supporting comparative roles. This is the showcase for crocodiles and their many kin, and The Anatomical Record is showing a toothy smile that we are able to present in such an extraordinary volume. Enjoy and learn, as we have. Welcome to the wild ride at “Crocodile Park”.
